A thin film sensor based on tetragonal SnO₂ nanoparticles was fabricated by combining the sol–gel method and a dip-coating technique on a cylindrical glass substrate. The sensing material was produced through a cycling annealing process at 400 and 600 °C, using tin chloride (IV) pentahydrate as a precursor in polyethylene glycol (PEG) solution as a surfactant. Materials were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD), revealing tetragonal phase formation with no impurities. The sensor′s assembly was done with low-cost materials such as Cu electrodes, Cu-Ni tube pins, and glass-reinforced epoxy laminate as the base material. For signal variation, an adequate voltage divider circuit was used to detect ethanol′s presence on the surface of the sensor. The fabricated sensor response to gaseous ethanol at its operating temperature at ambient pressure is comparable to that of a commercial sensor, with the advantage of detecting ethanol at lower temperatures. The sensor response (S = Ra/Rg) to 40 ppm of ethanol at 120 °C was 7.21. A reported mathematical model was used to fit the data with good results.

This research enhances ethanol sensing with Fe-doped tetragonal SnO₂ films on glass, improving gas sensor reliability and sensitivity. The primary objective was to improve the sensitivity and operational efficiency of SnO₂ sensors through Fe doping. The SnO₂ sensors were synthesized using a flexible and adaptable method that allows for precise doping control, with energy-dispersive X-ray spectroscopy (EDX) confirming homogeneous Fe distribution within the SnO₂ matrix. A morphological analysis showed a surface structure ideal for gas sensing. The results demonstrated significant improvement in ethanol response (1 to 20 ppm) and lower temperatures compared to undoped SnO₂ sensors. The Fe-doped sensors exhibited higher sensitivity, enabling the detection of low ethanol concentrations and showing rapid response and recovery times. These findings suggest that Fe doping enhances the interaction between ethanol molecules and the sensor surface, improving performance. A mathematical model based on diffusion in porous media was employed to further analyze and optimize sensor performance. The model considers the diffusion of ethanol molecules through the porous SnO₂ matrix, considering factors such as surface morphology and doping concentration. Additionally, the choice of electrode material plays a crucial role in extending the sensor’s lifespan, highlighting the importance of material selection in sensor design.

Traditional nanoparticle synthesis methods often rely on hazardous chemicals, raising concerns about their environmental impact. This study reports the green synthesis of zinc oxide (ZnO) nanoparticles using aqueous extracts from three distinct parts of Agave tequilana: the stalk (ZnO-S), heart (ZnO-H), and leaves (ZnO-L). The aim was to explore the influence of the different plant parts, each with their respective phytochemical profile, on the structural, optical, and antibacterial properties of the resulting nanoparticles. The synthesized ZnO-NPs were extensively characterized using UV–Vis spectroscopy, ATR-FTIR, X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and energy-dispersive X-ray spectroscopy (EDS). The results revealed that ZnO-S exhibited the smallest particle size (~18.3 nm), the highest crystallinity, and the most uniform morphology. Optical analysis showed bandgap energies of 3.13 eV (ZnO-S), 2.99 eV (ZnO-H), and 3.02 eV (ZnO-L), with ZnO-S demonstrating enhanced UV absorption and reactive oxygen species (ROS) generation potential. Antibacterial assays against Staphylococcus aureus and Escherichia coli confirmed strong bactericidal activity for all samples, with ZnO-S showing the largest inhibition zones, approaching the efficacy of the reference antibiotic kanamycin. This work highlights the fundamental roles of plant-derived phytochemicals as natural reducing and capping agents and emphasizes the valorization of agave stalk and leaves, traditionally treated as agricultural waste for cost-effective and eco-friendly nanomaterial production. The findings reveal the untapped potential of Agave tequilana as a sustainable source for high-performance nanomaterials, paving the way for green innovations in antimicrobial and environmental applications.