Synthesis Of Au@Ag Nanoparticles And Their Application In Ion Detection

In recent years,noble metal nanoparticles,especially Au@Ag nanoparticles(Au@Ag NPs),have been widely applied in the fields of chemical sensing,optical imaging and ion detection due to excellent optical properties,various synthesis methods,etc.Au@Ag NPs have great potential in the field of optical sensing because of its better stability and higher molar absorption coefficient,which can significantly improve the sensitivity of ion detection.However,owing to preparation condition and nanoparticles'stability,there are few studies for ion detection in aqueous solution by bare Au@Ag NPs.In this paper,firstly,we synthesized uniform gold nanoparticles,and then the layer of silver was encapsulated outside the gold nanoparticles by seed growth method.At that time,the Au@Ag NPs were successfully synthesized.We realized the sensitive detection of MnO4-,Cr3+,Cd2+ in aqueous solution by Au@Ag NPs.The details are summarized as follows:1.Au@Ag NPs were synthesized by seed growth method.Under the reduction of glucose,the silver atom gradually deposited at the surfaces of gold seed.The effects of silver nitrate,glucose and ammonia on the synthesis process of Au@Ag NPs were investigated.The size,morphology,homogeneity and dispersity of as-synthesized Au@Ag NPs were characterized by UV-visible spectrophotometer,transmission electron microscope and dark field microscope.The results showed that Au@Ag NPs are uniform and have good stability.2.Au@Ag NPs were used as optical probe for MnO4-ions detection in aqueous solution.The strong oxidizing property of MnO4-can etch silver shell of Au@Ag NPs,which results in a drastic decrease of the absorption of Au@Ag NPs.Meanwhile,the color of the solution changed during this process.This proposed method also exhibited high selectivity toward MnO4-over other anions.The linear range for the MnO4-ions is 0 to 10?M,and the detection limit of the probe is as low as 70 nM.Compared with the traditional methods,the proposed method is simple and fast.The composite nanoparticles needn't modify with other small molecules.This method possesses high sensitivity and low cost.3.In this section,we use the Au@Ag NPs as optical probe for colorimetric detection of Cr3+ or Cd2+ ions.For the Cr3+,the solution color changed darker with enhanced absorbance enhancement by Chromium doping under reduction of ascorbic Acid.For the Cd2+,the solution color changed from pale yellow to pale blue with aggregation-induced absorbance quenching.For the two ions,the liner ranges were from 0 to 10 ?M.The detection limit of the method for Cr3+ions or Cd2+ions were 105 nM and 85 nM,respectively.