posted on 2020-12-28, 06:05authored byHui Xu, Leah Beck Casabianca
Fluorescent
dyes and nanoparticles (NPs) have been widely used
together to make novel biosensors, taking advantage of their unique
characteristics. It is crucial to have techniques that enable us to
gain detailed and high-resolution information regarding the interaction
between NPs and fluorescent dyes. In this work, we chose rhodamine
B (RhB) and amidine- and carboxylate-modified polystyrene (CML) NPs
as models and employed both NMR (1H and STD-NMR) and optical
(UV–vis and fluorescence) techniques to investigate the interaction
between NPs and fluorescent dyes. From UV–vis and fluorescence
spectroscopy, we see that there are larger red shifts when rhodamine
B binds to carboxylate-modified polystyrene NPs than amidine-modified
NPs. Correspondingly, RhB has broader NMR peaks and a larger STD effect
when binding to CML NPs than amidine NPs. Results from these two techniques
validate each other. It is notable that the NMR techniques provide
more reliable data than UV–vis and fluorescence methods. Moreover,
we show that NMR techniques, especially STD-NMR, can provide more
atomic-level binding geometry information. The higher STD effect of
the smaller aromatic ring of RhB implies that this aromatic ring is
closer to the surface of NPs when binding to polystyrene NPs.