Improvement Of Electrochemiluminescence From CdS Nanocrystals And Design Of ECL Biosensors

Electrochemiluminescence (ECL) technique, which is chemiluminescence produced by electrochemical oxidation or reduction, has proved to offering chemiluminescent and electrochemical advantages. Compared to photoluminescence and florescence, ECL does not need external excited light source, which gives a low background signal. Besides, ECL detection also has the properties of high sensitivity and low cost etc. Nanocrystals (NCs), as a new kind of ECL material, have been widely used in ECL biosensors and induced number of new detection theories and methods due to their various types, easy synthesis and controllable luminescence-electrocity properties. NCs usually suffer from weak ECL emissions compared with conventional luminescent reagents like Ru(bpy)32+. Our group has established several kinds of methods to improve ECL properities of NCs and has proposed various ECL biosensors based on resonance energy transfer. Here, we developed a simple chemical treatment approach to improve ECL behaviors of CdS NCs. Besides, we found a new ECL RET donor-acceptor pair to achieve sensitive and selective detection of microRNA concentration. The details are discussed as following:1. Simultaneously Electrochemiluminescence and Electrochemical Detection of microRNA Concentration Using Oligonucleotide Encapsulated Silver Nanoclusters As LabelsA novel sensitive and selective detecting approach of microRNA concentration was presented using oligonucleotide encapsulated silver nanoclusters as labels. In the presence of target microRNA, ECL from CdS NCs coated on glass carbon electrode could be quenched by closely contacted Ag nanoclusters since ECL emission spectrum of CdS NCs was well matched with the absorption band of oligonucleotide encapsulated Ag nanoclusters, while the reduction peak current of coreactant K2S2O8 could be enhanced due to conductive properities of Ag nanoclusters. Thus, the quenching of ECL from CdS NCs and enhancement of reduction peak current of K2S2O8 could indicate the same biological binding event, which made the detection more convincing. This approach could sensitively detect the concentration of target microRNA in a wide range from 10 fM to 1 nM. Thus we believe that this study could be utilized for further development of other biosensors.2. In Situ Activation of CdS Electrochemiluminescence Film and Its Application in H2S DetectionIn this work, we proposed a simple in situ activation approach by dipping CdS NCs film on glass carbon electrode (CdS NCs/GCE) in an activation solution containing H2O2 and citric acid, resulting in a ～58-fold enhancement of ECL intensity in the presence of coreactant H2O2. During activation, CdS NCs were oxidized by H2O2 to smaller ones which resulted in more surface S vacancies; meanwhile, citric acid played an important role in stabilizing NCs. The ECL enhancing mechanism was investigated in detail, and the coordination of H2O2 to surface excess Cd2+ ions (S vacancies) on the CdS NCs surface formed in activation was the main factor which could stabilize the electrogenerated radicals, resulting in an enhanced ECL. ECL from the activated CdS NCs/GCE could be quenched in Na2S solution due to the bonding of S(II) to excess Cd2+ ions on the surface of CdS NCs. On the basis of this, we then used the activated CdS NCs/GCE as an ECL probe for the detection of Na2S which showed good performance including a wide linear range of 5nM to 20μM and good anti-interference ability. Moreover, this ECL probe was successfully applied for hydrogen sulfide (H2S) detection in a biological system.