High performance multi-purpose nanostructured thin films by inkjet printing: Au micro-electrodes and SERS substrates

Abstract

Nanostructured thin metal films are exploited in a wide range of applications, spanning from electrical to optical transducers and sensors. Inkjet printing has become a compliant technique for sustainable, solution-processed, and cost-effective thin films fabrication. Inspired by the principles of green chemistry, here we show two novel formulations of Au nanoparticle-based inks for manufacturing nanostructured and conductive thin films by using inkjet printing. This approach showed the feasibility to minimize the use of two limiting factors, namely stabilizers and sintering. The extensive morphological and structural characterization provides pieces of evidence about how the nanotextures lead to high electrical and optical performances. Our conductive films (sheet resistance equal to 10.8 ± 4.1 Ω per square) are a few hundred nanometres thick and feature remarkable optical properties in terms of SERS activity with enhancement factors as high as 10⁷ averaged on the mm² scale. Our proof-of-concept succeeded in simultaneously combining electrochemistry and SERS by means of real-time tracking of the specific signal of mercaptobenzoic acid cast on our nanostructured electrode.

Fig. 1. A schematic sketch of the stepwise processing of AuNPs. Every step shows its green chemistry principles.

Fig. 2. (a) Dark-field optical microscopy images with a 5× objective, (b) SEM images, and (c) AFM topography images. The colorbar at the right applies to all images and refers to the elevation in nanometers.

Fig. 3. (a) μ-Raman maps (633 nm excitation and 50× objective). (b) The EF was calculated for all replicates and averaged, at 633 nm excitation (red symbol) and 785 nm excitation (black symbols); the error bars represent the standard errors. (c) Padova University logo printed with the AuNP_PVA ink formulation with only one layer and any thermal curing. The colourmap represents Pearson's correlation coefficient with the PVA spectrum.

Fig. 4. Electrochemical-SERS experiments run on an MBA functionalized pAuNP_PVA_HT electrode. (a) 6 cyclic voltammetry cycles were run between −0.5 and −1.2 V. (b) Raman spectra were simultaneously acquired during the voltammograms. The characteristic 1580 cm⁻¹ band of MBA is recorded. The potential (c) and current (d) cycles are coherently shown with respect to panel b. The dashed line highlights the reference peak at 1580 cm⁻¹ before electrochemical desorption as an internal benchmark.