‘Turn-on’ fluorescence assay for inorganic phosphate sensing

• TGA capped CdTe QDs were synthesized in aqueous medium.
• Studied the effect of phosphate solution and europium nitrate on the CdTe solution.
• Europium quenches fluorescence of CdTe QDs while addition of phosphate solution to QD-Eu complex reversed the quenching.

Phosphorus (in the form of phosphate) is the second most abundant mineral in the human body and is essential for normal body activities. Abnormal concentrations of phosphate can cause serious disorders and may be fatal if not treated. One of the drawback of current phosphate sensing method is its lack of sensitivity and specificity. This issue can be overcome by using photoinduced electron transfer (PET) based fluorescent on/off sensors. Semiconductor quantum dots (QDs) are used for the purpose of phosphate sensing because of their excellent size tunable optical properties (fluorescence and absorbance). Here we report the synthesis and characterization of thiol capped cadmium telluride (CdTe) QDs and their use in ‘turn on’ assay for inorganic phosphate sensing. The assay utilizes europium nitrate which forms complex with CdTe QDs (QD-Eu complex) and quenches fluorescence of QDs through photoinduced electron transfer (PET) process. Addition of phosphate solution results in recovery of fluorescence intensity of TGA capped CdTe QDs. Fluorescence recovery was quantified in terms of the concentration of inorganic phosphate. The fluorescence intensity versus Pi concentration curve fits to the sigmoid shape after optimization for the desired range of phosphate concentration. This ‘turn on’ sensing assay method is reliable, repeatable and might be useful for determination of physiological inorganic phosphate level.