Force discrimination for enhanced biosensor specificity of micro-retroreflector assays

Immunoassays are commonly used in diagnostic assays, pathogen detection and in the detection of contamination of food supplies. The label is what is actually detected, and label detection sensitivity often limits assay sensitivity. This work introduces magnetic particles as light blocking labels in optical assays based on microfabricated retroreflectors. The detection surface is composed of arrays of micron-scale microfabricated retroreflector tetrads. Retroreflectors return light directly to its source and are readily detectable with inexpensive optics. The assay can easily detect the presence of a single particle bound to the surface. Results also show that one or two Rickettsia conorii bacteria can hold down a 1.0 μm magnetic particle coated with rabbit polyclonal anti-rickettsia antibodies, supporting the possibility of detecting a single target pathogen with this assay. The magnetic properties of the particles are used to discriminate against non-specific interactions, increasing the specificity of the assay.