A Novel Biosensor for Detecting Vitamin C in Milk Powder Based on Hg²⁺- Mediated DNA Structural Changes

Background: Detection of Vitamin C (Vc) is very important to protect human health. A lot of methods have been developed for the detection of Vc. However, many methods require complex material preparation and skilled operators. Thus, a simple, label-free biosensor is still urgently needed. Methods: In this work, N-methylmesoporphyrin IX (NMM)/G-quadruplex pair was used as a labelfree signal reporter. Without Vc, the G-quadruplex DNA and its incomplete complementary chain could form a duplex structure by T-Hg(II)-T mismatch. In this case, the G-quadruplex structure could not be formed. When Vc was added, the Hg²⁺ was reduced to Hg(0). Then, the G-quadruplex DNA became free and formed a G-quadruplex structure to emit fluorescence signals. Results: Under optimal conditions, this biosensor showed a good linear response in the range of 0.2 - 4.0 μM and a low limit of detection (19.9 nM). This biosensor also had good selectivity towards Vc. Meanwhile, the satisfactory recovery rates (93.2%-102.8%) suggested that this biosensor had potential for measuring Vc in real samples. Conclusion: In this work, a simple label-free fluorescent biosensor for the detection of Vc based on Hg²⁺-mediated DNA structural changes had been developed. The whole experiment was simple and all reagents were commercialized. The label-free detection was realized by NMM/G-quadruplex as a signal reporter. This biosensor was very sensitive with a low limit of detection. It had a potential practical application for Vc detection in milk powder.