Microretroreflector-Sedimentation Immunoassays for Pathogen Detection

Abstract

Point-of-care detection of pathogens is medically valuable but poses challenging trade-offs between instrument complexity and clinical and analytical sensitivity. Here we introduce a diagnostic platform utilizing lithographically fabricated micron-scale forms of cubic retroreflectors, arguably one of the most optically detectable human artifacts, as reporter labels for use in sensitive immunoassays. We demonstrate the applicability of this novel optical label in a simple assay format in which retroreflector cubes are first mixed with the sample. The cubes are then allowed to settle onto an immuno-capture surface, followed by inversion for gravity-driven removal of nonspecifically bound cubes. Cubes bridged to the capture surface by the analyte are detected using inexpensive, low-numerical aperture optics. For model bacterial and viral pathogens, sensitivity in 10% human serum was found to be 104 bacterial cells/mL and 104 virus particles/mL, consistent with clinical utility.

Salmonella Typhimurium Sensing Strategy Based on the Loop-Mediated Isothermal Amplification Using Retroreflective Janus Particle as a Nonspectroscopic Signaling Probe

“…This phenomenon can be easily induced by the various light source, such as nonmonochromatic light, and the reflected light has a significantly bright intensity. Based on these features, a number of studies have been introduced that apply the retroreflection principle to the development of biosensors, such as retroreflective Janus particle, , retroreflector cube, and photolithographically fabricated linear microreflector . In particular, RJPs can be observed with simple optical instruments such as a white LED and a CMOS camera; the newly developed platform can measure the concentration of the target gene by simply counting the number of observed RJPs.…”

Retroreflective Janus Microparticle as a Nonspectroscopic Optical Immunosensing Probe

“…Few studies have attempted to utilize retroreflectors as optical probes because they can only be fabricated by a sophisticated photolithographic process, limiting the commercialization of the probes. 21 Considering the facile fabrication, RJPs were prepared with a simple structure of a transparent ball lens retroreflector. In this study, transparent silica microparticles (SiO 2 , diameter ≈ 1.2 μm) synthesized using the Stober method were chosen as a ball lens material.…”

“…Optical biosensing technology with high accuracy and wide applicability has been intensively investigated for user-centered diagnostic devices in point-of-care-testing (POCT) concept. − Although numerous studies have been conducted, the commercialization of POCT optical biosensors has been limited because current approaches employ sophisticated spectrometric optics components (e.g., monochromator with halogen lamp, laser, optical filter, and spectrometer) for detecting optical signals of the employed optical probes. − The traditionally used optical signaling probes (e.g., enzymes, chromogens, nanoparticles, and fluorophores) generate varied spectroscopic signals such as color formation, spectral shifting, or fluorescence, which can be analyzed using only wavelength-selective optics components exhibiting limitations in commercialization and miniaturization such as excessive cost, high power consumption, and complicated configuration. − Thus, for the materialization of simple POCT optical biosensor, the introduction of a novel optical probe whose signal can be analyzed using a nonspectroscopic instrument, thereby enabling easy detection, is strongly desired. , To address this, we employed the retroreflection principle and retroreflectors, which are currently applied in various fields such as safety clothing, road signs, vehicles, and optical communications, for optical biosensing signal registration. − Retroreflection is a unique phenomenon of light irradiating a surface and being redirected back to the light source (Figure ). The material and its surface, inducing the retroreflection, are called a retroreflector.…”

An embedded microretroreflector-based microfluidic immunoassay platform

“…42 We have previously reported the fabrication of suspended 5 μm corner cube retroreflectors 43 and their use as optical immunoassay labels. 44 In this work, we use densely packed arrays of thousands of micron-scale linear retroreflectors (dimensions 100 μm length × 3 μm width × 5 μm height), fabricated with precise positioning on a microfluidic substrate and embedded in a bio-functionalizable transparent polymer, as a microfluidic optical sensing substrate. Linear retroreflectors have one less reflective surface than corner cube reflectors, and are brightest at one azimuth.…”