Label-free detection of folic acid using a sensitive fluorescent probe based on ovalbumin stabilized copper nanoclusters

In this work, ovalbumin (OVA) stabilized copper nanoclusters (OVA-Cu NCs) were prepared through a simple protein-stabilized synthetic method and applied for the sensitive determination of FA. Cu²⁺ ions were directly reduced to Cu (0) by a mild reducing agent, N₂H₄·H₂O, at room temperature without any other complicated procedure such as adjusting pH and controlling the temperature of the reaction mixture. The as-prepared OVA-Cu NCs showed good chemical stability, wonderful water solubility and excellent biocompatibility. The OVA-Cu NCs were obtained with an average particle size of 2.0 nm and good dispersibility in aqueous solution. They also showed strong red emitting at 625 nm with a quantum yield of 3.95%. The OVA-Cu NCs were then applied for label-free detection of FA based on a static quenching mechanism. The linear calibration curve of detecting FA served from 0.5 μM - 200 μM with a detection limit of 0.18 μM. In addition, the developed method was also successfully applied to determine the content of FA in tablet, spinach, orange juice and biological samples with quantitative spike recoveries from 96.9% to 100.9%. For these reasons, the developed OVA-Cu NCs-based fluorescent strategy can thus offer a convenient label-free biosensor platform for the detection of FA in biomedical applications.