C shell coated Ag nanoparticles-based substrates for surface-enhanced Raman scattering

Ag is the most common surface-enhanced Raman scattering(SERS) active element because of its great enhancement ability in the visible spectrum region.However,Ag has its serious drawbacks as SERS substrate:bad chemical stability and biological compatibility.In order to overcome these disadvantages,we propose a new kind of SERS-active Ag substrate in this work,C shell coated Ag(Ag@C) nanoparticles.Ag nanoparticles were prepared by Lee′s method and then C shells were coated on them in hydrothermal condition.To characterize the prepared core-shell nanoparticles,UV-vis absorption spectra,transmission electron micrograph(TEM) and SERS spectra are used.UV-vis absorption spectra show that when the Ag nanoparticles are not coated with C shell,the highest absorption peak is located at 417 nm,corresponding to the typical absorption band of Ag nanoparticles.As the Ag nanoparticles in the same size are coated with C shell,the peak is red-shifted to 426 nm due to the variation of dielectric constant induced by the presence of C shell.The results of the SERS experiment show that the SERS intensities of Rhodamine 6G(R6G),crystal violet(CV) and malachite green(MG) in Ag@C suspension can be significantly increased,as compared with that in Ag colloids.In addition,the variations of the intensities of different vibration bands in SERS spectra are distinguished.All the results indicate that extra enhancement should be attributed to chemical enhancement.The newly developed substrate has better chemical stability and biological compliance due to the presence of C.So the Ag@C nonoparticles are the potential SERS-active substrates.