Photothermal effect at the solid-liquid interface under laser illumination can generate a bubble and fluid flow1,2 to assemble dispersoids within a few minutes. Such a phenomenon enables us to colloidal lithography3 and concentration measurement of small objects (microparticles, bacteria, etc.)4. In this method, it is required to assemble various dispersoids (constituent material, size, etc.) at an arbitrary place with high efficiency and good reproducibility. However, there is little knowledge on physicochemical mechanism for the highly efficient assembly and the control of assembly dynamics. Here, focusing on the surface modulation of the bubble with a nonionic surfactant, we have clarified that this process greatly affects on assembly dynamics of polystyrene microparticles (PS) (Figure 1a) and improves assembly efficiency (= the number of assembled PS / total number of PS in liquid), 10-20 times in comparison with the case of no surfactant (Figure 1b)5. The number of assembled PS was obtained by dividing the volume of the assembled region by the volume of a PS. This result can extend the limit of measurable concentration by one order. Furthermore, we revealed the influence of concentration and constituent material of dispersoids (PS and bacteria, SA) on assembly efficiency (Figure 1c) and led to improvement of measurement precision. These results are significant for the laser-induced assembly leading to rapid concentration measurement of dispersoids available for the hygiene inspection, microfabrication, and so on.
References:
1. Baffou G.; Monneret S. et al.; J. Phys. Chem. C 2014, 118, 4890-4898.
2. Lin L.; Zheng Y.; Nano Lett. 2016, 16, 701-708.
3. Fujii S.; Haga M. et al.; Langmuir 2011, 27, 8605-8610.
4. Yamamoto Y.; Iida T.; Tokonami S. et al.; Opt. Mater. Exp. 2016, 6, 1280-1285.
5. Yamamoto Y.; Tokonami S.; Iida T.; in preparation.
Photonic & plasmonic nanomaterials , Nanoscale photothermal effects , Optical sensing from solid state to bio-medicine
