UV Lasers Turn Paper Into Graphene Circuits for Optical Sensors

By Muhammad OsamaReviewed by Sarah KellyOct 23 2026

*Important notice: This news reports on an unedited version of an accepted paper and is awaiting final editing. Therefore, the paper should not be regarded as conclusive or treated as established information.

Global electronic waste is projected to reach 82 million metric tons by 2030, posing significant environmental hazards. In light of this, a recent study published in the journal npj Flexible Electronics demonstrated a method to transform paper into electronics using ultraviolet (UV) light.

This process directly patterns laser-induced graphene (LIG) circuits onto lignin-rich paper without added chemicals, solvents, or vacuum chambers. Performing this process in ambient air enables a sustainable, scalable approach to electronic manufacturing. The resulting circuits exhibit stability, enabling their use as broadband optical sensors.

Challenges in Flexible Electronics Fabrication

Flexible electronics often rely heavily on plastic films, such as polyimide, or metal inks applied through inkjet or screen printing. These methods can suffer from ink bleeding and clogged nozzles and often use petroleum-based solvents.

While paper offers a low-cost, biodegradable alternative, cellulose typically burns or decomposes at temperatures between 250 and 420 °C. Traditional carbon dioxide (CO₂) lasers can combust and damage the paper. Although femtosecond lasers can prevent burning, their high costs limit large-scale production. Therefore, patterning graphene directly onto paper in ambient air requires precise control of light absorption and heat dissipation.

Advanced Laser Techniques for Graphene Integration

Researchers utilized an LPKF ProtoLaser U4 direct-write workstation featuring a pulsed, diode-pumped solid-state laser operating at 355 nm.

The laser had a pulse width of 20 ns and a repetition rate ranging from 25 to 250 kHz. A telecentric f-theta lens focused the beam to a 20 µm spot, while galvanometric scanners moved it across untreated kraft paper, which contained approximately 19.5% Klason lignin.

The study matched the laser wavelength to the paper's optical properties, with measurements indicating that the paper absorbed 94% of light at 355 nm, closely aligning with the 98% absorption measured for the synthesized graphene. This match facilitated controlled energy transfer during processing.

Various laser fluences, scanning speeds (15–140 mm/s), defocus offsets (0–6 mm), and pulse repetition rates were tested. Raman spectroscopy confirmed the formation of graphitic structures, while additional measurements assessed structure and electrical properties.

Optimizing Energy Control for Structural Integrity

The results demonstrated that laser defocusing played a key role in controlling energy delivery and surface heating, and offsetting the beam by approximately 6 mm reduced sheet resistance to about 147 Ω/sq. The best results were achieved at an average laser power of 0.6 W, a scanning speed of 20 mm/s, and a pulse repetition rate of about 200 kHz. These settings produced a 43 µm-thick porous graphitic layer with an ablation depth of 20–30 µm.

Raman spectra showed distinct D, G, and 2D bands, confirming the formation of few-layer turbostratic carbon derived from lignin. Higher laser powers (0.8–1 W) or very slow scanning speeds led to excessive heat buildup and oxidative damage. Conversely, speeds above 30 mm/s left cellulose fibers partly unconverted.

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The conductive tracks demonstrated impressive mechanical stability, withstanding repeated bending. At a bending angle of 180°, electrical resistance increased by 13.5% under tensile strain and decreased by approximately 1% under compression. In another experiment, the circuits also maintained stable electrical performance after 1,000 repeated bending cycles.

Kirigami cutouts allowed the structures to stretch by up to 300% while powering surface-mount LEDs (light-emitting diodes) without changes in light output.

Applications of Paper-Based Graphene Devices

Leveraging graphene’s electronic structure, researchers developed a flexible paper photodetector array that can house up to 720 sensor cells on a single sheet. These detectors responded to UV, visible, and near-infrared light across wavelengths of 370–1450 nm, operating through photoconductive charge collection.

Under 370 nm UV light, the devices achieved an external quantum efficiency of 10.9%. Gold electrodes enhanced the response in the green-to-red spectral range through localized surface plasmon resonance.

Additionally, the conductive paper tracks functioned as actuators. With a 48 V input, they reached a steady temperature of 122 °C through Joule heating, enabling them to act as soft robotic grippers. The actuators generated blocking forces of 46 mN, demonstrating their capability to handle delicate objects. Furthermore, a beeswax coating protected the paper circuits from moisture and allowed stable underwater operation for around 20 hours.

Sustainable Electronics for a Greener Future

This UV laser process produces circuits on paper without needing wet-chemical etching or toxic catalyst deposition. By combining digital laser patterning with low-cost paper, this method could facilitate large-scale production using roll-to-roll manufacturing.

The circuits can also be burned with only 3.7% solid residue by weight or composted for natural decomposition, providing sustainable options for disposal and data destruction.

Future work could explore integrating the graphitic circuits with halide perovskites, colloidal quantum dots, or natural dielectric materials to expand their functions. Potential applications include wearable health monitors, optical diagnostic strips, and other electronic devices.

Journal Reference

Le, T.-S. D., et al. (2026). Flexible, stretchable and sustainable paper electronics enabled by ultraviolet laser-induced graphene. npj Flexible Electronics. DOI: 10.1038/s41528-026-00649-y, https://www.nature.com/articles/s41528-026-00649-y.

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