5-hydroxymethylfurfural (HMF) is one of the food contaminants mainly formed by Maillard and caramelization reaction. Here, we developed a simple method to detect HMF based on split-DNAzyme assisted signal amplification via Quartz crystal microbalance . Firstly, two fragments of the split-DNAzyme (ESΙ and ESII) and AuNPs-ssDNA were prepared. In the absence of HMF, the amino group of ESΙ reacted with the aldehyde group of ESΙΙ by Schiff base condensation，which linked ESΙ and ESII as DNAzyme. With the help of Mg 2+ , this DNAzyme cleaved AuNPs-ssDNA, freeing the complementary sequence of capture DNA from the ssDNA. In the presence of the target HMF, the aldehyde group in its molecular structure preferred to react with ESΙ, which prevented the link of ESΙ and ESII. In this case, DNAzyme cannot be formed effectively and the ssDNA modified on AuNPs cannot be cleaved. Secondly, the capture DNA was immobilized on Au chip in the QCM chamber. Then, the intact AuNPs-ssDNA was introduced to hybridize with the capture DNA, resulted in a large frequency change (ΔF) of the QCM biosensor because of the huge increased mass of AuNPs. So, HMF can be detected based on the frequency change (ΔF) of the QCM biosensor. This QCM biosensor is more sensitive than previously reported methods, which provide a new direction for the analytical detection of HMF and other food contaminants.
This study aimed to develop a fluorescence assay for Cu2+ monitoring with cascade signal amplification using split Mg2+-dependent DNAzyme subunits as the sensing system and fluorescence as the signal reporter. A subunit of DNAzyme can be formed through a Cu2+-catalysed click reaction between azide- and alkyne-modified short sequences immobilized on magnetic beads, eliminating the washing steps of conventional assays. The immobilized subunit recruits the assisting oligonucleotides to form an autocatalytic DNAzyme as the signal amplifier and a caged fluorescent molecule as the signal reporter. This assay is ultrasensitive, enabling the detection of trace levels of Cu2+ as low as 2 nM, which enhances the detection sensitivity by approximately 100-fold. In addition, the whole reaction process does not require a long manipulation time or a complicated procedure, making the system simple and cost-effective. This method is robust and can be applied to the determination of spiked Cu2+ in water samples with satisfactory recovery. The combination of click chemistry with fluorescent DNAzyme for a simple on-site detection assay can be used for the rapid and sensitive screening of Cu2+.
危险品化学品经营许可证（带存储）