Robust Visualization and Discrimination of Nanoparticles by Interferometric Imaging

Single-molecule and single-nanoparticle biosensors are a growing frontier in diagnostics. Digital biosensors are those which enumerate all specifically immobilized biomolecules or biological nanoparticles, and thereby achieve limits of detection usually beyond the reach of ensemble measurements. Here, we review modern optical techniques for single nanoparticle detection and describe the single-particle interferometric reflectance imaging sensor (SP-IRIS). We present challenges associated with reliably detecting faint nanoparticles with SP-IRIS, and describe image acquisition processes and software modifications to address them. Specifically, we describe an image acquisition processing method for the discrimination and accurate counting of nanoparticles that greatly reduce both the number of false positives and false negatives. These engineering improvements are critical steps in the translation of SP-IRIS toward applications in medical diagnostics.