I. Abstract of the Paper’s Core Research

This study employs a room-temperature sodium borohydride reduction method to synthesize PVP‑capped gold nanoparticles. An iterative washing protocol is used to remove excess capping agents, and a ternary eco‑friendly solvent system comprising water, ethanol, and ethylene glycol is formulated to prepare a platform‑compatible aqueous gold nanoparticle ink. Comprehensive rheological, atomization, sintering, electrical, and patterning characterizations are systematically conducted, and micron‑scale gold interconnects are fabricated using aerosol jet printing and inkjet deposition techniques. The key findings are as follows:

Eco-friendly water-based ink compatible with both devices

The ink uses deionized water as its primary solvent and contains no toxic organic solvents. Its rheological properties are optimized to meet both the inkjet Z‑value range (1–14) and aerosolization requirements, enabling stable printing on Dimatix inkjet systems and Optomec aerosol‑based equipment without the need for re‑formulation—making it a rare cross‑system conductive paste in the industry.

Low‑cost coating formulations enable dense sintering at low temperatures.

The as‑prepared gold particles contain 30 wt.% PVP; after washing, only 5.5 wt.% of the coating remains. Conductivity is achieved at 250 °C, and upon annealing at 400 °C for 45 min, the film exhibits a resistivity as low as 9.6 ± 1.2 × 10⁻⁸ Ω·m—only four times that of bulk gold. Moreover, an ultrathin 400-nm film attains a highly conductive, continuous structure.

High-Precision Micro-Image Formation of Aerosols

A 300-μm nozzle paired with an optimal focus ratio of FR=2 ensures no material overflow at the edges of printed lines; a 150-μm nozzle enables the fabrication of precision gold microchannels smaller than 20 μm, delivering uniform prints free of filament breakage and stray deposits caused by satellite droplets.

Universal wetting performance on multiple substrates

The ink exhibits stable spreading on Kapton, PET, tattoo paper, silicon wafers, and PEL flexible substrates, with controllable contact angles, enabling the formation of complete conductive circuits without the need for intense plasma activation of the substrate.

Highly stable, biocompatible gold conductive layer

Gold thin films exhibit strong chemical inertness, with no ion migration and no cytotoxicity, making them well suited for electrochemical biosensors and wearable physiological sensors. During prolonged storage, the ink remains free of particle sedimentation, and continuous atomization printing prevents nozzle clogging.

II. Complete Preparation Procedure for Cross-Platform Gold–Oil Ink Aerosols

Gold nanoparticle synthesis: Aqueous chloroauric acid solution is mixed with PVP, and an alkaline sodium borohydride solution is added dropwise at room temperature to effect reduction; the mixture is stirred for 12 hours to obtain a crude gold colloid.

Multi-stage purification: Cross‑filtration followed by repeated centrifugation and washing removes excess PVP capping agent and concentrates the gold nanoparticle dispersion.

Ink formulation: A ternary blend of water, ethanol, and ethylene glycol is formulated to produce an aqueous gold ink with a solids content of 1–5 wt.%.

Dual-path device verification:

① Inkjet: Samba 10pL ink cartridge, substrate at 55°C, multi-layer stacked printing;

② Aerosol ultrasonic atomization : 300 μm ceramic nozzle, carrier gas 28–35 sccm, sheath gas 45–60 sccm, stage temperature 65–70°C;

Heat treatment: Gradient heating sintering; electrical properties were compared across groups at 200, 250, and 400 °C.

Characterization: TEM/SEM is used to observe particle and thin-film morphology; four-probe measurements are employed to determine resistivity; contact angle and rheological tests are conducted; and an optical profiler is utilized to characterize line width.

III. Five Core Process Advantages of Aerosol Spraying Systems

Micron-level ultra-high graphic precision, with extremely minimal flash.

Aerosol airflow can be precisely focused, with an optimized focusing ratio that yields sharply defined line edges; the minimum feature size is less than 20 μm, meeting the requirements for MEMS microelectrodes and RF micro‑interconnects.

Non-contact conformal printing, universally applicable to curved and flexible substrates.

3–5 mm adjustable standoff distance; PI, PET, and irregularly shaped wafers require no direct contact, eliminating the risk of scratching thin films and ensuring compatibility with 3D sensing components.

Precise, site-specific deposition of ink consumables

Only the target area is coated with gold paste, resulting in significantly lower precious-metal consumption compared to spin coating and dip coating, thereby substantially reducing the cost of fabricating gold interconnects.

Low-temperature molding compatible with heat-sensitive flexible substrates

The ink coating agent has a low content, enabling conductivity at 250°C, while standard commercial PI films do not undergo high-temperature carbonization or deformation.

Shares an ink system with inkjet equipment.

During the R&D phase, there is no need to prepare separate aerosol‑ and inkjet‑specific inks; a single sample can be used to simultaneously compare two fabrication processes, significantly shortening the device iteration cycle.

IV. Five Core Technological Innovations of This Study

Innovation 1: Aqueous Gold Nanoparticle Ink Compatible with Both Aerosol and Inkjet Printing

Breaking the industry’s “one‑machine‑one‑slurry” bottleneck, it offers a unified rheological window compatible with two mainstream maskless direct‑write systems, while employing a green, low‑toxicity solvent system.

Innovative two‑stage washing process for removing excess PVP coating

Significantly reduces organic residues in the ink, overcomes the challenge of traditional gold inks requiring sintering at temperatures above 500°C, and expands the range of compatible flexible substrates.

Innovation 3: Tri-component Solvent Regulation to Suppress Coffee Ring Formation via Marangoni Flow

The high-boiling-point ethylene glycol modifier balances the solvent evaporation rate, resulting in smooth, dense gold traces with no edge‑related particle buildup defects.

Innovative 4‑Aerosol Focusing Ratio and Precision Overflow‑Control Molding Process

By optimizing the sheath gas–carrier gas ratio, an optimal printing window with FR = 2 is established, enabling spurious‑free deposition of sub‑20 μm precision gold microstructures.

Innovative 5‑High‑Stability Inert Biocompatible Gold Conductive System

Compared with silver ink, this medical‑grade printed electronics material offers zero ion diffusion and no cytotoxicity, while simultaneously delivering high conductivity and long‑term chemical stability.

V. Current Industry Challenges and Corresponding Solutions

Challenge 1: Aerosols and inkjet inks have entirely different rheological requirements, necessitating separate formulations and resulting in high R&D costs.

✅ The ternary water-based formulation precisely controls viscosity and surface tension, making it compatible with both inkjet and gravure printing equipment and reducing the need to prepare multiple batches of ink.

Challenge 2: The commercial gold ink has a high coating agent content, with a sintering temperature exceeding 50°C, and the flexible PI substrate cannot withstand high temperatures.

✅ Multi‑stage washing removes most of the PVP; conductivity is achieved at 250°C, and a gold‑like low resistivity is attained at 400°C, making it compatible with the vast majority of flexible films.

Challenge 3: Severe material overflow during precious-metal ink spraying, resulting in rough lines and a high scrap rate for tiny electrodes.

✅ Aerosol focusing ratio optimized, with highly stable boundary convergence of the mist flow; the 20 μm microchannel profile is sharply defined, reducing gold material waste.

Challenge 4: Silver inks are prone to ion migration and exhibit significant biotoxicity, precluding their use in in vivo or skin‑based sensing applications.

✅ The gold thin film exhibits chemical inertness, with no leaching of metal ions, excellent biocompatibility, and ensures safety and reliability in medical applications.

Challenge 5: Oil-based gold inks have highly irritating solvents, posing a contamination risk in biological experiments.

✅ All‑water‑based, environmentally friendly system; free of toxic organic solvents, ensuring no solvent interference in cell culture and in vitro microchip applications.

VI. Future Diversified Industrial Application Scenarios

1 Medical Wearable Biosensing Electrodes

Sweat‑based and ECG‑monitoring flexible patches, featuring low‑toxicity gold conductive traces that remain skin‑friendly even with prolonged wear and deliver stable, drift‑free signals.

2 In vitro microfluidic biosensing chip

High-precision interdigitated gold electrodes, electrochemical detection of trace proteins and tumor biomarkers, and highly sensitive microsensor arrays.

3 Interconnection of Miniature RF and MEMS Devices

Silicon-based microchips and low-resistance gold interconnects for millimeter-wave passive components exhibit excellent thermal stability and oxidation resistance, ensuring stable long-term performance.

4 Flexible photodetectors, OLED micro-pixels

Stabilizing the work function of gold electrodes and achieving interface barrier matching enhance the response efficiency and lifespan of optoelectronic devices.

5 High-Throughput Printing R&D Platform for Laboratories

A set of inks was used to prepare control samples via both aerosol‑based and inkjet printing processes, enabling rapid screening of flexible electronic device architectures.

Image and Text Guide

Figure 1. Schematic diagram of multi‑nozzle (multi‑printer) compatibility with water‑based gold nanomaterial inks for printed electronics.

Table 1. Printing Parameters for Aerosol Jet Printing (Optomec 200, Ultrasonic Atomization)

Figure 2. Characterization of gold nanoparticles: (a) TGA, (b) DSC, (c) TEM, (d) UV–vis absorption spectrum

Figure 3. Contact angle and rheological characterization of gold ink: (a–d) contact angles, (e) surface tension, (f) DLS particle size, (g) shear stress, (h) viscosity.

Figure 4. Study of Printed Gold Structures and Sintering: (a–c) Printed gold contacts/structures; (d–h) Interconnections with different pitches; (i) Resistivity versus sintering temperature; (j, k) SEM images of the as-printed and sintered states.