Thermo Fisher Scientific IDD 1 article published in JoVE Chemistry Rapid Nanoprobe Signal Enhancement by In Situ Gold Nanoparticle Synthesis Jorge T. Dias1, Gustav Svedberg1, Mats Nystrand2, Helene Andersson-Svahn1, Jesper Gantelius1 1Division of Proteomics and Nanobiotechnology, Science for Life Laboratory, KTH Royal Institute of Technology, 2Global Research and Development, Thermo Fisher Scientific IDD In this work, a protocol for signal enhancement of nanoprobe-based biosensing is presented. The protocol is based on the reduction of chloroauric acid onto the surface of existing nanoprobes that consist of gold, silver, silica or iron-oxide nanoparticles.