Photography-based photometry: High throughput UV photometric analysis without scientific equipment based on contact printing photography and common imaging devices

Abstract

This work introduces photography-based photometry, as complementary to digital image colorimetry, by demonstrating that historical photography can be repurposed to enable UV photometric analysis, using inexpensive and ubiquitous materials. Analysis is performed by illuminating the samples with UV radiation and then capturing the transmitted irradiation on the surface of a photographic paper through photochemical reduction of its photosensitive coating. A visible image is then formed on the paper surface and is recorded as a digital photograph. The color intensity of the image is directly proportional to the concentration of the analytes in the sample and is quantified in the RGB color system. By selecting the appropriate light source and photosensitive paper, sensitivity to light can be selected to approximate the absorbance spectra of the target analyte thus accomplishing good selectivity and high sensitivity. On the basis of this principle, a variety of assays were used to demonstrate that photography-based photometry, can be used to perform accurate UV absorbance measurements over a wide spectral range, in a high throughput format (i.e. microtiter plates) and at low cost as compared to expensive microplate spectrophotometers. Depending on the photosensitivity of the photographic paper, linear ranges and detection limits that are similar or lower up to an order of magnitude to those obtained with standard spectrophotometry were achieved. Importantly, a single device configuration can be used for all assays, irrespectively of the maximum absorbance wavelength, which significantly simplifies its operation thus holding great promise for routine applications in resource-limited settings even by non-experts.