Detection of single nano-objects with low fluorescence quantum yields is a challenge. This can be overcome by using a technique called spatial modulation spectroscopy (SMS). The Vall�e group has pioneered efforts in establishing this technique over the past decade.1   In SMS the transmission of a laser beam is monitored as a nanoparticle is moved in-and-out of the focus. Most reports thus far have used deflection of a stage, wherein the position of the nanoparticle is modulated. In this work we scan the beam using either a galvo-mirror, or an acousto-optic modulator. The figure below shows an image of Au nanoparticles recorded using a continuous wave 532 nm laser as the source. The differences in the signal intensities from these individual particles arise due to high sensitivity of the Au nanoparticles to size and shape. Ultra high sensitivity is attained by deflecting the beam at a predetermined amplitude combined with lock-in detection at 2 kHz. The sample is raster scanned using a piezo stage and the transmitted light is detected using a Si switchable gain detector in the far field. Comparison of the levels of sensitivity obtained by this method of using galvano mirrors vs. an acousto optic deflector (AOD) will be presented.(1) Arbouet, A.; Christofilos, D.; Del Fatti, N.; Vall�e, F.; Huntzinger, J. R.; Arnaud, L.; Billaud, P.; Broyer, M. Physical Review Letters 2004  , 93, 127401.

Towards shot noise limited detection of single 10nm Au nanoparticles using spatial modulation spectroscopy

246th National Meeting (2013)

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