CO2-laser approach for nano-metal equipped paper-based opto-colorimetric devices manufacturing

The implementation of affordable technologies to fabricate optical and colorimetric paper-based analytical devices (PAD) integrating nanomaterials is a compelling challenge for the (bio)analytical community. In particular, the controlled decoration of flexible substrates with optical active metal nanoparticles (MNP), can offer infinite opportunities for the development of (bio)sensors and integrated analytical devices. However, implementing strategies to fabricate optical and colorimetric PAD integrating MNPs with a controlled pattern is still a difficult task. Recently, our group proposed an innovative and versatile approach to in-situ synthesize on-paper plasmonic active gold, silver, platinum (Pt), copper and nickel nanostructures employing a CO2-laser plotter [1]. This approach allows to 'write' MNPs onto paper according to the required design. The obtained MNPs demonstrated to possess two useful features, i.e., (i) the localized surface plasmon resonance that results in distinguishable visible colors, and (ii) catalytic features, these two phenomena are related to the MNPs' intrinsic chemistry and nanostructure. Laser-induced MNPs (LIMs) were integrated into different fully lab-made PAD coupled to smartphone-based readouts. In this presentation will be presented a Flip-PAD for the selective determination of ascorbic acid, where Pt-LIM oxidase-like activity allows a dye-based colorimetric readout without the need for external reagents (Figure A). The Pt-LIM was fully characterized, and the oxidase-like activity was deeply investigated. The proposed lab-on- paper device was designed in an analytical configuration conceived to facilitate analysis steps and was manufactured via low-cost benchtop technologies (i.e., laser/cutter-plotter, thermal-laminator, etc.) using office- grade substrates (i.e., polymeric-sheets, cellulosic substrates, etc.). Further, a paper-based device integrating LIMs based on aluminum (Al), for the selective detection of o-diphenols will be also presented; in this case, the analytical quantification of the analyte relise on the selective Al- nanostructures fluorescence enhancement induced by the interaction with the phenolic structures (Figure B). The Al-LIM based PAD sensing ability was carefully studied and optimized, eventually the PAD was employed for the selective detection of o-diphenols in foods. The proposed laser writing strategy can be considered a new nanopatterning technique, particularly prone to generate optical sensing zones in tailored colorimetric PADs.