Magnetic beads and GO-assisted enzyme-free signal amplification fluorescent biosensors for disease diagnosis.

Cancer detection is still a major challenge in public health. Identification of oncogene is the first step toward solving this problem. Studies have revealed that various cancers are associated with miRNA expression. Therefore, the sensitive detection of miRNA is substantially important to solve the cancer problem. In this study, let-7a, a representative substance of miRNA, was selected as the detection target. With the assistance of magnetic beads commonly used in biosensors and self-synthesized graphene oxide materials, specificity and sensitivity detection of the target gene let-7a were achieved via protease-free signal amplification. The limit of detection (LOD) was as low as 15.015pM. The fluorescence signal intensity showed a good linear relationship with the logarithm of let-7a concentration. The biosensor could also detect let-7a in complex human serum samples. Overall, this fluorescent biosensor is not only simple to operate, but also strongly specificity to detect let-7a. Therefore, it has substantial potential for application in the early diagnosis of clinical medicine and biological research.

DNAzyme-based cascade signal amplification strategy for highly sensitive detection of lead ions in the environment.

Lead ions are one of many common environmental pollutants, that can cause posing a serious threat to people's health, thus, their efficient and sensitive detection is important. We propose a cascade signal amplification sensor using a DNAzyme-based strand displacement amplification (SDA) and hybridization chain reaction (HCR) for the high-sensitivity detection of Pb2+. In the demonstrated sensor system, the target metal ion can activate DNAzyme to cause a strand displacement reaction. Under the synergistic action of polymerase and nickase, large numbers of DNA strands are generated that can initiate HCR. The subsequent HCR can restore the fluorescence intensity of the FAM quenched for the fluorescence resonance energy transfer effect, which exhibits a strong fluorescence signal. The DNAzyme-based sensor allowed the detection of Pb2+ down to 16.8 pM and resulted in a good dynamic line relationship ranging from 50 pM to 500 nM, and the biosensor also showed good selectivity. Furthermore, we confirmed that the proposed sensor can still detect lead ions in complex environments such as lake water, milk, and serum. We believe these findings will provide new ideas for the detection of toxic elements ions in the environment and food.