Evaluation of fluorescence emitting characteristics of a microparticle by illumination angle scanning utilizing a resin-based monolithic TAS chip

An optical sensor, such as a light waveguide implemented total analysis system (TAS), is one of the functional components that will be needed to realize a “ubiquitous human healthcare system” in the near future. We have already proposed the fundamental structure for a light waveguide capable of irradiating a living cell or particle running along a microfluidic channel, and of detecting fluorescence even from the extremely weak power of a minute particulate body. In order to foster advanced functions for obtaining information concerning the internal structure of living cells or particles conveniently, an angular scanning method that sequentially changes the direction in which the minute cell or particle is irradiated may be crucial. In this paper, we investigate fluorescence detection from resin particles attached to a fluorescent substance by switching irradiation direction of the exciting laser source power using a newly fabricated TAS chip with a unique intersection structure. To construct the experimental system cost effectively, we adopted a special light waveguide structure in which the intersection to a fluidic channel was arranged radially, with laser power inlet/outlet portions arranged in parallel. In addition, we incorporated a forced vibration mechanism on an optical fiber apex to construct a simple light-switching system. Preliminary experiments combining this unique TAS chip and the optical scanning mechanism revealed that the function of the radially arranged light waveguide switching worked adequately, and variation of transmittance of each light waveguide was accurately evaluated. Results were successfully applied to compensation of detected angular scanning signals. Finally, we performed an angular scanning experiment for a fluorescent substance attached to a microparticle under conditions of higher intersection-passing velocity of several 10s mm/s (single-shot scanning) and lower intersection-passing velocity of several mm/s (multiple-shot scanning). Based on the obtained scanning data, we successfully constructed directivities of emitting fluorescence from particles, and clarified that fluorescence emission indicated its peak at the forward and orthogonal directions of the incident light beam.