Fluorescence turn-off/turn-on biosensing of metal ions by gold nanoclusters, folic acid and reduced graphene oxide

Metal ions homeostasis plays an important role in biological processes. The ability to detect the concentration of metal ions in biological fluids is often challenged by the obvious interference or competitive binding nature of other alkaline metals ions. Common analytical techniques employed for metal ions detection are electrochemical, fluorescence and colorimetric methods. However, most reported metal ions sensors are complicated, time-consuming and involve costly procedures with limited effectiveness. Herein, a nanobiosensor for detecting sodium and potassium ions using folic acid-functionalised reduced graphene oxide-modified RNase A gold nanoclusters (FA-rGO-RNase A/AuNCs) based on fluorescence turn-off/turn-on is presented. Firstly, a facile and optimised protocol for the fabrication of RNase A/ AuNCs is developed. The activity of RNase A protein after the formation of RNase A/AuNCs is studied. RNase A/AuNCs is then loaded onto FA-rGO, in which FA-rGO is used as a potential carrier and fluorescence quencher for RNase A/AuNCs. Finally, a fluorescence turn-on sensing strategy is developed using the as-synthesised FA-rGO-RNase A/AuNCs to detect sodium and potassium ions. The developed nanobiosensor revealed an excellent sensing performance and meets the sensitivity required to detect both sodium and potassium ions. To the best of our knowledge, this is the first work done on determining the RNase A protein activity in RNase A/AuNCs and exploring the potential application of RNase A/AuNCs as a metal ion sensor. This work serves as a proof-of-concept for combining the potential of drug delivery, active targeting and therapy on cancer cells, as well as biosensing of metal ions into a single platform. (c) 2021 Elsevier B.V. All rights reserved.

Automated summary

A nanobiosensor using FA-rGO-RNase A/AuNCs for detecting sodium and potassium ions based on fluorescence turn-off/turn-on is presented. The fabrication of RNase A/AuNCs and the activity of RNase A protein after formation were studied. The nanobiosensor showed excellent sensing performance and has the potential to be used as a metal ion sensor.