A silicon nanowire field effect transistor (FET) straddled by the double-gate was demonstrated for biosensor application. The separated double-gates, G1 (primary) and G2 (secondary), allow independent voltage control to modulate channel potential. Therefore, the detection sensitivity was enhanced by the use of G2. By applying weakly positive bias to G2, the sensing window was significantly broadened compared to the case of employing G1 only, which is nominally used in conventional nanowire FET-based biosensors. The charge effect arising from biomolecules was also analyzed. Double-gate nanowire FET can pave the way for an electrically working biosensor without a labeling process.

Monolayer materials are sensitive to their environment because all of the atoms are at their surface. We investigate how exposure to the environment affects the electrical properties of CVD-grown monolayer MoS2 by monitoring electrical parameters of MoS2 field-effect transistors as their environment is changed from atmosphere to high vacuum. The mobility increases and contact resistance decreases simultaneously as either the pressure is reduced or the sample is annealed in vacuum. We see a previously unobserved, non-monotonic change in threshold voltage with decreasing pressure. This result could be explained by charge transfer on the MoS2 channel and Schottky contact formation due to adsorbates at the interface between the gold contacts and MoS2. Additionally, from our electrical measurements it is plausible to infer that at room temperature and pressure water and oxygen molecules adsorbed on the surface act as interface traps and scattering centers with a density of several 1012 cm−2 eV−1, degrading the electrical properties of monolayer MoS2.

Nanopores are now being used not only as an ionic current sensor but also as a means to localize molecules near alternative sensors with higher sensitivity and/or selectivity. One example is a solid-state nanopore embedded in a graphene nanoribbon (GNR) transistor. Such a device possesses the high conductivity needed for higher bandwidth measurements and, because of its single-atomic-layer thickness, could improve the spatial resolution of the measurement. Here we show two-channel measurements of ionic current through the nanopore during double-stranded DNA (dsDNA) translocation, along with the simultaneous response of the neighboring GNR due to changes in the surrounding electric potential. We observe cross-talk originating from capacitive coupling between the two measurement channels, resulting in a transient response in the GNR during DNA translocation; however, we do not observe a modulation in device conductivity via an electric field effect response, due to changes in local solution potential during DNA translocation. A field effect response would scale with GNR source-drain voltage (Vds), whereas the capacitive coupling does not scale with Vds. In order to take advantage of the high bandwidth potential of such sensors, the field effect response must be enhanced. We present potential field calculations to outline a phase diagram for detection within the device parameter space, charting a roadmap for future optimization of such devices.

A silicon nanowire field-effect transistor (SiNW FET) with local side-gates and Pd surface decoration is demonstrated for hydrogen (H2) detection. The SiNW FETs are fabricated by top-down method and functionalized with palladium nanoparticles (PdNPs) through electron beam evaporation for H2 detection. The drain current of the PdNP-decorated device reversibly responds to H2 at different concentrations. The local side-gates allow individual addressing of each sensor and enhance the sensitivity by adjusting the working region to the subthreshold regime. A control experiment using a non-functionalized device verifies that the hydrogen-sensitivity is originated from the PdNPs functionalized on the SiNW surface.

Self-heated silicon nanowire sensors for high-performance, ultralow-power hydrogen detection have been developed. A top-down nanofabrication method based on well-established semiconductor manufacturing technology was utilized to fabricate silicon nanowires in wafer scale with high reproducibility and excellent compatibility with electronic readout circuits. Decoration of palladium nanoparticles onto the silicon nanowires enables sensitive and selective detection of hydrogen gas at room temperature. Self-heating of silicon nanowire sensors allows us to enhance response and recovery performances to hydrogen gas, and to reduce the influence of interfering gases such as water vapor and carbon monoxide. A short-pulsed heating during recovery was found to be effective for additional reduction of operation power as well as recovery characteristics. This self-heated silicon nanowire gas sensor will be suitable for ultralow-power applications such as mobile telecommunication devices and wireless sensing nodes.

We demonstrated novel methods for selective surface modification of silicon nanowire (SiNW) devices with catalytic metal nanoparticles by nanoscale Joule heating and local chemical reaction. The Joule heating of a SiNW generated a localized heat along the SiNW and produced endothermic reactions such as hydrothermal synthesis of nanoparticles or thermal decomposition of polymer thin films. In the first method, palladium (Pd) nanoparticles could be selectively synthesized and directly coated on a SiNW by the reduction of the Pd precursor via Joule heating of the SiNW. In the second method, a sequential process composed of thermal decomposition of a polymer, evaporation of a Pd thin film, and a lift-off process was utilized. The selective decoration of Pd nanoparticles on SiNW was successfully accomplished by using both methods. Finally, we demonstrated the applications of SiNWs decorated with Pd nanoparticles as hydrogen detectors. We also investigated the effect of self-heating of the SiNW sensor on its sensing performance.

Early diagnosis of the highly pathogenic H5N1 avian influenza virus (AIV) is significant for preventing and controlling a global pandemic. However, there is no existing electrical biosensor for detecting biomarkers for AIV in clinically relevant samples such as chicken serum. Herein, we report the first use of an aptamer-functionalized field-effect transistor (FET) as a label-free sensor for AIV detection in chicken serum. A DNA aptamer is employed as a sensitive and selective receptor for hemagglutinin (HA) protein, which is a biomarker for AIVs. This aptamer is immobilized on a gold microelectrode that is connected to the gate of a reusable FET transducer. The specific binding of the target protein results in a change in the surface potential, which generates a signal response of the FET transducer. We hypothesize that a conformational change in the DNA aptamer upon specific binding of HA protein may alter the surface potential. The signal of the aptamer-based FET biosensor increased linearly with the increase in the logarithm of HA protein concentration in a dynamic range of 10 pM to 10 nM with a detection limit of 5.9 pM. The selectivity of the biosensor for HA protein was confirmed by employing relevant interfering proteins. The proposed biosensor was successfully applied to the selective detection of HA protein in a chicken serum sample. Owing to its simple and low-cost architecture, portability, and sensitivity, the aptamer-based FET biosensor has potential as a point-of-care diagnosis of H5N1 AIVs in clinical samples.

A label‐free biosensor based on a nanogap‐embedded field‐effect transistor is demonstrated. When biomolecules fill the molecular‐sized nanogap, the transistor parameters are remarkably changed by the gate dielectric constant. The transistor detects specific binding between the avian influenza antibody and an antigen with the silica‐binding protein.