This review presents a general overview on the progress of NP-preparation methods and NP-surface-functionalization procedures, in order to improve the sensitivity of the immunoassays involved. Other factors that must be taken into account are the type of solid-phase substrate (e.g., NP, microtiter plate, membrane and cover glass), format (i.e. direct or indirect) and the detection mode employed in the assay. Fluorescence has been used most as the detection mode. Also widely used has been time-resolved fluorescence with lanthanide ions as probes.
Finally, our review of recent literature showed that most published immunoassays using inorganic NPs were applied to biological samples.