Retroreflective Janus Microparticle as a Nonspectroscopic Optical Immunosensing Probe.

We developed retroreflective Janus microparticles (RJPs) as a novel optical immunosensing probe for use in a nonspectro-scopic retroreflection-based immunoassay. By coating the metals on the hemispherical surface of silica particles, highly re-flective RJPs were fabricated. Based on the retroreflection principle, the RJPs responded to polychromatic white light sources, in contrast to conventional optical probes, which require specific monochromatic light. The retroreflection signals from RJPs were distinctively recognized as shining dots, which can be intuitively counted using a digital camera setup. Using the devel-oped retroreflective immunosensing system, cardiac troponin I, a specific biomarker of acute myocardial infarction, was detected with high sensitivity. Based on the demonstrated features of the retroreflective immunosensing platform, we expect that our approach may be applied for various point-of-care-testing applications.