I. Abstract of the Paper’s Core Research

This study, based on the Optomec AJ300 aerosol‑printing system, prepared aqueous, biocompatible conductive inks containing silver nanowires, graphene, and PEDOT:PSS. Using these inks, we directly wrote interdigital transducers (IDTs) with varying line widths onto 128°Y‑cut lithium niobate piezoelectric substrates, fabricating SAW microfluidic devices operating across multiple frequency bands (5–20 MHz). We then conducted comprehensive acoustic and microfluidic validation by comparing these devices with lithographically patterned gold‑film reference structures. The key findings are as follows:

• Manufacturing efficiency has increased by a factor of dozens, and the dust-free lithography production line has been completely abandoned.

The conventional lithography–evaporation–lift‑off process takes approximately 40 hours; aerosol‑based maskless one‑step printing requires only 5 minutes, allows direct CAD‑driven modification of electrode periods, and enables same‑day prototyping of multi‑frequency chips without the need for custom lithographic masks.

• Three types of conductive inks are compatible with SAW devices across multiple application scenarios.

Silver nanowires: exhibit superior electrical conductivity, large acoustic vibration displacement, and are well-suited for high-power particle enrichment.

Graphene: Lightweight and thin, with low parasitic loading, resulting in less severe waveform distortion in high-frequency devices.

PEDOT:PSS: Transparent and biocompatible, suitable for visualization‑enabled cell‑observation chips.

• The resonant frequency of the printed device matches the theoretical value with high accuracy.

The electrode linewidth is precisely controllable within the range of 50–150 μm, and measured resonant frequencies exhibit negligible deviation from theoretical predictions. The aerosol‑based fabrication system achieves a minimum feature size of 10 μm, enabling the theoretical design of high‑frequency SAW devices operating at nearly 100 MHz.

• Successfully realized two core microfluidic acoustic functions.

Laser Doppler vibrometry confirms the effective excitation of acoustic waves; within a 5 μL droplet, acoustic vortices are generated and micron-sized particles are rapidly concentrated, with fluid flow rates and particle enrichment performance comparable to those of lithographic devices.

• Bio-friendly all-water-based ink system

A non‑toxic, heavy‑metal‑free slurry with excellent biocompatibility, suitable for direct use in biological experiments such as cell and exosome isolation.

II. Complete SAW Microfluidic Fabrication Process for Aerosol Jetting

• Complete SAW microfluidic control fabrication process flow

1) Lithium niobate substrates cut along the 128°Y orientation are ultrasonically cleaned in isopropyl alcohol and dried under dust-free conditions.

2) Prepare silver nanowire, graphene, and PEDOT:PSS aqueous conductive inks separately, and disperse them uniformly by ultrasonic treatment.

3) Aerosol ultrasonic atomization, with sheath gas at 30–32 SCCM for focusing, a 150 μm nozzle, and a printing speed of 4 mm/s to directly write an IDT interdigital transducer array.

4) The substrate is maintained at a constant temperature of 80°C for rapid drying, eliminating the need for high-temperature sintering or vacuum evaporation.

5) Silver epoxy leadframe packaging; construction of a signal source and a laser Doppler vibrometry system.

6) Acoustic vortex generation in droplets and microfluidic functional testing for particle enrichment.

• Five Core Process Advantages (Compared to Lithography / Electron-Beam Evaporation)

Maskless digital direct writing reduces the R&D cycle by 98%.

Eliminates the need for multiple steps such as plate-making, exposure, development, evaporation, and stripping; simply modify the design and print, perfectly meeting the high‑frequency iteration demands of laboratories.

Versatile for multiple conductive materials, covering metals, carbon, and conductive polymers.

A single piece of equipment can seamlessly switch between silver, graphene, and transparent PEDOT inks, enabling a single production line to handle three types of SAW chips: high‑power, high‑frequency, and transparent.

A fully water-based low-temperature process, with no thermal damage to the piezoelectric substrate.

The maximum substrate temperature is only 80°C, which does not cause degradation of the piezoelectric properties of lithium niobate and ensures compatibility with various thermally and chemically sensitive piezoelectric materials.

Low‑consumable, site‑specific deposition; substantial savings on precious metals.

Conductive materials are deposited only in the ID functional area, while photolithographic patterning of a full‑wafer gold film results in substantial material waste; consequently, small‑batch R&D costs are significantly reduced.

Non-contact forming, compatible with curved and irregularly shaped piezoelectric substrates.

A safe spray distance of 3–5 mm; in the future, flexible SAW sensor chips could be fabricated on curved piezoelectric substrates, whereas lithography is currently limited to planar wafers.

III. Five Core Technological Innovations of This Study

Innovation 1: The world’s first fully printed aerosol‑based functional SAW microfluidic chip

It has been demonstrated that AJP can fabricate complete surface acoustic wave microfluidic devices with fluid‑manipulation capabilities, thereby overcoming the conventional manufacturing bottleneck of SAW devices, which require cleanroom photolithography.

Innovation: Three Types of Functional Inks—Differentiated SAW Complete Preparation Solutions

The system quantifies the acoustic properties of silver nanowire, graphene, and PEDOT electrodes, and establishes material selection criteria for various microfluidic applications.

Innovative 3.5–20 MHz broadband aerosol IDT precision control process

By precisely matching the resonant frequency to the printed linewidth, an electrode‑size–frequency quantitative model is established, enabling scalability up to nearly 100 MHz high‑frequency devices.

Innovative 4‑Gas Aerosol SAW Acoustic Vortex + Particle Enrichment Dual‑Function Validation

We fully reproduced the core microfluidic acoustic effects of lithographic chips, demonstrating that aerosol‑printing devices can meet the requirements for biochemical sample pre‑processing.

Innovation 5: A Biocompatible Water-Based Additive Manufacturing Paradigm

All‑environmentally friendly, non‑toxic water‑based ink; the device leaves no chemical residues and is directly compatible with cells, exosomes, and biological fluids for non‑destructive analysis.

IV. Current Industry Challenges and Corresponding Solutions for Overcoming Them

Challenge 1: Traditional SAW manufacturing relies on cleanrooms, requiring substantial capital investment and long production cycles.

✅ The aerosol‑based desktop system enables direct processing, with a single step completing the fabrication in just 5 minutes—eliminating the need for masks and vacuum equipment, making it feasible for small and medium‑sized enterprises to set up their own lab platforms.

Challenge 2: The use of a single-metal gold film material limits the device’s application scenarios.

✅ Freely switch among three types of inks—silver, graphene, and transparent conductive polymers—meeting the demands of high-power, high-frequency, and visualizable biochips.

Challenge 3: The lithography process struggles to rapidly iterate multi-frequency experimental samples.

✅With CAD, you can modify the interdigital period with a single click and complete parallel comparisons of multi‑band SAW devices on the same day, significantly shortening the R&D cycle for materials and acoustic formulations.

Challenge 4: The cost of evaporating gold films is high, leading to significant waste of precious metals over large areas.

✅ Site-specific selective deposition of conductive traces, with coating applied only to functional areas, significantly reducing material costs.

Challenge 5: Conventional high-temperature processes can easily degrade the acoustic performance of piezoelectric crystals.

✅ The entire process employs low-temperature drying at 80°C, with no high-temperature annealing, thereby preserving the piezoelectric coupling properties of lithium niobate.

V. Future Diversified Industrial Application Scenarios

1 Portable microfluidic chip for in vitro diagnostics

Rapid custom fabrication of aerosol‑based SAW chips for blood exosome and cell sorting, with mass production of compact POCT diagnostic devices.

2 High-Throughput Bioacoustic Sorting Platform for Laboratories

University/Pharmaceutical‑industry desktop aerosol‑generation system, enabling rapid prototyping of microfluidic chips at various frequencies and acoustic‑based screening assays for cells and microorganisms.

3 Microenvironment Droplet Detection Sensor Chip

Enrichment of trace aqueous pollutants, rapid mass-spectrometric sample preparation, and portable on-site water-quality monitoring devices.

4 Flexible Curved-Surface SAW Acoustic Sensor

Arc-shaped piezoelectric substrate with sol–gel printing, enabling wearable devices for real-time monitoring of physiological signals and skin‑surface fluids.

5 Low-Cost Microfabrication Teaching and Research Tools

No lithography or cleanroom required; low-cost fabrication of acoustic microfluidic samples, suitable for teaching courses in micro‑ and nanofabrication and acoustofluidics.

Image and Text Guide

Figure 1. Process and mechanism for fabricating SAW microfluidic devices using AJP. a) The printed interdigital transducer is driven to generate surface acoustic waves that propagate along the lithium niobate surface; the resulting acoustic radiation force and acoustic streaming act on the droplet and the particles within it. b) An aerosol‑jet printer and the printed PEDOT:PSS device. c) A silver‑nanowire interdigital transducer fabricated on a lithium niobate substrate. d) A comparison of manufacturing time and process steps between cleanroom fabrication (approximately 40 hours, 4 steps) and AJP (approximately 5 minutes, 1 step).

Figure 2. AJP-printed interdigital transducers with different materials and widths. a) Schematic of the printing process: ink is atomized by ultrasonic atomization, carried by a nitrogen carrier gas and focused by a sheath gas, then deposited through a 150 μm nozzle; b) Printed silver‑nanowire SAW device; c,d) SEM images of the silver‑nanowire electrodes; e) Comparison between measured and designed electrode widths; f) Comparative electrical conductivity at both ends of the materials, with silver nanowires exhibiting the highest conductivity.

Figure 3. Acoustic response of the printed device and its comparison. a) Schematic illustration of laser Doppler vibrometry; b) Acoustic displacement field from numerical simulation; c) Experimentally measured displacement field of a silver nanowire device, in good agreement with the simulation results; d) Comparison between the measured resonance frequency and the theoretical value, showing excellent consistency; e) Normalized displacement comparisons for devices made of different materials, demonstrating that the acoustic response of all printed devices can be detected.

Figure 4. Demonstration of the microfluidic functionality of the printed SAW device. a) Schematic diagrams of two demonstrations: acoustic streaming and particle enrichment; b) 2D simulation of the velocity distribution of acoustic streaming within a droplet; c) Acoustic streaming experiment with 2-μm particles in a silver nanowire device (5 μL droplet, 65.2 Vpp); d) Particle image velocimetry analysis, yielding an average flow velocity of approximately 550 μm/s; e–g) Enrichment of 10-μm particles: comparison between the acoustic field off and on for 1 second, along with the temporal evolution of fluorescence intensity.