Room-Temperature Annealing-Free Gold Printing via Anion-Assisted Photochemical Deposition

Abstract

Metal patterning via additive manufacturing has been phasing-in to broad applications in many medical, electronics, aerospace, and automotive industries. While previous efforts have produced various promising metal-patterning strategies, their complexity and high cost have limited their practical application in rapid production and prototyping. Herein, a one-step gold printing technique based on anion-assisted photochemical deposition (APD), which can directly print highly conductive gold patterns (1.08 × 10⁷ S m^-1 ) under ambient conditions without post-annealing treatment, is introduced. Uniquely, the APD uses specific ion effects with projection lithography to pattern Au nanoparticles and simultaneously sinter them into tunable porous gold structures. The significant influence of kosmotropic or chaotropic anions in the precursor ink on tuning the morphologies and conductivities of the printed patterns by employing a series of different ions, including Cl^- ions, in the printing process is presented. Additionally, the resistance stabilities and the electrochemical properties of the APD-printed gold patterns are carefully investigated. The high conductivity and excellent conformability of the printed Au electrodes are demonstrated with reliable performance in electrophysiological signal delivery and acquisition for biomedical applications. This work exploits the potential of photochemical-deposition-based metal patterning in flexible electronic manufacturing.

Keywords: conformable electrodes; gold patterning; photoreduction; projection lithography; specific ion effects.

Figure 1.

a) Schematic of the DLP-based printing setup. b) The printed patterns on different substrates (top) and XRD spectrum of printed gold (bottom). c) Principle of the printing involving the reduction of gold ions, the seeding of AuNPs, and the growth of AuNPs network (top). The zoom-in AuNPs fusion occurs during the growth process (bottom).

Figure 2.

a–c) SEM images of the printed gold with illumination time of 5, 10, and 20 min. d–f) Zoom-in microstructures of the printed gold. g) Thickness of printed gold patterns as a function of printing time. h) Conductivity of printed gold patterns as a function of printing time. i) Porosities of printed gold patterns as a function of printing time. Data represent mean ± standard deviation, n = 5, significance determined by one-way ANOVA test. Scale bars: 1 μm for (a–c), 300 nm for (d–f).

Figure 3.

a–c) SEM image of printed Au using inks with NaCl concentrations of 0, 25, and 50 g L⁻¹ respectively. d) Porosity as a function of Cl⁻ anion concentrations. e) Particle sizes as a function of Cl⁻ anion concentrations. f) Thickness and conductivity as a function of Cl⁻ anion concentrations. g) Porosity of samples with different anions. h) Particle sizes of samples with different anions. i) Thickness/conductivity of samples with different anions. Data represent mean ± standard deviation, n = 5, significance determined by one-way ANOVA test. Scale bar: 200 nm for (a–c).

Figure 4.

a) Au circuit printed on rigid and flexible substrate connected with a LED light. b) Resistance stability of printed flexible Au electrode on PDMS substrate under inward and outward bending. c) Resistance stability of printed flexible Au electrode on PDMS substrate under stretching. d–f) Electrochemical impedance spectra (EIS) within a frequency range of 1–10⁴ Hz with an amplitude of 5 mV of sputtered gold and printed gold electrodes with different light intensity: d) Nyquist plots for the gold electrodes. e) Bode plots for the gold electrodes: impedance as a function of frequency. f) Bode plots for the gold electrodes: phase angle as a function of frequency.

Figure 5.

Conformable printed Au electrodes in electrophysiological signal delivery and acquisition. a) A pair of Au electrodes attached to the epicardium of the right ventricles for the porcine heart pacing with an electrical pulse. b) A pair of Au electrodes attached to the lower epidermis of a Venus flytrap lobe to modulate the lobe shift from “open” (left) to “close” (right) state with a square wave electrical stimulation. c) Action potential of the Venus flytrap actuator measured by the printed Au electrodes. d) The laminate structure diagram and optical image of the printed Au electrodes for ECG test. e) Pulse signal recording (10 s) and sample of a single beat (top), obtained by printed Au electrodes (red) and Ag/AgCl (blue) electrodes. f) Schematic of EMG and EEG test. g) EMG and EEG signal recordings during eye blink.