μPADs on Centrifugal Microfluidic Discs for Rapid Sample-to-Answer Salivary Diagnostics

A fully integrated device for salivary detection with a sample-in-answer-out fashion is critical for noninvasive point-ofcare testing (POCT), especially for the screening of contagious disease infection. Microfluidic paper-based analytical devices (mu PADs) have demonstrated their huge potential in POCT due to their low cost and easy adaptation with other components. This study developed a generic POCT platform by integrating a centrifugal microfluidic disc with mu PADs to realize sample-toanswer salivary diagnostics. Specifically, a custom centrifugal microfluidic disc integrated with mu PADs is fabricated, which demonstrated a high efficiency in saliva treatment. To demonstrate the capability of the integrated device for salivary analysis, the SARS-CoV-2 Nucleocapsid (N) protein, a reliable biomarker for SARS-CoV-2 acute infection, is used as the model analyte. By the chemical treatment of the mu PAD surface, and by optimizing the protein immobilization conditions, the on-disc mu PADs were able to detect the SARS-CoV-2 N protein down to 10 pg mL(-1) with a dynamic range of 10-1000 pg mL(-1) and an assay time of 8 min. The integrated device was successfully used for the quantification of the N protein of pseudovirus in saliva with high specificity and demonstrated a comparable performance to the commercial paper lateral flow assay test strips.

Automated summary

A fully integrated device for salivary detection, which operates in a sample-in-answer-out manner, is crucial for noninvasive point-of-care testing and screening of contagious diseases. This study developed a universal platform by integrating a centrifugal microfluidic disc with microfluidic paper-based analytical devices (mu PADs) for salivary diagnostics. The integrated device demonstrated high efficiency in saliva treatment and was able to detect the SARS-CoV-2 N protein with high specificity and comparable performance to commercial paper lateral flow assay test strips.