Time-Resolved Thickness and Shape-Change Quantification using a Dual-Band Nanoplasmonic Ruler with Sub-Nanometer Resolution

Time-resolved measurements of changes in the size and shape of nanobiological objects and layers are crucial to understand their properties and optimize their performance. Optical sensing is particularly attractive with h i g h throughput and sensitivity, and label-free operation. However, most state-of-the-art solutions require intricate modeling or multi-parameter measurements to disentangle conformational or thickness changes of biomolecular layers from complex interfacial refrac t i v e index variations. Here, we present a dual-band nanoplasmonic ruler comprising mixed arrays of plasmonic nanoparticles with spectrally separated resonance peaks. As electrodynamic simulations and model experiments show, the ruler enables real-time simultaneous measurements of thickness and refractive index variations in uniform and heterogeneous layers with sub-nanometer resolution. Additionally, nanostructure shape changes can be tracked, as demonstrated by quantifying the degree of lipid vesicle deformation at the critical coverage prior to rupture and supported lipid bilayer formation. In a broader context, the presented nanofabrication approach constitutes a generic route for multimodal nanoplasmonic optical sensing.

Automated summary

This paper presents a dual-band nanoplasmonic ruler that enables real-time simultaneous measurements of thickness and refractive index variations in uniform and heterogeneous layers, as well as tracking shape changes of nanostructures. The ruler offers sub-nanometer resolution and label-free operation, making it an important tool for nanobiological research and applications.