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

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 k omega vs. 6.30 k omega) 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 mu mol L-1) and quantification (22.1 mu mol L-1) and linear response from 20 to 750 mu mol 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. A fast approach for synthesizing gold nanoparticles over electrochemical paper-based devices is reported. The device was fabricated by paper laser pyrolysis carbonization followed by in situ laser synthesis of AuNPs.