Silicon-on-insulator (SOI) nanowire or nanoribbon field-effect transistor (FET) biosensors are versatile platforms of electronic detectors for the real-time, label-free, and highly sensitive detection of a wide range of bioparticles. At a low analyte concentration in samples, the target particle diffusion transport to sensor elements is one of the main limitations in their detection. The dielectrophoretic (DEP) manipulation of bioparticles is one of the most successful techniques to overcome this limitation. In this study, TCAD modeling was used to analyze the distribution of the gradient of the electric fields E for the SOI-FET sensors with embedded DEP electrodes to optimize the conditions of the dielectrophoretic delivery of the analyte. Cases with asymmetrical and symmetrical rectangular electrodes with different heights, widths, and distances to the sensor, and with different sensor operation modes were considered. The results showed that the grad E2 factor, which determines the DEP force and affects the bioparticle movement, strongly depended on the position of the DEP electrodes and the sensor operation point. The sensor operation point allows one to change the bioparticle movement direction and, as a result, change the efficiency of the delivery of the target particles to the sensor.

In thin films, we deal with such a physical phenomenon as the coupling-effect. In this study, this effect was used to redistribute charge carriers in silicon-on-insulator thin films to determine the effective mobility near the interface under study. Temperature dependences of mobility were applied to experimental results to extract components of effective mobility related to phonon and interface roughness scattering of the carriers. These components are more suitable to show differences in the interface quality of films than values of effective mobility. The suggested approach can be used for the non-destructive analysis of interface quality in films.

The condition of the same distribution of free carriers in thin films is necessary for comparing the mobility and analyzing the scattering mechanisms of carriers near semiconductor film/insulator interfaces. In thin film/insulator systems with different design parameters, it is difficult to ensure the same distribution of free carriers due to physical phenomenon such as the coupling effect. In this study, TCAD simulations of thin-film transistors, which have been used to monitor Si film properties, were applied to find parameters that allow tuning the potential distribution and, accordingly, the distribution of free carriers in films. It was found that such parameters are the film regime, the density of induced carriers, the gate voltage or threshold voltage of transistors. The conditions for the selection of parameters were found that ensure the same distribution of free carriers in thin-film structures for the cases of different thicknesses of films and the surrounding dielectrics. It was shown that the proposed approach can be used for a comparative analysis of the mobility in thin films and makes it possible to eliminate errors associated with different distributions of carriers in the films due to the coupling effect.

The recent outbreak of coronavirus disease caused by the respiratory syndrome coronavirus 2 (SARS-CoV-2) has highlighted the urgent need to develop fast and highly sensitive analytical tools and diagnostic devices to detect and study of the fundamental properties viruses and their nucleic acid and protein components [1]. Silicon-on-insulator field-effect transistors (SOI-FETs) based sensors provide the versatile platform for direct detection of biological species as excellent electrical signal converters. These devices have demonstrated applications for label-free, ultra-sensitive, and selective real-time detection of a wide range of biological species, including nucleic acids, proteins and viruses in either single-element or multiplexed formats [2-5]. Dielectrophoresis (DEP) and electro-hydrodynamic techniques are well known as the methods of selection and delivery of analytes to overcome limitations of diffusive transport to sensor elements without additional processing or labeling steps [6]. The aim of this study was to investigate the features of the behavior of the viruses when they are indicated by SOI-FET sensors with DEF-control. For this, SOI-FET sensors with lateral DEP-electrodes and multichannel sensors, for comparison, were used. Top-down technology with using optical lithography was applied for sensor fabrication. Devices manufacturing details are described elsewhere [3]. As an analyte, we used nuclear polyhedrosis viruses (NPVs), coronavirus virus-like particles (CVP) and suspension of specific antibodies to the virus created in the Federal research center of Virology and biotechnology "Vector" of Rospotrebnadzor. The results showed that the sensors used in the study provide the subatomolar level of virus detection. DEP-concentration of viruses increase the response of the sensors by factors of 2 to 9 (compared to the response of sensors without DEP control) and allows the false positives can be eliminated. NPVs lose their mobility with prolonged exposure to an alternating field in the sub-MHz range. The DEP-concentration of CVP leads to the formation of crystal-like structures (Fig.1). This study was supported by grant no. 18-29-02091 of the Russian Foundation for Basic Research. Sample preparation of biological materials was done within the framework of the State Task of Rospotrebnadzor. Referencies: WHO Director-General's opening remarks at the media briefing on COVID-19 – 23 April 2021 23 апреля 2021 г.https://www.who.int/director-general/speeches/detail/who-director-general-s-opening-remarks-at-the-media-briefing-on-covid-19-23-april-2021. Patolsky F., Zheng G., Hayden O., Lakadamyali M., Zhuang X., Lieber C. M. Electrical detection of single viruses // Proc. Natl. Acad. Sci. 2004, v. 101. p. 14017-14022. O. V. Naumova, V. M. Generalov, E. G. Zaitseva, A. V. Latyshev, A. L. Aseev, S. A. Pyankov, I. V. Kolosov, G. G. Ananko, A. P. Agafonov, E. V. Gavrilova, R. A. Maksyutov, and A. S. Safatov. Biosensors Based on Soi Nanowire Transistors for Biomedicine and Virusology. Russian Microelectronics, 2021, v. 50, N3, p. 137–145. Ivanov Y.D., Pleshakova T.O., Kozlov A.F., Malsagova K.A., Krohin N.V., Shumyantseva V.V., Shumov I.D., Popov V.P., Naumova O.V., Fomin B.I., Nasimov D.A., Aseev A.L., Archakov A.I. SOI nanowire for the high-sensitive detection of HBsAg and a-fetoprotein. Lab Chip. 2012, v. 12, p. 5104-5111. Dmitrienko E., Naumova O., Fomin B., Kupryushkin M., Volkova A., Amirkhanov N., Semenov D., Pyshnaya I., Pyshnyi D. Surface modification of SOI FET sensors for label-free and specific detection of short RNA analyte. Nanomedicine 2016, v. 11, N 16, p. 2073-2082. Lee S., Roh S.M., Lee E., Park Y., Lee B.C., Kwon Y., Kim H.J., Kim J. Applications of converged various forces for detection of biomolecules and novelty of dielectrophoretic force in the applications(Review). Sensors, 2020, v.20, p.3242. Fig.1 – Optical image of sensor with lateral DEP electrodes after CVP detection. In the left - CVP organized in crystal-like structures under DEP-concentration, in the right (green dots on dark field) - viruses with luminescent labels. S - source, D - drain. G1, G2 - lateral DEP electrodes. Figure 1