Near-field optical interferometer for refractive index sensing

Single-molecule sensing for biological physics predominantly uses fluorescence sensing due to the high signal to volume ratio. However, it is far from an ideal detection mode since fluorescence sensing requires the chemical modification of biological molecules. A better alternative is the sensing of refractive index changes due the introduction of a biomacromolecule. Here we introduce a near-field optical interferometer that detects the presence of nanoparticles and proteins by measuring the deflection of a light, and not transmission as commonly performed.