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High-performance integrated electro-optic modulators operating at low temperature are critical for optical interconnects in cryogenic applications. Existing integrated modulators, however, suffer from reduced modulation efficiency or bandwidth at low temperatures because they rely on tuning mechanisms that degrade with decreasing temperature. Graphene modulators are a promising alternative because graphene’s intrinsic carrier mobility increases at low temperature. Here, we demonstrate an integrated graphene-based electro-optic modulator whose 14.7 GHz bandwidth at 4.9 K exceeds the room temperature bandwidth of 12.6 GHz. The bandwidth of the modulator is limited only by high contact resistance, and its intrinsic RC-limited bandwidth is 200 GHz at 4.9 K.

High-performance integrated electro-optic modulators operating at low temperature are critical for optical interconnects in cryogenic applications. Existing integrated modulators, however, suffer from reduced modulation efficiency or bandwidth at low temperatures because they rely on tuning mechanisms that degrade with decreasing temperature. Graphene modulators are a promising alternative because graphene's intrinsic carrier mobility increases at low temperature. Here, we demonstrate an integrated graphene-based electro-optic modulator whose 14.7 GHz bandwidth at 4.9 K exceeds the room temperature bandwidth of 12.6 GHz. The bandwidth of the modulator is limited only by high contact resistance, and its intrinsic RC-limited bandwidth is 200 GHz at 4.9 K. [ABSTRACT FROM AUTHOR]

Abstract Graphene field-effect transistor (GFET) sensors are an attractive analytical tool for the detection of water pollutants. Unfortunately, this application has been hindered by the sensitivity of such sensors to nonspecific disturbances caused by variations of environmental conditions. Incorporation of differential designs is a logical choice to address this issue, but this has been difficult for GFET sensors due to the impact of fabrication processes and material properties. This paper presents a differential GFET affinity sensor for the selective detection of water pollutants in the presence of nonspecific disturbances. This differential design allows for minimization of the effects of variations of environmental conditions on the measurement accuracy. In addition, to mitigate the impact of the fabrication process and material property variations, we introduce a compensation scheme for the individual sensing units of the sensor, so that such variations are accounted for in the compensation-based differential sensing method. We test the use of this differential sensor for the selective detection of the water pollutant 17β-estradiol in buffer and tap water. Consistent detection results can be obtained with and without interferences of pH variations, and in tap water where unknown interferences are present. These results demonstrate that the differential graphene affinity sensor is capable of effectively mitigating the effects of nonspecific interferences to enable selective water pollutant detection for water quality monitoring. Highlights • An integrated differential graphene affinity sensor based on field-effect transistors. • First demonstration of the selective detection of analytes with nonspecific disturbances using a graphene sensor. • A compensation scheme reducing the impact of fabrication process and material property variations on differential sensing. • A compensation-based differential scheme for accurate nanosensing. [ABSTRACT FROM AUTHOR]

Abstract This paper presents an affinity graphene nanosensor for detection of biomarkers in undiluted and non-desalted human serum. The affinity nanosensor is a field-effect transistor in which graphene serves as the conducting channel. The graphene surface is sequentially functionalized with a nanolayer of the polymer polyethylene glycol (PEG) and a biomarker-specific aptamer. The aptamer is able to specifically bind with and capture unlabeled biomarkers in serum. A captured biomarker induces a change in the electric conductivity of the graphene, which is measured in a buffer of optimally chosen ionic strength to determine the biomarker concentration. The PEG layer effectively rejects nonspecific adsorption of background molecules in serum while still allowing the aptamer to be readily accessible to serum-borne biomarkers and increases the effective Debye screening length on the graphene surface. Thus, the aptamer-biomarker binding sensitively changes the graphene conductivity, thereby achieving specific and label-free detection of biomarkers with high sensitivity and without the need to dilute or desalt the serum. Experimental results demonstrate that the graphene nanosensor is capable of specifically capturing human immunoglobulin E (IgE), used as a representative biomarker, in human serum in the concentration range of 50 pM–250 nM, with a resolution of 14.5 pM and a limit of detection of 47 pM. Graphical abstract Image 1 Highlights • A graphene FET nanosensor is used for IgE detection in human serum. • Functionlized PEG rejects nonspecific adsorption while increases the effective Debye length. • Aptamers are attached to PEG to recognize IgE molecules. • IgE in serum with a concentration range from 50 pM to 250 nM is successfully quantified. [ABSTRACT FROM AUTHOR]

A fully integrated graphene field-effect transistor (GFET) nanosensor utilizing a novel high-κ solid-gating geometry for a practical biosensor with enhanced sensitivity is presented. Herein, an 'in plane' gate supplying electrical field through a 30 nm HfO2 dielectric layer is employed to eliminate the cumbrous external wire electrode in conventional liquid-gate GFET nanosensors that undesirably limits the device potential in on-site sensing applications. In addition to the advantage in the device integration degree, the transconductance level is found to be increased by about 50% over liquid-gate GFET devices in aqueous-media, thereby improves the sensitivity performance in sensor applications. As the first demonstration of biosensing applications, a small-molecule antibiotic, kanamycin A, is detected by means of an aptameric competitive affinity principle. It is experimentally shown that the label-free and specific quantification of kanamycin A with a concentration resolution at 11.5 × 10−9 m is achievable through a single direct observation of the 200 s fast bioassay without any further noise canceling. These results demonstrate the utility and practicability of the new devices in label-free biosensing as a novel analytical tool, and potentially hold great promise in other significant biomedical applications. [ABSTRACT FROM AUTHOR]

This work presents a fully integrated graphene field-effect transistor (GFET) biosensor for the label-free detection of lead ions (Pb 2+ ) in aqueous-media, which first implements the G-quadruplex structure-switching biosensing principle in graphene nanoelectronics. We experimentally illustrate the biomolecular interplay that G-rich DNA single-strands with one-end confined on graphene surface can specifically interact with Pb 2+ ions and switch into G-quadruplex structures. Since the structure-switching of electrically charged DNA strands can disrupt the charge distribution in the vicinity of graphene surface, the carrier equilibrium in graphene sheet might be altered, and manifested by the conductivity variation of GFET. The experimental data and theoretical analysis show that our devices are capable of the label-free and specific quantification of Pb 2+ with a detection limit down to 163.7 ng/L. These results first verify the signaling principle competency of G-quadruplex structure-switching in graphene electronic biosensors. Combining with the advantages of the compact device structure and convenient electrical signal, a label-free GFET biosensor for Pb 2+ monitoring is enabled with promising application potential. [ABSTRACT FROM AUTHOR]

Abstract Label-free electronic biosensors as the non-electrochemical analytical tools without requirement of sophisticated instrumentation have become attractive, although their application in competitive affinity sensing of uncharged small molecules is still hindered by a difficulty in the development of competing analogues. To break through this bottleneck, we report a novel analogue made by epitope-modified metal nanoparticles to enable the electronic signaling of small-molecule analyte recognition via competitive affinity. While the electronic signaling capability of metal nanoparticle analogues is demonstrated by a graphene field-effect transistor bioassay of small-molecule glucose as a proof-of-principle, interestingly, we discover a new electronic signaling mechanism in the metal nanoparticle affinity, different to the intuitive charge accumulation expectation. On the basis of Kelvin-probe force microscopic potential characterization and theoretical discussion, we fundamentally elucidated the signaling mechanism as a seldom used electrostatic shielding-effect, that is, in the analogue-receptor affinity, metal nanoparticles with the charge density lower than receptor biomolecules can reduce the collective electrical potential via charge dispersion. Further consider the convenient epitope-modifiability of metal nanoparticles, the easy-to-develop analogues for diverse target analyte might potentially be predictable in the future. And the application of label-free electronic biosensors for the competitive affinity bioassay of range-extended small molecules may thus be promoted based on the electrostatic shielding-effect. Highlights • The analogue use of epitope-modified metal nanoparticles. • A novel electronic signaling mechanism based on electrostatic shielding-effect. • A glucometer demonstration based on graphene field-effect transistor (GFET). • The application potential of easy-to-develop customizable analogues. [ABSTRACT FROM AUTHOR]