Coupled evanescent field molecular tagged velocimetry for nanofluidics

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The instrument requested in this proposal relates to an innovative non-intrusive flow measurement technique for micro/nano-scale devices which combines the molecular tagging velocimetry (MTV) with evanescent wave field. This will allow us to quantify the velocity field within a few hundred nanometers (nm) from the channel walls where phenomena like slip, wall charge interactions, etc. are dominant. Such velocity measurements will be important to validate the theoretical models for the near wall phenomena and will substantially improve our understanding of fluid flow in micro and nanochannels. Existing techniques rely on seed particles which are typically around 100 - 200 nm in diameter and hence are not able to accurately resolve the flow field at the wall. By using the proposed evanescent wave field, a phenomenon which is confined within a few hundred nanometers of the investigated surface and relies on the total internal reflection of the light source, in conjunction with the existing MTV system will allow us to resolve such flow fields. This coupling will be rendered by procuring a high numerical aperture objective and related optics and beam steering mechanisms, which will then be integrated with the existing "in-house" developed MTV system, thereby creating a unique measurement technique for microfluidics applications.