Polyoxometalates: formation, structures, principal properties, main deposition methods and application in sensing

Today, sensing represents one of the key topics in current science and technology. Polyoxometalates (POMs), which are defined as early transition metal clusters, are considered as one of the most growing fields of research and development in sensing. This paper discusses the promising prospects of POMs in sensing. The paper starts with brief definitions about the formation of POMs. The two basic structures of POMs, Keggin and Dawson, as well as some combined structures are discussed. The interesting properties of POMs particularly as acid catalysts, in medicine, in redox chemistry and in magnetism are briefly mentioned. The main methods used for the deposition of POMs on solid supports (substrates) including chemisorption, electrodeposition, encapsulation in polymers and sol-gels, immobilization using the Langmuir-Blodgett process, layer by layer assemblies as well as deposition via formation of hybrid POM-organic moieties are discussed with their advantages and disadvantages. Finally, the potential applications of immobilized POMs on solid substrates as sensors for the detection and determination of analytes both in liquid and in the gas phase are addressed and compared.