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Current serological antibody tests for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) require enzyme or fluorescent labels, and the titer well plates cannot be reused. By immobilizing histidine (His)-tagged SARS-CoV-2 spike (S1) protein onto tris‒nitrilotriacetic acid (tris-NTA) sensor and using the early association phase for mass-transfer-controlled concentration determination, we developed a rapid and regenerable surface plasmon resonance (SPR) method for quantifying anti-SARS-CoV-2 antibody. On a five-channel SPR instrument and with optimized S1 protein immobilization density, each of the four analytical channels is sequentially used for multiple measurements, and all four channels can be simultaneously regenerated once they have reached a threshold value. Coupled with a programmable autosampler, each sensor can be regenerated at least 20 times, enabling uninterrupted assays of more than 800 serum samples. The accuracy and speed of our method compare well with those of the enzyme-linked immunosorbent assay (ELISA), and the detection limit (0.057 μg mL

A porous reticulated vitreous carbon (RVC) electrode and a disk electrode coupled in tandem in an electrochemical flow cell has been used for electrolytic removal of interferents before amperometric glucose detection. The electrolytic efficiency at the upstream RVC electrode is 100% at a flow rate of 0.1 mL min(-1) or lower. Potential interferents such as acetaminophen, ascorbic acid, and uric acid can be completely eliminated by electrolysis at the RVC electrode. A mixed monolayer comprising glucose oxidase (GOD) and ferrocenyl-1-undecanethiol preformed at the downstream gold disk electrode was used as a mediator-based amperometric glucose sensor. The dependence of the amperometric current on the glucose concentration exhibits good linearity across over three orders of magnitude. The glucose measurements were also found to be reproducible (RSD

A simple, rapid, and sensitive determination of total free thiol groups in biological samples using cerium (IV) as a fluorescence probe is reported. The protocol is based on the oxidation of thiols by Ce(IV) and the formation the Ce(III) disulfide complex, which gives a fluorescence enhancement of Ce(III) at 352 nm. Using glutathione (GSH) and cysteine as model compounds, incubation with Ce(IV) at 25 °C for 6 min results in fluorescence, whose intensity is proportional to the thiol concentration in the range of 1.00–160 nM. The detection limits for GSH and cysteine are 0.05 and 0.08 nM, respectively. Other common metal ions and amino acids have little interference to the thiol detection. Cu(II) was used as a fluorescence quencher to eliminate potential interference from tryptophan. The method has been successfully applied to assays of free thiol contents in pig liver tissue samples, with a RSD lower than 2.5% and recovery between 100.6% and 102.3%.

Quantification of electroinactive dopants in conductive polypyrrole (PPY) films was performed with electrochemistry combined on-line with inductively coupled plasma-atomic emission spectrometry (EC/ICP-AES). Anion (HSO 4 − ) ejection out of a PPY film was first chosen as a model system and the results obtained with EC/ICP-AES were found to be comparable with values deduced by electrochemical quartz crystal microbalance (EQCM). The EC/ICP-AES approach was then extended to cases where EQCM findings become difficult to interpret (i.e. simultaneous insertion of Na + into and ejection of HSO 4 − out of PPY film). It is demonstrated that EC/ICP-AES can simultaneously quantify both cationic and anionic species involved in the PPY redox switching. This is in contrast with EQCM studies that can only detect the net mass change from the two competing processes. This study shows that EC/ICP-AES is a viable technique for providing accurate information concerning the doping/dedoping processes without the necessity of removing the polymer-modified electrode from the electrochemical flow cell. More importantly, the species investigated do not need to be electroactive. It is clear that the comparative study between the two techniques can be powerful in unraveling relatively complicated redox reactions and ion-transport processes in conductive polymer films.

In this work, thermal effect inherent in long-term irradiation of a focused laser beam may become a major source of error in surface plasmon resonance (SPR) measurements, especially when infinitesimal signals (e.g., reorganization of monolayers or conformational changes of immobilized proteins) are measured. The laser-induced thermal effect was examined by continuously monitoring changes brought about by injecting 2% ethanol solution into a flow cell housing bare and chemically modified gold films that had been irradiated by a laser beam for various times, and a maximum relative error of 21% was obtained. Factors affecting the SPR response, namely solution flow rate, compactness of the adsorbate layer, and power of the laser beam, were examined. The SPR dip shift (SPR angular shift) was shown to be dependent not only on the magnitude of the laser power but also on the thermal dissipation at the metal–solution interface. With a better understanding of the parameters affecting the thermal energy dissipation and the temperature dependence of the SPR signals, measures can be taken to improve the accuracy of SPR data. We show as an example that, if the laser-induced thermal effect is not considered or reduced, accuracy in determinating redox-triggered reorganization of a pre-immobilized 11-ferrocenylundecanethiol self-assembled monolayer (SAM) may be decreased by more than 40%, leading to an erroneous conclusion.