Ratiometric arginine assay based on FRET between CdTe quantum dots and Cresyl violet

The authors report on the design of a new Förster resonance energy transfer (FRET) based ratiometric nanoprobe for the determination of arginine. The method is based on the inhibition of the efficiency of FRET in assemblies formed between CdTe quantum dots capped with mercaptopropionic acid (QD-MPA) acting as energy donor, and the dye Cresyl Violet (CV) that acts as an energy acceptor at pH 8. Addition of arginine causes a displacement of the CV by arginine on the surface of the QD/MPA. Hence, the FRET between QD/MPA and CV is interrupted and fluorescence emission of the donor (QD/MPA) is restored. Arginine selectively binds to the QD/MPA via electrostatic and hydrogen bonding interactions between guanidinium and carboxylate. Under optimum conditions, the ratio of the fluorescence emissions peaking at 575 and 620 nm (under 400 nm excitation) is linear in the 1 to 30 μM arginine concentration range, and the detection limit is 0.51 μM. The nanoprobe displays good selectivity over 14 other amino acids, many metal ions, glucose, and ascorbic, tartaric and citric acids. The fluorescent nanoprobe was successfully applied to the determination of arginine in pure and spiked real samples and gave good recoveries. Its good selectivity, sensitivity, low-cost and rapidity make the QD-dye assembly a suitable nanoprobe for the quantitation of arginine.

Open image in new window

Graphical abstract Schematic of a FRET ratiometric nanoprobe for arginine. It is based on quantum dots acting as energy donors and Cresyl Violet acting as energy acceptor. The FRET process is interrupted by the addition of arginine which selectively interacts with carboxy groups via a guanidinium-carboxylate salt bridge.