Abstract
This paper presents the synthesis of silver nanoparticles (AgNPs) functionalized with fluorescent molecules, in particular with xanthene-based dyes, i.e., fluorescein isothiocyanate (FITC, λmax = 485 nm) and rhodamine B isothiocyanate (RITC, λmax = 555 nm). An in-depth characterization of the particle–dye systems, i.e., AgNPs–RITC and AgNPs–FITC, is presented to evaluate their chemical structure and optical properties due to the interaction between their plasmonic and absorption properties. UV–Vis spectroscopy and the dynamic light scattering (DLS) measurements confirmed the nanosize of the AgNPs–RITC and AgNPs–FITC. Synchrotron radiation X-ray photoelectron spectroscopy (SR-XPS) was used to study the chemical surface functionalization by structural characterization, confirming/examining the isothiocyanate–metal interaction. For AgNPs–RITC, in which the plasmonic and fluorescence peak are not superimposed, the transient dynamics of the dye fluorescence were also studied. Transient absorption measurements showed that by exciting the AgNPs–RITC sample at a wavelength corresponding to the AgNP plasmon resonance, it was possible to preferentially excite the RITC dye molecules attached to the surface of the NPs with respect to the free dye molecules in the solution. These results demonstrate how, by combining plasmonics and fluorescence, these AgNPs can be used as promising systems in biosensing and imaging applications.
Highlights
The interaction of organic molecules with metal nanoparticles (NPs) is of central importance for a large number of applications in several fields, such as chemical and biological sensing [1,2,3,4], optics [5,6,7], energy [8,9,10,11], catalysis [12,13,14,15], and nanomedicine [16,17,18,19]. Many of these applications are based on the effect of the localized surface plasmon resonance (LSPR) on the absorption, emission, and scattering of molecules attached to or in close vicinity to the NP surface [20,21,22,23]
Part of the reason for this apparent contradiction is that the interaction between fluorophores and the NP depends on the size and shape of the NPs, the distance of the fluorophore from the surface of the NPs, the orientation of the fluorophore dipole moment, and the overlap between the emission spectrum of the fluorophore and the plasmon resonance spectral feature of the NP [34,35,36]
This paper focuses on the synthesis of AgNPs capped by fluorescein isothiocyanate (FITC) or rhodamine B isothiocyanate (RITC)
Summary
The interaction of organic molecules with metal nanoparticles (NPs) is of central importance for a large number of applications in several fields, such as chemical and biological sensing [1,2,3,4], optics [5,6,7], energy [8,9,10,11], catalysis [12,13,14,15], and nanomedicine [16,17,18,19] Many of these applications are based on the effect of the localized surface plasmon resonance (LSPR) on the absorption, emission, and scattering of molecules attached to or in close vicinity to the NP surface [20,21,22,23]. The deep characterizations of these nanosystems allowed us to clarify the chemical structure and eValuate the optical properties due to the direct interaction between plasmonic nanoparticles and fluorescent dyes
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