Preparation Of Excellent Solid SERS Substrate And Its Application In Biochemical Detection

Surface-enhanced Raman scattering(SERS) refers to abnormal optical phenomena in which Raman spectra of analyte absorbed to the rough surface of the metal structure, obtain significantly enhance under light irradiate. After development of 40 years, SERS technique is confirmed as an ultra-sensitive analytical technique and considered to be a powerful analysis tool to analyze biological samples and chemical substances.In order to make SERS technology into a routine analyzing tool, SERS substrate with good performance is essential. Excellent SERS substra te should have powerful enhance ment ability, good uniformity, outstanding stability and stable repeatability of signals, easy to prepare, store and use. This thesis aims to prepare solid SERS substrate with superior performance based on chemical synthesis method. Content of this thesis is divided into the following three parts:Firstly, a SERS-active monolayer film of porous gold nanoparticles is prepared on a solid substrate by a facile in-situ growth approach. The growth solution is prepared by mixing aqueous ascorbic acid, chlorauric acid, and cetyltrimethylammonium chloride in a certain proportion, followed by being transferred onto a solid substrate which is pretreated by coating a layer of positive charges, and then the substrate is placed statically at 4oC to in-situ grow porous gold nanoparticles on the substrate. The growth time, feed ratio of the reagents, and repeat times of the in-situ growth are studied systematically to obtain optimal parameters for preparing excellent SERS substrate. The as-prepared optimal SERS substrate not only has good SERS performance with an enhancement factor up to ~1.10×106, but also shows good uniformity and stability.Secondly, a method based on physical deposition and electrostatic adsorption was proposed to prepare soild SERS substrate. The clean slide was modified with positive charges first using layer by layer method. Then big gold nanoparticles with rich SERS "hot spot" were synthesized by using ascorbic acid(AA) as a reducing agent, HAuC l4 as gold salt with cetyltrimethylammonium chloride(CTAC) as surfactant. These gold nanoparticles were pipetted onto the charge- modified surface to let the gold nanoparticle deposite onto the substrate by physical deposition together with electrostatic adsorption. The influence of charge treatments and deposite times on preparing the optmal SERS substrate were studied.Finally, the usability of the as-prepared SERS substrates was tested by detecing toxic organophosphate pesticide fonofos and lung cancer marker miRN A-21 respectively. The SERS substrate prepared by in-situ growth method exhits good sensitive for sensor fonofos and a good linear relationship between SERS signal and the concentration of pesticide was observed. The limit of detection is 5 ng/mL. Besides, the SERS substrate prepared by physical deposition combined electrostatic adsorption method was utilized to structure SERS sensor for miRNA-21 by modifing its surface with specific molecular beacons. The sensor showed good specificity and ultrasensitivity for detection miRNA-21 with a linear calibration curve between 100 aM to 100 pM, and the limit of detection was 100 aM. Thesee results indicate that both the two kinds of SERS substrates with excellent SERS performance which can be used as sensitive sensors for biochemical dectection.