In this work, graphene quantum dots (GQDs) synthesized by femtosecond laser ablation in liquid (LAL) using laser-induced graphene (LIG) as the carbon source. Nitrogen-doped graphene quantum dots (N-GQDs) were successfully synthesized by adding ammonia water to the graphene suspension. The GQDs/N-GQDs structure consist of a graphitic core with oxygen and nitrogen functionalities and particle size less than 10 nm, as demonstrated by X-ray photoelectron spectroscopy, Fourier infrared spectrometer spectroscopy and transmission electron microscopy. The absorption peak and PL spectrum and quantum yield of the N-GQDs were significantly enhanced compared with the undoped GQDs. Further, the possible mechanism of synthesis GQDs is discussed. Furthermore, the N-GQDs were used as a fluorescent probe for detection of Fe3+ ions. The N-GQDs may extend the application of graphene-based materials to bioimaging, sensor and, photoelectronic.

Direct laser writing (DLW) is a convenient approach for fabricating graphene-based flexible electronic devices. In this paper, laser-induced graphene was successfully prepared on a thin and transparent polyimide film through the DLW process. Experiments have demonstrated that interdigital thin film capacitor prepared by the DLW method has a high specific capacitance of 8.11 mF/cm2 and volume capacitance density of 3.16 F/cm3 (0.05 mA/cm2) due to the doped fluoride in the laser-induced graphene. The capacitance is about 20 times larger than the super-capacitor based non-transparent polyimide film of the same thickness. Owing to its thin, flexible, higher electrochemical characteristics, the transparent polyimide film is promising for integrating and powering portable and wearable electronics.

Paper-based strain sensors (PSS) have broad prospects in disposable products due to their low cost and easy degradation as environmentally friendly materials. Herein, a strain sensor made of a laser-induced carbonization electrode is created by direct laser writing with filter paper. The conductivity and gauge factor (GF) of this strain sensor are improved by adding lignin and applying strain engineering. This enables the sensor to simultaneously satisfy high sensitivity (GF % 408 and 91) for weak tension and compression strain, respectively, and with long-term reliability. The tensile strain GF factors of up to 201 are possible, even with a weak tensile strain of 0.00088%. Furthermore, the paper-based sensor for monitoring physiological activities like finger gestures, pulsing, swallowing, and eye blinking is demonstrated. The facile fabrication and superior performance of PSS fabricated by direct laser writing with strain engineering may pave the way for promising applications of flexible, portable, and wearable electronic devices.

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The performance of electrodes is a key factor affecting the development of smart fabrics. The preparation of common fabric flexible electrodes has defects such as high cost, complicated preparation, and complex patterning that limit the development of fabric-based metal electrodes. Therefore, this paper presented a simple fabrication method for preparing Cu electrodes using selective laser reduction of CuO nanoparticles. By optimizing laser processing power, scanning speed, and focusing degree), we prepared a Cu circuit with an electrical resistivity of ∼ 5.53 µΩ.m. Based on the photothermoelectric properties of Cu electrodes, a white light photodetector is developed. The detectivity of the photodetector reaches ∼2.14 mA/W at a power density of 10.01 mW/cm2. This method is instructive for preparing metal electrodes or conductive lines on the surface of fabrics, and provides specific techniques for manufacturing wearable photodetectors.