Research Highlight

Fluorescent quantum dots

doi:10.1038/nindia.2010.101 Published online 29 July 2010

Researchers have designed a new type of light-emitting nanoparticle using semiconducting crystals of cadmium sulphide (CdS).

The crystals were also capped with an amino acid to make them biocompatible. Known as fluorescent quantum dots, the amino-acid-capped nanoparticles were 1.7–3.39 nm in size and could be useful for making nanodevices for optoelectronics, drug and gene delivery, and biolabelling.

Nanoparticles can be easily coated with biomolecules to suit various practical applications. In this particular case, the researchers chose to cap the CdS nanoparticles with cysteine, a non-essential amino acid. To investigate how capping affects the optoelectronic properties of the nanoparticles, the researchers also prepared CdS nanoparticles capped with 3-mercaptopropionic acid (3-MPA) instead of cysteine.

Both solutions of capped nanoparticles exhibited almost identical optical absorption but showed a significant difference in their fluorescence properties. The amino-acid-capped quantum dots were almost three times more fluorescent than the 3-MPA-capped nanoparticles, which suggests that capping with amino acid results in better quality nanoparticles.

Quantum dots are important materials for making ultrafast, all-optical switches and logic gates. This research is significant because improvements in fluorescence may allow them to be used as biosensors and light-emitting diodes.


  1. Kalasad, N. M. et al. Facile synthesis of bioconjugated fluorescent CdS nanoparticles of tunable light emission. J. Phys. D 43, 305301 (2010) | Article