I. Abstract of the Paper’s Core Research

This study employs ethyl cellulose (EC)-exfoliated few-layer graphene as the conductive filler, supplemented with a small amount of nitrocellulose (NC) to enhance film adhesion. By systematically comparing single-, binary-, ternary-, and quaternary solvent systems, we selected a quaternary blended ink suitable for aerosol jet printing. We comprehensively characterized the ink’s rheological behavior, atomization performance, printed line morphology, and its electrical and electrochemical properties. The key findings are as follows:

Synergistic Regulation of Multi-Stage Drying Behavior by Quaternary Solvents

A ternary blend of isobutyl acetate (IBA, high volatility), diethylene glycol dimethyl ether (Dig, medium volatility), Cyrene, and glycerol (low viscosity, high boiling point) enables stepwise, controllable evaporation of droplets across three stages—atomization, flight, and deposition—thereby mitigating two major drawbacks: premature drying and material overflow, as well as excessive spreading upon impact.

Glycerol induces a colloidal gelation effect, significantly enhancing printing resolution.

The low surface tension of glycerol promotes localized gelation upon deposition of graphene particles, thereby suppressing lateral spreading. With a 200-μm nozzle, the minimum line width in a single pass can reach 40 μm, while a 150-μm nozzle enables ultra-fine traces as narrow as 21 μm; printing speeds are compatible with 1–5 mm/s.

Low-voltage stable atomization, simplifying equipment commissioning.

The atomization voltage of the quaternary ink is only 35 V, significantly lower than the 43 V required for single-solvent systems. Long-term printing results in no nozzle clogging, and graphene is uniformly dispersed without agglomeration; DLS analysis confirms stable colloidal particle size.

High electrical conductivity + strong mechanical adhesion in the thin film

The solidified graphene film exhibits a maximum electrical conductivity of 32.5 kS/m; in the cross‑hatch tape test, 93% of the coating thickness remains intact, with only a slight increase in resistance, indicating that the NC additive effectively enhances interparticle bonding.

Aerosol-printed graphene biosensor devices have been successfully commercialized.

A finger‑like electrochemical sensor was fabricated on a PI flexible substrate for the detection of parathion pesticide, exhibiting a linear range of 0.01–1 μM, a detection limit of 732 nM, and a sensitivity of 34 nA·μM⁻¹. It is suitable for the rapid screening of trace contaminants in water and food.

II. Preparation of Graphene Aerosol Ink + Complete Printing Process

1) Few-layer graphene coated with EC was prepared via liquid-phase shear exfoliation and purified by centrifugation.

2) A quaternary solvent system (IBA + Dig + Cyrene + glycerol) was formulated, with graphene and a small amount of NC binder added; ultrasonic treatment for 12 hours yielded a stable colloidal ink.

3) Optomec aerosol equipment employs ultrasonic atomization and sheath‑gas focusing for direct‑write circuit fabrication.

4) Pre-drying at 70°C removes volatile components, followed by high-temperature decomposition of the polymeric dispersant at 325°C to form a dense graphene conductive film.

5) The electrode is modified with acetylcholinesterase to construct an electrochemical detection platform for pesticide sensing.

III. Advantages of the Three- and Five‑Component Aerosol‑Compatible Ink Process (Comparison with Single‑Component and Two‑Component Inks, and Inkjet Printing)

Balances high printing speed with high-precision fine lines.

Increasing the speed of conventional inks inevitably leads to line broadening. In contrast, the quaternary system uses a glycerol gel to lock in the ink, resulting in extremely minimal linewidth variation across a wide speed range of 1–5 mm/s, thereby resolving the trade-off between printing speed and resolution.

Stable atomization throughout the entire process, with no nozzle clogging even during prolonged printing.

The multi‑gradient evaporation solvent balances droplet viscosity, yielding uniformly sized atomized droplets without dry graphene agglomeration that could clog the nozzle, making it well suited for continuous roll‑to‑roll mass production.

Excellent electrical conductivity and adhesion, with no need for a post‑coating.

The trace addition of NC does not compromise dispersibility; after sintering, it forms a crosslinked framework that resists delamination under bending and tape‑peel tests, thereby eliminating the need for a protective coating step.

Universal for both flexible and rigid substrates, suitable for multiple application scenarios.

The ink exhibits controllable wetting, enabling the formation of uniform, dense graphene films on PI, glass, and silicon wafers, with no cratering or pinhole defects.

The formulation can be extended to carbon nanotubes and MXene.

The solvent‑control mechanism is universally applicable; by making only minor adjustments to the filler ratio, one can develop specialized inks for aerosol‑based two‑dimensional materials.

IV. Five Core Technological Innovations of This Study

Innovation 1: A Quaternary Gradient Volatilization Aerosol Graphene Ink System

By pairing four classes of solvents with high, medium, and low boiling points, droplet flight and substrate drying are controlled in stages, addressing the two major forming defects—material overflow and spreading—at their root.

Innovation 2: A Novel Mechanism for In Situ Gel Formation Induced by Glycerol

It reveals the low vapor pressure of glycerol, which induces localized gelation of the graphene colloid at the deposition moment, thereby restricting lateral diffusion and enabling ultrafine-line printing at high speeds.

Innovative 3 EC+NC dual-bonding synergistic formulation

EC ensures long-term dispersion of graphene, while trace amounts of NC enhance the mechanical strength of the sintered film layer, balancing ink storage stability with adhesion of the finished product.

Innovation 4 Ink – Comprehensive Matching Standards for Printing Parameters

A correlation has been established between the focusing ratio, printing speed, atomization voltage, and solvent ratio, providing a readily reusable process window for aerosol‑based graphene fabrication.

Innovative Complete Solution for Direct Aerosol Printing of Graphene-Based Electrochemical Sensors

Without lithography, digital direct‑write interdigitated microelectrodes enable highly sensitive detection of trace amounts of pesticides, thereby establishing a low‑cost manufacturing pathway for two‑dimensional material‑based sensors.

V. Current Industry Challenges and Corresponding Solutions

Challenge 1: Single-solvent inks exhibit uncontrollable drying, leading to severe ink bleeding at high printing speeds.

✅ A four-component gradient‑evaporating solvent system ensures moderate dehydration during the droplet flight phase and, upon impact, forms a gel that locks in the material, thereby eliminating widespread dispersion and overflow.

Challenge 2: As printing speed increases, the line width expands significantly, making it impossible to achieve both high speed and high precision.

✅ Glycerol induces a colloidal gelation effect, suppressing post-deposition spreading; even at a high scan speed of 5 mm/s, the line width remains tightly confined to 40 μm.

Challenge 3: Graphene ink tends to agglomerate, leading to nozzle clogging during prolonged printing.

✅ A multi-solvent formulation reduces the colloidal surface tension, enhances graphene dispersion stability, and enables stable atomization at low voltage.

Challenge 4: Pure graphene films exhibit poor adhesion and tend to delaminate upon bending or during testing.

✅ After sintering, the trace NC binder forms a continuous support network, and the tape‑tested coating retains 93% of its original thickness.

Challenge 5: Existing graphene inks are only suitable for low-speed laboratory prototyping and cannot be scaled up for mass production.

✅ Wide ink atomization window, broad speed compatibility, and compatible with roll-to-roll continuous aerosol production lines.

VI. Future Diversified Industrial Application Scenarios

1 Flexible Electrochemical Sensing Test Strip

Single-use electrodes for rapid detection of food contaminants, water quality parameters, and heavy metals; low-cost batch printing of aerosol‑based sensors.

2 Wearable physiological sensing electrodes

Graphene-based, highly conductive and flexible thin films; non-invasive sweat- and electrocardiogram‑monitoring patches.

3 MEMS micro‑interdigital sensor arrays

Gas and humidity micro‑nano sensors, with maskless, high‑precision custom circuitry.

4 Flexible Transparent Conductive Grid

Foldable displays, photovoltaic‑based ITO replacement, and lightweight, low‑loss conductive layers.

5 General-purpose ink for two-dimensional material research and development in universities

A universal solvent system for aerosol printing of carbon nanotubes and MXenes, enabling rapid iteration of device prototypes.

Image and Text Guide

Figure 1. Schematic of the AJP process, criteria for the ideal graphite state, and characterization of graphene feedstock.

Figure 1(a): AJP principle: a piezoelectric ultrasonic transducer atomizes the ink, while a carrier gas transports the aerosol to the print head; a sheath gas prevents droplets from colliding with the walls and focuses them into a beam that strikes the substrate. On the right, three types of inks are compared: an ideal ink exhibits consistent high line width and minimal overspray; a “dry” ink suffers from premature evaporation of the aerosol, leading to excessive overspray; and a “wet” ink shows irregular edges due to droplet spreading on the substrate. Figure 1(b): Raman spectrum of graphene after annealing: the D, G, D’, and 2D peaks are well resolved, with I_D/I_G ≈ 0.65 and I_G/I_2D ≈ 1.96, confirming the presence of few-layer graphene. Figures 1(c) and 1(d): AFM analysis—average flake diameter 97.89 ± 4.07 nm, average thickness 1.59 ± 0.12 nm (≈4–5 layers).

Figure 2. DLS screening of solvent systems, viscosity of four formulations, and formulation table

Figure 2(a) DLS measurements of the hydrodynamic particle size, Z_ave, of EC in different solvents: the solid‑colored bars represent the printing solvent systems, while the white bar corresponds to the reference solvent (not used for printing); solid shading indicates complete dissolution of EC, and hatching denotes a turbid suspension. IBA+Gly promotes EC aggregation (Z_ave = 6400 nm), whereas Dig+Gly stabilizes it; a 1:1 IBA:Dig ratio falls intermediate between the two. Figure 2(b) Viscosities of four candidate inks—Quaternary, Gly‑free, Dig‑free, and IBA‑free—at shear rates ranging from 10 to 1000 s⁻¹: all lie within 0.004–0.010 Pa·s, making them suitable for ultrasonic atomization; the inset shows the finished ink bottle containing a black suspension. Table 1 lists the four formulations: EC–graphene at 10 mg/mL plus NC at 5 mg/mL, with varying ratios of the primary solvents IBA/Dig and adjustments to Gly/Cyr.

Figure 3. Profilometer topography and linear deposition rate for four formulations.

Figure 3(a): Single‑track profiles for four formulations at a focus ratio FR = 5 (Quaternary/Gly‑free/Dig‑free/IBA‑free printed at 35/40/40/43 V, scale bar = 0.5 mm): Quaternary exhibits the smoothest edges, Gly‑free shows the roughest surface, Dig‑free yields the most uniform three‑dimensional cross‑section, and IBA‑free displays pronounced overspray. Figure 3(b): Average cross‑sectional profiles: Quaternary is the narrowest and most symmetrical, while Gly‑free has the widest base. Figure 3(c): Speed‑normalized linear deposition rates across FR = 3–10: Gly‑free increases from ~8 to ~12 μm²/mm as FR rises, whereas the other three remain in the 4–8 μm²/mm range; Quaternary and Dig‑free demonstrate the greatest stability.

Figure 4. SEM morphologies and electrical conductivity of four formulations

Figure 4(a–d): SEM images of Si wafers (scale bar: 5 μm): Quaternary and Gly‑free surfaces are dense and uniform (40 vol% IBA + Dig, with rapid drying locking in the structure), whereas Dig‑free and IBA‑free samples exhibit numerous pores and a rougher morphology. Figure 4(e): Four‑probe conductivity versus FR: Quaternary shows 27.5–32.5 kS/m, Dig‑free 25–32 kS/m—both significantly higher than Gly‑free (14–20 kS/m) and IBA‑free (4–6 kS/m)—with the porous structure reducing the effective conductive pathways.

Figure 6. Adhesion testing of Kapton and AJP graphene pesticide sensor

Figure 6(a): Relative changes in cross-sectional area and sheet resistance of the tape‑on‑Kapton test; both retention rates exceed 90%, demonstrating strong adhesion on the flexible substrate. Figure 6(b): The cross-sectional profiles before and after the tape test nearly overlap. Figure 6(c): Current response of the graphene amperometric sensor to the addition of ATCC (acetylcholinesterase), showing a stepwise increase. Figure 6(d): Dose–response calibration curve for ATCC. Figure 6(e): Time‑dependent response to different concentrations of the pesticide parathion (0, 0.05, 0.1, 1, 10, and 100 μM); higher concentrations result in stronger current inhibition. Figure 6(f): Linear fit of current change versus parathion concentration, with a detection limit of 0.01–1 μM.