Electrochemical characterization of the clay-enhanced luminol ecl reaction

Clay modified electrodes were prepared with iron-containing clay particles (montmorillonite K10) and characterized for their ability to promote electrogenerated chemiluminescence (ecl) in a solution containing luminol and hydrogen peroxide. Electrochemical impedance spectroscopic (EIS) measurements showed that the charge-transfer resistance measured for the clay electrode decreased systematically with the addition of luminol or H₂O₂, leading to a linear relationship between the exchange current and the concentration of H₂O₂ or luminol in the region where [luminol]/[H₂O₂] or [H₂O₂]/[luminol] < 1. Analysis of the parallel conductance and capacitance showed that the iron species contained in the clay particles behaved as an efficient electron mediator for the luminol ecl reaction and the content of the iron species was roughly 40 ± 20 mg of clay. This clay-enhanced reaction showed potential for the detection of glucose after further modification with glucose oxidase (GOx). However, a gradual decay in the ecl signal was noted when the luminol was not immobilized. By using aminopropyltrimethoxysilane as an anchoring agent, a rapid and stable ecl response to glucose resulted and persisted for several minutes. Further attempts to enhance the electrode response to glucose were made by using fluorescein as an energy transfer mediator. The quantum efficiency of this energy-transfer reaction was about 1%. This low yield was tentatively ascribed to a light scattering or absorption by the enzyme layer.