Critical Effect of Film Thickness on Preconcentration Electroanalysis with Oriented Mesoporous Silica Modified Electrodes

Electrogenerated silica thin films exhibiting a regular hexagonal packing of vertically-aligned mesopore channels are promising for preconcentration electroanalysis. This work demonstrates the critical role of film thickness on their sensing performance using paraquat as a model analyte, based on mesoporous silica films prepared by electrochemically assisted self-assembly performed for various deposition times. Films prepared with too short synthesis times (<10s) led to deposits covering partially the electrode surface and suffered from rather poor sensing performance. Then, uniformly deposited films were obtained (between 10 and 15s), and sensitivity rose up by increasing deposition times, whereas some limitations started to occur with much thicker films (>15s deposition times) as a result of less electrochemically accessible paraquat accumulated far away from the electrode surface and restricted mass transport through the whole film thickness. These limitations were also confirmed on the basis of multi-layered mesoporous silica films, suggesting a behavior that might be typical for other types of film-modified electrodes.