Utilizing Fluorescent Probes for the Detection of TiO₂ Nanoparticles of Known Characteristics and Their Photocatalytic Activity in Drinking Waters

To support the safe use of photocatalytic nanomaterials, it is essential to have portable and affordable methods to rapidly detect residual photocatalysts in water. Technologies with low detection limits are based upon mass quantification, which requires expensive analytical equipment and complex sample preparation. Therefore, we developed a portable method that utilizes the photocatalytic reactivity of titanium dioxide (TiO₂) nanoparticles to detect and quantify TiO₂ in treated drinking water. The method involves UV excitation of TiO₂ nanoparticles in solution, which hydroxylates terephthalic acid, resulting in an increase in fluorescence emission, detected by a portable device. Within a 15 min analysis period, the detection limit for a NIST reference TiO₂ in distilled water is 0.388 ppb with a quantitation limit of 1.30 ppb. However, these limits increased for soft (2.12 and 7.07 ppb) and hard (64.3 and 214 ppb) water, respectively. Interference from natural organics depended on the amount of TiO₂ present. At 100 ppb of TiO₂, the detection assay can operate in matrices containing up to 703 ppb of humic acid, within a 95% confidence interval. Overall, the presented assay is a reliable, sensitive, and accurate method for detecting TiO₂ nanoparticles of known characteristics in drinking water, accomplished using affordable and portable instrumentation.