Laser-induced nanozymatic metal nanoparticles for paper-based analytical devices

Nowadays, manufacturing easy-to-use and sustainable point-of-need devices is a hot topic. In this framework, the colorimetric approaches, which employ optical variation easily monitorable by naked eye or smartphone, can offer captivating opportunities. Due to its high availability, 3D structure, capillarity, mechanical resistance, flexibility, and biocompatibility, the paper represents an excellent substrate for fabricating analytical devices (PAD). However, there is still a need for affordable technologies that enable precise patterning/cutting of paper substrates, as well as strategies for integrating functional nanomaterials on them. Herein, 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 cellulosic substrates, including Whatman papers, conventional office paper, and recycled/byproducts-based papers. LIM formation mechanisms will be discussed together with the main variables to modulate their properties. In brief, the laser allows LIMs’ design, shaping, and anchoring onto paper in a single stroke in a few seconds with the desired configuration. LIMs possess useful features for sensing purposes, resulting in plasmonically active, catalytic, and photoluminescent according to their chemistry and morphology. To prove the LIM potentialities in PADs, a disposable LIM-PAD for the rapid and selective smartphone-based colorimetric determination of ascorbic acid (AA) will be presented. The PAD is equipped with a laser-induced platinum nanostructured catalytic paper (LIM-Pt) coupled to 3,3’,5,5’-tetramethylbenzidine (TMB) loaded fiberglass, assembled in an array format to allow the simultaneous determination of 5 samples in 1 minute. The LIM-Pt enables instantaneous TMB oxidation, given the proven oxidase-mimicking activity, ensuring the instantaneous conversion of uncolored-TMB to blue-colored TMBox, without additional reagents. AA induces a TMB-catalytic conversion inhibition resulting in a colorimetric signal ‘switch-off’. The linear AA dose-response ranged from 31 to 250 mg Kg1 (R2= 0.992), returning a detection limit of 6 mg Kg-1 ; analytical performance remained constant over 6 weeks (RSD= 4%). The Flip-PAD exploitability was proved through AA determination in food and pharmaceutical samples, returning accurate (Rec. 92−114%; R.E. −11/+4%) and reproducible data (RSD≤ 10%; n= 3). Summing up, 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 manufacturing within everyone's reach PADs.