Enhancement of Molecular Fluorescence near the Surface of Colloidal Metal Films

Abstract

Fluorescence enhancement was studied on silver colloidal metal films (CMFs) using two systems: (1) Langmuir--Blodgett monolayers of fluorescein-labeled phospholipids separated from the surface of the films by spacer layers of octadecanoic acid and (2) biotin--fluorescein conjugates captured by avidin molecules adsorbed on top of a multilayer structure formed by alternating layers of bovine serum albumin--biotin conjugate (BSA--biotin) and avidin. The dependence of fluorescence intensity on the number of lipid or protein spacer layers deposited on the surface of the CMF was investigated. The results demonstrate the requirement for adsorbate location within the region between Ag particles for maximal enhancement. The density of avidin molecules on the surface of the BSA--biotin/avidin multilayers adsorbed on the CMF was also determined. A procedure for forming a rigid, uniform silica layer around the Ag particles on the CMF is described. The layer protects the particles from undesirable chemical reactions such as etching by halide ions, for example, and provides the requisite stability for bioanalytical applications. Colloidal films composed of Ag particles covered by approximately 10-nm-thick silica layers were tested for fluorescence enhancement using goat immunoglobulin and a conjugate of rabbit anti-goat immunoglobulin with 6-(N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)-amino)hexanoate. An enhancement factor of approximately 20 was obtained.

Polyelectrolyte Layer-by-Layer Assembly To Control the Distance between Fluorophores and Plasmonic Nanostructures

“…The ratio of fluorescence quantum yields in the presence and absence of metal is interrelated as (13) The changes in the rates of emission (N r ) and excitation (N ex ) as a function of the metalfluorophore distance (d) could be written as (14) (15) R r and R ex are the characteristic distances over which N r and N ex decrease to 1/e exponentially. The measured emission intensity with (I m ) or without (I 0 ) metal could be related as (16) Combining eqs 13-16, the total fluorescence intensity could more explicitly be written as (17) We analyzed our experimental steady-state intensities and fluorescence lifetimes data of SRB at various distances from the plasmonic metal-nanostructured surfaces. By fitting the experimental steady-state and time-resolved data with eq 17, the values of the free parameters , R r = 17 nm, and R ex = 5 nm were obtained.…”

“…Because of these applications, it is important to understand these interactions in terms of the effects of chemical nature, size, shape of the nanostructure, and its distance from the interrogating fluorophore. [15][16][17][18][19] A detail understanding of the MEF and its distance dependence nature is vital for its potential application in biomedical sensing. [20][21][22] Layer-by-layer (LbL) assembly [23][24][25][26][27][28][29][30][31][32][33][34][35][36] is based on the sequential adsorption of polycations and polyanions from dilute aqueous solution onto a solid substrate as a consequence of the electrostatic interaction and complex formation between oppositely charged polyelectrolytes.…”

Exciton-plasmon coupling interactions: from principle to applications

“…When the incident light is irradiated onto the surface of the metal nanostructure, it will react with the subwavelength metal and the fluorescent groups are adsorbed on the metal surface. The metal-generated SPs can greatly increase the luminous intensity of the fluorescent substance [180]. The enhancement of the local electric field is due to the fact that the optical cross-section of the gold and silver subwavelength particles is many times larger than the geometric scattering cross-section [181].…”

Untitled

“…Following passage of the current, the silver structures on glass were soaked in 10 µM FITC-HSA overnight at 4°C, which is thought to result in a monolayer of surface bound HSA [22,23].…”