Analytical particle measurements in an optical microflume.

In this work, microscopic particles in a fluid flow are manipulated using forces generated by a high power laser beam. The resulting manipulations on the particles are imaged using a microscope lens connected to a CCD camera. Differential forces on particles of varying physical and chemical composition have been measured. The goal is to measure the optical forces on a diverse range of particles and catalog the associated chemical and physical differences to understand which properties and mechanisms result in the largest force differentials. Using these measurements our aim is to better understand differences between similar microspheres in terms of size, morphology, or chemical composition. Particles of the same size, but different composition show large variations in optical pressure forces and are easily discernable in the present analytical system. In addition, we have demonstrated the ability to differentiate a 70 nm size difference between two NIST precision size standard polystyrene microspheres, corresponding to a 2.0 pN difference in optical force. Lastly, the instrument was used to measure differences between biological samples of similar size, demonstrating the ability to make precise analytical measurements on microorganism samples.