Single nano-particle flow detection and velocimetry using optical feedback interferometry

We present a sensing technique based on the Optical Feedback Interferometry (OFI) scheme in a laser diode that enables single particle detection at micro and nano-scales through the Doppler-Fizeau effect. Thanks to the proposed signal processing, this sensing technique can detect the presence of single spherical micro/nanoparticles and measure their velocity, even while their diameter is below half the laser wavelength. The method was validated with polystyrene spheres with diameter ranging from 196 nm to 10.14 μm flowing in diluted aqueous solutions. These results indicate potential applications for the biomedical and chemical engineering fields.