Portable integrated digital PCR system for the point-of-care quantification of BK virus from urine samples

This paper presents a portable integrated digital PCR (PI-dPCR) system with a self-partitioning SlipChip (sp-SlipChip) microfluidic device for the quantitative analysis of BK virus (BKV) viral load directly from raw urine samples. Digital PCR is an accurate nucleic acid quantification method with single-molecule sensitivity, but the complexity of the instrument and the limited integration of the operation workflow greatly limit its application in clinical diagnostics, especially point-of-care testing (PoCT). Our PI-dPCR system has a small footprint, is lightweight, and is fully integrated with the thermal control and fluorescence imaging modules. Unlike the traditional SlipChip device, which requires the precise overlapping of microfeatures on the contacting surfaces to establish the fluidic loading path, this sp-SlipChip device utilizes microchannels with alternating depth and width for fluidic manipulation. This system can quantify BKV directly from raw urine samples with a simple "sample-to-digital-result" operation workflow without complex nucleic acid extraction and purification steps. The current design of the system provides a dynamic range of 3.0 × 10⁴ to 1.5 × 10⁸ copies/mL of BKV DNA in clinical urine samples within 2 h. We tested the system for the quantification of BKV viral load in thirty archived urine samples from kidney transplantation recipients and twelve additional samples from six patients before and after the adjustment of immunosuppressive treatment. This integrated system provides a promising method for both the detection and monitoring of viral infection in a point-of-care setting.