Bridging the Gap between Digital Assays and Point-of-Care Testing: Automated, Low Cost, and Ultrasensitive Detection of Thyroid Stimulating Hormone

Medical diagnostics is moving toward disease-related target detection at very low concentrations because of the (1) quest for early-stage diagnosis, at a point where only limited target amounts are present, (2) trend toward minimally invasive sample extraction, yielding samples containing low concentrations of target, and (3) need for straightforward sample collection, usually resulting in limited volume collected. Hence, diagnostic tools allowing ultrasensitive target detection at the point-of-care (POC) are crucial for simplified and timely diagnosis of many illnesses. Therefore, we developed an innovative, fully integrated, semi-automated, and economically viable platform based on (1) digital microfluidics (DMF), enabling automated manipulation and analysis of very low sample volumes and (2) low-cost disposable DMF chips with microwell arrays, fabricated via roll-to-roll processes and allowing digital target counting. Thyroid stimulating hormone detection was chosen as a relevant application to show the potential of the system. The assay buffer was selected using design of experiments, and the assay was optimized in terms of reagent concentration and incubation time toward maximum sensitivity. The hydrophobic-in-hydrophobic microwells showed an unparalleled seeding efficiency of 97.6% +/- 0.6%. A calculated LOD of 0.0013 mu IU/mL was obtained, showing the great potential of the platform, especially taking into account the very low sample volume analyzed (1.1 mu L). Although validation (in biological matrix) and industrialization (full automation) steps still need to be taken, it is clear that the combination of DMF, low-cost DMF chips, and digital analyte counting in microwell arrays enables the implementation of ultrasensitive and reliable target detection at the POC.

Automated summary

Medical diagnostics is increasingly focusing on low-concentration target detection for early-stage diagnosis. This paper introduces an innovative platform based on digital microfluidics and low-cost disposable chips, enabling ultrasensitive detection of disease-related targets. The potential of the system is demonstrated through thyroid stimulating hormone detection.