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Light-induced heating on a solid–liquid interface can generate a vapor submillimeter bubble and fluid flow, which enables us to densely and rapidly assemble dispersoids into a desired position (photothermal assembly). Here, we revealed that the surface modulation of the light-induced bubble by a surfactant dominates the assembly dynamics of nanoparticles and microparticles as dispersoids, which results in highly efficient photothermal assembly under the surfactant-controlled fluid flow. This mechanism can facilitate the concentration measurement of small objects (microparticles, bacteria, viruses, etc.). Particularly, we found that the surfactant-controlled fluid flow and bubble enable high-density assembly of dispersoids and remarkable enhancement of assembly efficiency, achieving 10–20 times in comparison with the case of no surfactant. This result can extend the limit of measurable concentration by one order. Furthermore, this study revealed the influence of concentration, size, and constituent material of the dispersoids on the assembly efficiency for the improvement of measurement precision. These findings are crucial for laser-induced assembly for the rapid concentration measurement of various microbes without a cultivation process as bioanalysis, for the high-sensitivity detection of harmful particles, and for the colloidal lithography.

Some bacteria are recognized to produce useful substances and electric currents, offering a promising solution to environmental and energy problems. However, applications of high-performance microbial devices require a method to accumulate living bacteria into a higher-density condition in larger substrates. Here, we propose a method for the high-density assembly of bacteria (106 to 107 cells/cm2) with a high survival rate of 80 to 90% using laser-induced convection onto a self-organized honeycomb-like photothermal film. Furthermore, the electricity-producing bacteria can be optically assembled, and the electrical current can be increased by one to two orders of magnitude simply by increasing the number of laser irradiations. This concept can facilitate the development of high-density microbial energy conversion devices and provide new platforms for unconventional environmental technology.

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A photothermal film (PTF) with densely assembled gold nanoparticle-fixed beads on a polymer substrate is fabricated. Remarkably, a temperature rise higher than 40 °C is achieved in the PTF with only 100 seconds of artificial solar irradiation, and the output power of the thermoelectric device was enhanced to be one order higher than that without PTF. These results will pioneer a rapid solar thermoelectric device.