SERS Substrates Based On Silver-Coated Gold Nanostars For Detection Of 6-thioguine

Surface-enhanced Raman spectroscopy(SERS)is a powerful analytical technique that exhibits high sensitivity and high molecular specificity for trace-level detection of chemical and biological molecules.SERS possesses large potential for application in the fields of analytic chemistry and biodiagnose etc,mainly attributing to its advantages of stability and efficiency in detection,resistance to photo bleaching,and low interference on water signals etc.In order to achieve highly enhanced SERS signals,it is essential to fabricate high performance SERS substrates with outstanding sensitivity,uniformity and reproducibility.Noble metal-based nanostructures attracted great attention,due to their convenient for fabrication,excellent SERS activity and stability.Among all gold nanoparticles,Au nanostars have been previously exhibited superior SERS enhancement to nanospheres,due to their multiple sharp branches that can act with "lightning rods".In addition,Au-Ag bimetallic nanoparticle exhibit excellent optical properties,owing to the synergistic effect of Au and Ag components.The paper reports the preparation of gold star-shaped nanoparticles via seed-mediated growth approach,and then preparation of silver coated gold nanostars with higher SERS enhancement,by employing the as-prepared gold nanostars as the growing core.Based on evaporation assembly technique,silver coated gold nanostars are concentrated on the surface of silica modified candle soot layer(SMCSL)with superhydrophobic property,and closely packed for the fabrication of AuNS@Ag/SMCSL substrates with highly densely distributed "hot spots".The obtained SERS substrates exhibit excellent SERS sensitivity,reproducibility and positive detection capabilities for detecting realistic molecules,and achieved trace-level detection of 6-thioguine in artificial urine,a close structural analogue of guanine.The details are as follows:1.Based on a gold seed-mediated growth method,we have prepared star shaped gold nanoparticles with multiple sharp branches.With the deposition of silver,we have achieved silver coated gold nanostars,by employing gold nanostars as growing core.The amount of deposited silver are tailorable by the concentration of silver nitrate added into the reaction system.Based on X-ray powder diffraction(XRD),scanning electron microscopy(SEM),transmission electron microscopy(TEM),we have characterized the components and nanostructure of the obtained silver coated gold nanostars.The deposition of silver onto the surface of gold nanostars noticeably facilitate the SERS activity,compared to the gold nanostars.As the concentration of added silver nitrate solution is at 5 mM,the as prepared nanomaterials exhibits optimal performance in SERS detection.2.In this work,efficient SERS substrates containing dense hot spots were fabricated by assembling AuNS@Ag on SMCSL superhydrophobic platforms,based on evaporation assembly technique.The scanning electron microscopy images and Raman images reveals that the star-shaped nanoparticles were closely packed on the SMCSL surfaces,giving rise to high density of hot spots.The as-prepared AuNS@Ag/SMCSL substrates exhibited higher SERS enhancement than AuNPs/SMCSL substrates.Furthermore,the SERS substrates showed low detected concentration of Nile blue A(10'12 M),and excellent signal reproducibility(RSD-6.3%).Moreover,the results of simulated electric field distribution also proved higher SERS enhancement of the SERS substrates based on star-shaped particles.Additionally,ultrasensitive detection of OPD and HGB demonstrated that the AuNS@Ag/SMCSL substrates possess the capability of trace detection for realistic molecule.3.In this work,the as-prepared AuNS@Ag/SMCSL substrates are successfully applied for trace detection of 6-thioguine in various solution environment.Firstly,we detected 6-TG in PBS solution with different pH(from 5.8 to 8.0),and choose suitable PBS solution with pH at 5.8,Additionally,we demonstrate that the SERS substrates can achieve high selectivity at detection of 6-TG,with addition of different coexisting ions or molecules.Furthermore,based on the AuNS@Ag/SMCSL substrates with high density of hot spots,we successfully achieve the ultrasensitive detection of 6-TG at low concentration(10-9 M)in artificial urine.