Svetlana A. Vitusevich

Liquid‐gated transistor biosensors, fabricated using complementary metal‐oxide‐semiconductor (CMOS)‐compatible technology, face significant challenges relating to their long‐term stability when utilized in complex bio‐liquid environments. In this study, we use diamond‐like carbon (DLC) layers of nanometer‐scale thicknesses, ranging from 1 to 14 nm, to modify the surface properties of a low‐defect‐density SiO ₂ layer. By analyzing the capacitance–voltage characteristics and stability time traces of DLC‐covered silicon‐based structures, we registered three well‐separated regions of the flat‐band voltage values. The DLC layers demonstrate advanced properties: enhanced stability compared to the bare SiO ₂ layer and good sensitivity. X‐ray photoemission and Raman spectroscopy results enable an analysis of DLC material and the estimation of sp ² graphitic and sp ³ diamond components. Measurements of different pH and biological C‐reactive protein solutions show that DLC‐modified structures, including nanowire field‐effect transistors (FET), have great potential for bio‐signal monitoring. The mechanism of long‐term stability is established using impedance spectroscopy and modeling data analysis. This study opens up prospects for the design of dielectric layer‐covered structures and their surface modification at the liquid–solid interface of biosensors, providing valuable insights into DLC interface engineering for the development of highly sensitive and reliable FET biosensors.

Graphene field-effect transistors (GFETs) functionalized with lipid monolayers provide a sensitive platform for probing membrane protein dynamics. Here, we analyze the effect of peripheral membrane proteins on this assay. We focused on the prenylated Rab7 GTPase Ypt7 and its interacting HOPS tethering complex using liquid-gated GFETs combined with low-frequency noise spectroscopy. Current–voltage (I–[ ] transfer measurements reveal no or only very small changes upon binding of Ypt7 and after addition of HOPS. In contrast, noise analysis reveals pronounced flicker (1/[ ] noise level growth after Ypt7 binding, most likely due to conformational dynamics of Ypt7. Recruitment of the HOPS complex by Ypt7 to membranes inhibits these fluctuations, suggesting structural stabilization of Ypt7 via HOPS binding. Our findings demonstrate that noise spectroscopy allows for enhancing the sensitivity of GFET-based biosensing, offering insights into protein–membrane and protein–protein interactions beyond traditional electronic readouts.

Gallium nitride (GaN) nanowires are promising for nanoelectronic and biosensing applications due to their unique electronic properties and stability. However, understanding electron transport in AlGaN/GaN nanowires, particularly the influence of edge depletion and trap states, remains limited. Here, we investigate electronic transport in AlGaN/GaN transistor‐like heterostructures patterned into nanowires of varying widths (185–1110 nm), analyzing current–voltage characteristics under dark and ultraviolet (UV) illumination. External UV excitation influences the depletion widths in NWs, modulates space‐charge‐limited current (SCLC), and provides information about the distribution range of traps in NW structures. We observe a transition from Ohmic to SCLC regimes, with UV excitation modulating depletion widths and enhancing conductivity by releasing trapped carriers. Temperature‐dependent measurements allow us to estimate trap energy distributions in the range of 150–200 meV, confirmed by noise spectroscopy data. These findings demonstrate that optical excitation effectively controls SCLC transport in GaN nanowires, offering insights for designing sensitive nanoelectronic and biosensing devices leveraging trap‐mediated charge dynamics.

Microwave (MW) studies of biochemical liquids require the precise determination of permittivity and a convenient sample placement in a sterile channel, which must be cleaned or replaced after testing. These requirements can be effectively met using the proposed MW characterization technique. This technique is based on a high-quality whispering-gallery mode (WGM) quartz resonator. The liquid under test is filled in a capillary tube (CT), which is placed in the resonator hole. A calibration approach based on simulations for the extraction of complex permittivity values of biochemical liquids of sub-microliter volumes was demonstrated and successfully verified. This was achieved through a special procedure for the analysis of the interaction of the electromagnetic field with the liquid in a CT inside a WGM quartz resonator and measurements of its frequency response. The reliability of the technique was validated by simulation and the measurement of liquids with known characteristics. The approach was successfully applied to obtain the complex permittivity of glucose in water solutions in the Ka-band.

Highly sensitive high-speed biosensors are key devices for precise diagnostics, which allows the application of medical treatment in a short time. In this paper, noise spectra and characteristic time constants are studied in nanotransistors with channel sizes below 30[ ]nm. The quantization effect due to the formation of a quantum dot channel is analyzed based on the transport and noise properties of the device structures. Ultra-low flicker noise at the quantum level with a Hooge parameter of about 10[ ] is registered. A strong dependence of the characteristic switching time on the modulation effect is revealed with a slope ([ ]) that considerably exceeds the value of 1, which is typically obtained in large-area device structures. This reflects the fact that a 700% amplification of sensitivity in nanotransistor biosensors can be obtained. A dimensionless R-factor introduced by the ratio of the emission time constant to the capture time constant as a function of gate voltage reveals a slope equal to 20, which is promising for the extraction of very small signals from biomolecules with 20 times higher sensitivity.

Liquid gate‐all‐around (LGAA) field‐effect transistor (FET) biosensors represent advanced material device structures responding electrically to surface potential change and allowing ultra‐high sensitivity to biochemical liquids and human bodily fluids. However, the origin and physical working mechanisms for such a type of signals in different complex biochemical solutions remain still many opened questions. Here, noise spectroscopy and impedance methods are applied to study liquid–solid interface properties in LGAA FETs working in adjusted physiological solutions of different pH values. High‐quality liquid LGAA Si nanowire (NW) FET biosensors demonstrate the high electronic performance of I–V characteristics in good agreement with modeling data. Impedance spectroscopy measurements allow for analyzing the double‐layer capacitances and ion behavior under different pH conditions. Moreover, the noise spectra of the current fluctuations in the biosensors for several solutions are analyzed at different applied liquid‐gate and drain‐source voltages. The results demonstrate accurate detection of the dynamic ion processes on the nanowire surface. Charge inversion effect is revealed in single‐valent ion solutions. Tiny signal characterization results obtained using the LGAA NW FET biosensors provide broader insights into the optimization of sensor parameters for biomedical molecular detection.

The structural and electrical properties of ionic metal‐alkanoate nanocomposites obtained based on a cadmium octanoate matrix with individual carbon and gold nanoparticles (NPs) as well as their combination are studied. Carbon and gold NPs were chemically synthesized within the smectic A phase of Cd⁺²(C₇H₁₅COO⁻)₂, which served as a well‐ordered nanoreactor. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) data provide information on NPs location and allow the estimation of the sizes of the synthesized NPs inside the glassy liquid crystalline matrix. It is shown that the size and shape of the NPs were precisely controlled during synthesis, resulting in highly stable and organized nanocomposites. The electrical characteristics were studied in a wide temperature range corresponding to different phase states of the nanocomposites. We compared the electrical properties of both pure matrix and nanocomposites with carbon and gold NPs to identify the potential of the nanocomposite materials for designing new sensor structures. Notably, the nanocomposites exhibited anisotropic conductivity, highlighting the structural anisotropy of the material. In addition, using NPs allows fine‐tuning of the electrical properties of a metal‐alkanoate host matrix. The obtained nanocomposites open prospects for the development of electro‐optical sensors with high sensitivity and specificity that can be used to detect a variety of chemical and physical parameters including temperature, composition of substances, and environment.

Highly sensitive biosensors which operate based on the utilization of random telegraph signal (RTS) noise spectroscopy might allow for the detection of diseases at the earliest stage. In this work, we provide an overview of our findings concerning RTS behavior in liquid-gated (LG) field-effect transistors (FETs). We propose different kinds of LG FET structures supported by modeling data for the extraction of characteristic RTS parameters for different carrier concentrations and operating voltages in the devices. We demonstrate the innovative aspects and opportunities of noise and fluctuations for biosensing applications. Moreover, we show that light excitation can be used to tune RTS parameters and increase the sensitivity of biosensors by at least 1.5 times. We also discuss challenges related to the utilization of RTS in different research fields, including biosensors and quantum information technology as well as ways of finding solutions to the problems.