Developing the next generation of smart, wearable devices involves the ability to continuously sense and respond to stimuli in the surrounding environment all in a flexible, miniature form factor. Synthesis and patterning techniques that have the capability to create and integrate a vast number of different materials, particularly with a microscale footprint, onto a single device are therefore crucial. Direct laser writing (DLW) has emerged as a powerful manufacturing tool for highly customized micro-patterning of a wide variety of materials that are useful for microsensors and wearable devices. Here we will present a DLW technique termed laser-induced thermal voxels (LITV), which combines the patterning flexibility inherent to DLW with the compositional control of hydrothermal synthesis. LITV generates a miniature solvothermal reactor by irradiating an optical absorber with a focused laser. When a solution of metal ions is present at the absorption site, the high temperatures generated cause localized thermal decomposition of the metal ion precursor solution, simultaneously synthesizing, depositing, and patterning nanoparticles. The identity of the synthesized material can be easily controlled by exchanging the precursor for a solution of different metal ions, allowing multiple materials to be patterned in close proximity on the micro scale. We describe the use of LITV in depositing materials for gas sensing and biosensing applications, studying the efficacy of LITV in these fields using metal, metal-oxide, and mixed-metal oxide depositions to respond to a variety of oxidizing and reducing gases as well as H<sub>2</sub>O<sub>2</sub> in a phosphate buffer solution.

Direct laser writing of microscale metal- and metal-oxide-based gaseous and biological sensors

ACS Fall 2021

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