No abstract

The recent Coronavirus Disease 2019 (COVID‐19) outbreak strongly propels advancements in biosensor technology, leading to the emergence of novel methods for virus detection. Among them, those using nanostructured field‐effect transistors (FETs) provide an ultrasensitive approach toward point‐of‐care diagnostics. However, the application of these biosensors in analyzing biofluids has been limited by their reduced screening length in high ionic strength liquids. To address this challenge, a solution is presented involving the surface modification of FETs with a hydrogel based on star‐shaped polyethylene glycol. This hydrogel is loaded with specific antibodies against the severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) spike protein. By incorporating the hydrogel, the effective Debye length is effectively increased, thereby preserving the sensitivity in biofluids. The efficacy of this approach is demonstrated by employing silicon nanonet‐based FETs for the detection of viral antigens in both buffer and saliva, as well as cultured viral particle dispersions. Moreover, positive and negative patient samples are successfully differentiated, showcasing the practical application of this method. Finally, a theoretical frame is proposed to elucidate the underlying mechanism behind the preservation of sensitivity.

The recent COVID-19 outbreak has strongly pushed the field of biosensors, resulting in multiple new approaches for quantitative virus detection. Among them, those using nanostructured field-effect transistors (FETs) as transducers provide an ultrasensitive approach requiring simple setups for their miniaturization toward point-of-care diagnostics of the disease. However, this type of biosensors suffer from limited sensitivity when it comes to analyzing biofluids due to their shortened screening length in presence of complex liquids with high ionic strength. In this work we propose a solution to this problem, which consists on the surface modification of the FETs with a hydrogel based on star-shaped polyethylene glycol and loaded with specific antibodies against SARS-CoV-2 spike protein. The hydrogel increases the effective Debye length, allowing to preserve the sensitivity in high ionic strength solutions. We provide the demonstration employing silicon nanonet-based FETs for the detection of viral antigens in buffer and in saliva, as well as cultured viral particles. We finally discriminate positive and negative patient samples (nasopharyngeal swab), and propose the theoretical frame that discusses the mechanism of the sensitivity preservation based on the presence of the pegylated hydrogel.

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