Interface Study on Zinc Oxide Quantum Dots Using Fluorometric and Regression Analysis in View of Optical Sensing

Abstract

A study has been performed to investigate the interface property of zinc oxide quantum dots (ZnO-Qdots) for optical sensing ability. Bare and L-cysteine capped ZnO-Qdots were prepared using simple sol-gel hydrolysis method at ambient conditions and the surface property was evaluated using a fluorometric technique. Data were interpreted and modeled using regression analysis, taking into account the effect of temperature and quencher concentration. The capping of L-cysteine caused the fluorescent yield to decrease up to 16-fold as compared to the bare ZnO-Qdots. Upon addition of an external quencher, emission of both bare and capped samples was quenched accordingly and dependent upon the concentration of the quencher. Regression analysis has confirmed with a significant low p-value (<0.05) that bare ZnO-Qdots obtained a dynamic quenching mechanism in the presence of copper (II) ion. Conversely, the capped ZnO-Qdots had a static quenching mechanism. Based on the interface mechanism understanding, it was found that capping effort reduced the sensing sensitivity while the bare one portrayed good sensing potential with a detection limit down to 41.30 ± 0.05 nM. A multi-variable model was constructed for the bare ZnO-Qdots and successfully predicted the concentration of copper (II) ion accurately even at different temperature conditions.

Keywords:

• Copper (II) ion
• Fluorescence quenching
• Optical sensing
• Regression analysis
• Surface functionalization
• Zinc oxide quantum dots

Acknowledgments

This work was supported by Seed Grant 2-5243 by Swinburne University of Technology Sarawak Campus. The authors would also like to thank all supportive staff and technicians that have contributed to this work.