Designing sensing material with fractal geometry: A gateway for enhanced ethanol sensing under ambient conditions

Abstract

In this work, a comparative study of ethanol vapor sensing is reported for tin oxide based vertical fractal structures (VFSs) against non-fractal structures (NFSs). The materials were synthesized by cost-effective microwave synthesis route followed by controlled drying of tin oxide colloidal solution. A thin layer of fractal material was coated on an ordinary glass capillary that served as the tubular sensor. While the VFS sensor responded well to ethanol vapors under ambient conditions with faster response (τres) of ∼ 8.2 ±0.5 s and recovery time (τrec) of ∼ 10.3 ± 0.5 s, respectively, the NFS sensor exhibited τres ∼15.2±1.0 s and τrec∼ 38.4±1.8 s. The performance of the VFSs was found to be satisfactory when tested under varying humid conditions (∼ 45 RH% to 90 RH%). The sensor exhibited a low detection limit of 1 ppm ethanol vapor. The better sensing properties are attributed to the characteristic patterned growth of fractals with interconnections ranging from nano to macro-scale, inter-crossing of fractal branches, surface as well as 3D roughness which are hallmarks of fractal geometry. In addition to this remarkable ethanol vapor sensing characteristics, easy and cost-effective fabrication process encourages to develop "single use" sensors as breath analyzer devices that can curb the risk of infection from person to person. This study projects the use of VFS samples and sensors fabricated thereof as reliable and economical disposable sensors.