Prospects of NIR fluorescent nanosensors for green detection of SARS-CoV-2.

The pandemic of the novel coronavirus disease 2019 (COVID-19) is continuously causing hazards for the world. Effective detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) can relieve the impact, but various toxic chemicals are also released into the environment. Fluorescence sensors offer a facile analytical strategy. During fluorescence sensing, biological samples such as tissues and body fluids have autofluorescence, giving false-positive/negative results because of the interferences. Fluorescence near-infrared (NIR) nanosensors can be designed from low-toxic materials with insignificant background signals. Although this research is still in its infancy, further developments in this field have the potential for sustainable detection of SARS-CoV-2. Herein, we summarize the reported NIR fluorescent nanosensors with the potential to detect SARS-CoV-2. The green synthesis of NIR fluorescent nanomaterials, environmentally compatible sensing strategies, and possible methods to reduce the testing frequencies are discussed. Further optimization strategies for developing NIR fluorescent nanosensors to facilitate greener diagnostics of SARS-CoV-2 for pandemic control are proposed.

Multiplexed evaluation of immunity against SARS-CoV-2 variants using surface enhanced fluorescence from a nanostructured plasmonic chip.

Generated by the immune system post-infection or through vaccination, the effectiveness of antibodies against emerging SARS-CoV-2 variants is crucial for protecting individuals from the COVID-19 pandemic. Herein, a platform for the multiplexed evaluation of SARS-CoV-2 neutralizing antibodies against various variants was designed on the basis of near-infrared (NIR) surface enhanced fluorescence by nano-plasmonic gold chip (pGOLD). Antibody level across variants (Wild-type, Alpha, Beta, Delta, Omicron) was confirmed by the sera from recovered-individuals who were unvaccinated and had infected with Wild-type, Delta, Omicron variants. However, the neutralizing activity against Omicron variant was markedly decreased for individuals infected by Wild-type (~ 5.6-fold) and Delta variant (~ 19.1-fold). To the opposite, neutralizing antibody from individuals recovered from Omicron variant infection showed weak binding strength against non-Omicron variants. Antibody evolution over time was studied with individuals 196-530 days post Wild-type infection. Decreasing IgG antibody titer accompanied by increasing IgG binding avidity with elongated post-infection period were observed for the sera from Wild-type recovered-individuals with different post-infection times, suggesting that after the primary infection, a great number of antibodies were generated and then gradually decreased, while the antibody matured over time. By comparing the IgG level of individuals vaccinated for 27-51 days with individual post-infection, we found that ca. 1 month after two doses of vaccination, the antibody level was comparable to that of 500 days post-infection, and vaccination could enhance IgG avidity more efficiently. This work demonstrated a platform for the multiplexed, high-throughput and rapid screening of acquired immunity against SARS-CoV-2 variants, providing a new approach for the analysis of vaccine effectiveness, immunity against emerging variants, and related serological study.

An electrochemical biosensor based on hemin/G-quadruplex DNAzyme and PdRu/Pt heterostructures as signal amplifier for circulating tumor cells detection.

Metastasis due to circulating tumor cells (CTCs) shed from the original tumor accounts for the majority of cancer-related death. Efficient CTCs detection is pivotal to the diagnosis of early cancer metastasis. In this work, Platinum nanoparticles (PtNPs) decorated hyperbranched PdRu nanospines (PdRu/Pt) hierarchical structures were firstly synthesized to detect CTCs with the assistance of DNAzyme. Meanwhile, Super P and gold nanoparticles (AuNPs) acted as sensing medium to improve electrical conductivity and immobilization of anti-EpCAM antibody to specifically capture model CTCs. After immune-conjugation of anti-EpCAM-MCF-7-signal probes on the gold electrode, PtNPs, PdRu nanospines (PdRuNSs) and hemin/G-quadruplex co-catalyzed substrate H2O2 to realize multiplexed signal amplification, which significantly improves the analytical performance of the electrochemical biosensor. As-proposed biosensor reached a limit of detection (LOD) down to 2 cells mL-1 and showed a wide detection range of 2 to 106 cells mL-1. Application of the biosensor to detect MCF-7 cells spiked human blood samples further demonstrated the feasibility for early cancer evaluation in clinic.

Validation of IgG, IgM multiplex plasmonic gold platform in French clinical cohorts for the serodiagnosis and follow-up of Toxoplasma gondii infection.

We report the use of the multiplexed T. gondii IgG, IgM test on plasmonic gold (pGOLD) platform in the setting of T. gondii infection by analyzing 244 sera from Nice, France (seroconversion, chronically infected, non-infected and newborns serum samples). Results were compared with commercial tests for the detection of IgG and IgM and their overall clinical final interpretation of a complete serological profile. The IgG and IgM test results on the platform were in agreement in, respectively, 95% and 93% with the commercial kits. When comparing with the overall clinical interpretation of the serological profile, the agreement reached 99.5% and 97.7% for IgG and IgM, respectively. This innovative pGOLD platform allows detection of both IgG and IgM simultaneously with only ~1 microliter of serum. The multiplexed IgG/IgM test on pGOLD platform is a strong candidate for its use in the massive screening programs for toxoplasmosis during pregnancy.