Abstract
Reactive and pharmaceutical-grade heparins were used as biologically compatible reducing and stabilizing agents to photochemically synthesize colloidal gold nanoparticles. Aggregates and anisotropic shapes were obtained photochemically under UV black-light lamp irradiation (λ = 366 nm). Heparin-functionalized gold nanoparticles were characterized by Scanning Electron Microscopy and UV-Vis spectroscopy. The negatively charged colloids were used for the Surface Enhanced Raman Spectroscopy (SERS) analysis of differently charged analytes (dyes). Measurements of pH were taken to inspect how the acidity of the medium affects the colloid-analyte interaction. SERS spectra were taken by mixing the dyes and the colloidal solutions without further functionalization or addition of any aggregating agent.
Highlights
Spectroscopy methods based on Raman Effect are very useful techniques for chemical and physical analysis
The pharmaceutical-grade synthesized nanoparticles show two absorption peaks, one at 532 nm and another one at 824 nm, which means that such products are anisotropic, having a longitudinal as well as a transverse mode (Figure 1a)
The SERS spectra show that reactive-grade heparin prepared nanoparticles (RGHep lines) lead to better SERS signals than the pharmaceutical-grade heparin products (PhGHep lines), the only differences arising from the different charges of the analytes, that is, the best interactions were obtained from the oppositely charged one (Methylene Blue) while not being the case with same-charged (Bengal) and neutral (Neutral Red) molecules
Summary
Spectroscopy methods based on Raman Effect are very useful techniques for chemical and physical analysis. Much more sensitive Raman techniques have been developed such as Surface Enhanced Raman spectroscopy (SERS) This method gives almost the same information on the molecules and their local interactions as normal Raman spectroscopy but ensures a great sensitivity. The Raman scattering from a compound (or ion) adsorbed on a nanostructured metal surface (or within its proximity) can significantly increase in comparison to the anayte in solution. This phenomenon was observed first time by Fleischman in 1974 and was partially explained by Jean Maire and Van Vuyne in 1977 [1]. Black light is used to trigger heparin’s reducing action exploiting its reactivity in the UV range This photochemical method provides a good green chemistry alternative, and in addition, its setup cost is low. The effects of analyte charge and the performance of these nanoparticles for SERS are discussed
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