Recent progress on colloidal metal nanoparticles as signal enhancers in nanosensing.

Colloidal metal nanoparticles present very special optical and electromagnetic properties at the nanoscale range. Such plasmonic properties have derived in a huge research field that encompasses the understanding of nanoparticle formation mechanisms for the ultimate goal of developing novel materials for real-life applications. Plasmonic sensing is experiencing a rapid transition by taking advantage of the characteristic properties of colloidal metal nanoparticles. However, a rational design of novel nanoplasmonic substrates, which gathers as much as the required properties for a substrate to be a 'good' sensor is critical through the development of applications that can be effectively transferred as applied technologies. Also, the chosen sensing technique is a key factor when planning the design of a new plasmonic-based sensor. Several factors such as composition, shape, size, particle interactions or stability among others will define the final quality of the nanomaterial as sensing platform. Herein, we review the latest and most promising state-of-the art of nanoplasmonic-based sensors in four differentiated areas regarding the surface-enhanced spectroscopy detection technique being LSPR-, SERS- and SEIRA-, and SEF based platforms.