Single-Stroke laser scribing of optical-active nanostructures on cellulosic substrates for colorimetric and photoluminescent-based sensing strategies

The implementation of affordable technologies to manufacture optical and colorimetric paper-based analytical devices (PAD) integrating optical active nanostructures is still a challenge. Therefore, the development of strategies to fabricate colorimetric PAD integrating nanostructured sensing surfaces with a controlled pattern is of great interest. Recently, our group proposed an innovative and versatile approach to in-situ synthesize optical active gold, silver, platinum, copper, nickel, and aluminum (Al) metal nanoparticles (MNPs) on paper, employing a CO2- laser plotter1. This approach allows laser-induce MNPs well anchored onto paper substrates according to customized designs; these laser-induced MNPs (LIMs) demonstrated captivating and useful features, including (i) localized surface plasmon resonance, (ii) catalytic and (iii) photoluminescent feature-related to the MNPs chemistry and morphology. In this presentation, completely lab-made PADs integrating LIM coupled with smartphone-based readouts will be discussed. In detail, a photoluminescent Al-based paper-nanostructure employed for the implementation of a fluorometric PAD for the selective detection of o-diphenols will be presented; in this case, the Al-nanostructure fluorescence turn-on, induced by the interaction with the phenolic structures, is exploited for their detection. This peculiar optical behavior was investigated according to the laser-induced nanostructure synthesis, studying the Al-fluorescence turn-on mechanism towards several phenolic structures. Further, a laser approach to induce paper nanostructuration and carbon dots (CDs) formation will be also presented; in particular, the synthesis of laser-induced CDs (LiCDs) doped with different surface functionalizations (i.e., - SH, -COOH, -OH, etc.) will be shown. LiCDs give rise to enhanced fluorescence phenomena according to the surface chemistry; the use of the latter for (bio)sensing purposes will per presented. Summing up, the proposed CO2 laser strategy is particularly prone to generate colorimetric and photoluminescent sensing zones in tailored paper-based devices, resulting in a new sustainable nanopatterning technique useful for (bio)sensing and nanochemistry.