A Flexible SERS Film That Bends, Freezes, and Still Reads Pesticide Vapor

Thiram is read on its S–S and C–N modes; both return after abuse. Illustrative schematic; Does the signal survive bending, freezing and acid?

Most SERS substrates are rigid, flat, and fragile. This one bends around a curved surface, survives acid and sub-zero cold, and still catches its target straight from vapor.

Surface-enhanced Raman scattering (SERS) is prized for its sensitivity, but most high-performance SERS substrates are built on rigid silicon or glass — a real limitation for anything that needs to sample a curved, irregular, or hard-to-reach surface in the field. Flexible, transparent materials like PDMS solve the mechanical problem, but only if the plasmonic nanostructure deposited on top can be made dense, uniform, and durable enough to survive real handling — bending, twisting, stretching — without losing its signal.

The Obstacle — Flexible Doesn’t Automatically Mean Sensitive or Durable

A patterned PDMS surface can provide the physical texture needed for a high density of SERS “hot spots,” and silver nanowires (Ag NWs) are an established, high-performance plasmonic material. But simply depositing Ag NWs onto an unmodified PDMS surface doesn’t guarantee they’ll adhere well, distribute evenly, or survive mechanical stress — and without solving adhesion and distribution first, neither the sensitivity nor the durability advantages of a flexible substrate actually materialize.

The Innovation — A Recycled CD, a Surface Modification, and Self-Assembly

In a study published in Applied Physics A (Liu, Long, Huang & Xiao, 2025, Appl. Phys. A, 131, 115, DOI: 10.1007/s00339-024-08227-7), researchers at Shanghai Normal University built a flexible SERS substrate from three layered design choices. First, an ordinary compact disc’s grating structure served as a low-cost, high-throughput template to imprint a periodic nanopattern onto a PDMS film. Second, that grating PDMS surface was chemically modified with 3-aminopropyltriethoxysilane (APTES), grafting amino groups onto the surface to make it more hydrophilic — the film’s water contact angle dropped from 105° to 66° after modification. Third, silver nanowires were self-assembled onto that modified surface at room temperature, forming a dense, interlaced nanowire network anchored far more effectively than it would be on the unmodified film.

Each layer solves a different piece of the problem: the grating provides physical texture and light-interference effects, the APTES modification improves wettability so nanowires adhere more densely and evenly, and the self-assembly step — rather than sputtering or evaporation — is a genuinely low-cost, low-equipment way to deposit the final plasmonic layer.

Key Results — Sensitivity, Uniformity, and Real-World Durability, All Confirmed

Six results build the case: layer-by-layer signal gain, a hundred-fold sensitivity jump from the surface chemistry, uniformity and reproducibility, mechanical durability, environmental extremes, and — most unusually — detection straight from vapor.

Layering Three Design Choices Builds the Strongest SERS Signal

SERS spectra comparing bare PDMS, grating PDMS, APTES-modified grating PDMS, and the final silver-nanowire-decorated substrate, plus dilution-ratio optimization

Comparing four substrate versions side by side — bare PDMS, grating PDMS, APTES-modified grating PDMS, and the final Ag NW-decorated version — each added layer measurably increased SERS signal intensity for a 10-5 M thiram probe, with the fully assembled Ag NWs/M-CDG/PDMS substrate performing best. Optimizing the Ag NW dilution ratio showed a clear tradeoff: too concentrated (1:5) and nanowires coalesce, closing off hot-spot gaps; too dilute (1:15, 1:20) and coverage becomes too sparse. A 1:10 dilution gave the strongest signal and was used for every subsequent test.

APTES Modification Drops the Detection Limit From 10-6 M to 10-8 M

Measured on a ProTrusTech PTT-MRI laser micro-Raman spectrometer (532 nm, 5 mW, 20 s integration), the APTES-modified substrate detected thiram down to 10-8 M — a hundred-fold improvement over the unmodified substrate’s 10-6 M limit. That is direct confirmation that the surface-chemistry step, not just the nanowire deposition itself, is what unlocks the substrate’s full sensitivity.

SERS thiram concentration series comparing the unmodified and APTES-modified silver-nanowire grating-PDMS substrates and their detection limits

Uniform Across the Surface, Reproducible Across Batches

Uniformity, batch reproducibility, and storage-stability plots for the thiram SERS signal on the modified silver-nanowire PDMS substrate

SERS signal intensity across 20 randomly selected points on the modified substrate gave relative standard deviations of 8.7% and 9.9% at the two characteristic thiram peaks — down from 19.3% and 26.5% on the unmodified substrate — while batch-to-batch testing across multiple independently prepared substrates showed consistent signal intensity, with only a slight decline over extended storage.

Bend It, Twist It, Peel It, Stretch It — the Signal Barely Moves

After 100 cycles each of bending and 180° twisting, the substrate’s characteristic thiram peak showed only negligible change. A scotch-tape adhesion test across three peeling cycles gave the same result, confirming the Ag NWs are robustly anchored to the modified PDMS rather than loosely sitting on top. Stretching did have a measurable effect — SERS intensity dropped 30–40% as the substrate was stretched from 0 to 1.2 cm — but it remained functional throughout, and the change reversed once the stress was released.

Thiram SERS spectra measured after bending, 180-degree twisting, tape-peel adhesion, and stretching of the flexible silver-nanowire PDMS substrate

Works in Acid, Base, Deep Cold, and Through the Substrate Itself

Thiram SERS signal across a wide pH and temperature range and mixed-analyte detection on the transparent flexible substrate

The substrate held a strong thiram signal across an extreme pH range (2–14) and a wide temperature window from −40°C to 120°C, and could simultaneously resolve thiram and malachite green when the two were mixed — a genuine anti-interference, multi-analyte capability. Because the film is optically transparent, SERS spectra collected from its front and back sides were nearly identical, meaning it can be read through from either direction — a practical advantage for sampling a surface it has been pressed against.

The Substrate Also Catches Its Target Straight From Vapor, No Liquid Sample Needed

Time-resolved vapor-phase SERS spectra of thiram detected on the flexible substrate at increasing evaporation times

Placed over a small container of heated thiram powder, the substrate picked up a genuine SERS signal from the vapor phase itself — no dropcasting, no liquid sample required — with signal strength peaking at 8 minutes of evaporation before declining. Vapor-phase SERS detection is comparatively rare in the literature, and this result extends the substrate’s practical reach beyond liquid and swab-based sampling.

Why ProTrusTech Is Featuring This Research

Every quantitative claim in this paper — the 10-8 M detection limit, the RSD uniformity numbers, the mechanical-stability and environmental-robustness tests, the vapor-phase result — comes from the same ProTrusTech PTT-MRI Raman spectrometer, run at a fixed 532 nm / 5 mW / 20 s setting across dozens of measurement conditions. That consistency is what makes the paper’s comparisons meaningful: modified versus unmodified, one dilution ratio versus another, before versus after 100 bending cycles — all measured the same way on the same instrument.

Engineering the Solution

The fabrication route deliberately avoids specialized equipment: a recycled compact disc as a nanopattern template, a straightforward chemical surface treatment, and room-temperature self-assembly for the final nanowire layer. No magnetron sputtering, no ion-beam deposition, no cleanroom step — every stage is achievable with commodity lab equipment, which is a meaningful part of the paper’s practical pitch alongside its sensitivity numbers.


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Why This Matters

This paper sits within a family of silver-nanoparticle and silver-nanowire SERS substrates we’ve featured. The rigid, glass-based nanoparticle films — laser-dewetted AgCuAl, hybrid-dewetted silver for melamine, and two-step-dewetted silver — are optimized around particle size and distribution for benchtop sensitivity. This paper takes the opposite substrate strategy: a genuinely flexible, transparent film built around nanowires rather than nanoparticles, pushing mechanical durability under real deformation, environmental extremes, and vapor-phase sampling — none of which the rigid glass-based substrates were tested against. And where our automatic-written silver-nanowire arrays on paper (from this same Shanghai Normal University group) chase raw ultratrace sensitivity on a disposable paper support, this film chases durability and reusability on a flexible one. The practical takeaway for anyone choosing a SERS platform: rigid nanoparticle films for benchtop sensitivity, paper for lowest cost-per-test, and flexible nanowire films for in-situ sampling of curved or hard-to-reach surfaces. Compare them side by side in our SERS Substrates: A Raman Field Guide.

What’s Next

  • Testing on genuinely curved, real-world surfaces. The mechanical tests here are controlled lab deformations; testing on an actual curved produce surface or irregular object would be the natural field-validation step.
  • Extending the vapor-phase method to other volatile analytes. The 8-minute optimal evaporation window was established for thiram specifically; whether it generalizes to other pesticides or volatile organic compounds is untested.
  • Longer-term storage and reuse durability. Storage stability is shown over the tested period, but multi-month or repeated-use data would strengthen the case for field deployment.

Working on flexible SERS substrate design, silver nanowire self-assembly, or vapor-phase Raman detection of your own? Get in touch with our team.

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Key Takeaways

  • Three layered design choices — a recycled-CD grating template, APTES surface modification, and room-temperature Ag NW self-assembly — build a flexible, transparent SERS substrate from commodity materials.
  • APTES modification alone dropped the thiram detection limit from 10-6 M to 10-8 M, measured on a ProTrusTech PTT-MRI Raman spectrometer.
  • The substrate stayed SERS-active through 100 cycles of bending and twisting, three adhesion-peel cycles, and stretching up to 1.2 cm.
  • Performance held across pH 2–14 and −40°C to 120°C, with the ability to resolve two mixed analytes simultaneously.
  • The substrate detected its target directly from the vapor phase — no liquid sample required — a capability rarely demonstrated in flexible SERS substrates.


Featured Publications:

Self-assembly of Ag NWs on the surface of modified grating PDMS film for flexible SERS sensors.

– Liu, Xinshuo; Long, Youchang; Huang, Lei; Xiao, Guina., Applied Physics A, 2025, 131, 115
https://doi.org/10.1007/s00339-024-08227-7

Related publication from the same group: Wang, K. et al., “Preparation and SERS performance of silver nanowires arrays on paper by automatic writing method,” Spectrochimica Acta Part A, 2022, 281, 121580 — featured here as A Machine That Writes Like a Pen Builds a Femtomolar SERS Substrate.

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