I. Abstract of the Paper’s Core Research

• Plasma‑assisted precise fabrication of silver nanoparticle hot‑spot arrays in aerosols

1–6 layers of controllably printed silver nanofilm, with a four-layer deposition architecture yielding optimal plasmonically enhanced hotspots; fluorescein and rhodamine achieve detection limits as low as 10⁻⁷ M, the array exhibits excellent signal uniformity, and Raman two-dimensional mapping reveals no pronounced intensity gradients.

• Silver/graphene composites significantly enhance PFAS adsorption and detection sensitivity.

Graphene enhances the adsorption of PFAS molecules via van der Waals forces and electrostatic interactions, with optimal detection performance observed under alkaline conditions (pH = 9). The detection limits are as low as 10⁻¹² M for PFOS (≈0.4 ppt) and 10⁻⁹ M for PFOA, surpassing the EPA’s drinking‑water safety standards.

• Ultra-long-term stability at room temperature

The substrate can be stored at room temperature, protected from light, for 9 months, with a fluorescence peak signal decay of only 10%, significantly outperforming commercially available SERS substrates (which typically have a shelf life of 30–60 days). This makes it well suited for batch fabrication and field‑based, staged sampling.

• Low-Interference Polyimide Flexible Substrate

Kapton film is used in place of filter paper, eliminating cellulose‑derived spectral interferences that obscure the Raman signals of organic contaminants. The substrate can be cut into wipe‑type sampling pads for direct swabbing of soil or pipe surfaces to concentrate target pollutants.

• Digital Maskless Batch Fabrication of Flexible Substrates

The aerosol can be freely engineered into independent 1 mm² sensing micro‑spots, with 8 mm spacing between spots to prevent cross‑contamination of samples. It is compatible with a wide range of flexible, curved substrates and supports rapid iterative development in small batches.

II. Complete Aerosol Spray S-Substrate Preparation Process and Core Advantages

(1) Complete composite SERS substrate printing process

• 127 μm Kapton film was ultrasonically cleaned with isopropyl alcohol and dried with nitrogen to remove surface contaminants.
• Ultrasonic‑atomized graphene water‑based ink, with a two‑pass printing process to create an enhanced graphene substrate adhesion layer.
• Switch to silver‑nanoparticle terpineol ink and print plasma‑silver arrays in 1–6 aerosol layers;
• Sinter at 200°C in a constant-temperature oven for 1 hour to form nanoparticle agglomeration–induced plasma hotspots.
• After completion, store away from light; the sample can be directly applied with a pollutant solution or cut into wipe‑type sampling pads for on‑site testing.

(II) Five Major Process Advantages (Comparison of Photolithography, Inkjet, Screen Printing, and Paper-Based SERS)

• Flexible, low‑interference substrate direct writing, with no cellulose–related peaks.

Kapton substrates exhibit extremely low Raman background and do not overlap with the characteristic peaks of PFAS or organic contaminants, making them suitable for fabrication into flexible swab strips optimized for on-site sampling of solid surfaces.

• Multi-layer, precisely controllable deposition; hotspot intensity can be digitally adjusted.

By precisely controlling the number of printing layers, the thickness of the silver film and the degree of nanoparticle aggregation can be finely tuned; the enhancement factor is optimized with a single click, and process parameters are standardized for scalable, reproducible manufacturing.

• Multi-ink layered integrated printing, in-situ composite silver–graphene structure

A single device sequentially deposits an adsorption layer and a plasma-enhanced layer, eliminating the need for transfer and coating‑stacking processes; this results in stronger interfacial adhesion and a significant improvement in molecular adsorption efficiency.

• Maskless, low-cost rapid prototyping—no vacuum lithography production line required.

By eliminating the need for costly equipment such as electron-beam lithography and magnetron sputtering, desktop aerosol‑based tools enable rapid prototyping, significantly lowering the barrier to entry for environmental‑sensing R&D.

• Curved-surface compatibility, material savings, and on-demand, location-specific printing with sensing micro‑spots.

Aerosol: 3–5 mm working distance; the curved tube wall and irregular component surfaces can be directly printed with a sensing array, while precious metals are deposited only in the sensing region, thereby reducing silver material consumption.

III. Five Core Technological Innovations of This Study

Innovation 1: A Hierarchical Composite Ag/Graphene Flexible SERS Architecture

Innovation 2: A Long-Term Stable Flexible Sensing Substrate Solution

Innovative 3 PFAS High-Selectivity Trace Detection System

Innovation 4: A Digitally Controllable Plasma Hotspot Fabrication Method

Innovation 5: A Wipeable, All-in-One Flexible Sampling and Sensing Platform

IV. Current Industry Challenges and Corresponding Solutions for Overcoming Them

Challenge 1: Raman peaks of cellulose in the paper-based SERS substrate interfere with the signal of the target analyte.

Challenge 2: Conventional lithography and vacuum‑based SERS substrates are expensive and cannot support flexible, on‑site sampling.

Challenge 3: A single silver substrate exhibits weak adsorption capacity for PFAS, resulting in a relatively high detection limit.

Challenge 4: Commercial SERS substrates have a short shelf life and are highly susceptible to oxidation, leading to rapid deactivation.

Challenge 5: Conventional processing cannot achieve layered composite adsorption—plasma dual-functional layer.

V. Future Diversified Industrial Application Scenarios

• Rapid Screening of PFAS in Environmental Water Samples

• Sampling of Equipment Contamination in Industrial Plant Areas

• Rapid Detection of Organic Contaminants in Food Safety

• Public Safety Trace Hazardous Chemical Detection

• Rapid Prototyping in University Environmental and Materials Laboratories

Figure 1. Structure and characterization of the AJP SERS sensor on a Kapton substrate. (a) Optical image of silver nanoparticle arrays printed on a Kapton film, showing, from top to bottom, different numbers of printing cycles (1–4), with the specific cycle number indicated on the right side of the image. (b) Dependence of the average array height on the number of printing cycles, obtained by optical profilometry. (c) Representative SEM image of an array shown in (a), revealing agglomerates formed by the silver nanoparticles; the inset, at higher magnification, shows individual silver nanoparticles. (d) Absorption spectrum of the silver nanoparticle array depicted in (a), exhibiting a peak near 570 nm; the Raman excitation wavelengths used in this study (532 nm and 633 nm) are indicated vertically by dashed lines in (d).

Figure 2. SERS detection results for fluorescein. (a) SERS spectra acquired at an excitation wavelength of 532 nm, recorded on fluorescein solutions ranging from 10⁻⁴ to 10⁻⁷ M deposited on four types of printed Ag nanoparticles. (b) Plot of the average intensity of the 1185 cm⁻¹ peak as a function of fluorescein concentration; solid and hollow data points correspond to intensities measured in the presence and absence of graphene, respectively. (c) Optical image of a printed Ag nanoparticle film loaded with 10⁻⁴ M fluorescein; (d) The corresponding Raman spectrum shows the distribution of fluorescein’s absorption intensity at 1185 cm⁻¹.

Figure 3. Long-term stability of the AJP SERS substrate. Fluorescein at a concentration of 10⁻⁴ M was deposited on the printed silver nanoparticle surface, and SERS spectra were acquired over time using 532 nm excitation light. Each spectrum represents the average of Raman spectra obtained from more than ten measurement points on the same sample chip. In each experiment, fluorescein was deposited on a different sample chip, while the spectral acquisition parameters remained constant. The inset shows the temporal evolution of the peak intensity at 1185 cm⁻¹.

Figure 4. SERS detection of PFOS and PFOA using an AJP Ag⁺–graphene array. The figure shows surface-enhanced Raman spectra obtained at an excitation wavelength of 633 nm for (a) PFOS and (b) PFOA, with the molecular structures labeled above the corresponding spectra.

Figure 5. SERS intensities of PFOS and PFOA with and without graphene. Box plots show the interquartile range and overall range of the SERS intensities for the C–F stretching vibrational mode near 1350 cm⁻¹ for (a) PFOS and (b) PFOA; the mean and extreme values (1st and 99th percentiles) are indicated by square and triangular data points, respectively; the raw data are overlaid with a normal distribution plotted on the left side of the box. For both PFOS and PFOA, the addition of graphene to the silver nanoparticles significantly enhances the SERS intensity.