Fluorescence dye as novel label molecule for quantitative SERS investigations of an antibiotic.

Within this contribution, the proof-of-principle for a new concept for indirect surface-enhanced Raman spectroscopy (SERS) detection is presented. The fluorescence dye FR-530 is applied as a label molecule for the antibiotic erythromycin. The antibiotic binds directly to the label molecule. Changes within the SERS spectrum of the fluorescence dye appearing with the presence of the antibiotic are utilized for the detection and quantitative investigations of erythromycin. With the new concept of binding the label molecule directly to the analyte molecule, the application of linkage compounds like antibodies or any other recognition molecules becomes dispensable.

Spectroscopic Properties of Azobenzene-Based pH Indicator Dyes: A Quantum Chemical and Experimental Study.

The UV-visible absorption spectra of six new optical sensors based on acidochromic azobenzenes have been measured and assigned with the help of quantum chemical calculations. The investigated compounds are able to monitor the pH in the range from pH 3-10. Using the hybrid density functional PBE0 and including solvent effects with a polarized continuum model, the agreement between the experimental and theoretical UV/vis spectra of the dyes in their neutral and anionic forms is very good. The spectroscopic ππ* states, responsible for the optical properties of the sensors, are described within an accuracy of 0.1 eV. Similar accuracy is demonstrated in the nπ* states. The ππ* states can be assigned as a charge transfer from the aromatic π orbital localized in the azo-phenol moiety to the antibonding π* of the azo group. Under basic conditions, the spectrum is bathochromically shifted and more intense than in acid media. Upon substitution in the phenyl moiety, red- or blue-shifts of the UV-visible bands are observed depending on whether the substituent is electron-donor or -withdrawing, respectively. These effects are stronger at high pH values and can be rationalized in terms of the stabilization and/or destabilization of the involved frontier orbitals.

On the design of fluorescent ratiometric nanosensors.

Advances in nanoparticle technology have recently offered new tools to the bioanalytical field of research. In particular, new nanoparticle-based sensors have appeared able to give quantitative information about different species (ions, metabolites, biomolecules) in biosamples through ratiometric measurements. This article describes the methodologies developed so far in the design of such nanosensors. In particular, the different approaches to immobilize fluorescent chemosensor dyes to nanoparticles are presented. Concept designs of ratiometric nanosensors in terms of composition and architecture are also described and illustrated with examples taken from the literature.

Ratiometric pH-nanosensors based on rhodamine-doped silica nanoparticles functionalized with a naphthalimide derivative.

This paper describes the preparation of two-dye-doped silica nanoparticles for ratiometric pH measurements in the biologically relevant pH-range. While a rhodamine derivative is embedded in a silica core and used as the reference, a pH-sensitive naphthalimide dye is immobilized on the previously amino-functionalized core through two different approaches. Either the naphthalimide's carboxylic group is activated to a succinimidyl-ester to form an amide bond or the system can be built up via solid-phase organic synthesis in only two steps. Both types of nanosensors are characterized in terms of morphology (dynamic light scattering, transmission electron microscopy) and optical properties (steady-state fluorescence spectroscopy). In terms of application, e.g. reproducibility and handling of the synthesis, the first approach gave very good results with respect to size and size distribution and a pK(a) value of 6.55 was found that is comparable to the free indicator dye in solution. The solid-phase organic synthesis method proves the possibility of covalent immobilization of naphthalimides to amino-functionalized surfaces, showing the stability of the polymeric substrate and achieving comparable results for pH sensing.

Novel pH indicator dyes for array preparation via NHS ester activation or solid-phase organic synthesis.

We present two ways of fast and easy immobilisation of a naphthalimide chromophore with a pH-sensor function. The immobilised dyes exhibit absorbance and emission in the visible spectral range, large Stokes' shift, fluorescence properties that are comparable to their water-soluble form, and full reversibility in pH response.

Design of acidochromic dyes for facile preparation of pH sensor layers.

Eight new acidochromic dyes have been synthesised that can be used for optically monitoring pH in the range from 3 to 12. Their corresponding pK(a) values have been both measured and calculated theoretically by means of density functional theory. The synthesis of these new dyes is facile without the need for chromatographic purification. The dyes can be covalently linked to polymers containing hydroxyl functions such as cellulose, polyurethane hydrogel, and hydroxyalkyl methacrylate. The resulting sensor layers exhibit significant colour changes both in the UV and in the visible spectral range.

A fluorescent water-soluble naphthalimide-based receptor for saccharides with highest sensitivity in the physiological pH range.

A new water-soluble fluororeactand for the optical detection of saccharides is presented. We have combined the functional naphthalimide fluorophore with the well-known ability of boronic acids to bind to the diol moiety of saccharides. The fluororeactand exhibits sensitivity in the mM range, absorbance and emission in the visible spectral range, large Stokes' shift and fluorescence increase in the physiological pH range.