Background: Gold nano-clusters (Au-NCs) are non-toxic bio–markers, with higher potentials
as compared to quantum dots, and hence the present work was focused on the synthesis of Au-
NCs using Cysteine (Cys) as the reducing and protecting agent.
Method: The properties of the resulting Cys-Au-NCs were evaluated through scanning electron microscopy
(SEM), as well as FT-IR, fluorescence and UV–Vis spectroscopy. Synthesis of the gold
nano-clusters was conducted by adding chloroauric acid solution to fresh Cys solutions under stirring.
The resultant was kept under stirring in a water bath at 37 °C overnight.
Objectives: Considering the low stability of Cys-CuNCs, we decided to study a new approach for
determination of Cys through the synthesis of size-selected Au-NCs in the presence of cysteine as a
reducing and stabilizing agent, to acquire nanoclusters with higher stability.
Results: The spectroscopic results showed various intensities which were attributed to the size of the
Cys-Au-NCs. It was also considered that the enhanced fluorescence intensity of Au-NCs observed
parallel to increasing the concentration of cysteine could be used for developing proper detection
systems for cysteine in aqueous and blood serum samples. This was achieved in the course of the
formation of different Cys-Au-NCs with various sizes. Under optimal conditions, the nano-clusters
was used as a nano-biosensor and showed excellent selectivity for Cysteine as opposed to the other
amino acids tested and produced linear response in the range of 20 to 200 µM. The detection limit of
the system was evaluated to reach as low as 8.4 µM.
Conclusion: Cysteine-stabilized Au-NCs were successfully synthesized and were found to be stable
in aqueous media even after 6 months. Results of the fluorescence emission of the Cys-Au-NCs was
found to be selective towards Cys. The nano-biosensor was also successfully used in serum samples
for Cys detection.