Particle size enlargement and 6-fold fluorescence enhancement of colloidal CdS quantum dots induced by selenious acid.

Herein, colloidal CdS QDs have been synthesized by using cysteine as a stabilizing agent. The interaction between the CdS QDs and selenious acid was monitored by using UV-visible, fluorescence and Fourier transform infrared (FTIR) spectroscopy. The onset of absorption of the CdS QDs (430 nm) was progressively red-shifted upon increase in the concentration of selenious acid at pH 10. It indicated enlargement of the particle size which was confirmed by the dynamic light scattering (DLS) measurements. Interestingly, the addition of 100 μM selenious acid at pH 6 resulted in a 6-fold enhancement of the red emission (λ = 617 nm) of the CdS QDs. The particle size enlargement of CdS was due to an electrostatic interaction between selenious acid and QD stabilizer cysteine. The 6-fold fluorescence enhancement was of the CdS QDs was explained on the basis of hydrogen-bonding interaction between selenious acid and cysteine. The fluorescence-based method was applied for the sensing of selenious acid at pH 6.