Ultrasensitive Aptamer Sensor Based On Au@Ag Core-shell Nanoparticles For SERS Detection Of 17β-estradiol

17β-estradiol is the most active endocrine disrupting compounds,which has critical impacts on normal endocrine function of animals and humans.17β-estradiol is ubiquitous in aquaculture due to its anabolic effects,and thus enters into human’s body through food chain.The chronic exposure of human to 17β-estradiol,even at extremely low level,can cause numerous deleterious effects.Considerable efforts have been employed to the sensitive detection of 17β-estradiol,including conventional methods such as HPLC(High Performance Liquid Chromatography)and GC-MS(Gas Chromatography-Mass Spectrometer),fluorescence and electrochemical methods.Although chromatography possesses low limit of detection,these assays are rather complicated,expensive,and time-consuming.Electrochemical methods are simple and low-cost,however,the ordinary electrode is lack of sensitivity and selectivity.Therefore,the development of sensitive approach to detect 17β-estradiol is essential for protecting environment and public health.Surface enhanced Raman spectroscopy(SERS)methods exhibit a great deal of merits like high sensitivity and fingerprint information.The combination of recognition/separation methods and SERS has attracted much attention.This paper combined the SERS and aptamer,providing a promising sensing platform,a SERS-based aptamer sensor.The aptamer sensors were fabricated based on gold core-silver shell nanoparticles(Au@Ag NPs).Herein,Au@Ag NPs had greatly enhanced the performance of SERS.Based on the relationship between the concentration of 17β-estradiol and SERS signal intensity,a highly sensitive quantification of 17β-estradiol was achieved.The specific of this work were as follow:The synthesis and characterization of SERS-active Au@Ag NPs.Based on seed-mediated method,different size of Au@Ag NPs were synthesized by overgrowth of Ag shell on the surfaces of quasi-spherical Au NPs.The as-prepared Au@Ag NPs were characterized by UV-vis spectroscopy,transmission electron microscopy,high-resolution transmission electron microscopy,dynamic light scattering,SERS spectra.When the diameter of the Au core was 31nm,and the thickness of Ag shell was 9 nm,Au@Ag NPs of this size possessed the strongest SERS enhancement,the enhancement factor was estimated to be 9.81×10~7.Besides,the presence of certain ion can further enhance the SERS active.The reproducibility of Au@Ag NPs was verified by the SERS intensity of rhodamine 6G,and the relative standard deviation was 11.53%,indicating good reproducibility.When the Au@Ag NPs was stored at 4℃for 14days,the substrates retained 90.31%of its original SERS intensity,exhibiting good stability of the as-prepared SERS substrates.Fabricating of aptamer sensor for detection of 17β-estradiol.The aptamer was embedded into Au@Ag NPs to make an ultrasensitive and selective aptamer sensor.By using this aptamer sensor,we were able to detect as low as 2.75 fM of 17β-estradiol with high selectivity,which was much lower than previously reported.Furthermore,a relative standard deviation of 4.7%was achieved,indicating good reproducibility.When stored at 4℃for one week,the aptamer sensor retained 95.4%of its original SERS intensity,exhibiting good stability of the aptamer sensor.Evaluation of the as-prepared aptamer sensor.To confirm the applicability of this SERS-based aptamer sensor for the real sample detection,a colorimetric assay was introduced to compare with the aptamer sensor.Both of the two methods were applied to real sample detection.The practical detection was carried out by spiking 17β-estradiol into aquaculture water,lake water,tap water.As a result,aptamer sensor provided better recovery,which suggested the sensor was highly effective to real word application.