# Continuous bubble-free laser printing of plasmonic nanostructures enabling annealing-free ohmic conduction and multifunctional trapping/spectroscopy studies

## TL;DR

This paper introduces a bubble-free laser method to print plasmonic nanostructures that can conduct electricity and be used for trapping cells and spectroscopy.

## Contribution

A novel bubble-free laser printing method for plasmonic nanoparticles that enables annealing-free ohmic conduction and multifunctional applications.

## Key findings

- Printed plasmonic patterns show ohmic conduction without post-annealing.
- The method enables electrothermal trapping of biological cells and surface-enhanced Raman spectroscopy.
- Optimized printing yields excellent electrical conductivity and Raman signal enhancement.

## Abstract

Direct optical printing of nanoparticles shows tremendous potential as it enables the fabrication of arbitrary plasmonic patterns and affordable designs for diverse applications. Although significant attention has been paid to the bubble-assisted printing of nanoparticles, the requirement for complex arrangement, tedious optimization processes, high laser power, and double-hump printing profile make it a less favorable methodology as compared to the bubble-free printing of particles from colloids. Thus, a bubble-free approach to the optical patterning of plasmonic nanoparticles is highly desirable. Here, we demonstrate a laser-assisted, bubble-free optical patterning method for plasmonic nanoparticles directly from a colloidal solution. Furthermore, we investigated the role of laser writing speed and power in the printed plasmonic pattern. Interestingly, the I–V characteristics of the printed patterns exhibit ohmic conduction without the need for post-annealing, highlighting the potential of printed metallic nanoparticles for microelectronic applications. As a proof of concept, the fabricated conducting circuit via printing is used for the electrothermal trapping of biological cells. In addition, the spectroscopic applications of the printed plasmonic patterns are explored via surface-enhanced Raman spectroscopy, with crystal violet as a probe molecule. Through the optimized direct optical printing, we demonstrate the optical printing of metallic nanoparticles that exhibit excellent electrical conductivity and Raman scattering signal enhancement, thus providing a versatile platform for multi-analytical approaches.

A laser-assisted, bubble-free optical printing of plasmonic nanoparticles from the colloid is demonstrated, and the printed conducting patterns are used for electrothermal trapping of objects and surface-enhanced Raman spectroscopy applications.