Ultrahigh surface sensitivity of deposited gold nanorod arrays for nanoplasmonic biosensing

The biosensing performance of plasmonic nanostructures critically depends on detecting changes in the local refractive index near the sensor surface, which is referred to as surface sensitivity. For biosensing applications at solid-liquid interfaces, recent efforts to boost surface sensitivity have narrowly focused on laterally isotropic nanostructures, while there is an outstanding need to explore laterally anisotropic nanostructures such as nanorods that have distinct plasmonic properties. Herein, we report the development of plasmonic gold nanorod (AuNR) arrays that exhibit ultrahigh surface sensitivity to detect various classes of biomacromolecular interactions with superior biosensing performance. A colloidal deposition strategy was devised to fabricate AuNR-coated glass substrates, along with experimental measurements and analytical calculations to investigate how nanorod dimensions and local dielectric environment affect plasmonic properties. To validate the sensing concept, real-time biosensing experiments involving protein adsorption and peptide-induced vesicle rupture were conducted and revealed that rationally tuning nanorod dimensions could yield AuNR arrays with the highest reported degree of surface sensitivity compared to a wide range of plasmonic nanostructures tested in past studies. We discuss plasmonic factors that contribute to this ultrahigh surface sensitivity and the measurement capabilities developed in this study are broadly extendable to a wide range of biosensing applications.