Flow through Fluorescence Detection of Phosphate in Human Saliva Based on Sensitized Turn-On Photoluminescence of CdS Quantum Dots

The development of fluorescent turn-on probes for the determination of inorganic anions based on fluorescent semiconductor nanocrystals (quantum dots) has recently attracted great attention. Methods reported so far enable anion sensing at elevated concentration levels and usually with low selectivity against other abundant matrix components. In this work, we describe an alternative approach that combines the appropriate modulation of nanocrystal surface chemistry (i.e., stabilization) with rational design and modulation of the experimental conditions (i.e., flow injection analysis) in order to deliver an expedient flow through method that enables the determination of phosphate at low concentration levels and with good selectivity. The developed method was successfully applied to the determination of phosphate in artificial and human saliva with good analytical features in terms of reproducibility and repeatability (2.3–9.2%), recoveries from fortified samples (96.0–112.0%), linearity of response curves to phosphate concentrations (R2 > 0.99), and satisfactory sensitivity (<1 µM), providing a significant improvement to previous fluorescent turn-on quantum dot probes.