Focusing microwaves at electrodes a review: Localised microwave effects at electrochemical sensors

Microwaves hove become a versatile tool in chemical laboratories where faster processes and carefully controlled reaction conditions are desirable. The applicator for microwave-enhanced processes is usually based on a cavity system with dimensions designed to allow a good interaction of the sample and a uniformly distributed electro-magnetic wave with a typical wave length of 12 cm (at 2.45 GHz). In spite of the considerable wave length, focusing microwave energy into a very small volume can be achieved when small metal electrodes are employed. Focusing microwave energy at the tip of the metal electrode (i) allows power minimisation, (ii) introduces high temperature gradients, (iii) induces faster mass transport, and (iv) results in new localised energy dissipation phenomena based on thermal cavitation. This mini-review describes some recent advances in exploiting focused microwaves in electrochemical processes. The future limits of miniaturisation of this technology to nano-metric dimensions (e.g. for extremely localised thermally activated electroanalysis between or within living cells) are discussed.