Biofunctionalization of Graphene‐Based FET Sensors through Heterobifunctional Nanoscaffolds: Technology Validation toward Rapid COVID‐19 Diagnostics and Monitoring

Abstract

The biofunctionalization of graphene field-effect transistors (GFETs) through vinylsulfonated-polyethyleneimine nanoscaffold is presented for enhanced biosensing of severe acute respiratory-related coronavirus 2 (SARS-CoV-2) spike protein and human ferritin, two targets of great importance for the rapid diagnostic and monitoring of individuals with COVID-19. The heterobifunctional nanoscaffold enables covalent immobilization of binding proteins and antifouling polymers while the whole architecture is attached to graphene by multivalent π-π interactions. First, to optimize the sensing platform, concanavalin A is employed for glycoprotein detection. Then, monoclonal antibodies specific against SARS-CoV-2 spike protein and human ferritin are anchored, yielding biosensors with limit of detections of 0.74 and 0.23 nm, and apparent affinity constants ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow><mml:msubsup><mml:mi>K</mml:mi> <mml:mi>D</mml:mi> <mml:mrow><mml:mi>G</mml:mi> <mml:mi>F</mml:mi> <mml:mi>E</mml:mi> <mml:mi>T</mml:mi></mml:mrow> </mml:msubsup> </mml:mrow> </mml:math> ) of 6.7 and 8.8 nm, respectively. Both biosensing platforms show good specificity, fast time response, and wide dynamic range (0.1-100 nm). Moreover, SARS-CoV-2 spike protein is also detected in spiked nasopharyngeal swab samples. To rigorously validate this biosensing technology, the GFET response is matched with surface plasmon resonance measurements, exhibiting linear correlations (from 2 to 100 ng cm^-2) and good agreement in terms of <i>K</i> _D values. Finally, the performance of the biosensors fabricated through the nanoscaffold strategy is compared with those obtained through the widely employed monopyrene approach, showing enhanced sensitivity.