The potential application of electrochemical biosensors in the COVID-19 pandemic: A perspective on the rapid diagnostics of SARS-CoV-2.

Electrochemical biosensors combine the selectivity of electrochemical signal transducers with the specificity of biomolecular recognition strategies. Although they have been broadly studied in different areas of diagnostics, they are not yet fully commercialized. During the COVID-19 pandemic, electrochemical platforms have shown the potential to address significant limitations of conventional diagnostic platforms, including accuracy, affordability, and portability. The advantages of electrochemical platforms make them a strong candidate for rapid point-of-care detection of SARS-CoV-2 infection by targeting not only viral RNA but antigens and antibodies. Herein, we reviewed advancements in electrochemical biosensing platforms towards the detection of SARS-CoV-2 through studying similar viruses.

A Nanostructured Gold/Graphene Microfluidic Device for Direct and Plasmonic-Assisted Impedimetric Detection of Bacteria.

Hierarchical 3D gold nano-/microislands (NMIs) are favorably structured for direct and probe-free capture of bacteria in optical and electrochemical sensors. Moreover, their unique plasmonic properties make them a suitable candidate for plasmonic-assisted electrochemical sensors, yet the charge transfer needs to be improved. In the present study, we propose a novel plasmonic-assisted electrochemical impedimetric detection platform based on hybrid structures of 3D gold NMIs and graphene (Gr) nanosheets for probe-free capture and label-free detection of bacteria. The inclusion of Gr nanosheets significantly improves the charge transfer, addressing the central issue of using 3D gold NMIs. Notably, the 3D gold NMIs/Gr detection platform successfully distinguishes between various types of bacteria including Escherichia coli (E. coli) K12, Pseudomonas putida (P. putida), and Staphylococcus epidermidis (S. epidermidis) when electrochemical impedance spectroscopy is applied under visible light. We show that distinguishable and label-free impedimetric detection is due to dissimilar electron charge transfer caused by various sizes, morphologies, and compositions of the cells. In addition, the finite-difference time-domain (FDTD) simulation of the electric field indicates the intensity of charge distribution at the edge of the NMI structures. Furthermore, the wettability studies demonstrated that contact angle is a characteristic feature of each type of captured bacteria on the 3D gold NMIs, which strongly depends on the shape, morphology, and size of the cells. Ultimately, exposing the platform to various dilutions of the three bacteria strains revealed the ability to detect dilutions as low as ∼20 CFU/mL in a wide linear range of detection of 2 × 101-105, 2 × 101-104, and 1 × 102-1 × 105 CFU/mL for E. coli, P. putida, and S. epidermidis, respectively. The proposed hybrid structure of 3D gold NMIs and Gr, combined by novel plasmonic and conventional impedance spectroscopy techniques, opens interesting avenues in ultrasensitive label-free detection of bacteria with low cost and high stability.