Multilayer rhodamine

Figure 5.25 — Flow-through ion-selective optrode based on a multilayer lipidic membrane prepared by the Langmuir-Blodgett method. (A) Cross-sectional view of the composite six-layer membrane (four layers of arachidic acid/ valinomycin covered by an arachidic acid and rhodamine dye bilayer). (B) Optical arrangement integrated with the sensor, which is connected to a flow system. LS light source Ml and M2 excitation and emission monochromator, respectively FI and F2 primary filters M mirror LB lipid-sensitive membrane in a glass platelet FC flow-cell A amplifier D display P peristaltic pump. (Reproduced from [107] with permission of the Royal Society of Chemistry).

The clear transition in the polarization behaviour that occurs at about 6 pM shows that the structure of the interface has changed. It is likely that this corresponds to reaching a critical packing density at which a change of phase takes place and the adsorbed layer corresponds to a collection of dye dimers at the interface. The formation of multiple layers has been observed with spin-coated films although multilayers of Rhodamine B have been deposited from solution without a change being observed in the layer structure. Similarly the predominance of dimers at interfaces has been inferred previously but in the current situation we are able to observe the transition between monomers and dimers at the interface. 

The multilayer coating of particles and formation of ultrathin microcapsules were verified by confocal laser scanning microscopy (CLSM, Leica) and atomic force microscopy (AFM, NanoScope). For AFM measurements, a drop of each sample was deposited onto the silicon support (with a PEl/PSS sublayer) and dried. For CLSM analysis, the coated particles and multilayer capsule suspensions were preliminary colored with rhodamin C. 

Four (PtS/AlA) bilayers were formed on the calcium carbonate cores as described above. The initial cores are monodisperse and have a spherical form with the diameter of approximately 3 pm (Fig. la). A direct evidence for polyelectrolyte (PtS/AlA)4 coating of the matrix is provided in the corresponding fluorescence image (Fig. lb). It shows the distribution of fluorescence due to rhodamin C, which is adsorbed in the polyelectrolyte shell. The appearance of fluorescent rings confirms that the dye molecules interact only with the (PtS/AlA)4 multilayer coating and do not penetrate into the interior of the CaC03 cores. The multilayer coatings on the carbonate cores were stable for several days when stored in the aqueous medium at pH 5.5. 

Cross section Layer structure Proof of similarity or dissimilarity for multilayered flakes even white house paints can be studied by staining with rhodamine and observing with a fluorescence microscope 45... 

Finally, studies of the Forster resonance energy transfer between 6-carboxyfluorescein (6-CF) and rhodamine B-labeled melamine formaldehyde particles covered by PAH/PSS multilayers showed that 6-CF interacts with PAH when the outer polyelectrolyte layer is PAH [96] upon increasing the 6-CF concentration, an increase of the fluorescence intensity is observed only above a critical concentration, assumed to correspond to the saturation of the charged groups of PAH by the anionic 6-CF. This phenomenon has been used to titrate the number of amino sites of PAH not interacting with PSS in the polyelectrolyte multilayer film it has been estimated as 1.6/nm. ... 

In contrast, much more studies have been devoted to the ditfusion of small molecules in the multilayers, because of its importance in applications like permeation membranes or biosensing. Both IR spectroscopy [316] and fluorescence measurements [317] have shown the diffusion of protons in the multilayers, and thus an influence of the pH of the outer solution even far inside the films. The influence of water on the thickness of the multilayers is also well-documented [111,318]. Diffusion of radiolabeled salt ions has also been measured [125,312], Voltamperometry showed that PAH/PAA films had little effect on the diffusion of Fe(CN)g , but that PAH/PSS films could hinder its transport [116], 6-CF [96], acridine orange [81], daunomycin [251], 2 -3 cyclic adenosine monophosphate [252], bisulfite [313], and different diazonium salts [147,313] have been shown to permeate deeply in multilayers built by ESA. Immunoglobulin G (IgG) could permeate or not in a superlattice made of anti-IgG layers and PAH/PSS spacer layers, depending on the thickness of the spacer layer. The diffusion constants of rhodamine and of 2,2,6,6,-tetramethyl-4-piperidinol-l-oxide (TEMPOL) in PAH/PSS multilayers have been quantified [113,114],... 

Caruso, F., Donath, E., Mohwald, H. Influence of polyelectrolyte multilayer coatings on forster resonance energy transfer between 6-caiboxyfluorescein and rhodamine b-labeled particles in aqueous solution. J. Phys. Chem. B 102, 2011-2016 (1998)... 

---