The Highly Effecitve And Reproducible Surface Enhanced Raman Scattering Substrates Based On Noble Metal/Semiconductor: Design, Fabrication And Application For Dye Detection

Due to its ability to provide vibrational signatures associated with chemical and structural information of the analyzed object, Raman scattering is regarded as a powerful analytical tool for detecting and identifying specific targets. However, Raman scattering is very weak due to the small cross-section of molecules. The surface enhanced Raman scattering(SERS) effect can overcome this drawback and exhibit average enhancement factors(EFs) of ~106 or even greater.However, whether SERS can be applied as a practical application really depended on the SERS-active materials, the reproducibility of the fabrication of substrates and the uniformity of the SERS signals. The latter two ensured that the observed information by SERS was reliable and accurate. Although various techniques have been developed for fabricating the high-performance SERS-active substrates, some disadvantages still need to be overcome:(1) the fabrication process was often complex and time-consuming;(2) some complex and expensive instruments were required in the fabrication process;(3) the fabrication of SERS substrates with a large area was difficult. Hence, it was highly desirable to prepare the high-performance SERS-active substrates by a green, time-saving and high-throughput method.In this paper, we prepared three SERS substrates based on the noble metal-semiconductor, and investigated the SERS perfomacne of thess SERS substrates detailly. Besides, we also investigated the modulation of photoluminescence for graphene quantum dots through gamma-ray irradiation. The main results were as follows:(1) Ge was chosen because it is also an important semiconductor with narrow band-gap. The electric field intensities were simulated by assumption same diameter noble metal nanoparticles(Au or Ag) decorated on Ge or Si wafer, respectively. The simulation clearly showed that the maximum electric field intensity of noble metal/Ge substrate was the larger one. Ag/Ge and Ag/Si substrates were chosen in the experiments to verify the theoretical simulation. The Ag nanoparticles(NPs) were grown on the Ge or Si wafer by solution methods, which were served as SERS substrates in the detection of Rhodamine 6G(R6G) and 4-mercaptobenzoic acid(MBA). Both substrates showed high sensitivity and reproducibility of the Raman signals in SERS detection. Moreover, the enhancement factor(1.3 × 109) and relative standard deviation values(less than 11%) of Ag/Ge substrate were both better than those of Ag/Si(2.9 × 107 and less than 15%, respectively), which was consistent with the FDTD simulation.(2) A two-step galvanic replacement method was proposed to directly fabricate SERS substrates based on Ag-Au nanoparticles(NPs) grown on the Ge wafer. The method was green, time-saving and low-cost. Only three ingredients, AgNO3, germanium, and HAuCl4 were required in the fabrication process. Finite difference time domain(FDTD) method was employed to calculate the near-field distribution on the surface of our proposed structures. Except the remarkable SERS activity, the as-prepared SERS substrates also showed the outstanding relative standard deviation(RSD) of less than 7% for Rhodamine 6G(R6G)(1 × 10-9 M) and less than 8% for crystal violet(CV)(1 × 10-8 M) in the aqueous detection.(3) The SERS substrate based on Ag-Pt nanoparticles grown in situ on Ge wafer was prepared through a two-step galvanic replacement reaction. The fabrication process was also green, time-saving and low-cost. The Ag-Pt nanoparticles were composed of the large Ag nanoparticle covered with many small Pt nanoparticles. Compared with the single-component Ag nanoparticle, the Ag-Pt nanoparticles with larger surface area increased the surface adsorption capacity to target molecules. The SERS substrate not only shows good enhancement with enhancement factor to be 9.1 × 106, but also exhibited the outstanding relative standard deviation of less than 10% in dection of R6 G or CV aqueous solutions.(4) Graphene quantum dots(GQDs), as an important fluorescent carbon nanomaterials, have generated considerable research interest due to their fascinating merits in resistance to photobleaching, low toxicity, excellent biocompatibility, low cost, and abundance of raw materials in nature. In this study, four synthetic GQDs(represented as GQD-OH, GQD-NH2, GQD-N2H3 and m-GQDs) and one prepared carbon QDs(CQDs) were chosen as samples. Gamma-ray irradiation was employed to modulate the PL of GQDs with irradiation doses ranging from 0 to 500 k Gy. The green luminescent GQD-OH with simple compositions and defined structures was firstly employed to investigate the modulation of PL and stability of GQDs under the gamma-ray irradiation: the wavelength of GQD photoluminescence may be shifted up to 127 nm; and the intensity may increase 5 times under proper irradiation conditions. According to the results, the mechanism of the gamma-ray irradiation to the GQD-OH was proposed. Other three prepared GQDs were also investigated and demonstrated that the PL of GQDs can be modulated by controlling the irradiation conditions.