Remote Floating-Gate Field-Effect Transistor with 2-Dimensional Reduced Graphene Oxide Sensing Layer for Reliable Detection of SARS-CoV-2 Spike Proteins.

Despite intensive research of nanomaterials-based field-effect transistors (FETs) as a rapid diagnostic tool, it remains to be seen for FET sensors to be used for clinical applications due to a lack of stability, reliability, reproducibility, and scalability for mass production. Herein, we propose a remote floating-gate (RFG) FET configuration to eliminate device-to-device variations of two-dimensional reduced graphene oxide (rGO) sensing surfaces and most of the instability at the solution interface. Also, critical mechanistic factors behind the electrochemical instability of rGO such as severe drift and hysteresis were identified through extensive studies on rGO-solution interfaces varied by rGO thickness, coverage, and reduction temperature. rGO surfaces in our RFGFET structure displayed a Nernstian response of 54 mV/pH (from pH 2 to 11) with a 90% yield (9 samples out of total 10), coefficient of variation (CV) < 3%, and a low drift rate of 2%, all of which were calculated from the absolute measurement values. As proof-of-concept, we demonstrated highly reliable, reproducible, and label-free detection of spike proteins of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in a saliva-relevant media with concentrations ranging from 500 fg/mL to 5 µg/mL, with an R2 value of 0.984 and CV < 3%, and a guaranteed limit of detection at a few pg/mL. Taken together, this new platform may have an immense effect on positioning FET bioelectronics in a clinical setting for detecting SARS-CoV-2.

Specific Chemical Modification of Nanohole Edges in Membrane Graphene for Protein Binding

The vital role of biosensors in our lives is steadily increasing due to their wide range of applications. As part of our striving efforts to develop affordable and highly sensitive biosensing technologies, we present here the successful chemical modification of-and biological molecule attachment to-holes' edges formed in a sheet of graphene, named nanomembrane graphene (NMG). This work complements our previous work, which showed that NMG could be used as a mid-IR biosensor, in which it becomes essential to overcome the challenge of the specific chemical modification of the holes' edges. In this work, we formed the NMG on reduced graphene oxide (rGO) layer using Au nanoparticles (Au NPs) and nano-islands (Au NIs). The formation methods were optimized by applying a matrix of variable concentration, size, and deposition time, as well as by chemical modification of substrate. The optimum scenarios were defined as having an extremely thin rGO layer, Au NPs, or NIs with size and center-to-center distance of 20-35 and 40-60 nm, respectively, and to have weak interaction between the metal and the substrate to allow etching leading to the formation of holes. The chemical groups at the edges were investigated to define the best method to attach biological molecules to them. Finally, we demonstrated the successful measurement of the binding between SARS-CoV-2 spike protein and its antibody (ACE2);real-time binding measurements revealed an affinity constant of 0.93 × 109 M-1. We consider these results important as they demonstrate a new route to a low-cost and high-sensitivity biosensor. © 2022 American Chemical Society.

Graphene Oxide/Fe3O4/Chitosan-Coated Nonwoven Polyester Fabric Extracted from Disposable Face Mask for Enhanced Efficiency of Organic Dye Adsorption

Owing to the COVID-19 pandemic, huge amounts of disposable face masks have been manufactured and used, and these discarded face masks have to be treated. In this study, we propose a simple approach for reusing the nonwoven polyester fabric (NWPF) from disposable face masks. In this approach, NWPF is utilized as a supporter for coating of a layer of graphene oxide/Fe3O4/chitosan (GFC) to form a GFC/NWPF adsorbent at room temperature via a simple spray coating method that does not require any solvent. The specific properties of GFC, NWPF, and the GFC/NWPF adsorbent were analysed via X-ray diffraction, transmission electron microscopy, ultraviolet-visible spectroscopy, vibrating sample magnetometry, and field-emission scanning electron microscopy. Results showed that the presence of NWPF enhanced the adsorption capacity of GFC towards organic dyes. At high concentrations of the organic dyes, the adsorption efficiency of the GFC/NWPF adsorbent to the dyes reached 100% within 24 h. The adsorption capacity (qmax) of the GFC/NWPF adsorbent to methylene blue, methyl orange, Congo red, and moderacid red was 54.795, 87.489, 88.573, and 29.010 mg g-1, respectively, which were considerably higher than that of bulk GFC (39.308, 82.304, 52.910, and 21.249 mg g-1, respectively). © 2022 Hoang V. Tran et al.