Optical force aggregation of gold nanoparticles as a tool to fabrication a multifunctional sensor

Optical nano-printing provides a versatile platform to print various nanoparticles into arbitrary configurations. Optical printing, the use of light to direct the formation of a desired structure, has been of significant interest in the last two decades. For particles much smaller than the laser wavelength, optical forces can be well described in the dipole approximation. For a focused laser beam, two main optical force components are identified: the gradient force, which attracts particles toward the high-intensity focal spot, and the scattering force, which tends to push particles along the beam propagation direction. When the wavelength light is close to the particle localized surface plasmons resonance, a scattering force is dominant and can be used to efficiently push nanoparticles along the beam optical axis onto a substrate. In this context, optical forces can be applied to optically print nanoparticles into patterns aggregated on surfaces such as glass. Here, we report on use optical nanoprinting of plasmonic nanoparticles to create an active aggregate in a solution containing dyes or nanoplastics. The active aggregate, produced by optical forces, serves as a sensitive sensor which is used to detect dyes in concentrations below the limit of detection for Raman spectroscopy and/or to detection of plastic nanoparticles.