SERS And Colorimetric Detection Based On Nanoparticles For Bacteria Biological Analysis

Surface enhanced Raman scattering(SERS) is new spectral analysis method based on Raman scattering. SERS technique has considerable applications in the field of materials science, surface science, analytical chemistry, biology, medicine and so on for the advantages of its narrow bandwidth, high sensitivity, resistance to photobleaching, resistance to water, glass and other interference. A series of novel biosensors focused on the study of bacterial have been developed with high sensitivity, simple operation and rapid response, which made full use of SERS and colorimetric technology. The main contents are as follows:(1) Surface enhanced Raman spectra for the analysis of DNA detection based on nanomolecular junctions. “Chapter 2”This chapter developed a SERS sensor for high sensitive detection of DNA based on dendritic nanoparticles and signal amplification technology according to the distance effect in the mechanism of electromagnetic field. The electric field strength increased with the increase of distance drastically reduced, that is: the closer distance between Raman dye and the nanoparticles active base, the stronger the Raman signal. This paper, by using magnetic bead separation enrichment and completely complementary hybridization of two DNA strands, verify feasibility by layers of self-assembly to form the molecular junctions of nanoparticles to realize Raman signal amplification, made the detection SERS signal significantly enhanced, which can measure the DNA sensitively.(2) SERS sensor of Magnetic Beads induced nanoparticles aggregation for Detection of bacterial DNA. “Chapter 3”On the basis of the previous chapter, in order to overcome the drawback of expensive of double-modified DNA strand and difficulty of layers modification assembly. This chapter will put Raman dye of 5, 5'-2 thiol-double(2-nitro benzoic acid)(DTNB) to decorate on the surface of active basement directly and explore the feasibility of the method with a model of bacterial DNA. Using magnetic beads aggregation to tempt to shorten the distance between particles and produced the plasma resonance coupling effect, which lead to the results that SERS signal is significantly enhanced. T he results showed that, under the optimized conditions, the concentration from 5 p M to 5 n M performed a good linear relationship between Raman intensity and DNA concentration, and this method also has high selectivity. The method is simple design, low cost, can be used in the sensitive and selective detection of bacterial DNA.(3) Gold nanoparticles as dual functional sensor to detect E.coli DH5? as a model for Gram-negative bacteria. “Chapter 4”This chapter developed a new dual functional sensor based on the 4-aminothiophenol-modified gold nanoparticles( PAT P-Au NPs) for SERS and colorimetric detection of E.coli DH5? as a model of gram-negative bacteria detection. The nano-probes were easy to prepare through Au-S bonding. Under optimized conditions, the PAT P-Au NPs surface with positive charge can bind E.coli DH5? with negatively charged via electrostatic adhesion. Since the bacteria are more than three orders of magnitude larger in size(~1?m) than that of the PATP-Au NPs, the electrostatic interaction would draw thousands of Au NPs particles around each bacterium and induce obvious aggregation of Au NPs, resulting in a quick color change from red to blue, and also a dramatic SERS signal enhancement from thousands of Au NPs aggregated on the surface of bacteria because PATP is also a Raman molecule. For colorimetric analysis, it is the first time that the classical partial least square(PLS) regression was utilized to deal with the relationship between adsorption and E.coli DH5? concentrations. Excellent linear relationship was observed from 1.1×107 to 1.3×108cfu m L-1with the average relative error(ARE) of 5.430, which was more accurate than the traditional extinction ration method. When coupled with confocal Raman microscope, this PATP-Au NPs probes could be used to detection SERS signals produced from even single bacterium. T his bioassay is rapid, less expensive and convenient for bacteria detection and analysis. Therefore, this method is simple design, low cost and real-time, can used for sensitive and selective detection of bacterial DNA in a considerable wide range.