conductivity, specific surface area, and cycle stability of the material. [2][3][4] Various methods for processing and preparing electrode materials have gained widespread attention among researchers. [5][6][7] Carbon-based materials, such as carbon nanotubes, graphene, and glass carbon, are the most common materials studied and have been researched for use in various electrochemical sensors. [8] Especially, graphene demonstrates excellent detection performance because of its high carrier mobility and chemical stability. In addition, the microscopic morphology of the electrode material has a profound effect on the increase in the surface area of the electrochemical reaction. [9] Researchers have confirmed that metal nanoparticles have an ultrahigh reactive surface area, excellent electrical conductivity, and high catalytic activity; thus, the use of electroplating and electro sputtering to deposit nanoparticles onto the electrode surface during post-processing can further improve the detection limits and sensitivity of the sensor. [3,4,10,11] In recent years, researchers have revealed that laser direct writing is one of the easiest way to prepare graphite materials with controllable morphology and arbitrary patterns. [12] Based on the concept of green development, precursor materials for laser induction have shifted from polymers (such as polyimide and polysulfone membranes) to natural materials that are renewable but more susceptible to ablation. [13] To reduce the thermal ablation of carbon dioxide (CO 2 ) lasers, renewable precursors (wood, paper, and cardboard) were transformed into porous graphene electronics by irradiating them in a reducing gas chamber, adding flame retardant and using multiple scanning methods, respectively. [14,15] Lignin is the main component of the widely used natural precursor materials that can be carbonized. [16] However, the lignin content in natural precursors is unstable. This can lead to incomplete carbonized structures, which can affect the performance of electronics. Lignin is a type of phenylpropane-based composite network aromatic polymer and has abundant hydroxyl, carboxyl groups, and other reducing functional groups, which is often discarded because it cannot be effectively recycled in the papermaking process.The next generation of green electronic products will be flexible, eco-friendly, have arbitrary patterning, and be produced using simple methods. Here, a silver nanoparticles (Ag NPs)-graphite carbon composite-based electrochemical sensor is patterned on a flexible substrate by one-step in situ femtosecond (fs) laser fabrication. Alkali lignin is used as a precursor and nontoxic natural reducing agent to reduce aqueous silver nitrate to produce Ag NPs. The fs laser carbonization process converts lignin into graphite carbon electrodes with diverse three-dimensional (3D) micro/nano morphologies, causing less thermal damage to the Ag NPs and thin substrate. The 3D micro/nano morphologies combined with Ag NPs effectively increase the active surface area, conductivity, and...

Dental caries has attracted widespread concern because of its universality. However, the current diagnosis of dental caries depends largely on naked eyes and dentists' experience, which causes considerable randomness and inaccuracy in the diagnosis. In this study, temporally shaped double pulse (DP) femtosecond laser-induced breakdown spectroscopy (LIBS) has been used for tooth composition detection for the first time. Under the laser fluence of 20 J/cm2, the spectra intensity for DP LIBS with a pulse delay of 200 ps was 13 times higher than that of single pulse. For further prediction, the detection model based on DP LIBS and partial least squares discrimination analysis could discriminate dentin, enamel, and caries with a prediction accuracy of above 90%. This method may provide rapid and accurate feedback to dentists for real-time diagnosis in the future.

Miniaturized resistance-based portable bending sensors have been widely used for human health monitoring in recent years. Their sensitivities are defined by their resistance variations (ΔR/R), which strongly rely on the conductivity and minimum line width of the sensing unit. Laser-induced carbonization is a fast and simple method to fabricate porous-sensing structures. However, the fabrication resolution of conductive and deformation-sensitive structures is limited by the thermal effect of commonly used laser sources. With the assistance of femtosecond laser temporal shaping, plasma ejection confinement, and silver nitrate doping, the sheet resistance of the sensing structure was improved from 15 to 0.0004 Ω/□. A thin line with a lateral resolution of 6.5 μm is fabricated as the sensing unit. The fFabricated structures are characterized by electron microscopy, Raman spectroscopy, energy-dispersive spectroscopy, X-ray scattering, and time-resolved images. The strain sensor demonstrates a ΔR/R of 25.8% with a rising edge of 109 ms in the cyclic bending test. The sensor is further applied for detecting human pulse and finger bending.