Highly sensitive SERS behavior and wavelength-dependence charge transfer effect on the PS/Ag/ZIF-8 substrate

Abstract

In this work, the monodisperse polystyrene colloidal particles/Ag/zeolite imidazole framework (PS/Ag/ZIF-8) substrate was successfully prepared and served as SERS active substrate. The composition, structure and morphology of the PS/Ag/ZIF-8 substrates were studied by XRD, SEM, UV-Vis and XPS measurements. The main finding of this study was that the as-prepared PS/Ag/ZIF-8 substrate could exhibit outstanding SERS property when 4-mercaptobenzoic acid (4-MBA) was used as the SERS probes. The SERS mechanism was attributed to the combined effect of the electromagnetic enhancement and chemical enhancement (CT). In addition, the SERS behavior of the sandwich PS/Ag/ZIF-8 substrate exhibit a laser wavelength-dependence CT effect with changing the laser source (473 nm, 514 nm, 633 nm and 785 nm). The wavelength-dependence CT mechanism were discussed briefly in the article. The results showed that the chemical interaction in the structure is a necessary condition for occurrence of the CT. The CT process can be evaluated quantitatively by the charge transfer degree (ρ_CT). Moreover, the enhancement factor (EF) of 1.23 × 10⁶ was obtained with 4-MBA probes adsorbed on the synthesized PS/Ag/ZIF-8 substrate. More importantly, our research may open the door for developing the SERS substrate research with the well-studied metal-organic frameworks nanostructures materials.

Keywords: Charge transfer; MOF; Mechanism; SERS; Wavelength-dependence.