Thin insulating films on conductive substrates have been used for tunnel emission of hot electrons into aqueous solution. The hydrated electrons thus formed induce electrochemiluminescence (ECL) in various luminophores, e.g. rare-earth metal chelates, which can be detected in sub-nanomolar concentrations. The luminophores can be used as labels for antibodies, enabling simple and highly sensitive immunoassays. This paper compares thermal silicon dioxide, low pressure chemical vapor deposited silicon nitride, plasma enhanced chemical vapor deposited silicon dioxide and nitride, atomic layer deposited alumina, and liquid phase deposited silicon dioxide for electrodes in ECL applications. (C) 2009 Elsevier B.V. All rights reserved.