Laser activated voltammetry: Mass transport, surface effects and analytical applications

The voltammetry of various well-characterized aqueous and nonaqueous electr ochemical systems has been studied at platinum and gold disk electrodes und er illumination from a 10 Hz pulsed Nd:YAG laser frequency doubled to opera te at 532 Mm. A simple Nemst diffusion layer model is established to quanti fy the slight enhancement in mass transport observed as a function of laser intensity in the thermoelastic region where light energy absorbed by the m etal is insufficient to cause localized melting or vaporization but does le ad to a partial thinning of the diffusion layer thickness through surface h eating/vibration. This leads to sigmoidal shaped voltammograms whilst maint aining a clean, reproducible electrode surface. Above the ablation threshol d, the minimum laser intensity required to cause electrode damage, atomic f orce microscopy (AFM) is used to probe the nature of the surface damage and its relationship to the laser intensity. The Nernst-diffusion model is ver ified by means of potential step chronoamperometric measurements in water a nd acetonitrile where good agreement with theory is seen for transport acro ss a diffusion layer of a thickness corresponding to that inferred from ste ady-state voltammetry. Applications of the laser activation technique are i llustrated by three systems found to be passivating in aqueous media; the t wo electron reduction of toluidine blue dye, iodide oxidation and the oxida tion of ferrocyanide in the presence of the brood protein, fibrinogen. In a ir cases clean, reproducible and quantitative voltammetry is seen in contra st to that observed in the absence of laser activation, demonstrating the e xcellent surface-cleaning effects of LAV.