Nanoparticle immunoagglutination Rayleigh scatter assay to complement microparticle immunoagglutination Mie scatter assay in a microfluidic device

In this work, particle immunoagglutination assays for pathogen detection, utilizing light scattering measurements at a fixed angle from incident light delivery, are explored in both Rayleigh and Mie scatter regimes through scatter intensity simulations and compared to experimental results. The average size of immunoagglutinated particles obtained from microscope images correspond to the particle size parameter from simulations. Mie scatter measurements yield a greater signal increase with increasing pathogen concentration than Rayleigh scatter measurements, but with a non-monotonic relationship that is not observed in the Rayleigh scatter regime. These two similar yet distinctly different sources of information could easily be integrated into a single device through fabrication of a simple microfluidic device containing two y-channels, each for performing the respective light scattering measurement. Escherichia coli was used as a representative target, and detected in a microfluidic device down to a concentration of 1 colony forming units (CFU) per mL.