Laser-Based Facile Fabrication of Plasmonic Gold Nanostructures and Their Sensory Applications

Plasmonic nanostructures presenting localized surface plasmon response (LSPR) have attracted great attention in diverse sensory applications. Susceptible change of LSPR peak wavelength to the environmental stimulus, such as molecular binding, has been exploited to detect rare biomolecules at extremely low concentrations. In addition to such biomolecule sensing, the LSPR peak change to the distance variation between individual plasmonic nanostructures has been used to equipment-free colorimetric sensing of mechanical strain. Various nanolithography techniques have been employed to craft plasmonic metal nanostructures to realize the above-mentioned sensor applications; however, there is still a need for a low-cost, simple, fast, and scalable fabrication method to achieve reliable and reproducible LSPR sensors. Herein, we introduce a laser scribing-based technique for rapid formation and patterning of plasmonic gold nanostructures. In our process, a high-power laser beam melts a thin gold film on glass or quartz substrates, and subsequent dewetting of the melted gold results in nano-island structures consisting of surface-bound gold nanoparticles with an average diameter of 42 nm. We have been successfully applied the plasmonic structures to the highly-sensitive and selective immunoassay of the SARS-CoV-2 nucleocapsid protein, enabling the diagnosis of recently prevalent infectious disease, COVID-19. On the other hand, we have also developed a technique to transfer the gold nanostructures from the hard quartz substrate to the soft and flexible elastomer tape, aiming to create convenient colorimetric strain sensors capable of detecting mechanical motions of human bodies or mechanical behaviors of building structures.