Statistical Particle Tracking Velocimetry using Single Molecule and Quantum Dot Tracers

Particle Tracking Velocimetry (PTV) with nanometer resolution is demonstrated using single molecules and quantum dots (QD) as tracer particles. Several problems are unique to this regime, including: shot noise from intensified cameras, large drop- in/drop-out (due to Brownian motion and QD blinking), sub-pixel tracer intensity profiles and lastly issues associated with tracking with high particle seeding densities. We have developed a statistical particle tracking method to successfully address these problems. The algorithm tracks all possible particles, removing non-physical matches using the global statistical properties of the system, leaving the true particle displacement distribution (and hence velocity). The algorithm is validated using FITC-Dextran molecules and QDs. Experiumental results concerning the velocity and diffusion characteristics of the nanoscale tracers are reported.