Plasmonic/catalytic nanoparticles-based lateral flow devices for point-of-care diagnostics

Rapid and portable point-of-care (POC) testing technologies are a promising diagnostic solution alternative to laboratory based-assay, which application is often limited by time- and cost-consuming procedures, use of complex equipments, and invasiveness. POC testing can be employed in various fields, for instance as early diagnostics methodology in healthcare and as quality control tool in food industry and nutrition. In particular, lateral flow devices (LFD) represent efficient paper-based methods for the colorimetric evaluation of a variety of targets. Here we report the exploitation of the plasmonic properties of gold nanoparticles (AuNPs) and of the catalytic functionality of platinum nanoparticles (PtNPs) to develop two effective LFDs for the naked-eye evaluation of i) salivary cortisol and ii) antioxidant levels in saliva or fruit juices. In the first assay, two differently shaped plasmonic AuNPs (60 nm nanostars and 35 nm nanospheres) were combined to develop a dual-color plasmonic immunosensor for the evaluation of salivary cortisol, known as one of the main stress-related biomarkers. The dual-color system facilitated immediate and easy evaluation of cortisol levels, thanks to a blue-to-pink color change of the detection zone. The second device allowed the assessment of total antioxidant capacity (TAC) in different matrices, namely saliva and fruit juices, exploiting the peroxidase-like properties of 5 nm PtNPs. Particularly, the colorimetric LFD was engineered with a multi-line PtNP-based detection zone, relying on three sequential test lines with increasing concentrations of Pt nanozymes. Notably, both strategies showed potential applicability as non-invasive, rapid (10 min) and accurate monitoring systems, allowing to discriminate different target concentrations.