Isoelectric focusing on microfluidic paper-based chips.

Isoelectric focusing (IEF), a powerful technique for protein separation and enrichment, was successfully integrated into microfluidic paper-based analytical devices (µPADs) in this work. The µPADs for isoelectric focusing were fabricated by octadecyltrichlorosilane (OTS) silanization and subsequent region-selective plasma treatment. The system of IEF on µPADs could be easily assembled. And a series of conditions of the system were investigated, including the suitable concentration of ampholyte to create good pH gradient, the effect of polyvinylpyrrolidone (PVP) on electroosmotic flow (EOF) suppression, and focusing voltage applied on the paper channel. After optimization, simultaneous separation and enrichment of protein sample containing myoglobin and cytochrome C was successfully demonstrated. Besides, parallel IEF on multichannels were also achieved for the separation of multiple protein samples on one single chip, and their performance was compared with that of the conventional gel-IEF system. The developed IEF on µPADs exhibits appealing features such as low cost, simplicity, and disposability and are believed to have great application potentials.

Detection of SARS-CoV-2 Specific Antibodies in Saliva Samples.

Molecular assays on nasopharyngeal swabs act as a confirmatory test in coronavirus disease (COVID-19) diagnosis. However, the technical requirements of nasopharyngeal sampling and molecular assays limit the testing capabilities. Recent studies suggest the use of saliva for the COVID-19 diagnostic test. In this study, 44 patients diagnosed with COVID-19 in The Third People's Hospital of Shenzhen were enrolled. Saliva and serum specimens were obtained at different time points and the immunoglobulins against SARS-CoV-2 were measured. The results showed that saliva IgA presented a higher COI value than IgG and IgM. In matched saliva and serum samples, all saliva samples presented lower IgG levels than serum samples, and only one saliva sample presented a higher IgM level. The conversion rates of saliva IgA and the detection of viral nucleic acids were analyzed in the first and second weeks after hospitalization. The positive rates increased when combining saliva IgA and viral nucleic acid detection. In conclusion, our results provide evidence that saliva IgA could serve as a useful index for the early diagnosis of COVID-19.