Holographic Micro Flow Meter for Biological Sensing

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Ever been caught by a speed camera? Most work by taking two images in quick succession the speed of your car being calculated from the separation of its images. We have invented a similar technique for measuring the speed of micron sized objects moving within a fluid. Our technique relies on optical tweezers, tightly focussed beam of light to trap and hold micro-sized test particles in the fluid. Pulsing the tweezers repeated releases the objects into the fluid flow and the speed camera records their velocity, before the particles are re trapped. The result of many measurements is averaged to give the velocity of the fluid flow to an accuracy of one micron per second. One area where we will apply our technique is micro-fluidics, micron-sized networks of fluid channels allowing the transfer and mixing of chemical reagents, probes or bio-objects. Such systems are the basis of 'lab on chip' technology, cheaper, more compact and faster than their full sized lab equivalents. The small scale of lab chips means that fluid behaviour is non-intuitive, water flow being more like concrete, hence the ability to measure the fluid is both elegant and instructive. Beyond gaining an understanding of micro-fluidic flow, our aim is to apply the technique to various bio-applications. Fluid flow around a cell creates mechanical stress, modifying the cell response with a parameter that is not understood; motile cells can swim in a fluid, but again the interplay between the creation and sensing of fluid flow is poorly understood. We believe that our ability to measure the fluid flow with both spatial and temporal resolution combined with our proven expertise in other imaging and sensing technologies will allow us to address these and many other interesting issues.