Development of an immunoassay lollipop using syringe-autoinjected visual distance readout for point-of-care testing

Pressure-based detection has drawn increasing interest for developing immunoassays but is still challenged in point-of-care testing (POCT). In this work, a pressure-based immunoassay "lollipop" was developed using syringe-autoinjected visual distance readout. The "lollipop" consisted of a disposable syringe "stick" as the immuno-recognition host and a chip "head" as the signal readout element. Using urinary microalbuminuria (mALB) as a model target, we constructed the immunoassay system on the interior cylinder surface of the syringe. In the presence of H₂O₂, the peroxidase-mimicking activity of platinum nanoparticles (Pt NPs) immuno-captured in the cylinder drove the automatic injection of dye liquids from the syringe into a spiral capillary catheter in the chip. The concentration of mALB in the "lollipop stick" was thereby visually displayed as the syringe-autoinjected distance signals in the "lollipop head". The assay exhibited a limit of detection (LOD) of 5 ng/mL for mALB quantification and linear response in a range from 0.006 μg/mL to 6 μg/mL with reliable accuracy in clinical urine sample analysis. Taking advantage of the versatility of syringes, the immunoassay "lollipop" works without the aid of any laboratory liquid handlers (e.g., pipettes), specific detectors (e.g., manometers) and complex chip operations (e.g., reagent loading), showing great promise in POCT.