Au@Ag core-shell nanoparticles for microRNA-21 determination based on duplex-specific nuclease signal amplification and surface-enhanced Raman scattering.

A novel surface-enhanced Raman scattering (SERS) analysis strategy has been designed combining Au@DTNB@Ag core-shell nanoparticles (DTNB attachment on gold nanoparticles, then encapsulated in Ag shell nanoparticles named as ADANPs) and duplex-specific nuclease signal amplification (DSNSA) platform. Firstly, ADANPs and magnetic substrate of Fe3O4 nanoparticles were covalently attached to the 3'- and 5'- end of capture probe (CP) targeting miRNA-21. Upon the addition of target miRNA-21, these heteroduplexes were specifically cleaved by DSN and resulted in ADANPs that were released from the surface of Fe3O4 nanoparticles (Fe3O4 NPs). At the same time, miRNA-21 remained intact and can rehybridize another DNA probe to trigger the signal-amplifying reaction. Based on this principle, the developed SERS method exhibited good linearity in the range 0 to 1 nM for miRNA-21 with a limit of detection (LOD) of 0.084 fM and has an ability to differentiate even a single-base mismatched sequence on the target sequence or other miRNA sequence. The results provide a novel SERS method which can successfully been applied to the miRNA-21 detection in human serum. Graphical abstract a shows the synthesis of Fe3O4 NPs and the conjugation of Au@DTNB@Ag NPs (ADANPs) for the detection of miRNA-21, b shows the operating principle of DSN-assisted signal amplification strategy for miRNA detection based on Fe3O4@CP@ADA NPs.

A highly sensitive DNAzyme-based SERS biosensor for quantitative detection of lead ions in human serum.

Lead ions (Pb2+), one form of the toxic heavy metal, have drawn significant attention due to their harmful effects on human health and the environment. Although many analytical techniques have been developed over the past few decades, the development of a sensitive, selective, and rapid method to detect Pb2+ remains a challenge. In this work, we developed a sensitive surface-enhanced Raman scattering (SERS) biosensor for highly sensitive detection of Pb2+ by using DNAzyme-modified Fe3O4@Au@Ag nanoparticles (Fe3O4@Au@Ag NPs). Firstly, the thiolated 5'-Cy3 DNA probe was modified on the surface of Fe3O4@Au@Ag NPs, which hybridized with the Pb2+-specific DNAzyme to form a SERS biosensor, and the Cy3 labels were used to detect Pb2+. In the presence of Pb2+, the DNAzyme cleaves the Cy3-labeled DNA probe, leading to the release of Cy3-labeled DNA probe from the Fe3O4@Au@Ag NPs. Therefore, the Raman intensity of the Cy3 labels decreases. The proposed biosensor exhibited excellent linearity in the range from 0.01 to 1.0 nM, with a limit of detection for Pb2+ of 5 pM. It features superior selectivity to Pb2+ over other interfering metal ions and good application in the determination of Pb2+ in tap water and human serum samples. The SERS biosensor provides a novel' simple and sensitive method for detection of Pb2+ and sheds new light on the design and synthesis of analogous SERS biosensors for the detection of other heavy metal ions.

A graphene oxide-based hairpin probe coupling duplex-specific nuclease signal amplification for detection and imaging of mRNA in living cells.

In situ imaging of mRNA in living cells can help to monitor the real time mRNA expression and also useful for diagnosis and prognosis of the diseases. In this study, a new strategy was designed for simple, sensitive, and selective platform to detect the mRNA levels by combining a hairpin probe-graphene oxide (HP1/GO) and duplex-specific nuclease signal amplification (DSNSA). Initially, the DNA probe was adsorbed on the surface of GO to protect it from enzymatic digestion. Then, the target mRNA (T1) was hybridized with a partial hairpin probe which formed a duplex. Finally, under the action of DSN nuclease, the ssDNA in the DNA/RNA hybrid was selectively cleaved and produced small fragments. Then, T1 triggered the next reaction cycle, constituting a new circular exponential amplification. Here, we conclude that this assay is highly sensitive for the detection of target mRNA with the lower detection limit of 1 fM under optimal conditions. Furthermore, this strategy was successfully used for imaging of mRNA in living cells.

A "turn-off" SERS aptasensor based DNAzyme-gold nanorod for ultrasensitive lead ion detection.

It is great significance to precisely monitor lead (II) ions (Pb2+) for environment protection and human health monitoring. We designed a sensitive detection strategy for sensitive and selective determination of Pb2+, based on a Pb2+-specific DNAzyme as the catalytic unit, Cy3-labeled DNA modified gold nanorods (AuNRs) as SERS reporter. Firstly, AuNRs surface were employed as a platform for the immobilization of thiolated probe DNA, and then hybridized with DNAzyme catalytic beacons. By taking advantage of DNAzyme digest, a molecular beacon, causes a "turn-off" SERS signal by disrupting the labeled probes. Under the optical conditions, the DNAzyme-AuNRs sensor system exhibited high sensitivity, acceptable stability and reproducibility with a wide linear range from 0.5 to 100 nM (R2 = 0.9973), and an ultra-low detection limit of 0.01 nM. The proposed strategy has additional advantages of being less time-consuming, low-cost and remote query, and avoids the interference of some metals such as Fe3+, Cd2+, Ba2+, Cu2+, Zn2+. The SERS biosensor system has been successfully applied for detecting Pb2+ in real samples with a satisfactory result. The result indicated that the proposed sensing strategy not only enriches SERS platform of monitoring Pb2+ but also exhibits potential for the point-of-care diagnostic application of the clinical screening in complicated biological samples.