We develop next-generation biosensing principles based on plasmonic nanoparticles and photonic crystals, and bound-states in the continuum (BIC). We work on label-free (direct) assays that convert molecular binding to a resonance shift that is caused by local changes in refractive index. Secondly, we develop sandwich and competition assays based on plasmon-enhanced fluorescence. Plasmon-enhanced single-molecule fluorescence enables single-molecule detection at high concentrations and on short timescales. We develop these principles toward highly sensitive, specific, and continuous biosensors for monitoring in the environment, industrial processes, and healthcare.
We investigate the coupling between single molecules and plasmons under optical excitation. This coupling modifies the properties of the molecule (e.g. enhancement of fluorescence) but also the properties of the plasmon (e.g. wavelength shifts and broadening). We use these mechanisms to enhance single-molecule signals and achieve biosensors with a high sensitivity, specificity, and signal-to-noise ratio. These studies include both numerical simulations (e.g. BEM or FDTD) and single-molecule experiments. Detailed understanding of signal-generation mechanisms enables us to achieve single-molecule detection at very high (micromolar) concentrations and on very short (microsecond) timescales.