This work describes the preparation of a reusable, reversible dye doped nanofibrous silica and silica/copolymer membrane and its function as a low cost optical sensor. The colourimetric sensing of the volatile phase, specifically ammonia and HCl vapours, is effected by the doped dye, pH sensitive Bromothymol blue, in the nanofibrous membrane. The larger surface area, and narrow, submicron fibre diameter of the nanofibres allow the rapid adsorption and optimal retention of analyte for sensitive detection, and recovery by thermal desorption. The physical structure of the dye doped electrospun silica and silica/copolymer nanofibres was examined by Scanning Electron Microscopy (SEM), nitrogen adsorption-desorption analysis, and X-ray Diffraction while the chemical composition has been elucidated by their infrared spectra, SEM-EDS, and Thermogravimetric Analysis (TGA), The colourimetric response of the sensor is modulated by the porosity and hydrophobic/hydrophilic nature of the matrix, depending on the copolymer component polymethyrnethacrylate/polyvinylpyrrolidone respectively. The colourimetric sensing is visually detected, measured by diffuse reflectance spectrometry, and tracked by image analysis of colourimetric parameters with respect to time and concentration (ppm) of exposure to volatiles, at room temperature. The reliable and reproducible visual sensor performance along with its flexible and porous nature allows for easy usage while detecting volatiles relevant to environmental safety, air quality monitoring and in tracing stability to spoilage in fresh food storage.