High Spatial and Temporal Resolution Velocimetry Measurements for Microfluidic Devices

The overall goal of the proposed research is to develop a commercially-viable micro/nano-PIV instrument that can measure fluid motion in microchannels with 100 nanometer out-of-plane spatial resolution, 1 micron in-plane spatial resolution, and 1 microsecond temporal resolution. The instrument will also be capable of measuring bulk fluid motion in 100 nanometer channels.The 100 nanometer out-of-plane resolution will be achieved by using an evanescent field to illuminate flow-tracing particles near a waveguide surface. The PIV instrument will be well-suited for investigating near-wall slip flow, boundary layer regions, and electro-osmotic flow in microfluidic devices. Although this form of micro-PIV has been reported by several researchers, it has not yet been commercialized. We will use low-cost laser diodes, and well-designed optical coupling strategies, to improve the evanescent illumination and to develop a low-cost commercial instrument.In order to take full advantage of evanescent wave illumination and to measure flows in 100 nanometer channels, the size of the flow-tracing particles must be reduced to order 20 - 50 nm. These particles must be small enough to flow within a ~100 nanometer channel or within an evanescent field, while being large enough to sufficiently dampen Brownian motion, and emit sufficient fluorescent light. We will investigate the use of single quantum dots (QDs) or clusters of QDs. QDs are well known for their broad excitation curves, and bright emission signals. Several research groups have suggested using quantum dots as seed particles but to date there has been no report in the the literature that this has been done.