A thin film-mediated omnidirectional spiral surface acoustic waves in combination with porous hydrogel microparticles for rapid immuno-biosensing.

Surface acoustic waves (SAWs) are an optimal method for manipulating small biomolecules because of their non-contact, tunable, and buffer-compatible characteristics. Numerous prior studies have demonstrated various manipulative strategies for inorganic particles by SAWs, yet little has focused on biosensing so far. To address this gap in the scientific community, we employed a powerful SAW tool, known as omnidirectional spiral SAWs (OSSAWs), as the principal driving mechanism to realize enhanced particle manipulation. The manipulation was performed in a 3D-printed well with a thin elastomeric film on the reverse side of an OSSAW substrate to reduce cross-contamination, surface wear, and electrode fouling. Instead of solid microparticles, porous hydrogel microparticles (PHMs) composed of gelatin methacryloyl were used as probes to detect target biomolecules associated with diseases. In the presence of biomarker proteins, sandwich immunocomplexes (capture antibody-antigen-probe antibody) conjugated with fluorescent polystyrene particles were immobilized within the PHMs. Subsequently, the immunocomplexed PHMs were concentrated in the center of the well by OSSAWs, enhancing immunofluorescence. Experimental results showed that the immunofluorescence of 5 μL of suspension was enhanced within 3 min, surpassing the conventional 2 h immunoassay in a tube. The specificity for lipocalin 1 (LCN1) surpassed that of other unrelated proteins, whereas a limit of detection of 31.1 pg/μL was achieved. Practical use was verified through preliminary clinical tests using human tear samples from diabetic retinopathy (DR) patients and healthy individuals. Results successfully showed elevated LCN1 concentrations in DR samples compared to healthy controls, confirming LCN1 as a biomarker for DR. This study marks the first attempt of an OSSAW-based biosensor integrated with PHMs and a disposable well for rapid disease diagnosis. Therefore, the successful demonstration provides insight into future point-of-care testing.