Synthesis Of Gold Nanoparticles By High Gravity Technology And Its Application In Biosensor

It has been more than 150 years since gold nanoparticles were synthesized for the first time.Gold nanomaterials have attracted extensive attention because of their Surface Plasmon Resonance effect,which is closely related to the size,shape and aggregation state of particles.Functionalization of gold nanoparticles with different protective agents and various surface modification methods is conducive to its application in the fields of biomedicine,chemical sensing,analysis and detection,and so on.Therefore,effective regulation of the product on nanoscale is critical for both stability and consistency of the obtained particles.At present,there are many problems in the preparation of gold nanoparticles.For example,particle size is not uniform and the products of different batches vary greatly.In this paper,high gravity technology was introduced to the preparation and modification of gold nanoparticles,which could strengthen the mass transfer and microscopic mixing between fluids to synthesize gold nanoparticles with narrow particle size distribution.The obtained products were then used to prepare Surface-enhanced Raman Scattering(SERS)-active substrates,enabling SERS detection of Rhodamine B and imidacloprid.The main works and conclusions of this paper are as follows:(1)Sodium citrate-stabilized gold nanoparticles were prepared by traditional stirring(STR)method.By changing the molar ratio of sodium citrate and chloroauric acid,the trend of particle size of the products was explored.The results showed that when the molar ratio reached 8,the obtained gold nanoparticles were regular spherical with an average particle size of 17.5 nm,and particle size tended to be stable.Subsequently,in order to realize the coating by silica,surface modification of gold particles by cetyltrimethylammonium bromide(CTAB)was carried out by high gravity technology and STR method,respectively.The results showed that,compared with STR method,high gravity technology could greatly shorten the modification time and the obtained product had better stability.In the process of preparing silica@nano-gold sphere,effect of the dosage of tetraethyl orthosilicate(TEOS)on the thickness of silica layer was investigated.The results showed that the thickness of silica shell layer increases with the increase of the amount of TEOS ethanol solution in the range of 0.8-1.2 m L.When the dosage was 1.0 m L,effect of silica coating was the best,and the ratio of silica shell thickness to gold core diameter was 1.0.(2)High gravity technology was used to prepare small-sized gold nanoparticles,and effects of liquid flow rate,rotating speed and high gravity cycle time on the particle size of the product were investigated.The results showed that when sodium borohydride: chloroauric acid=4:1(molar ratio),CTAB: chloroauric acid=100:1(molar ratio),liquid flow rate was in the range of 17.8 L/h-25.4 L/h,rotating speed was in the range of 1200-1800 rpm,and no high gravity cycle,the size of obtained gold nanoparticles was minimum.The average particle size of the product was about 2 nm with narrow size distribution.The surface of the particles was wrapped by CTAB molecules which made them well dispersed in water.For comparison,STR experiment was carried out under the same conditions.The results showed particle size of the product synthesized by STR was relatively large and particle size distribution was wide,indicating that high gravity technology had a prominent advantage in the preparation of small-sized gold nanoparticles.(3)SERS properties of the obtained gold nanoparticles of two sizes were explored.SERS active substrates were prepared by loading gold particles on a hydrophilic silicon wafer by self-assembly method.The test results showed that qualitative detection of rhodamine B and pesticide imidacloprid at low concentration was realized because their Raman signals were enhanced greatly on the SERS active substrates and the characteristic peaks that were originally difficult to identify were shown in Raman spectrum.The results showed that the enhancement effect of different sites on the substrate was related to the concentration of gold nanoparticles,and this gold nanoparticle-based SERS active substrates had good reproducibility,feasibility and practicality.