Metal nanoparticles laser-writing on cellulosic substrates for colorimetric paper-based analytical device development

In this presentation, a CO2-laser plotter-based versatile strategy to in-situ synthesize on paper plasmonic active gold (Au), silver (Ag), platinum (Pt), copper (Cu), cerium (Ce), nickel (Ni), and aluminium (Al) nanostructures will be presented [1]. This approach allows the formation of metal-nanostructures, named Laser-Induced Metal nanoparticles (LIMs), on different cellulosic substrates including Whatman paper, office paper, and recycled/byproducts-based papers without the need for external reagents. The laser allows LIMs’ design, shaping, and anchoring onto paper in a single stroke in a few seconds with the desired configuration. Noteworthy, LIMs possess features useful for sensing purposes, resulting in plasmonically active, catalytic, and photoluminescent according to their chemistry and morphology. LIMs have been used to equip different lab- made colorimetric paper-based analytical devices (PAD), conceived to work with smartphone-based readouts. The proposed PADs were manufactured using low-cost benchtop technologies (i.e., laser/cutter-plotter, thermal-laminator, etc.) and office-grade substrates (i.e., polymeric and cellulosic substrates). In this presentation, different LIM- based PADs will be presented, including, (i) a three-channel paper fluidic device (LF3) equipped with Ag, Au, and Ce-LIMs for the hypochlorite determination in milk, in the framework of bleaching frauds; (ii) a 'Flip-PAD' for the rapid (1 min) and selective determination of ascorbic acid in food and supplements, in this case, the device working mode relies on the Pt-LIM oxidase-like activity that allows colorimetric dye conversion; (iii) a fluorometric PAD equipped with photoluminescent Al-LIM for the selective quali- quantitative detection of o-diphenols in food samples. The herein proposed laser writing strategy turns out an innovative and sustainable nanopatterning technique, prone to generate optical sensing zones useful to develop (bio)sensing strategies and manufacture within everyone's reach PAD.