Introducing polymer conductance in diagnostically relevant transduction

Electrochemical capacitance spectroscopy based determination of antibodies against SARS-CoV-2 virus spike protein

In this study, we are reporting a novel electrochemical capacitance spectroscopy (ECS) platform designed for the sensitive and label-free detection of antibodies against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus spike protein (anti-rS) in diluted blood serum. The determination of anti-rS is crucial for identification individuals who have been infected by SARS-CoV-2 virus and may have acquired immunity. The rS protein was immobilized on a screen-printed carbon electrode, which was incubated in diluted blood serum containing anti-rS antibodies. Label-free ECS was applied for the determination of interaction between immobilized rS and free-standing anti-rS. Here reported bioanalytical platform demonstrated high sensitivity and specificity in detecting anti-rS, achieving a limit of detection of 4.38 nM. This versatile platform could be further enhanced by applying various electrode materials and adapting this platform to detect antibodies against some other proteins. Our findings have significant implications for the development of affordable, scalable biosensing platforms capable to provide rapid and accurate public health screening and monitoring, particularly in the context of the coronavirus disease 2019 (COVID-19) pandemic.

Introducing Nanoscale Electrochemistry in Small-Molecule Detection for Tackling Existing Limitations of Affinity-Based Label-Free Biosensing Applications

Electrochemical sensing techniques for small molecules have progressed in many applications, including disease diagnosis and prevention as well as monitoring of health conditions. However, affinity-based detection for low-abundance small molecules is still challenging due to the imbalance in target-to-receptor size ratio as well as the lack of a highly sensitive signal transducing method. Herein, we introduced nanoscale electrochemistry in affinity-based small molecule detection by measuring the change of quantum electrochemical properties with a nanoscale artificial receptor upon binding. We prepared a nanoscale molecularly imprinted composite polymer (MICP) for cortisol by electrochemically copolymerizing β-cyclodextrin and redox-active methylene blue to offer a high target-to-receptor size ratio, thus realizing "bind-and-read" detection of cortisol as a representative target small molecule, along with extremely high sensitivity. Using the quantum conductance measurement, the present MICP-based sensor can detect cortisol from 1.00 × 10-12 to 1.00 × 10-6 M with a detection limit of 3.93 × 10-13 M (S/N = 3), which is much lower than those obtained with other electrochemical methods. Moreover, the present MICP-based cortisol sensor exhibited reversible cortisol sensing capability through a simple electrochemical regeneration process without cumbersome steps of washing and solution change, which enables "continuous detection". In situ detection of cortisol in human saliva following circadian rhythm was carried out with the present MICP-based cortisol sensor, and the results were validated with the LC-MS/MS method. Consequently, this present cortisol sensor based on nanoscale MICP and quantum electrochemistry overcomes the limitations of affinity-based biosensors, opening up new possibilities for sensor applications in point-of-care and wearable healthcare devices.

Electrochemical Determination of Interaction between SARS-CoV-2 Spike Protein and Specific Antibodies

The serologic diagnosis of coronavirus disease 2019 (COVID-19) and the evaluation of vaccination effectiveness are identified by the presence of antibodies specific to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). In this paper, we present the electrochemical-based biosensing technique for the detection of antibodies specific to the SARS-CoV-2 proteins. Recombinant SARS-CoV-2 spike proteins (rSpike) were immobilised on the surface of a gold electrode modified by a self-assembled monolayer (SAM). This modified electrode was used as a sensitive element for the detection of polyclonal mouse antibodies against the rSpike (anti-rSpike). Electrochemical impedance spectroscopy (EIS) was used to observe the formation of immunocomplexes while cyclic voltammetry (CV) was used for additional analysis of the surface modifications. It was revealed that the impedimetric method and the elaborate experimental conditions are appropriate for the further development of electrochemical biosensors for the serological diagnosis of COVID-19 and/or the confirmation of successful vaccination against SARS-CoV-2.