Control of Heat Transfer in Chips with Nanometer-Sized Channels for Greatly Enhancing the Photothermal Detection Sensitivity

Abstract

ABSTRACTIn chips with nanometer-sized channels, photothermal lens microscopy (TLM) suffers quite low detection sensitivity, due to the ultrashort optical path length and the heat loss to the substrate. For a given optical path length, one feasible way to enhance the sensitivity of TLM is to control the heat (i.e., the photothermal effect) in nanospace. In this article, I show that by introducing two coatings with favorable thermophysical properties into a chip, the detection sensitivity can be enhanced from a few times to over 100 times for different optical path lengths from ~10 nm to ~1 µm. A detailed theoretical investigation on the periodic heat transfer and related photothermal effect in such a chip structure was presented. This photothermal effect strengthening method was experimentally demonstrated on a TiO2-coated cell with an optical path length of, for example, 300 nm, on which a sensitivity enhancement of 18 times was achieved in comparison with a cell without coatings and an absorption detection limit down to 2.5 × 10–2 cm−1 can be expected. This work illuminates the importance of heat control to the sensitivity enhancement of photothermal microscopy in nanospaces.