Role Of Tio2 Nanoparticles And Uv Irradiation In The Enhancement Of Sers Spectra To Improve Levamisole And Cocaine Detection On Au Substrates

The original goal of this study was the employment of surface-enhanced Raman spectroscopy (SERS) for the analysis of real cocaine samples (containing adulterants) on composite Au-TiO2 nanomaterials to achieve low detection limits suitable for the analysis of illicit drugs and controlled substances and to exploit the photodegradation activity of TiO2 to recycle the SERS substrate for repeated analyses. The photodegradation (self-cleaning) effects of the Au-TiO2 composite nanomaterials by ultraviolet (UV) radiation are known. These effects were investigated on large-area SERS substrates immersed in the TiO2 nanoparticle aqueous suspension. The cocaine samples were measured on electrochemically gold-plated platinum targets. Surprisingly, the intensity of SERS spectra of the pure cocaine did not change after immersion in a suspension of TiO2 under UV irradiation. However, for some real cocaine samples, the overall intensity of the SERS spectra was even higher after the treatment by TiO2 and UV radiation as compared to the usual Au substrate. This unexpected signal amplification (valuable for illicit drug detection) was found to be caused mainly by the contained levamisole, which is used as a medical drug and is one of the frequent adulterants of cocaine. Both the sole effect of TiO2 on the levamisole spectrum intensity and the role of UV irradiation were inspected separately. Finally, an investigation of both the TiO2 and UV radiation treatments was performed, demonstrating (i) the necessity of both factors for selective SERS signal enhancement of the adulterant and (ii) the revision of general anticipation of the role of TiO2 in SERS systems.