Fabrication and characterization of vacuum deposited fluorescein thin films

Simple vacuum evaporation technique for deposition of dyes on various solid surfaces has been developed. The method is compatible with conventional solvent-free nanofabrication processing enabling fabrication of nanoscale optoelectronic devices. Thin films of fluorescein were deposited on glass, fluorine-tin-oxide (FTO) coated glass with and without atomically layer deposited (ALD) nanocrystalline 20 nm thick anatase TiO2 coating. Surface topology, absorption and emission spectra of the films depends on their thickness and the material of supporting substrate. On a smooth glass surface the dye initially formes islands before merging into a uniform layer after 5 to 10 monolayers. On FTO covered glass the absorption spectra are similar to fluorescein solution in ethanol. Absorption spectra on ALD-TiO2 is red shifted compared to the film deposited on bare FTO. The corresponding emission spectra at {\lambda} = 458 nm excitation show various thickness and substrate dependent features, while the emission of films deposited on TiO2 is quenched due to the effective electron transfer to the semiconductor conduction band.Comment: 24 pages including 5 figure

Siderophore-based detection of Fe(iii) and microbial pathogens

Siderophores are low-molecular-weight iron chelators that are produced and exported by bacteria, fungi and plants during periods of nutrient deprivation. The structures, biosynthetic logic, and coordination chemistry of these molecules have fascinated chemists for decades. Studies of such fundamental phenomena guide the use of siderophores and siderophore conjugates in a variety of medicinal applications that include iron-chelation therapies and drug delivery. Sensing applications constitute another important facet of siderophore-based technologies. The high affinities of siderophores for both ferric ions and siderophore receptors, proteins expressed on the cell surface that are required for ferric siderophore import, indicate that these small molecules may be employed for the selective capture of metal ions, proteins, and live bacteria. This minireview summaries progress in methods that utilize native bacterial and fungal siderophore scaffolds for the detection of Fe(III) or microbial pathogens.Massachusetts Institute of Technology. Dept. of Chemistr

Influences of Acid on Molecular Forms of Fluorescein and Photoinduced Electron Transfer in Fluorescein-Dispersing Sol-Gel Titania Films

Fluorescein-dispersing titania gel films were prepared by the acid-catalyzed sol-gel reaction using a titanium alkoxide solution containing fluorescein. The molecular forms of fluorescein in the films, depending on its acid-base equilibria, and the complex formation and photoinduced electron transfer process between the dye and titania surface were investigated by fluorescence and photoelectric measurements. The titanium species were coordinated to the carboxylate and phenolate-like groups of the fluorescein species. The quantum efficiencies of the fluorescence quenching and photoelectric conversion were higher upon excitation of the dianion species interacting with the titania, i.e. the dye-titania complex. This result indicated that the dianion form was the most favorable for formation of the dye-titania complex exhibiting the highest electron transfer efficiency. Using nitric acid as the catalyst, the titania surface bonded to the fluorescein instead of the adsorbed nitrate ion during the steam treatment. The dye-titania complex formation played an important role in the electron injection from the dye to the titania conduction band.ArticlePHOTOCHEMISTRY AND PHOTOBIOLOGY. 90(4):747-759 (2014)journal articl

Photoelectrochemical properties of dye-dispersing allophane–titania composite electrodes

Dye-dispersing allophane-titania composite electrodes were prepared from titanium alkoxide sols containing dye and allophane. The photoelectric conversion properties of the electrodes were investigated by photoelectrochemical measurements. The photocurrent values in the UV range decreased with an increase in the allophane content, whereas those in the visible range were increased by adding 1.0% (Al/Ti ratio) allophane. As a small amount of allophane nanoparticles were highly dispersed in the titania electrodes, the dye molecules were dispersed in the electrodes without decreasing the efficiency of the electron injection from the dye to the titania conduction band. The dye molecules dispersed on the titania nanoparticle surface were capped with allophane nanoparticles which prevented desorption. The dye molecules strongly interacted with the titania nanoparticle surface and efficiently injected the excited electrons into the titania conduction band. (C) 2015 Elsevier B.V. All rights reserved.ArticleAPPLIED CLAY SCIENCE. 107:138-144 (2015)journal articl

A novel fluorescein-bisphosphonate based diagnostic tool for the detection of hydroxyapatite in both cell and tissue models

Abstract A rapid and efficient method for the detection of hydroxyapatite (HAP) has been developed which shows superiority to existing well-established methods. This fluorescein-bisphosphonate probe is highly selective for HAP over other calcium minerals and is capable of detecting lower levels of calcification in cellular models than either hydrochloric acid-based calcium leaching assays or the Alizarin S stain. The probe has been shown to be effective in both in vitro vascular calcification models and in vitro bone calcification models. Moreover we have demonstrated binding of this probe to vascular calcification in rat aorta and to areas of microcalcification, in human vascular tissue, beyond the resolution of computed tomography in human atherosclerotic plaques. Fluorescein-BP is therefore a highly sensitive and specific imaging probe for the detection of vascular calcification, with the potential to improve not only ex vivo assessments of HAP deposition but also the detection of vascular microcalcification in humans

Development and Applications of Chemometric Methods for Spectral Deconvolution

Chemometric methods are very useful in analyzing complex mixtures. In this thesis two methods are presented that allow resolution of overlapping spectra from mixtures without knowledge of the pure component spectra. It also includes applications of these methods, in which the spectroscopic properties of the fluorescein system are characterized.<p /> The first method is applicable to samples that contain interacting components and is used to study thermodynamic equilibria. It uses the equilibrium expression relating the components and a prerequisite for this method is that the equilibrium expression is known. If the exact expression is not known, it might be used to distinguish between different equilibrium models. The method is easy to use and gives unique solutions.<p /> The other method is based on the Procrustes rotation of matrices. It requires that two kinds of spectra, composed of the same spectral profiles but different intensities of the components, can be measured on each sample. An advantage of this method is that it is not restricted to samples that contain interacting components, and requires no knowledge of equilibrium expression. The solution is also always found in a single step by diagonalizing one matrix.<p /> Using these two techniques, we have characterized the spectroscopic properties of fluorescein. The protolytic equilibrium constants that relate the four protolytic forms of fluorescein and the absorption spectra of the four protolytic species are determined by the equilibrium constraint method. The Procrustes rotation method is used to determine the fluorescence excitation and emission spectra of the fluorescein mono- and dianion. The methods are also used to study the changes of the spectroscopic properties of fluorescein upon attachment to nucleic acids