Revisiting the use of gold and silver functionalised nanoparticles as colorimetric and fluorometric chemosensors for metal ions

•AuNPs as colorimetric and fluorimetric chemosensors.•Sensing metal ions with Au and Ag nanoparticles.•AgNPS as colorimetric and fluorimetric chemosensors.•Biomedical and environmental applications. In the last decade, metallic nanoparticles of noble metal ions as gold and silver have received much attention mainly due to their colorimetric properties. These metallic functionalised nanoparticles offered an enormous possibility of applications in many scientific and technical fields. As hybrid materials combining large surfaces with important optic and electronic properties demonstrate to be highly sensitive to the presence of metal ions in their surroundings. Special attention has being paid to the applications of gold, silver and alloys nanoparticles as fluorescent and/or colorimetric systems for detection of metals, mainly in the presence of heavy and toxic metal ions. In the present review we have focused on the advances and novelties reported in the field during the last 5 years.