Advancing Thermoplasmonic Sensing: Gold Nanobypiramis for Enhanced Light-to-Heat Conversion

Abstract

Thermoplasmonic detection is a newly emerging application of the rapidly growing and promising field of thermoplasmonics. In this context, this work aims to provide an in-depth evaluation of thermoplasmonic performances of gold nanobipyramids (AuBPs) in colloidal solution as well as immobilized onto a filter paper substrate, leading thus to efficient and sensitive thermoplasmonic detection of simple and complex molecules. Concretely, AuBPs in aqueous solution with optical responses in and out of resonance with the 808 nm laser line were synthesized and their intrinsic light-to-heat conversion performances were assessed, resulting in photothermal efficiencies (η) up to 74 %. Next, the colloidal AuBPs were functionalized with 4-mercaptobenzoic acid (4-MBA) – as a simple small molecule. Consequently, η decreased by up to 4 %. Further, after their immobilization of Whatman No. 1 filter paper through immersion, their optical properties and intrinsic thermoplasmonic activity were preserved. To test the thermoplasmonic detection capabilities of the plasmonic paper, 4-MBA and thiol-polyethylene glycol-amine - as a thermo-sensitive complex polymer, were tested. Following the functionalization of the plasmonic paper, the photothermal activity was significantly decreased causing an increase in the cooling time constant, thus both 4-MBA and thiolated PEG were evidenced via thermoplasmonic detection. Moreover, a LOD of 0.19 nM and LOQ of 0.58 nM were determined for 4-MBA, proving the high biosensing efficiency of the plasmonic paper. Hence, these results contribute to the consolidation of the versatile thermoplasmonic detection of both simple and complex interactions, being a stepping stone in the development of simple and efficient thermoplasmonic nanosensors.