Micron-Scale Retroreflectors As Labels for Sensitive Point-of-Care Diagnostics

Timely diagnosis and treatment of infectious diseases calls for highly sensitive, point-of-care diagnostic assays. Recent technological advances have enabled the development of such point-of-care tests including microfluidic chip sensors, paper-based fluidic devices and lateral flow assays (LFAs). Many of these diagnostic methods, however, require elaborate sample preparation and  many of the most common labels (typically a dye, enzyme or fluor) can suffer from low signal strength or photo-bleaching (of fluors), and can require elaborate instrumentation for their detection.

Here, we propose a combination of diagnostic platforms utilizing micron-scale, lithographically fabricated corner cube retroreflectors and high refractive index barium titanate microspheres as ultra-bright, highly detectable, optical labels. The retroreflector cubes, and barium titanate spheres are easily detected using inexpensive, low-numerical aperture optics, are not susceptible to photo-bleaching and do not require any signal amplification. Furthermore, the detectable nature of these particles minimize or eliminate altogether labor intensive sample preparation processes required for complex matrices.

We demonstrate the applicability of these novel assay formats by the two, and single-step, direct detection of pathogenic organisms and protein biomarkers in sub-milliliter volumes of various sample matrices.