Laser-induced fabrication of gold nanoparticles onto paper substrates and their application on paper-based electroanalytical devices

Abstract

A novel and quick (sub-minute) method for synthesizing gold nanoparticles (AuNPs) onto electrochemical paper-based devices (ePADs) using a CO₂ laser is presented. An ePAD, fabricated by laser-scribing carbonization of kraft paper, is modified by the in situ synthesis of AuNPs onto a working electrode, driven by the CO₂ laser reduction of a precursor solution (HAuCl₄). Cyclic voltammograms recorded in H₂SO₄ and energy dispersive spectroscopy confirm the presence of Au structures embedded in the carbonized paper matrix. A gold modified electrode (LSAu-ePAD) shows an improved electrochemical response towards the ferri/ferrocyanide redox probe, with decreased peak potential separation, a 13-fold increase in peak current, and reduced charge transfer resistance (0.11 kΩ vs. 6.30 kΩ) compared to unmodified electrodes. Scanning electrochemical microscopy reveals an increase in the electrode's electron transfer rate by the Au modification, reflected in the voltammetric profile in bulk measurements. LSAu-ePAD repeatability and reproducibility are 0.4% (n = 10) and 9.7% (n = 5), with a shelf life of up to 30 days. Additionally, a novel field-deployable batch-injection analysis paper-based cell (BIA-ePAD) coupled to the LSAu-ePAD platform is designed for amperometric analyses. The BIA-ePAD is used for hypochlorite (NaClO) detection, reaching low limits of detection (6.70 μmol L⁻¹) and quantification (22.1 μmol L⁻¹) and linear response from 20 to 750 μmol L⁻¹. The variability of the amperometric signals between measurements and between devices is 4.7% (n = 12) and 5.3% (n = 6), respectively, with a sampling frequency estimated as 127 h⁻¹, which is remarkable considering the device's simple and quick fabrication. Analyses of real swimming pool and tap water samples spiked with NaClO showed good recovery values (93 ± 6%). Overall, the developed approach is promising for fast modification of ePADs with AuNPs (and possibly other metals), and coupling them with paper-based BIA cells allows for simple, inexpensive, and high-performance analyses in a fully-integrated portable platform.