Biosensor technology based on the labelling entities having particle reporters provides cost competitive readily manufactured assay devices. Sub-micron particles of uniform dimension in metals, polymers, glasses, ceramics and biological structures such as phages are used as the labelling entities. Such reporter particles greatly increase the sensitivity and accuracy, and provide a variety of assay techniques for determining analyte presence in a sample. The particles may have dielectric, paramagnetic and/or phosphorescent properties, such particles are particularly useful in a variety of competition type assays. Novel phosphor and phage particles are provided for use as unique labelling entities.