Signal amplification in immunoassays by using noble metal nanoparticles: a review

This review (with 147 references) summarizes the state of the art in methods for signal amplification in immunoassays by using noble metal nanoparticles (MeNPs). Following an introduction into the field, a first large section covers MeNPs as signal tracers. The next sections describes the use of MeNPs as carriers for biomolecules, and of doped, decorated or functionalized MeNPs. A next large section covers MeNPs as used in aggregation-based assays that result in a change of color or dynamic light scattering (DLS). This is followed by a discussion of MeNPs that undergo etching, size reduction, or growth and thereby change color and DLS, with subsections on methods based on etching, particle growth or particle formation. We then rview methods where MeNPs acts as catalysts (enzyme mimics), with subsections on MeNPs and on doped or composed MeNPs. A final large section discusses the synergies of MeNPs or multiple signal amplification strategies in immunoassays. Several Tables are presented that give an overview on the wealth of methods and materials. A concluding section summarizes the current status, addresses current challenges, and gives an outlook on potential future trends. Graphical AbstractNoble metal nanoparticles have been widely used as essential components of signal amplification strategies to enhance the sensitivity of the immunoassays. This review summarizes various signal amplification strategies using metal NPs serving as (a) signal tracers, (b) carriers, (c) aggregators, (d) enzyme mimics, (e) in growth or etching of NPs, and (f) in synergistic effects.