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UCSB researchers develop ultra sensitive biosensor from molybdenite semiconductor

Move over, graphene. An atomically thin, two-dimensional, ultrasensitive semiconductor material for biosensing developed by researchers at UC Santa Barbara promises to push the boundaries of biosensing technology in many fields, from health care to environmental protection to forensic industries.

Based on molybdenum disulfide or molybdenite (MoS2), the biosensor material — used commonly as a dry lubricant — surpasses graphene’s already high sensitivity, offers better scalability and lends itself to high-volume manufacturing. Results of the researchers’ study have been published in ACS Nano.

Concept art of a molybdenum disulfide field-effect transistor based biosensor demonstrated by UCSB researchers with ability to detect ultra-low (femtomolar) concentrations with high sensitivity that is 74-fold higher than that of graphene FET biosensors. - Photo Credit: Peter Allen

Concept art of a molybdenum disulfide field-effect transistor based biosensor demonstrated by UCSB researchers with ability to detect ultra-low (femtomolar) concentrations with high sensitivity that is 74-fold higher than that of graphene FET biosensors. – Photo Credit: Peter Allen

“This invention has established the foundation for a new generation of ultrasensitive and low-cost biosensors that can eventually allow single-molecule detection — the holy grail of diagnostics and bioengineering research,” said Samir Mitragotri, co-author and professor of chemical engineering and director of the Center for Bioengineering at UCSB. “Detection and diagnostics are a key area of bioengineering research at UCSB and this study represents an excellent example of UCSB’s multifaceted competencies in this exciting field.”

The key, according to UCSB professor of electrical and computer engineering Kaustav Banerjee, who led this research, is MoS2’s band gap, the characteristic of a material that determines its electrical conductivity.

Semiconductor materials have a small but nonzero band gap and can be switched between conductive and insulated states controllably. The larger the band gap, the better its ability to switch states and to insulate leakage current in an insulated state. MoS2’s wide band gap allows current to travel but also prevents leakage and results in more sensitive and accurate readings.

The limitations of graphene

While graphene has attracted wide interest as a biosensor due to its two-dimensional nature that allows excellent electrostatic control of the transistor channel by the gate, and high surface-to-volume ratio, the sensitivity of a graphene field-effect transistor (FET) biosensor is fundamentally restricted by the zero band gap of graphene that results in increased leakage current, leading to reduced sensitivity, explained Banerjee, who is also the director of the Nanoelectronics Research Lab at UCSB.

Graphene has been used, among other things, to design FETs — devices that regulate the flow of electrons through a channel via a vertical electric field directed into the channel by a terminal called a “gate.” In digital electronics, these transistors control the flow of electricity throughout an integrated circuit and allow for amplification and switching.

In the realm of biosensing, the physical gate is removed, and the current in the channel is modulated by the binding between embedded receptor molecules and the charged target biomolecules to which they are exposed. Graphene has received wide interest in the biosensing field and has been used to line the channel and act as a sensing element whose surface potential (or conductivity) can be modulated by the interaction (known as conjugation) between the receptor and target molecules that results in net accumulation of charges over the gate region.

However, said the research team, despite graphene’s excellent characteristics, its performance is limited by its zero band gap. Electrons travel freely across a graphene FET — hence, it cannot be “switched off” — which in this case results in current leakages and higher potential for inaccuracies.

Much research in the graphene community has been devoted to compensating for this deficiency, either by patterning graphene to make nanoribbons or by introducing defects in the graphene layer — or using bilayer graphene stacked in a certain pattern that allows band gap opening upon application of a vertical electric field — for better control and detection of current.

Enter MoS2, a material already making waves in the semiconductor world for the similarities it shares with graphene, including its atomically thin hexagonal structure, and planar nature, as well as what it can do that graphene can’t: act like a semiconductor.

“Monolayer or few-layer MoS2 have a key advantage over graphene for designing an FET biosensor: They have a relatively large and uniform band gap (1.2-1.8 eV, depending on the number of layers) that significantly reduces the leakage current and increases the abruptness of the turn-on behavior of the FETs, thereby increasing the sensitivity of the biosensor,” said Banerjee.

‘The best of everything’

Additionally, according to Deblina Sarkar, a PhD student in Banerjee’s lab and the lead author of the article, two-dimensional MoS2 is relatively simple to manufacture.

“While one-dimensional materials such as carbon nanotubes and nanowires also allow excellent electrostatics and at the same time possess band gap, they are not suitable for low-cost mass production due to their process complexities,” she said. “Moreover, the channel length of MoS2 FET biosensor can be scaled down to the dimensions similar to those of small biomolecules such as DNA or small proteins, still maintaining good electrostatics, which can lead to high sensitivity even for detection of single quanta of these biomolecular species,” she added.

“In fact, atomically thin MoS2 provides the best of everything: great electrostatics due to their ultra-thin body, scalability (due to large band gap), as well as patternability due to their planar nature that is essential for high-volume manufacturing,” said Banerjee.

The MoS2 biosensors demonstrated by the UCSB team have already provided ultrasensitive and specific protein sensing with a sensitivity of 196 even at 100 femtomolar (a billionth of a millionth of a mole) concentrations. This protein concentration is similar to one drop of milk dissolved in a hundred tons of water. An MoS2-based pH sensor achieving sensitivity as high as 713 for a pH change by one unit along with efficient operation over a wide pH range (3-9) is also demonstrated in the same work.

“This transformative technology enables highly specific, low-power, high-throughput physiological sensing that can be multiplexed to detect a number of significant, disease-specific factors in real time,” commented Scott Hammond, executive director of UCSB’s Translational Medicine Research Laboratories.

Biosensors based on conventional FETs have been gaining momentum as a viable technology for the medical, forensic and security industries since they are cost-effective compared to optical detection procedures. Such biosensors allow for scalability and label-free detection of biomolecules — removing the step and expense of labeling target molecules with florescent dye. “In essence,” continued Hammond, “the promise of true evidence-based, personalized medicine is finally becoming reality.”

“This demonstration is quite remarkable,” said Andras Kis, professor at École Polytechnique Fédérale de Lausanne in Switzerland and a leading scientist in the field of 2D materials and devices.

“At present, the scientific community worldwide is actively seeking practical applications of 2D semiconductor materials such as MoS2 nanosheets. Professor Banerjee and his team have identified a breakthrough application of these nanomaterials and provided new impetus for the development of low-power and low-cost ultrasensitive biosensors,” continued Kis, who is not connected to the project.

Wei Liu and Xuejun Xie from UCSB’s Department of Electrical and Computer Engineering and Aaron Anselmo from the Department of Chemical Engineering also conducted research for this study. Research on this project was supported by the National Science Foundation, the California NanoSystems Institute at UCSB and the Materials Research Laboratory at UCSB, a National Science Foundation MRSEC.

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UCSB researchers develop ultra sensitive biosensor from molybdenite semiconductor

Move over, graphene. An atomically thin, two-dimensional, ultrasensitive semiconductor material for biosensing developed by researchers at UC Santa Barbara promises to push the boundaries of biosensing technology in many fields, from health care to environmental protection to forensic industries.

Based on molybdenum disulfide or molybdenite (MoS2), the biosensor material — used commonly as a dry lubricant — surpasses graphene’s already high sensitivity, offers better scalability and lends itself to high-volume manufacturing. Results of the researchers’ study have been published in ACS Nano.

Concept art of a molybdenum disulfide field-effect transistor based biosensor demonstrated by UCSB researchers with ability to detect ultra-low (femtomolar) concentrations with high sensitivity that is 74-fold higher than that of graphene FET biosensors. - Photo Credit: Peter Allen

Concept art of a molybdenum disulfide field-effect transistor based biosensor demonstrated by UCSB researchers with ability to detect ultra-low (femtomolar) concentrations with high sensitivity that is 74-fold higher than that of graphene FET biosensors. – Photo Credit: Peter Allen

“This invention has established the foundation for a new generation of ultrasensitive and low-cost biosensors that can eventually allow single-molecule detection — the holy grail of diagnostics and bioengineering research,” said Samir Mitragotri, co-author and professor of chemical engineering and director of the Center for Bioengineering at UCSB. “Detection and diagnostics are a key area of bioengineering research at UCSB and this study represents an excellent example of UCSB’s multifaceted competencies in this exciting field.”

The key, according to UCSB professor of electrical and computer engineering Kaustav Banerjee, who led this research, is MoS2’s band gap, the characteristic of a material that determines its electrical conductivity.

Semiconductor materials have a small but nonzero band gap and can be switched between conductive and insulated states controllably. The larger the band gap, the better its ability to switch states and to insulate leakage current in an insulated state. MoS2’s wide band gap allows current to travel but also prevents leakage and results in more sensitive and accurate readings.

The limitations of graphene

While graphene has attracted wide interest as a biosensor due to its two-dimensional nature that allows excellent electrostatic control of the transistor channel by the gate, and high surface-to-volume ratio, the sensitivity of a graphene field-effect transistor (FET) biosensor is fundamentally restricted by the zero band gap of graphene that results in increased leakage current, leading to reduced sensitivity, explained Banerjee, who is also the director of the Nanoelectronics Research Lab at UCSB.

Graphene has been used, among other things, to design FETs — devices that regulate the flow of electrons through a channel via a vertical electric field directed into the channel by a terminal called a “gate.” In digital electronics, these transistors control the flow of electricity throughout an integrated circuit and allow for amplification and switching.

In the realm of biosensing, the physical gate is removed, and the current in the channel is modulated by the binding between embedded receptor molecules and the charged target biomolecules to which they are exposed. Graphene has received wide interest in the biosensing field and has been used to line the channel and act as a sensing element whose surface potential (or conductivity) can be modulated by the interaction (known as conjugation) between the receptor and target molecules that results in net accumulation of charges over the gate region.

However, said the research team, despite graphene’s excellent characteristics, its performance is limited by its zero band gap. Electrons travel freely across a graphene FET — hence, it cannot be “switched off” — which in this case results in current leakages and higher potential for inaccuracies.

Much research in the graphene community has been devoted to compensating for this deficiency, either by patterning graphene to make nanoribbons or by introducing defects in the graphene layer — or using bilayer graphene stacked in a certain pattern that allows band gap opening upon application of a vertical electric field — for better control and detection of current.

Enter MoS2, a material already making waves in the semiconductor world for the similarities it shares with graphene, including its atomically thin hexagonal structure, and planar nature, as well as what it can do that graphene can’t: act like a semiconductor.

“Monolayer or few-layer MoS2 have a key advantage over graphene for designing an FET biosensor: They have a relatively large and uniform band gap (1.2-1.8 eV, depending on the number of layers) that significantly reduces the leakage current and increases the abruptness of the turn-on behavior of the FETs, thereby increasing the sensitivity of the biosensor,” said Banerjee.

‘The best of everything’

Additionally, according to Deblina Sarkar, a PhD student in Banerjee’s lab and the lead author of the article, two-dimensional MoS2 is relatively simple to manufacture.

“While one-dimensional materials such as carbon nanotubes and nanowires also allow excellent electrostatics and at the same time possess band gap, they are not suitable for low-cost mass production due to their process complexities,” she said. “Moreover, the channel length of MoS2 FET biosensor can be scaled down to the dimensions similar to those of small biomolecules such as DNA or small proteins, still maintaining good electrostatics, which can lead to high sensitivity even for detection of single quanta of these biomolecular species,” she added.

“In fact, atomically thin MoS2 provides the best of everything: great electrostatics due to their ultra-thin body, scalability (due to large band gap), as well as patternability due to their planar nature that is essential for high-volume manufacturing,” said Banerjee.

The MoS2 biosensors demonstrated by the UCSB team have already provided ultrasensitive and specific protein sensing with a sensitivity of 196 even at 100 femtomolar (a billionth of a millionth of a mole) concentrations. This protein concentration is similar to one drop of milk dissolved in a hundred tons of water. An MoS2-based pH sensor achieving sensitivity as high as 713 for a pH change by one unit along with efficient operation over a wide pH range (3-9) is also demonstrated in the same work.

“This transformative technology enables highly specific, low-power, high-throughput physiological sensing that can be multiplexed to detect a number of significant, disease-specific factors in real time,” commented Scott Hammond, executive director of UCSB’s Translational Medicine Research Laboratories.

Biosensors based on conventional FETs have been gaining momentum as a viable technology for the medical, forensic and security industries since they are cost-effective compared to optical detection procedures. Such biosensors allow for scalability and label-free detection of biomolecules — removing the step and expense of labeling target molecules with florescent dye. “In essence,” continued Hammond, “the promise of true evidence-based, personalized medicine is finally becoming reality.”

“This demonstration is quite remarkable,” said Andras Kis, professor at École Polytechnique Fédérale de Lausanne in Switzerland and a leading scientist in the field of 2D materials and devices.

“At present, the scientific community worldwide is actively seeking practical applications of 2D semiconductor materials such as MoS2 nanosheets. Professor Banerjee and his team have identified a breakthrough application of these nanomaterials and provided new impetus for the development of low-power and low-cost ultrasensitive biosensors,” continued Kis, who is not connected to the project.

Wei Liu and Xuejun Xie from UCSB’s Department of Electrical and Computer Engineering and Aaron Anselmo from the Department of Chemical Engineering also conducted research for this study. Research on this project was supported by the National Science Foundation, the California NanoSystems Institute at UCSB and the Materials Research Laboratory at UCSB, a National Science Foundation MRSEC.

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UCSB researchers develop ultra sensitive biosensor from molybdenite semiconductor

Move over, graphene. An atomically thin, two-dimensional, ultrasensitive semiconductor material for biosensing developed by researchers at UC Santa Barbara promises to push the boundaries of biosensing technology in many fields, from health care to environmental protection to forensic industries.

Based on molybdenum disulfide or molybdenite (MoS2), the biosensor material — used commonly as a dry lubricant — surpasses graphene’s already high sensitivity, offers better scalability and lends itself to high-volume manufacturing. Results of the researchers’ study have been published in ACS Nano.

Concept art of a molybdenum disulfide field-effect transistor based biosensor demonstrated by UCSB researchers with ability to detect ultra-low (femtomolar) concentrations with high sensitivity that is 74-fold higher than that of graphene FET biosensors. - Photo Credit: Peter Allen

Concept art of a molybdenum disulfide field-effect transistor based biosensor demonstrated by UCSB researchers with ability to detect ultra-low (femtomolar) concentrations with high sensitivity that is 74-fold higher than that of graphene FET biosensors. – Photo Credit: Peter Allen

“This invention has established the foundation for a new generation of ultrasensitive and low-cost biosensors that can eventually allow single-molecule detection — the holy grail of diagnostics and bioengineering research,” said Samir Mitragotri, co-author and professor of chemical engineering and director of the Center for Bioengineering at UCSB. “Detection and diagnostics are a key area of bioengineering research at UCSB and this study represents an excellent example of UCSB’s multifaceted competencies in this exciting field.”

The key, according to UCSB professor of electrical and computer engineering Kaustav Banerjee, who led this research, is MoS2’s band gap, the characteristic of a material that determines its electrical conductivity.

Semiconductor materials have a small but nonzero band gap and can be switched between conductive and insulated states controllably. The larger the band gap, the better its ability to switch states and to insulate leakage current in an insulated state. MoS2’s wide band gap allows current to travel but also prevents leakage and results in more sensitive and accurate readings.

The limitations of graphene

While graphene has attracted wide interest as a biosensor due to its two-dimensional nature that allows excellent electrostatic control of the transistor channel by the gate, and high surface-to-volume ratio, the sensitivity of a graphene field-effect transistor (FET) biosensor is fundamentally restricted by the zero band gap of graphene that results in increased leakage current, leading to reduced sensitivity, explained Banerjee, who is also the director of the Nanoelectronics Research Lab at UCSB.

Graphene has been used, among other things, to design FETs — devices that regulate the flow of electrons through a channel via a vertical electric field directed into the channel by a terminal called a “gate.” In digital electronics, these transistors control the flow of electricity throughout an integrated circuit and allow for amplification and switching.

In the realm of biosensing, the physical gate is removed, and the current in the channel is modulated by the binding between embedded receptor molecules and the charged target biomolecules to which they are exposed. Graphene has received wide interest in the biosensing field and has been used to line the channel and act as a sensing element whose surface potential (or conductivity) can be modulated by the interaction (known as conjugation) between the receptor and target molecules that results in net accumulation of charges over the gate region.

However, said the research team, despite graphene’s excellent characteristics, its performance is limited by its zero band gap. Electrons travel freely across a graphene FET — hence, it cannot be “switched off” — which in this case results in current leakages and higher potential for inaccuracies.

Much research in the graphene community has been devoted to compensating for this deficiency, either by patterning graphene to make nanoribbons or by introducing defects in the graphene layer — or using bilayer graphene stacked in a certain pattern that allows band gap opening upon application of a vertical electric field — for better control and detection of current.

Enter MoS2, a material already making waves in the semiconductor world for the similarities it shares with graphene, including its atomically thin hexagonal structure, and planar nature, as well as what it can do that graphene can’t: act like a semiconductor.

“Monolayer or few-layer MoS2 have a key advantage over graphene for designing an FET biosensor: They have a relatively large and uniform band gap (1.2-1.8 eV, depending on the number of layers) that significantly reduces the leakage current and increases the abruptness of the turn-on behavior of the FETs, thereby increasing the sensitivity of the biosensor,” said Banerjee.

‘The best of everything’

Additionally, according to Deblina Sarkar, a PhD student in Banerjee’s lab and the lead author of the article, two-dimensional MoS2 is relatively simple to manufacture.

“While one-dimensional materials such as carbon nanotubes and nanowires also allow excellent electrostatics and at the same time possess band gap, they are not suitable for low-cost mass production due to their process complexities,” she said. “Moreover, the channel length of MoS2 FET biosensor can be scaled down to the dimensions similar to those of small biomolecules such as DNA or small proteins, still maintaining good electrostatics, which can lead to high sensitivity even for detection of single quanta of these biomolecular species,” she added.

“In fact, atomically thin MoS2 provides the best of everything: great electrostatics due to their ultra-thin body, scalability (due to large band gap), as well as patternability due to their planar nature that is essential for high-volume manufacturing,” said Banerjee.

The MoS2 biosensors demonstrated by the UCSB team have already provided ultrasensitive and specific protein sensing with a sensitivity of 196 even at 100 femtomolar (a billionth of a millionth of a mole) concentrations. This protein concentration is similar to one drop of milk dissolved in a hundred tons of water. An MoS2-based pH sensor achieving sensitivity as high as 713 for a pH change by one unit along with efficient operation over a wide pH range (3-9) is also demonstrated in the same work.

“This transformative technology enables highly specific, low-power, high-throughput physiological sensing that can be multiplexed to detect a number of significant, disease-specific factors in real time,” commented Scott Hammond, executive director of UCSB’s Translational Medicine Research Laboratories.

Biosensors based on conventional FETs have been gaining momentum as a viable technology for the medical, forensic and security industries since they are cost-effective compared to optical detection procedures. Such biosensors allow for scalability and label-free detection of biomolecules — removing the step and expense of labeling target molecules with florescent dye. “In essence,” continued Hammond, “the promise of true evidence-based, personalized medicine is finally becoming reality.”

“This demonstration is quite remarkable,” said Andras Kis, professor at École Polytechnique Fédérale de Lausanne in Switzerland and a leading scientist in the field of 2D materials and devices.

“At present, the scientific community worldwide is actively seeking practical applications of 2D semiconductor materials such as MoS2 nanosheets. Professor Banerjee and his team have identified a breakthrough application of these nanomaterials and provided new impetus for the development of low-power and low-cost ultrasensitive biosensors,” continued Kis, who is not connected to the project.

Wei Liu and Xuejun Xie from UCSB’s Department of Electrical and Computer Engineering and Aaron Anselmo from the Department of Chemical Engineering also conducted research for this study. Research on this project was supported by the National Science Foundation, the California NanoSystems Institute at UCSB and the Materials Research Laboratory at UCSB, a National Science Foundation MRSEC.

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UCSB researchers develop ultra sensitive biosensor from molybdenite semiconductor

Move over, graphene. An atomically thin, two-dimensional, ultrasensitive semiconductor material for biosensing developed by researchers at UC Santa Barbara promises to push the boundaries of biosensing technology in many fields, from health care to environmental protection to forensic industries.

Based on molybdenum disulfide or molybdenite (MoS2), the biosensor material — used commonly as a dry lubricant — surpasses graphene’s already high sensitivity, offers better scalability and lends itself to high-volume manufacturing. Results of the researchers’ study have been published in ACS Nano.

Concept art of a molybdenum disulfide field-effect transistor based biosensor demonstrated by UCSB researchers with ability to detect ultra-low (femtomolar) concentrations with high sensitivity that is 74-fold higher than that of graphene FET biosensors. - Photo Credit: Peter Allen

Concept art of a molybdenum disulfide field-effect transistor based biosensor demonstrated by UCSB researchers with ability to detect ultra-low (femtomolar) concentrations with high sensitivity that is 74-fold higher than that of graphene FET biosensors. – Photo Credit: Peter Allen

“This invention has established the foundation for a new generation of ultrasensitive and low-cost biosensors that can eventually allow single-molecule detection — the holy grail of diagnostics and bioengineering research,” said Samir Mitragotri, co-author and professor of chemical engineering and director of the Center for Bioengineering at UCSB. “Detection and diagnostics are a key area of bioengineering research at UCSB and this study represents an excellent example of UCSB’s multifaceted competencies in this exciting field.”

The key, according to UCSB professor of electrical and computer engineering Kaustav Banerjee, who led this research, is MoS2’s band gap, the characteristic of a material that determines its electrical conductivity.

Semiconductor materials have a small but nonzero band gap and can be switched between conductive and insulated states controllably. The larger the band gap, the better its ability to switch states and to insulate leakage current in an insulated state. MoS2’s wide band gap allows current to travel but also prevents leakage and results in more sensitive and accurate readings.

The limitations of graphene

While graphene has attracted wide interest as a biosensor due to its two-dimensional nature that allows excellent electrostatic control of the transistor channel by the gate, and high surface-to-volume ratio, the sensitivity of a graphene field-effect transistor (FET) biosensor is fundamentally restricted by the zero band gap of graphene that results in increased leakage current, leading to reduced sensitivity, explained Banerjee, who is also the director of the Nanoelectronics Research Lab at UCSB.

Graphene has been used, among other things, to design FETs — devices that regulate the flow of electrons through a channel via a vertical electric field directed into the channel by a terminal called a “gate.” In digital electronics, these transistors control the flow of electricity throughout an integrated circuit and allow for amplification and switching.

In the realm of biosensing, the physical gate is removed, and the current in the channel is modulated by the binding between embedded receptor molecules and the charged target biomolecules to which they are exposed. Graphene has received wide interest in the biosensing field and has been used to line the channel and act as a sensing element whose surface potential (or conductivity) can be modulated by the interaction (known as conjugation) between the receptor and target molecules that results in net accumulation of charges over the gate region.

However, said the research team, despite graphene’s excellent characteristics, its performance is limited by its zero band gap. Electrons travel freely across a graphene FET — hence, it cannot be “switched off” — which in this case results in current leakages and higher potential for inaccuracies.

Much research in the graphene community has been devoted to compensating for this deficiency, either by patterning graphene to make nanoribbons or by introducing defects in the graphene layer — or using bilayer graphene stacked in a certain pattern that allows band gap opening upon application of a vertical electric field — for better control and detection of current.

Enter MoS2, a material already making waves in the semiconductor world for the similarities it shares with graphene, including its atomically thin hexagonal structure, and planar nature, as well as what it can do that graphene can’t: act like a semiconductor.

“Monolayer or few-layer MoS2 have a key advantage over graphene for designing an FET biosensor: They have a relatively large and uniform band gap (1.2-1.8 eV, depending on the number of layers) that significantly reduces the leakage current and increases the abruptness of the turn-on behavior of the FETs, thereby increasing the sensitivity of the biosensor,” said Banerjee.

‘The best of everything’

Additionally, according to Deblina Sarkar, a PhD student in Banerjee’s lab and the lead author of the article, two-dimensional MoS2 is relatively simple to manufacture.

“While one-dimensional materials such as carbon nanotubes and nanowires also allow excellent electrostatics and at the same time possess band gap, they are not suitable for low-cost mass production due to their process complexities,” she said. “Moreover, the channel length of MoS2 FET biosensor can be scaled down to the dimensions similar to those of small biomolecules such as DNA or small proteins, still maintaining good electrostatics, which can lead to high sensitivity even for detection of single quanta of these biomolecular species,” she added.

“In fact, atomically thin MoS2 provides the best of everything: great electrostatics due to their ultra-thin body, scalability (due to large band gap), as well as patternability due to their planar nature that is essential for high-volume manufacturing,” said Banerjee.

The MoS2 biosensors demonstrated by the UCSB team have already provided ultrasensitive and specific protein sensing with a sensitivity of 196 even at 100 femtomolar (a billionth of a millionth of a mole) concentrations. This protein concentration is similar to one drop of milk dissolved in a hundred tons of water. An MoS2-based pH sensor achieving sensitivity as high as 713 for a pH change by one unit along with efficient operation over a wide pH range (3-9) is also demonstrated in the same work.

“This transformative technology enables highly specific, low-power, high-throughput physiological sensing that can be multiplexed to detect a number of significant, disease-specific factors in real time,” commented Scott Hammond, executive director of UCSB’s Translational Medicine Research Laboratories.

Biosensors based on conventional FETs have been gaining momentum as a viable technology for the medical, forensic and security industries since they are cost-effective compared to optical detection procedures. Such biosensors allow for scalability and label-free detection of biomolecules — removing the step and expense of labeling target molecules with florescent dye. “In essence,” continued Hammond, “the promise of true evidence-based, personalized medicine is finally becoming reality.”

“This demonstration is quite remarkable,” said Andras Kis, professor at École Polytechnique Fédérale de Lausanne in Switzerland and a leading scientist in the field of 2D materials and devices.

“At present, the scientific community worldwide is actively seeking practical applications of 2D semiconductor materials such as MoS2 nanosheets. Professor Banerjee and his team have identified a breakthrough application of these nanomaterials and provided new impetus for the development of low-power and low-cost ultrasensitive biosensors,” continued Kis, who is not connected to the project.

Wei Liu and Xuejun Xie from UCSB’s Department of Electrical and Computer Engineering and Aaron Anselmo from the Department of Chemical Engineering also conducted research for this study. Research on this project was supported by the National Science Foundation, the California NanoSystems Institute at UCSB and the Materials Research Laboratory at UCSB, a National Science Foundation MRSEC.

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UCSB researchers develop ultra sensitive biosensor from molybdenite semiconductor

Move over, graphene. An atomically thin, two-dimensional, ultrasensitive semiconductor material for biosensing developed by researchers at UC Santa Barbara promises to push the boundaries of biosensing technology in many fields, from health care to environmental protection to forensic industries.

Based on molybdenum disulfide or molybdenite (MoS2), the biosensor material — used commonly as a dry lubricant — surpasses graphene’s already high sensitivity, offers better scalability and lends itself to high-volume manufacturing. Results of the researchers’ study have been published in ACS Nano.

Concept art of a molybdenum disulfide field-effect transistor based biosensor demonstrated by UCSB researchers with ability to detect ultra-low (femtomolar) concentrations with high sensitivity that is 74-fold higher than that of graphene FET biosensors. - Photo Credit: Peter Allen

Concept art of a molybdenum disulfide field-effect transistor based biosensor demonstrated by UCSB researchers with ability to detect ultra-low (femtomolar) concentrations with high sensitivity that is 74-fold higher than that of graphene FET biosensors. – Photo Credit: Peter Allen

“This invention has established the foundation for a new generation of ultrasensitive and low-cost biosensors that can eventually allow single-molecule detection — the holy grail of diagnostics and bioengineering research,” said Samir Mitragotri, co-author and professor of chemical engineering and director of the Center for Bioengineering at UCSB. “Detection and diagnostics are a key area of bioengineering research at UCSB and this study represents an excellent example of UCSB’s multifaceted competencies in this exciting field.”

The key, according to UCSB professor of electrical and computer engineering Kaustav Banerjee, who led this research, is MoS2’s band gap, the characteristic of a material that determines its electrical conductivity.

Semiconductor materials have a small but nonzero band gap and can be switched between conductive and insulated states controllably. The larger the band gap, the better its ability to switch states and to insulate leakage current in an insulated state. MoS2’s wide band gap allows current to travel but also prevents leakage and results in more sensitive and accurate readings.

The limitations of graphene

While graphene has attracted wide interest as a biosensor due to its two-dimensional nature that allows excellent electrostatic control of the transistor channel by the gate, and high surface-to-volume ratio, the sensitivity of a graphene field-effect transistor (FET) biosensor is fundamentally restricted by the zero band gap of graphene that results in increased leakage current, leading to reduced sensitivity, explained Banerjee, who is also the director of the Nanoelectronics Research Lab at UCSB.

Graphene has been used, among other things, to design FETs — devices that regulate the flow of electrons through a channel via a vertical electric field directed into the channel by a terminal called a “gate.” In digital electronics, these transistors control the flow of electricity throughout an integrated circuit and allow for amplification and switching.

In the realm of biosensing, the physical gate is removed, and the current in the channel is modulated by the binding between embedded receptor molecules and the charged target biomolecules to which they are exposed. Graphene has received wide interest in the biosensing field and has been used to line the channel and act as a sensing element whose surface potential (or conductivity) can be modulated by the interaction (known as conjugation) between the receptor and target molecules that results in net accumulation of charges over the gate region.

However, said the research team, despite graphene’s excellent characteristics, its performance is limited by its zero band gap. Electrons travel freely across a graphene FET — hence, it cannot be “switched off” — which in this case results in current leakages and higher potential for inaccuracies.

Much research in the graphene community has been devoted to compensating for this deficiency, either by patterning graphene to make nanoribbons or by introducing defects in the graphene layer — or using bilayer graphene stacked in a certain pattern that allows band gap opening upon application of a vertical electric field — for better control and detection of current.

Enter MoS2, a material already making waves in the semiconductor world for the similarities it shares with graphene, including its atomically thin hexagonal structure, and planar nature, as well as what it can do that graphene can’t: act like a semiconductor.

“Monolayer or few-layer MoS2 have a key advantage over graphene for designing an FET biosensor: They have a relatively large and uniform band gap (1.2-1.8 eV, depending on the number of layers) that significantly reduces the leakage current and increases the abruptness of the turn-on behavior of the FETs, thereby increasing the sensitivity of the biosensor,” said Banerjee.

‘The best of everything’

Additionally, according to Deblina Sarkar, a PhD student in Banerjee’s lab and the lead author of the article, two-dimensional MoS2 is relatively simple to manufacture.

“While one-dimensional materials such as carbon nanotubes and nanowires also allow excellent electrostatics and at the same time possess band gap, they are not suitable for low-cost mass production due to their process complexities,” she said. “Moreover, the channel length of MoS2 FET biosensor can be scaled down to the dimensions similar to those of small biomolecules such as DNA or small proteins, still maintaining good electrostatics, which can lead to high sensitivity even for detection of single quanta of these biomolecular species,” she added.

“In fact, atomically thin MoS2 provides the best of everything: great electrostatics due to their ultra-thin body, scalability (due to large band gap), as well as patternability due to their planar nature that is essential for high-volume manufacturing,” said Banerjee.

The MoS2 biosensors demonstrated by the UCSB team have already provided ultrasensitive and specific protein sensing with a sensitivity of 196 even at 100 femtomolar (a billionth of a millionth of a mole) concentrations. This protein concentration is similar to one drop of milk dissolved in a hundred tons of water. An MoS2-based pH sensor achieving sensitivity as high as 713 for a pH change by one unit along with efficient operation over a wide pH range (3-9) is also demonstrated in the same work.

“This transformative technology enables highly specific, low-power, high-throughput physiological sensing that can be multiplexed to detect a number of significant, disease-specific factors in real time,” commented Scott Hammond, executive director of UCSB’s Translational Medicine Research Laboratories.

Biosensors based on conventional FETs have been gaining momentum as a viable technology for the medical, forensic and security industries since they are cost-effective compared to optical detection procedures. Such biosensors allow for scalability and label-free detection of biomolecules — removing the step and expense of labeling target molecules with florescent dye. “In essence,” continued Hammond, “the promise of true evidence-based, personalized medicine is finally becoming reality.”

“This demonstration is quite remarkable,” said Andras Kis, professor at École Polytechnique Fédérale de Lausanne in Switzerland and a leading scientist in the field of 2D materials and devices.

“At present, the scientific community worldwide is actively seeking practical applications of 2D semiconductor materials such as MoS2 nanosheets. Professor Banerjee and his team have identified a breakthrough application of these nanomaterials and provided new impetus for the development of low-power and low-cost ultrasensitive biosensors,” continued Kis, who is not connected to the project.

Wei Liu and Xuejun Xie from UCSB’s Department of Electrical and Computer Engineering and Aaron Anselmo from the Department of Chemical Engineering also conducted research for this study. Research on this project was supported by the National Science Foundation, the California NanoSystems Institute at UCSB and the Materials Research Laboratory at UCSB, a National Science Foundation MRSEC.

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UCSB researchers develop ultra sensitive biosensor from molybdenite semiconductor

Move over, graphene. An atomically thin, two-dimensional, ultrasensitive semiconductor material for biosensing developed by researchers at UC Santa Barbara promises to push the boundaries of biosensing technology in many fields, from health care to environmental protection to forensic industries.

Based on molybdenum disulfide or molybdenite (MoS2), the biosensor material — used commonly as a dry lubricant — surpasses graphene’s already high sensitivity, offers better scalability and lends itself to high-volume manufacturing. Results of the researchers’ study have been published in ACS Nano.

Concept art of a molybdenum disulfide field-effect transistor based biosensor demonstrated by UCSB researchers with ability to detect ultra-low (femtomolar) concentrations with high sensitivity that is 74-fold higher than that of graphene FET biosensors. - Photo Credit: Peter Allen

Concept art of a molybdenum disulfide field-effect transistor based biosensor demonstrated by UCSB researchers with ability to detect ultra-low (femtomolar) concentrations with high sensitivity that is 74-fold higher than that of graphene FET biosensors. – Photo Credit: Peter Allen

“This invention has established the foundation for a new generation of ultrasensitive and low-cost biosensors that can eventually allow single-molecule detection — the holy grail of diagnostics and bioengineering research,” said Samir Mitragotri, co-author and professor of chemical engineering and director of the Center for Bioengineering at UCSB. “Detection and diagnostics are a key area of bioengineering research at UCSB and this study represents an excellent example of UCSB’s multifaceted competencies in this exciting field.”

The key, according to UCSB professor of electrical and computer engineering Kaustav Banerjee, who led this research, is MoS2’s band gap, the characteristic of a material that determines its electrical conductivity.

Semiconductor materials have a small but nonzero band gap and can be switched between conductive and insulated states controllably. The larger the band gap, the better its ability to switch states and to insulate leakage current in an insulated state. MoS2’s wide band gap allows current to travel but also prevents leakage and results in more sensitive and accurate readings.

The limitations of graphene

While graphene has attracted wide interest as a biosensor due to its two-dimensional nature that allows excellent electrostatic control of the transistor channel by the gate, and high surface-to-volume ratio, the sensitivity of a graphene field-effect transistor (FET) biosensor is fundamentally restricted by the zero band gap of graphene that results in increased leakage current, leading to reduced sensitivity, explained Banerjee, who is also the director of the Nanoelectronics Research Lab at UCSB.

Graphene has been used, among other things, to design FETs — devices that regulate the flow of electrons through a channel via a vertical electric field directed into the channel by a terminal called a “gate.” In digital electronics, these transistors control the flow of electricity throughout an integrated circuit and allow for amplification and switching.

In the realm of biosensing, the physical gate is removed, and the current in the channel is modulated by the binding between embedded receptor molecules and the charged target biomolecules to which they are exposed. Graphene has received wide interest in the biosensing field and has been used to line the channel and act as a sensing element whose surface potential (or conductivity) can be modulated by the interaction (known as conjugation) between the receptor and target molecules that results in net accumulation of charges over the gate region.

However, said the research team, despite graphene’s excellent characteristics, its performance is limited by its zero band gap. Electrons travel freely across a graphene FET — hence, it cannot be “switched off” — which in this case results in current leakages and higher potential for inaccuracies.

Much research in the graphene community has been devoted to compensating for this deficiency, either by patterning graphene to make nanoribbons or by introducing defects in the graphene layer — or using bilayer graphene stacked in a certain pattern that allows band gap opening upon application of a vertical electric field — for better control and detection of current.

Enter MoS2, a material already making waves in the semiconductor world for the similarities it shares with graphene, including its atomically thin hexagonal structure, and planar nature, as well as what it can do that graphene can’t: act like a semiconductor.

“Monolayer or few-layer MoS2 have a key advantage over graphene for designing an FET biosensor: They have a relatively large and uniform band gap (1.2-1.8 eV, depending on the number of layers) that significantly reduces the leakage current and increases the abruptness of the turn-on behavior of the FETs, thereby increasing the sensitivity of the biosensor,” said Banerjee.

‘The best of everything’

Additionally, according to Deblina Sarkar, a PhD student in Banerjee’s lab and the lead author of the article, two-dimensional MoS2 is relatively simple to manufacture.

“While one-dimensional materials such as carbon nanotubes and nanowires also allow excellent electrostatics and at the same time possess band gap, they are not suitable for low-cost mass production due to their process complexities,” she said. “Moreover, the channel length of MoS2 FET biosensor can be scaled down to the dimensions similar to those of small biomolecules such as DNA or small proteins, still maintaining good electrostatics, which can lead to high sensitivity even for detection of single quanta of these biomolecular species,” she added.

“In fact, atomically thin MoS2 provides the best of everything: great electrostatics due to their ultra-thin body, scalability (due to large band gap), as well as patternability due to their planar nature that is essential for high-volume manufacturing,” said Banerjee.

The MoS2 biosensors demonstrated by the UCSB team have already provided ultrasensitive and specific protein sensing with a sensitivity of 196 even at 100 femtomolar (a billionth of a millionth of a mole) concentrations. This protein concentration is similar to one drop of milk dissolved in a hundred tons of water. An MoS2-based pH sensor achieving sensitivity as high as 713 for a pH change by one unit along with efficient operation over a wide pH range (3-9) is also demonstrated in the same work.

“This transformative technology enables highly specific, low-power, high-throughput physiological sensing that can be multiplexed to detect a number of significant, disease-specific factors in real time,” commented Scott Hammond, executive director of UCSB’s Translational Medicine Research Laboratories.

Biosensors based on conventional FETs have been gaining momentum as a viable technology for the medical, forensic and security industries since they are cost-effective compared to optical detection procedures. Such biosensors allow for scalability and label-free detection of biomolecules — removing the step and expense of labeling target molecules with florescent dye. “In essence,” continued Hammond, “the promise of true evidence-based, personalized medicine is finally becoming reality.”

“This demonstration is quite remarkable,” said Andras Kis, professor at École Polytechnique Fédérale de Lausanne in Switzerland and a leading scientist in the field of 2D materials and devices.

“At present, the scientific community worldwide is actively seeking practical applications of 2D semiconductor materials such as MoS2 nanosheets. Professor Banerjee and his team have identified a breakthrough application of these nanomaterials and provided new impetus for the development of low-power and low-cost ultrasensitive biosensors,” continued Kis, who is not connected to the project.

Wei Liu and Xuejun Xie from UCSB’s Department of Electrical and Computer Engineering and Aaron Anselmo from the Department of Chemical Engineering also conducted research for this study. Research on this project was supported by the National Science Foundation, the California NanoSystems Institute at UCSB and the Materials Research Laboratory at UCSB, a National Science Foundation MRSEC.

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An all-carbon optical diode for photonic computing

Researchers have demonstrated the experimental realization of the first all-carbon optical diode that is ready for scalable integration along with being inherently broadband in operation with no restrictions on polarization or phase-matching criteria. As they show, harnessing the optical properties of graphene-based materials offers an opportunity to create the all-photonic analogs of diodes, transistors, and photonic logic gates that will one day enable construction of the first all-photonic computer.

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In rapidly changing display industry, metal oxide TFT backplanes are promising

MarketResearchReports.Biz released a new market research report this week entitled “Metal Oxide TFT Backplanes For Displays 2014-2024: Technologies, Forecasts, Players.”

According to the new report, metal oxide display backplanes have already gone commercial. Sharp has invested in establishing a Gen8 IGZO plant at its Kameyama plant in Japan while LG has also selected IGZO backplanes for its large-sized white OLED technology. At the same time, Chinese companies such as BOE are fast playing catch up with both prototype and production capacity announcements.

IDTechEx estimates that 7 km sqr of metal oxide backplanes will be used in the OLED industry in 2024, enabling a 16 billion USD market at the display module level. The LCD display market will add an extra demand of at least 1 km sqr per year in 2024 for metal oxide backplanes.

The display industry continues to rapidly change and seek new markets. Long term trends are still prevalent and shape global activity. Examples include reducing power consumption, improving image resolution, and decreasing device thickness. At the same, the need to differentiate and capture new markets such as wearable electronics is first bringing in robust and then flexible and bendable displays. These trends will drastically affect the technology requirements at many levels including the backplane level. This will stretch several existing solutions beyond likely performance limits, thereby creating openings and opportunities for new entrants and the technology space for backplanes is complex. It consists of (a) mature technologies such as amorphous and polycrystalline silicon, (b) emerging technologies such as organic and metal oxides and (c) early state technologies such as graphene, carbon nanotubes, nanowires, etc. No single technology offers a one-size-fits-all solution and many technologies will co-exist in the market. Betting on the right technology will remain a decision-making nightmare.

It is within this emerging, complex yet changing space that metal oxide are emerging. They promise low leakage currents, high mobility, amorphousity, stability and wide bandgap. These attributes promise to enable, respectively, power consumption reduction, compatibility with current-driven OLEDs and/or 3D displays, image uniformity over large areas, long lifetime and transparency.

In the short term, this will help enable higher resolution and lower power consumption levels in displays including LCDs (particularly in medium- to large-sized displays); while in the medium- to long-term metal oxides will help enable uniform medium- to large-sized OLED displays.

The report specifically addresses the big picture – including OLED displays and lighting, to thin film photovoltaics to flexible sensors and much more. Importantly, it includes not only electronics which are printed, organic and/or flexible now, but it also covers those that will be. Realistic timescales, case studies, existing products and the emergence of new products are given, as are impediments and opportunities for the years to come.

Over 3,000 organizations are pursuing printed, organic, flexible electronics, including printing, electronics, materials and packaging companies. While some of these technologies are in use now – indeed there are three sectors which have created billion dollar markets – others are commercially embryonic.

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In rapidly changing display industry, metal oxide TFT backplanes are promising

MarketResearchReports.Biz released a new market research report this week entitled “Metal Oxide TFT Backplanes For Displays 2014-2024: Technologies, Forecasts, Players.”

According to the new report, metal oxide display backplanes have already gone commercial. Sharp has invested in establishing a Gen8 IGZO plant at its Kameyama plant in Japan while LG has also selected IGZO backplanes for its large-sized white OLED technology. At the same time, Chinese companies such as BOE are fast playing catch up with both prototype and production capacity announcements.

IDTechEx estimates that 7 km sqr of metal oxide backplanes will be used in the OLED industry in 2024, enabling a 16 billion USD market at the display module level. The LCD display market will add an extra demand of at least 1 km sqr per year in 2024 for metal oxide backplanes.

The display industry continues to rapidly change and seek new markets. Long term trends are still prevalent and shape global activity. Examples include reducing power consumption, improving image resolution, and decreasing device thickness. At the same, the need to differentiate and capture new markets such as wearable electronics is first bringing in robust and then flexible and bendable displays. These trends will drastically affect the technology requirements at many levels including the backplane level. This will stretch several existing solutions beyond likely performance limits, thereby creating openings and opportunities for new entrants and the technology space for backplanes is complex. It consists of (a) mature technologies such as amorphous and polycrystalline silicon, (b) emerging technologies such as organic and metal oxides and (c) early state technologies such as graphene, carbon nanotubes, nanowires, etc. No single technology offers a one-size-fits-all solution and many technologies will co-exist in the market. Betting on the right technology will remain a decision-making nightmare.

It is within this emerging, complex yet changing space that metal oxide are emerging. They promise low leakage currents, high mobility, amorphousity, stability and wide bandgap. These attributes promise to enable, respectively, power consumption reduction, compatibility with current-driven OLEDs and/or 3D displays, image uniformity over large areas, long lifetime and transparency.

In the short term, this will help enable higher resolution and lower power consumption levels in displays including LCDs (particularly in medium- to large-sized displays); while in the medium- to long-term metal oxides will help enable uniform medium- to large-sized OLED displays.

The report specifically addresses the big picture – including OLED displays and lighting, to thin film photovoltaics to flexible sensors and much more. Importantly, it includes not only electronics which are printed, organic and/or flexible now, but it also covers those that will be. Realistic timescales, case studies, existing products and the emergence of new products are given, as are impediments and opportunities for the years to come.

Over 3,000 organizations are pursuing printed, organic, flexible electronics, including printing, electronics, materials and packaging companies. While some of these technologies are in use now – indeed there are three sectors which have created billion dollar markets – others are commercially embryonic.

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In rapidly changing display industry, metal oxide TFT backplanes are promising

MarketResearchReports.Biz released a new market research report this week entitled “Metal Oxide TFT Backplanes For Displays 2014-2024: Technologies, Forecasts, Players.”

According to the new report, metal oxide display backplanes have already gone commercial. Sharp has invested in establishing a Gen8 IGZO plant at its Kameyama plant in Japan while LG has also selected IGZO backplanes for its large-sized white OLED technology. At the same time, Chinese companies such as BOE are fast playing catch up with both prototype and production capacity announcements.

IDTechEx estimates that 7 km sqr of metal oxide backplanes will be used in the OLED industry in 2024, enabling a 16 billion USD market at the display module level. The LCD display market will add an extra demand of at least 1 km sqr per year in 2024 for metal oxide backplanes.

The display industry continues to rapidly change and seek new markets. Long term trends are still prevalent and shape global activity. Examples include reducing power consumption, improving image resolution, and decreasing device thickness. At the same, the need to differentiate and capture new markets such as wearable electronics is first bringing in robust and then flexible and bendable displays. These trends will drastically affect the technology requirements at many levels including the backplane level. This will stretch several existing solutions beyond likely performance limits, thereby creating openings and opportunities for new entrants and the technology space for backplanes is complex. It consists of (a) mature technologies such as amorphous and polycrystalline silicon, (b) emerging technologies such as organic and metal oxides and (c) early state technologies such as graphene, carbon nanotubes, nanowires, etc. No single technology offers a one-size-fits-all solution and many technologies will co-exist in the market. Betting on the right technology will remain a decision-making nightmare.

It is within this emerging, complex yet changing space that metal oxide are emerging. They promise low leakage currents, high mobility, amorphousity, stability and wide bandgap. These attributes promise to enable, respectively, power consumption reduction, compatibility with current-driven OLEDs and/or 3D displays, image uniformity over large areas, long lifetime and transparency.

In the short term, this will help enable higher resolution and lower power consumption levels in displays including LCDs (particularly in medium- to large-sized displays); while in the medium- to long-term metal oxides will help enable uniform medium- to large-sized OLED displays.

The report specifically addresses the big picture – including OLED displays and lighting, to thin film photovoltaics to flexible sensors and much more. Importantly, it includes not only electronics which are printed, organic and/or flexible now, but it also covers those that will be. Realistic timescales, case studies, existing products and the emergence of new products are given, as are impediments and opportunities for the years to come.

Over 3,000 organizations are pursuing printed, organic, flexible electronics, including printing, electronics, materials and packaging companies. While some of these technologies are in use now – indeed there are three sectors which have created billion dollar markets – others are commercially embryonic.

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