Multifold Fluorescence Enhancement in Nanoscopic Fluorophore–Clay Hybrids in Transparent Aqueous Media

Abstract

Valuable emissive properties of organic fluorophores have become indispensable analytical tools in biophotonics, but frequently suffer from low solubilities and radiationless deactivation in aqueous media, that is, in biological ambience as well. In this report, nanoscaled dye-clay hybrids based on laponite, Na0.7 {(Li0.3 Mg5.5 )[Si8 O20 (OH)4 ]}, are taken advantage of to solubilize neutral dyes, which are natively not encountered in water. Previously reported efficiency and solubility bottlenecks of such hybrids can to a large extent be overcome by comparably simple chemical measures, as demonstrated here for two prominent examples, the fluorescent dyes Nile Red and Coumarin 153. On controlled co-adsorption of small bifunctional quaternary ammonium ions (Me3 N(+) C2 H5 OH and Me3 N(+) C2 H5 NH2 ) we observed an outright efficiency boost by an order of magnitude, and a 30-fold brightness gain. Even at higher concentrations, transparency and stability of the hybrid dispersions are retained, rendering them useful for employment as optically functional nanoparticles in bioassays and beyond.

Patterning of Nanoclays on Positively Charged Self-Assembled Monolayers via Micromolding in Capillaries

“…For fluorescence microscopy analyses, laponite was loaded with rhodamine B according to a previously published procedure . The rhodamine B-modified laponite was immobilized by MIMIC as described before.…”

“…To this end, laponite particles were loaded with Nile Red, which typically forms H-dimers on such surfaces, strongly diminishing the fluorescence quantum yield of the dye. However, upon incubation with choline, the interaction of Nile Red dimers on the laponite surface is weakened, and the H-dimers dissociate to a certain extent . In this way, a response of the surface indicating the presence of choline is generated, which is observable with fluorescence microscopy or spectroscopy.…”

“…For the loading of the laponites with dyes, the required amounts of laponite and dye were calculated according to a published procedure. , Typically, 300 mg of laponites were stirred in absolute ethanol and 480 μL of a dye stock solution (1 mmol/L) was added. After 1 h, the solution was filtered, and the laponites were dried in vacuum.…”

“…It consists of exterior [SiO 4 ] tetrahedra, sandwiching octahedral [Mg, Li (O, OH)] units organized in a so-called TOT (tetrahedral-octahedral-tetrahedral) structure. Due to the ion distribution, the 1-nm-thick and 25-nm-wide disc shaped laponite particles are negatively charged, leading to highly adsorptive behavior for a wide variety of molecules such as phthalocyanine (Pc) , or rhodamine . In addition, the negative surface charges are compensated by intercalated sodium atoms, which can be released upon dispersion in water, resulting in individual platelets and hence transparent dispersions.…”

Spectroscopic Studies of the Interactions between a Cationic Cyanine Dye and a Synthetic Phyllosilicate: From Photophysics to Hybrid Materials

“…In this case, the interlayer cations (such as sodium) balance the negative charges of the sheet (see Scheme ). Smectites, which belong to this group, are known for their ion-exchange properties with applications in many fields such as water depollution, catalysis, or drug delivery systems − The interlayer compensation cations can be replaced by a wide range of cations, either mineral or organic, such as organic cationic dyes. ,− In this case, the interactions of the clay mineral surface with the molecules of the dyes can modify their photochemistry and optical properties. ,− Recently, we have shown that phyllosilicates can be used to control the photophysics of the triarylmethane dye crystal violet . The interaction of the cationic dye, attracted by the negative octahedral charge of a commercially available synthetic 2:1 phyllosilicate (Laponite), with the platelet surface turns the nonemissive dye into a fluorescent compound .…”