This work focuses on the possible application of gold nanoparticles on flexible cotton fabric as acetone- and ethanol-sensitive substrates by means of impedance measurements. Specifically, citrate- and polyvinylpyrrolidone (PVP)-functionalized gold nanoparticles (Au NPs) were synthesized using green and well-established procedures and deposited on cotton fabric. A complete structural and morphological characterization was conducted using UV–VIS and Fourier transform infrared (FT–IR) spectroscopy, atomic force microscopy (AFM), and scanning electron microscopy (SEM). A detailed dielectric characterization of the blank substrate revealed interfacial polarization effects related to both Au NPs and their specific surface functionalization. For instance, by entirely coating the cotton fabric (i.e., by creating a more insulating matrix), PVP was found to increase the sample resistance, i.e., to decrease the electrical interconnection of Au NPs with respect to citrate functionalized sample. However, it was observed that citrate functionalization provided a uniform distribution of Au NPs, which reduced their spacing and, therefore, facilitated electron transport. Regarding the detection of volatile organic compounds (VOCs), electrochemical impedance spectroscopy (EIS) measurements showed that hydrogen bonding and the resulting proton migration impedance are instrumental in distinguishing ethanol and acetone. Such findings can pave the way for the development of VOC sensors integrated into personal protective equipment and wearable telemedicine devices. This approach may be crucial for early disease diagnosis based on nanomaterials to attain low-cost/low-end and easy-to-use detectors of breath volatiles as disease markers.

This paper presents the development of chemo resistive sensors for the detection of volatile organic compounds (VOCs). The proposed sensor is based on citrate-functionalized gold nanoparticles (AuNPs) serving as a sensitive layer deposited on cotton fabric. Impedance variations due to VOC/substrate interaction are used as a detection principle. Specifically, this work focuses on acetone detection after exposing the AuNP-decorated cotton to a CH3COCH3 aqueous solution. Such an interaction resulted in a reduction of the total impedance (i.e., magnitude) of the system. This behavior can be ascribed to Van der Waals forces existing between the C=O group and the citrate moieties adsorbed on the gold nanoparticles, which favor charge injection to the substrate. Response to water was also tested for comparison, assuring that the solvent interacts with the sensitive layer by a different adsorption mechanism, not influencing the overall results. Sensor selectivity was also verified by considering ethanol (representative of alcohol group). Indeed, impedance curves reflect the different type of chemical interaction between the analyte and the substrate. In addition, sensor limit of detection for acetone was found to be 1% v/v, in the considered frequency range. Furthermore, sensor performance in terms of reusability was evaluated, showing that the Au-cotton ability in VOCs detection could be restored after about 90 min with a percentage up to 97 % in the frequency of 1Hz. These results can be considered the starting point for the development of portable, sensitive and user-friendly devices.

This work presents a portable system developed to perform biochemical analyses requiring both temperature sensing for the thermal sample treatment and optical sensing to detect the analyte. To achieve this goal, we coupled a system-on-glass, hosting on a single glass substrate a thin film transparent heater and two temperature sensors, with interface electronics able to drive the heating source and control the temperature. The system-on-glass has been optimized to ensure temperature uniformity better than ±1.4 °C over a large-area (6 cm ² ) and sensor resolution better than 0.01 °C. Moreover, the presented device operates at a remarkably low power of only 2.4 W/cm ² to achieve a temperature of 100 °C, significantly below the power requirements of most comparable devices available on the market. The electronics has been designed to minimize electromagnetic interferences between the heater and the biological samples. The temperature-controlled platform has been enclosed in a 3D-printed black resin-made box whose dimensions are 11 cm · 10 cm · 2.4 cm, while the electronics is enclosed in a metallic box (12.55 cm · 8.05 cm · 4.32 cm), connected with the 3D-printed box by an Ethernet cable. The compactness and low weight (below 0.5 kg) of the two boxes ensures the system portability while the easy coupling of the system-on-glass with different kinds of microfluidic networks allows its employment for a large variety of biosensing applications.