Two Jobs, One Laser Pass — a Flexible CO Sensor Written Directly Onto Film
Carbon monoxide gives no warning. The sensor that catches it usually needs a hotplate and a rigid chip. This one is written onto a bendable film in a single femtosecond-laser sweep and works at room temperature.
Carbon monoxide is produced wherever hydrocarbons burn incompletely — heaters, engines, industrial processes — and it kills quietly because it is odourless. Metal-oxide gas sensors can detect it, but most need to be heated to a few hundred degrees to work, which drains power and rules out flexible, wearable formats. Graphene-family materials sense CO at room temperature, but turning a graphene-oxide film into a working, patterned device usually means several steps: chemical or thermal reduction, then separate electrode deposition. A 2026 study in Applied Surface Science from a Taiwanese team (National Taiwan Normal University and collaborators) collapses that into one femtosecond-laser pass.
The Obstacle
A practical flexible gas sensor needs three things that fight each other: a room-temperature-active sensing material (so no hotplate), a conductive, patterned electrode structure, and a flexible substrate that survives fabrication. Chemically reducing graphene oxide uses harsh reagents; thermally reducing it cooks the plastic substrate; and either way you still have to add electrodes in a separate lithography step. You want a single, non-contact, low-heat process that reduces the film and draws the electrodes at once — without melting the flexible backing.
The Innovation
The device is a TiO2/graphene-oxide (GO) composite coated on a flexible substrate, processed by a femtosecond laser in one pass. Femtosecond pulses deposit energy faster than heat can spread, so they photothermally reduce GO to rGO (restoring the conductive sp2 carbon network) and ablate/pattern the electrode geometry in the same scan — a low-thermal-effect, non-contact route compatible with heat-sensitive plastics. Optimised laser parameters — 100 kHz repetition rate, 50 mm/s scanning speed, 0.34 J/cm2 fluence — gave the best reduction without over-ablating (above 0.34 J/cm2 the film began to re-oxidise). The TiO2 adds room-temperature CO sensitivity and, under UV, a photocatalytic boost. (Chen, Chang, Tseng, Hsiao & Hsu; Applied Surface Science, 2026, 737, 166898; DOI 10.1016/j.apsusc.2025.166898.)
Key Results
Four results carry the story: one laser pass both reduces and patterns the film, Raman confirms it is genuine reduction, the sensor detects CO at room temperature with a UV boost, and it keeps working when bent.
One Pass Reduces and Patterns — and the Resistance Proves It
As laser fluence rose, sheet resistance fell as GO reduced to conductive rGO, reaching a low of ~3.1 kΩ at 0.34 J/cm2; beyond that, partial re-oxidation raised it again. The same scan drew the electrodes directly, and the embedded TiO2 survived the process intact — a genuinely one-step device.
Raman Confirms the Reduction
Recording Raman spectra on the MRID (532 nm), the team saw the characteristic TiO2 modes together with the carbon D-band and G-band; the change in the D/G intensity ratio after laser processing is the direct fingerprint that oxygen groups were removed and the sp2-conjugated carbon network was restored — i.e. that the laser reduced the film rather than merely burning it. (XPS and FTIR corroborated: C–O down, C=C up, Ti–O retained.)
It Senses CO at Room Temperature — and UV Makes It Better
The optimised sensor gave a CO response of 39.6% at room temperature (25 °C), rising to a maximum of 43.8% under 365 nm UV toward 500 ppm CO, with a fast response time under 10 seconds. UV drives TiO2 photocatalysis, dropping the baseline resistance and easing charge transfer — a low-power way to sharpen sensitivity without heating.
It Survives Bending
Under repeated flexing the sensor held its performance past 50 bending cycles with only modest resistance change, and responded across a range of bend angles — the mechanical robustness a flexible, wearable CO monitor needs.
Why ProTrusTech Is Featuring This Research
The headline is “the laser reduced the film” — and that is a Raman claim. On the MRID at 532 nm, the carbon D/G bands (alongside the TiO2 modes) are what distinguish real reduction from ablation, and they anchor the whole fabrication story. It is a clean showcase of Raman as the go-to probe for carbon-material quality in device fabrication.
Featured Instruments:
Why This Matters
Room-temperature, flexible, low-power gas sensing is where air-safety monitoring is heading — wearables, distributed indoor sensors, disposable safety tags. A one-step laser process that both reduces the active film and patterns the electrodes on plastic is directly manufacturable and endlessly customisable (any electrode shape the laser can draw). And Raman is the fast quality check that keeps the reduction on-spec.
What’s Next
- Selectivity against interferents (H2, humidity) and quantified detection limits at sub-100 ppm.
- Fully printed / roll-to-roll laser patterning for scale.
- Integrating the sensor with flexible readout for a self-contained wearable CO tag.
Working on laser-processed carbon films, flexible sensors, or metal-oxide gas sensing — and need Raman to verify reduction and film quality? Get in touch with our team.
Key Takeaways
- A single femtosecond-laser pass both reduces TiO2/GO to TiO2/rGO and patterns the electrodes on a flexible substrate — optimum at 0.34 J/cm2, giving ~3.1 kΩ.
- The sensor detects CO at room temperature (39.6%), boosted to 43.8% under 365 nm UV, with <10 s response, and survives 50+ bending cycles.
- Raman on the MRID (532 nm) — TiO2 modes plus carbon D/G bands — confirmed the laser genuinely reduced the film.
