| Electrochemiluminescence (ECL) intrinsically shows a connection between electrochemistry and spectroscopy. The technique as a promising tool has attracted much attention in sensing and detecting trace amounts of samples, especially for the quantum dots (QDs)-based ECL method. Considering that most ECL nanoemitters are capable of photoluminescence (PL) emission, it is natural to adapt their PL strategies concerning about fluorescence resonance energy transfer into ECL systems, giving rise to the methodology of ECL resonance energy transfer (ERET). Further, the dual-potential ratiometric ECL strategy was developed based on ERET and applied to bioanalysis. These works expand the applications of QDs ECL, and provide the powerful tools for the detection in complex samples. The main works include two parts as follows:1. Highly Selective Detection of MicroRNA Based on Distance-Dependent Electrochemiluminescence Resonance Energy Transfer between CdTe Nanocrystals and Au NanoclustersA distance-dependent electrochemiluminescence resonance energy transfer (ERET) system based on CdTe nanocrystals and Au nanoclusters (AuNCs) was designed with the aid of ligase for highly selective detection of microRNA (miRNA). First, AuNCs functionalized hairpin DNA was synthesized via Au-S chemistry, and characterized with transmission electron microscopy and dynamic light scattering. The resulting hairpin DNA-AuNCs composite can be bound to the carboxylated CdTe nanocrystals via amide reaction on glass carbon electrode. The strong interaction between CdTe nanocrystals and AuNCs led to the electrochemiluminescence (ECL) quenching of CdTe nanocrystals. In the presence of assistant DNA and miRNA, the ligase can selectively ligate both of them on the strand of the hairpin DNA to form long DNA-RNA heteroduplexes. Thus the ECL signal was recovered due to the blocking of the ERET. As a comparison, when directly opening the hairpin DNA by the target, the ECL emission signal is weak owing to the presence of ERET effect at the short distance. Based on the distance-dependent ERET, a’signal on’ECL system was utilized for the detection of miRNA with the advantages of 6 orders magnitude linear range and excellent sequence specificity. The total detection processing time of the biosensor was approximately 70 min. By substituting the hairpin DNA with different sequences, this strategy as a new signal transduction approach could be conveniently extended for detection of other short miRNA and DNA.2. Design and Biosensing of Mg2+-Dependent DNAzyme Triggered Ratiometric ElectrochemiluminescenceA dual-potential ratiometric electrochemiluminescence (ECL) sensing approach is designed by Mg2+-dependent DNAzyme-regulated ECL signals of luminol and CdS QDs. The system consists of DNAzyme strand functionalized QDs as capture probes and cathode ECL emitters, luminol-reduced gold nanoparticles (Au@luminol) as anode ECL emitters, and an Mg2+ substrate strand modified with a cyanine dye (Cy5) fluorophore as the quencher. In the absence of Mg2+ ions, the cathode ECL of the QDs is quenched by electrochemiluminescence resonance energy transfer between CdS QDs and Cy5 molecule while the anode ECL from Au@luminol is introduced into the system. On the other hand, in the presence of Mg2+ ions, the DNAzyme cleaves the substrate strand, and then releases the Cy5 and Au@luminol, which results in the recovery of the cathode ECL of the QDs, and the decrease of the anode ECL simultaneously. Based on the ratio of ECL intensities at two excitation potentials, this approach could measure the concentration of Mg2+ in a linear range from 10μM to 10 mM, and has been applied in the detection of Mg2+ in Hela cell extract. DNAzyme-triggered ratiometric ECL strategy with potential resolution would provide a reliable and sensitive method in biosensing and clinical diagnosis. |
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