Sensitive Determination of Concentration of Nonfluorescent Species in an Extended-Nano Channel by Differential Interference Contrast Thermal Lens Microscope

摘要

A photothermal detector, named differential interferencencontrast thermal lens microscope (DIC-TLM), was usednto determine the concentration of a nonfluorescent solutionnin a nanochannel. This method exploits a local changenin the refractive index of a solution caused by lightnabsorption. A solution was introduced into a 100-nmnscale channel by a pressure-driven nanofluidic controlnsystem and its concentration was determined by DICTLM.nThe limit of detection (LOD) was 2.4 μM in annanochannel that was 21 μm wide and 500 nm deep. ThenLOD was 3 orders of magnitude smaller than that ofnconventional method. Moreover, the detection volume wasnaccurately determined to be merely 0.25 fL by using annanochannel with an optical path length of 500 nm. Basednon these results, the number of detected molecules wasncalculated to be 390. In addition, the concentration of ansolution in a nanochannel that was 790 nm wide and 500nnm deep could be determined. Finally, the relationshipnbetween sensitivity and channel size was investigated andnthe sensitivity was found to decrease with decreasingnnanochannel size, which indicates that the changes in thenrefractive indices of water and silica cancel each other out.nThe DIC-TLM realizes sensitive detection of nonfluorescentnspecies in nanochannels without requiring anynspecial fabrication techniques. Therefore, DIC-TLM isnexpected to be a highly useful analytical technique innnanofluidics.