A Low-Cost, Programmable, And Multi-Functional Droplet Printing System For Low Copy Number Sars-Cov-2 Digital Pcr Determination

Droplet digital polymerase chain reaction (ddPCR) is a rapidly developing technology used for accurate, quan-titative analysis of rare samples. However, ddPCR has only been implemented in research field but rarely in clinical trials due to its relatively high cost and negative user experiences compared with qPCR. We developed a novel programmable on-demand droplet generator based on a microfluidic adaptive printing system (MAP-ddPCR) to create a cost-effective ddPCR process. This process easily produces low-volume, spot-on-demand droplet dispensing and data analysis using simple equipment and workflow. Compared with the existing droplet generation systems that rely on surface-assistant, the proposed MAP system generates a variety of droplet arrays on regular non-surface-treated glass slides. This system directly processes PCR and performs data analysis without requiring a secondary droplets transfer. The static and independent properties of each droplet dramatically avoid cross-contamination during PCR, provide the opportunity to trace droplets in real-time and simplify the analysis. We demonstrated that the MAP-ddPCR produces reliable data using gradient concentra-tions of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) in human genomic cDNA. These concentrations were further verified by quantitative PCR (qPCR). In addition, a very low viral load of SARS-CoV-2 was precisely detected and quantified by the MAP-ddPCR system. Finally, this system is affordable and simpler to integrate compared to other more expensive commercial digital PCR methods. Therefore, the proposed MAP-ddPCR sys-tem is expected to have a significant impact on market applications.