Time-Resolved Thickness and Shape-ChangeQuantication using a Dual-Band NanoplasmonicRuler with Sub-Nanometer Resolution

Time-resolved measurements of changes in size and shape of nanobiological objects and layers arecrucial to understand their properties and optimize their performance. Optical sensing is particularlyattractive with high throughput and sensitivity, and label-free operation. However, most state-of-the-artsolutions require intricate modelling or multiparameter measurements to disentangle conformational orthickness changes of biomolecular layers from complex interfacial refractive index variations. Here, wepresent a dual-band nanoplasmonic ruler comprising mixed arrays of plasmonic nanoparticles withspectrally separated resonance peaks. As electrodynamic simulations and model experiments show, itenables real-time simultaneous measurements of thickness and refractive index variations in uniformand heterogeneous layers with sub-nanometer resolution. Additionally, nanostructure shape changes canbe tracked, as demonstrated by quantifying the degree of lipid vesicle deformation at the critical coverageprior to rupture and supported lipid bilayer formation. In a broader context, the presented nanofabricationapproach opens the door to multimodal nanoplasmonic optical sensing.