Fabrication and optical stability of silanized gold nanorods as multifunctional transducers of near infrared light

We give new insight into multifunctional nanoparticles with light extinction in the therapeutic window, optical stability even on aggregation, as well as possibility of bio-conjugation. The optical response of these particles rests on gold nanorods, which interact with near infrared (NIR) light via plasmonic oscillations, i.e. a boundary effect which depends on all physiochemical conditions at the interface with their environment. Therefore their feasibility for biomedical applications is challenged by a poor definition of their dispersion medium, aggregation (e.g. inside endocytic vesicles) and shape transformations, which typically occur in the biological sample and under excitation and jeopardize their optical features. Here silanization of the gold nanorods is proposed as one effective solution to overcome these issues. A shell of porous silica confers isolation from the local environment and additional stability, and also proves suitable for PEGylation and bio-conjugation with e.g. biological macromolecules. In particular we engineer models of aggregation of these particles, in order to investigate its principal effect on their optical response. While in the absence of silica gold nanorods undergo substantial degradation of their plasmon oscillations, silanization proves excellent to maintain pristine optical properties even after critical flocculation