Composite electrodes for hot electron-induced electrochemiluminescence applications

The present thesis primarily focuses on the applicability of carbon black containing composite electrodes for hot electron-induced electrochemiluminescence (HECL) applications. HECL is an analytical method that utilizes electrogenerated hydrated electrons as mediators in chemical reactions that lead to luminescence, typically in the visible part of the electromagnetic spectrum. The high energy of hydrated electrons makes them the ideal chemical species for chemiluminescence reactions taking place in the liquid phase. The quantitative analysis of chemical species is typically performed by labelling the analytes with a suitable luminophore. The main advantages of HECL are sensitivity, accuracy and low-cost instrumentation when compared to similar, chemiluminescence based, methods.  The generation of hydrated electrons via electrochemical means is complicated by the narrow electrochemical window of water. There are no expected changes in the current-potential curves at high cathodic potentials. The only observed process, even at mercury electrodes, is hydrogen evolution. To circumvent problems related to the hydrogen evolution, the HECL experiments are typically carried out at insulating thin-film covered electrodes such as aluminum and silicon. The energy of the electrons at the electrode/electrolyte-interface at these materials is sensitive to the thickness of the insulating film. A variation of a few nanometers in the film thickness leads to noteworthy changes in the observed HECL emission intensity. The main applications of HECL lie in the healthcare sector where high accuracy is demanded from the analytical methods. Consequently, the traditional electrodes utilized in HECL applications have to be manufactured in a clean room environment by thin-film deposition techniques that increases the cost to run a single test.  The approach taken in the present study for decreasing the total electrode cost is the use of novel conductive composite materials as the working electrode. The introduction of conductive carbon black particles to a polymer (e.g. polystyrene) matrix makes it possible to manufacture electrodes by e.g. screen-printing method. The results presented in this thesis show that the conductive carbon containing composite materials are well suited for HECL applications. The reproducibility of HECL signal between electrodes is high and the detection limits are practically equal to what is achieved with conventional electrode materials. These pioneering studies show that the electrochemical generation of hydrated electrons is considerably easier than previously thought.