Time dependent investigation of copper colloids SERS-activity

Abstract

The applicability potential of surface-enhanced Raman scattering spectroscopy strictly depends on the properties, especially the stability of the prepared substrates. In the case of copper-based substrates, the properties of the surface are variable in time therefore the age of the specific system plays a significant role in terms of the observed spectral response and the electromagnetic and chemical contribution of the enhancement. More apparent changes are in the case of copper colloidal systems than in the case of large-scaled substrates. This study aims to assess the effect of several experimental conditions such as excitation wavelength, analyte concentration, and especially ageing of the system on final SERS-activity of copper nanoparticles (CuNPs). Series of colloidal systems of CuNPs with different concentrations (from 1·10−4 to 1·10−7 mol·L−1) of a model probe 4-aminobenzenthiol (4-ABT) were prepared and characterised. All investigated experimental conditions significantly influence the resulting SERS signal, although individual conditions contribute to the signal enhancement differently. The analyte concentration mostly involved the changes of CuNPs diameters, which is then reflected in the position of surface plasmon resonance maximum by which the final enhancement is slightly variable at the level of enhancement factor of 104. This parameter can also affect the choice of excitation source. The most significant examined parameter was the age of the systems. We repeatedly observed several stages in the SERS spectra from the analyte adsorption, through stable-stated signal to system degradation. In optimal case, systems were able to exhibit SERS-activity over more than 10 h.