Noble Metal Nanoparticle Biosensors

Abstract

Receptor-ligand binding assays are central to medical diagnostics, proteomics, drug discovery, environmental monitoring and food processing. A typical binding assay uses a “capture molecule” (often loosely termed as the “receptor”) which is typically an antibody, DNA, peptide, or protein, that binds to a target analyte (ligand) of interest in a sample with high affinity and specificity. Binding of the analyte to the “receptor” is coupled to a transduction step to enable detection of the binding event and quantification of the analyte concentration in the sample. Based on their mode of detection, most binding assays can be divided into two categories. The first category includes assays that require a label or tracer-a radioisotope, chromophore or fluorophore-to transduce the binding event into a quantifiable signal. The second category of analyte binding assays is label-fi-ee assays that do not require the addition of extrinsic reagents or labels. Instead, a change in a physical parameter upon analyte binding such as the mass, thickness, or refractive index, is directly transduced into a measurable signal. These two categories are broad, and some overlap exists between them. For example, recent protein engineering approaches have yielded direct fluorescence biosensors, in which binding is coupled to a change in the fluorescence of the receptor through allostery.