Direct Observation of SERS Enhancement using Discrete Picoliter Reaction Chambers

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Microfluidic droplet generator that merges two aqueous streams before the droplet generating junction. The generated picoliter-sized droplets contain small, controlled numbers of SERS active AgNPs. Raman interrogation of the droplets will provide an insight to the particle aggregation dynamics, and the effects of AgNP isolation.

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Surface-enhanced Raman spectroscopy by small nanoparticle aggregates of silver or gold is known to provide enhancement factors of up to ~108. In our applications we optimize the SERS signals by controlling the nanoparticle aggregation rate and extent using novel microfluidic strategies, while at the same time optimizing the concentration of the analyte and ensuring favorable exposure of the analyte to the SERS-active nanoparticle aggregates. While it is known that large aggregates produce lower enhancements than small aggregates, the dimensions of the nanoparticle aggregates at which enhancement becomes unacceptably low (and introduces other limitations to their use in sensing) is not currently known. One of our goals will be to investigate the sensing efficacy of silver nanoparticle aggregates containing varying numbers of monomers as chemical sensors. This will lead to the most comprehensive body of knowledge regarding SERS enhancement as a function of nanoparticle aggregate size that should fundamentally impact the use of SERS in chemical sensing and detection both in our labs and in the scientific and engineering community at large.



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