AuNP-Decorated Textile as Chemo Resistive Sensor for Acetone Detection

Volatile Organic Compounds (VOCs) are emitted from both natural and human-made sources, and they easily evaporate, affecting indoor and outdoor air quality. Toxic VOCs like formaldehyde and acetone pose health risks at high levels. For example, prolonged exposure to acetone (CH₃COCH₃) above 0.1% can cause respiratory irritation, while levels exceeding 1% may lead to confusion and headaches. Therefore, monitoring and adhering to health-related exposure thresholds are essential. Due to the limitations of traditional methods, there is growing interest in portable, low-cost sensors.

This study explores the potential of combining textiles and nanomaterials to create a Volatile Organic Compound (VOC) sensor. To meet the demand for low-cost, portable, and smart devices for periodic monitoring of VOC exposure limits, a cotton substrate coated with citrate-functionalized gold nanoparticles (AuNPs) was developed as a sensor. These AuNP-decorated textiles were fabricated and tested as chemoresistive sensors for the detection of acetone.

Sensor fabrication utilizes sodium citrate (Na₃C₆H₅O₇) and tetrachloroauric acid (HAuCl₄), which together create a negatively charged shell around the gold nanoparticles (AuNPs). This helps stabilize the nanostructures, controlling nanoparticle size and distribution. Drop-casting the solution onto cotton results in a visible white-to-pink colour change, confirming successful nanomaterial deposition and formation of the sensitive layer. Subsequent morphological characterization using Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM), along with structural analysis via UV-Vis spectroscopy, reveals uniformly distributed, circular nanostructures approximately 40 nm in diameter along the cotton fibers.

This configuration forms a non-continuous network of nanoparticles, functioning as a resistive component, alongside an interface between the sensing layer and porous substrate that behaves as a non-ideal capacitive component. When analytes in an aqueous solution interact with the active sites, they affect both components: the real part of the impedance through chemical interactions and the imaginary part through alterations in the dielectric constant.

Electrochemical Impedance Spectroscopy (EIS) was employed to assess the sensor's performance in detecting target analytes over a frequency range of 1 Hz to 10 kHz. The electrical response to acetone was compared with that of distilled water (used as the solvent baseline) and ethanol (an alcohol used to assess selectivity). The absorption of aqueous solutions at the active sites resulted in a three-order-of-magnitude change in impedance, highlighting the baseline effect of water. In contrast, 40% acetone resulted in a 1.6% deviation, and 40% ethanol in just 0.2%. These differences correspond to their dielectric constants—water ≈ 78, ethanol ≈ 24, and acetone ≈ 21—which influence the double-layer capacitance. Water and ethanol form stronger hydrogen bonds, while acetone interacts primarily through weaker Van der Waals forces.

The time-dependent impedance response reflects the volatility of the analytes, with acetone showing a faster recovery rate than water. Minimal variation after 48 hours of sensor use confirms the coated textile’s stability and suitability for repeated measurements.

The proposed AuNP-textile sensor offers several advantages, including a simple, eco-friendly preparation process, cost-effectiveness—thanks to minimal gold usage and inexpensive disposable cotton—and the potential for integration into wearable formats, such as workers’ uniforms.