Surface-enhanced electrochemiluminescence with mesoporous gold: understanding the electrochemical and optical effects

Surface-enhanced electrochemiluminescence (SEECL) is a promising optical biosensing technique for ultrasensitive molecular detection in clinical diagnostics. Herein, we show that mesoporous gold (mesoAu) is an appropriate substrate for SEECL. A mesoAu electrode was fabricated with electrodeposition using polystyrene-<i>block</i>-polyethylene oxide (PS-<i>b</i>-PEO) on a silicon substrate. The electrode was characterized by scanning-electron microscopy (SEM), X-ray photo-electron spectroscopy (XPS), Brunauer-Emmett-Teller (BET) analysis, nitrogen adsorption isotherm measurement and X-ray diffraction (XRD), respectively. Spectroelectrochemical studies were performed using cyclic voltammetry (CV) and <i>i</i>-<i>t</i> amperometry, using the known ECL probe tris-2-2'-bipyridyl ruthenium [Ru(bpy)₃]²⁺. It was found that the enhancement was closely related to the pore size, with a maximum ratio of ∼80 when the diameter of the pore was tuned to ∼50 nm. By measuring the double-layer capacitance current of the non-faradaic region at different scan rates, it was shown that enhancements due to electrochemical effects and optical coupling could be studied separately. This work suggests that SEECL with mesoAu is a combination of electrochemical, optical and mass transport effects. This indicates that the careful design of the sensing interface is crucial to obtain optimal analytical performance with mesoAu-enabled SEECL bioassays.