Stephen E. Flower

A water-soluble boronate-based fluorescent probe for the selective detection of peroxynitrite and imaging in living cells

A water-soluble boronate-based fluorescent probe was evaluated for the detection of peroxynitrite (ONOO−) in the presence of a monosaccharide. The enhanced fluorescence of the probe when bound with D-fructose was switched off in the presence of peroxynitrite. In contrast, other reactive oxygen/nitrogen species (ROS/RNS) led to only slight fluorescence decreases due to protection by an internal N–B interaction. The interaction of the probe with D-fructose not only strengthens the fluorescence signal, but also protects the boronic acid from oxidation by other ROS/RNS. Therefore, under conditions generating various ROS/RNS, the boronate-based saccharide complex preferentially reacts with peroxynitrite. The probe was used in cell imaging experiments for the detection of endogenous and exogenous peroxynitrite. The sensor displays good “on–off” responses towards peroxynitrite, both in RAW 264.7 cells and HeLa cells.

“Integrated” and “insulated” boronate-based fluorescent probes for the detection of hydrogen peroxide

Integrated and insulated boronate-based fluorescent probes have been evaluated for the detection of hydrogen peroxide in the presence of saccharides.

Diol Appended Quenchers for Fluorescein Boronic Acid

Fluorescein isothiocyanate is treated with 3-aminophenylboronic acid to provide a fluorescently tagged boronic acid derivative which is used to assess Förster resonance energy transfer (FRET) quenching upon boronate ester formation with a series of bespoke diol appended quenchers. Fluorescence spectroscopy comparison of quenching efficiency between treatment of fluorescein and its boronic acid appended congener with quencher appended diol reveals boronate ester formation (covalently linked) to be the more efficient regime and from the panel of quenchers which also included nucleosides.

Boronic acid based photoinduced electron transfer (PET) fluorescence sensors for saccharides

A simple three step synthesis was developed to provide six novel modular sensors, consisting of three para sensors, and three meta sensors with naphthalene, anthracene and pyrene fluorophores. The interaction of the six sensors with the saccharides: D-glucose, D-fructose, D-galactose, and D-mannose, were evaluated. All sensors displayed increasing fluorescence intensity upon the addition of these saccharides, with all of the sensors showing enhanced selectivity for D-glucose over D-galactose, D-fructose and D-mannose. High affinity (Kobs) was also observed for the meta sensors with respect to the para sensors. The naphthalene and anthracene meta sensors showed particularly high affinity (Kobs) for D-galactose. Circular dichroism spectroscopy was used to probe the structures of the complexes formed. Cyclic complexes were formed between all six sensors and D-glucose. Whilst naphthalene and anthracene meta sensors which displayed high affinity for D-galactose also formed cyclic complexes with that saccharide.

Hydrothermal conversion of one-photon-fluorescent poly-(4-vinylpyridine) into two-photon-fluorescent carbon nanodots

A novel two-photon-fluorescent N,O-heteroatom-rich carbon nanomaterial has been synthesized and characterized. The new carbon nanoparticles were produced by hydrothermal conversion from a one-photon-fluorescent poly(4-vinylpyridine) precursor (P4VP). The carbonized particles (cP4VP dots) with nonuniform particle diameter (ranging from sub-6 to 20 nm with some aggregates up to 200 nm) exhibit strong fluorescence properties in different solvents and have also been investigated for applications in cell culture media. The cP4VP dots retain their intrinsic fluorescence in a cellular environment and exhibit an average excited-state lifetime of 2.0 ± 0.9 ns in the cell. The cP4VP dots enter HeLa cells and do not cause significant damage to outer cell membranes. They provide one-photon or two-photon fluorescent synthetic scaffolds for imaging applications and/or drug delivery.

Biotinylated boronic acid fluorophore conjugates: Quencher elimination strategy for imaging and saccharide detection

A biotinylated boronic acid fluorophore conjugate bound to a diol-quencher via a boronic ester linkage demonstrated a fluorescence increase upon exposure to model saccharides. The sensing motif was attached to SuperAvidin microspheres where the sensing regime was imaged by fluorescence microscopy.

Colorimetric enantioselective recognition of chiral secondary alcohols via hydrogen bonding to a chiral metallocene containing chemosensor

An operationally simple colorimetric method for enantioselective detection of chiral secondary alcohols via hydrogen bonding interactions using a chiral ferrocene derivative is reported.

A simple and effective colorimetric technique for the detection of boronic acids and their derivatives

A rapid and facile TLC staining method is reported for the qualitative analysis of boronic acids and related boron-containing derivatives. A red colouration is observed when boron is present due to the formation of a boron–curcumin complex. The structure of the phenylboronic acid–curcumin complex was confirmed using single crystal X-ray diffraction data.

Analysis of protein glycation using fluorescent phenylboronate gel electrophoresis

Glycated proteins are important biomarkers for age-related disorders, however their analysis is challenging because of the complexity of the protein-carbohydrate adducts. Here we report a method that enables the detection and identification of individual glycated proteins in complex samples using fluorescent boronic acids in gel electrophoresis. Using this method we identified glycated proteins in human serum, insect hemolymph and mouse brain homogenates, confirming this technique as a powerful proteomics tool that can be used for the identification of potential disease biomarkers.

Suzuki homo-coupling reaction based fluorescent sensors for monosaccharides

Palladium catalysed, aryl boronic acid homocoupling, is explored as a fluorescence sensing regime for saccharides. The catalytic formation rate of fluorescent bi-aryls, under control of a palladium catalyst, is modulated by the presence of saccharides. The nature of the aryl group, rate of biaryl formation and limits of detection are investigated.