Freestanding ZnO Nanosheets: A Unique Flexible Material for Highly Sensitive Chemiresistive Sensors

摘要

Exhaled human breath consists mixture of numerous organic and inorganic compounds with concentrations ranging from ppb to ppm. Currently, number of biomarkers were identified in breath samples that could be used to identify the diseases. Among which ammonia (NH_3) has been proposed as a potential biomarker in monitoring hemodialysis (HD) adequacy. In the last few decades, many materials have been developed for NH_3 sensor, but still there is a huge demand for highly sensitive, flexible and suitable to integrate with embedded systems is needed. In this scenario, free standing nanosheets may offer excellent flexibility as well as high sensing characteristics, moreover can be deposited on biocompatible substrates like Poly lactic acid (PLLA). Many nanomaterials can be deposited on single nanosheets and can be used a skin patch. At first, polyvinyl alcohol (PVA)/PLLA layers were initially spin coated on Si substrates and then zinc oxide (ZnO) was deposited on PLLA by RF magnetron sputtering technique. Then, PVA layer was sacrificed in water and free standing PLLA/ZnO layer was collected. Finally the PLLA/ZnO nanosheets were transferred into interdigitated electrode for sensing studies. Meanwhile, their structural, elemental and morphological properties were investigated by XRD, EDS, XPS and FE-SEM. To probe the selectivity nature of the sensing elements, PLLA/ZnO nanosheets were tested with various interfering compounds. Results showed that, the sensing response towards ammonia was higher than others. The transient resistance response, stability, response and recovery times were also investigated.