Hydrogel-coated nanonet-based field-effect transistors for SARS-CoV-2 spike protein detection in high ionic strength samples

The SARS-CoV-2 pandemic has triggered many studies worldwide in the area of biosensors, leading to innovative approaches for the quantitative assessment of COVID-19. Nanostructured field-effect transistor (FET) are one type of the devices shown to be ultrasensitive for virus determination. FETs can be used as transducers to analyze changes in electrical current caused by the bonding of viral molecules to the surface of the semiconducting nanomaterial layer of the FETs¹. Although nano-transistors require simple setups amenable to be miniaturized for point-of-care diagnostic of COVID 19, this type of sensors usually have limited sensitivity in biological fluids. The reason behind is the shortened screening length in the presence of high ionic strength solutions². In the frame of this study, we propose a methodology consisting on the FET surface modification with a hydrogel based on the star-shaped polyethylene glycol (starPEG), which hosts specific antibodies against SARS-CoV-2 spike protein in its porous structure. The deposition of the hydrogel increases the effective Debye length, preserving the biosensor’s sensitivity. We demonstrate the capability of silicon nanonet-based FETs to detect the viral antigens and cultured viral particles in phosphate-buffered saline (PBS) as well as in human purified saliva. Finally, we discriminated positive and negative patients’ nasopharyngeal swab samples.

1. Ibarlucea B, Fawzul Akbar T, Kim K, et al. Ultrasensitive detection of Ebola matrix protein in a memristor mode. Nano Res. 2018;11(2):1057-1068. doi:10.1007/s12274-017-1720-2
2. Stern E, Wagner R, Sigworth FJ, Breaker R, Fahmy TM, Reed MA. Importance of the Debye Screening Length on Nanowire Field Effect Transistor Sensors. Nano Lett. 2007;7(11):3405-3409. doi:10.1021/nl071792z