Final Report Summary - SINGLESENS (Single metal nanoparticles as molecular sensors) Optical spectroscopy of single plasmonic nanoparticles (NPs) has evolved into a recognized tool for nanoscopic sensing applications, using the sensitivity to the NP's environment, charge, size, shape, and proximity to other NPs. The goal of the SingleSens ERC project was to take advantage of the nanoparticle’s minuscule size approaching molecular dimensions in novel ways. Single particle plasmon sensors are in many ways the smallest possible giving unprecedented access to molecular events. The small size amplifies fluctuations by molecular events, allows massive parallel detection of analytes within tiny devices, and to monitor single nanoparticle formation and electrochemical surface reactions in real time. The main objectives of this project were to develop and explore single-particle plasmon spectroscopy as a novel tool to study such molecular processes. We have built setups progressing far beyond previous technology. With those we have increased time resolution, spectral sensitivity, and parallelization capability many orders of magnitude. Five years ago, collecting a single particle plasmon spectrum took several seconds and resulted in an accuracy of the peak position of more than one nanometer. Statistics were typically recorded on 10-20 particles. Now, we routinely record particle spectra in less than one millisecond, investigate 100-1000 particles within one sample and archive spectral accuracies well below 0.1nm.We have synthesized nanoparticles with optimal plasmon sensing properties, and simulated plasmon properties to guide the experiments and understand the physics behind the observed phenomena. The single-particle plasmon spectroscopy technique has been demonstrated for single protein detection, the parallel detection of many analytes in a multiplexed microfluidic device, and for biophysical studies of oscillating molecular systems. Electrochemical and biochemical applications are in the process of being published.The broad range of possible applications, some of which were not anticipated at the start of the project (e.g. drug screening) makes us considering commercialization of the developed techniques.
