| Nanomaterials have special structure， which results in serials of interestingchemical and physical properties. The unique chemical and physical of metalnanoparticles make them extremely suitable for designing new and improved sensingdevices, especially electrochemical sensors and optical sensors. Due to the largespecific surface area and surface free energy of gold nanoparticles, the goldnaoparticles can absorb biomolecues strongly and play an important role in theimmobilization of biomolecues in biosensors construction. Recent advances innanomaterials have produced a new class of fluorescent labels by biocognitionmolecules to fluorescent noble-metal nanoclusters such as Au, Ag, Cu and so on. Theemission wavelength of metallic nanoclusters can be tuned by changing excitation ofall different-emissive nanoclusters, which is similar to semiconductor quantum dots.High-quality nanoclusters are more biocompatible and stable against photobleachingcompared with organic dyes. These novel optical properties render the fluorescentnoble-metal nanoclusters ideal fluorophores for multiplexing applications inbiomedical and environmental monitoring. Here we mainly focus on gold nanoparticlesand copper clusters.In this research, we develop a serial of electrochemical and optical sensors basedon gold nanoparticles and copper clusters for the purpose of improving the long-termstability and the higher sensitivity of biosensors. The details are summarized asfollows:(1)A novel electrochemical immunosensor has been developed for the detectionof human immunoglobulin G (IgG) by using gold nanoparticles (AuNPs) andtelomerase extension reaction as dual signal amplification. The immunosensor wasimplemented based on a heterogeneous sandwich procedure on the gold electrodesurface. Goat anti-human IgG (Ab) and telomerase primer P1co-labelled goldnanoparticles (Ab-DNA-AuNP complexes) was used as secondary antibody fortelomerase extension and binding with human IgG. After the telomerase extensionreaction, the extension products then hybridized with the biotinylated probe P2,following with binding of streptavidin-labelled alkaline phosphatase (SA-ALP). TheALP converted ascorbic acid2-phosphate (AA-P) into ascorbic acid, which reducedthe silver ions in the solution into metal silver, leading to the deposition of silver onto the electrode surface. Linear sweep voltammetry (LSV) was used to quantify theamount of the deposited silver which was proportional to the concentration of humanIgG. The electrochemical immunosensor showed a dynamic range of0.1-100μg mL-1with a detection limit of0.02μg mL-1, acceptable precision, reproducibility andstability.(2)This chapter was based on dual signal amplification of gold nanoparticles andtelomerase extension reaction to develop an electrochemical DNA sensor. This DNAsensor is based on a “sandwich†detection strategy, which involves capture probe DNAimmobilized on gold eletrodes and S1-R1-AuNP complexes that flank the target DNAsequence. In the presence of telomerase, telomerase extension reaction is initiated toadd TTAGGG tandem repeat unites to the3’-end of the primer. Probe P2is designedfor hybridization with telomerase extension product. Then streptavidin labelledalkaline phosphatase (SA-ALP) is employed to connect ALP onto electrode surface viaspecific binding between biotin and streptavidin. The ALP converted ascorbic acid2-phosphate (AA-P) into ascorbic acid, which reduced the silver ions in the solutioninto metal silver, leading to the deposition of silver onto the electrode surface. Linearsweep voltammetry (LSV) was used to quantify the amount of the deposited silverwhich was proportional to the concentration of target DNA. This novel DNA sensorshowed fairly good reproducibility, stability, and reusability.(3)According to Wang’s report, poly T ssDNA can act as an efficient template forcopper nanolusters synthesis and the formed copper nanoclusters have excellentfluorescence. In this chapter, we developed a simple, rapid, sensitive and low-costfluorescence method for Pb2+assay based on poly T-template copper nanoclusters. Wechoose poly T strand (T30) as the template for Cu2+reduction and copper nanoclustersformation. The poly T-template copper nanoclusters exhibited excellent fluorescenceperformance which acts as sensitive signal report probes. However, in the presence ofthe Pb2+, as the Pb2+can easily interact with Cu+through a metallophilic interactionthat disturbs the effective reduction of Cu+to Cu0in the copper nanoclusters synthesisprocess. So quite low fluorescence signal is observed. These changes in fluorescenceintensity of copper nanoclusters allow analysis of Pb2+rapidity (<10min), simplicity(label-free), sensitivity (LOD0.4nM), selectivity (no interference from other metalions) and low-cost (without any labels and sophisticated operation). We validated thepracticality of using copper nanoclusters for the determination of Pb2+inenvironmental samples through analyses of tap water samples. |
