Fluorescence detection of minute particles using a resin-based optical total analysis system with a high-aspect-ratio light waveguide core

It has long been thought that an optical sensor, such as a light waveguide implemented total analysis system (TAS), is one of the essential functional components needed to realize a "ubiquitous human healthcare system". In accordance with this, we have proposed the fundamental structure for a light waveguide capable of illuminating a cell or particle running along a microfluidic channel and detecting fluorescence even from the extremely weak power of such a minute particle. We successfully trial-manufactured an optical TAS chip with a microfluidic channel containing a 15 × 20-μm cross-section, and a higher aspect ratio (6-μm wide, 10-μm high) core of a light waveguide. To obtain extremely weak forward- and side-direction emitted fluorescence within the chip, we utilized the L- or T-shaped microfluidic channels used in previous studies. As we could predict the fluorescent substances would have very low efficiency, we created a high-power light source using a semiconductor laser (488-nm-wavelength), and a high-performance fluorescence detecting optical system, consisting mainly of a dichroic mirror and interference filters. With this system, we were able to obtain fluorescent responses emitted from substances attached to a particle, adjusting gains in value of the maximum photoelectron multiplier tube modules. Response signal waveforms indicated higher signal-to-noise ratio in forward-direction emitted fluorescence and side-direction emitted. These two detected fluorescences and the side-scattered source light were fully synchronized. Furthermore, a series of experiments revealed that the forward-direction and side-direction emitted fluorescence components had approximately the same order of magnitude. Typical pulse magnitude detected in both directions ranged from 1 pW to several hundreds of pW.