Shilei Zhu

Highly water-soluble BODIPY-based fluorescent probes for sensitive fluorescent sensing of zinc(II)

A zinc(ii) chelator bis(pyridin-2-ylmethyl)amine moiety has been incorporated into three different highly water-soluble dyes, 2-formyl-BODIPY, 2,6-diformyl BODIPY, and 2,6-diformyl-1,7-distyryl-BODIPY, at 2-position and 2,6-positions, resulting in three highly water-soluble BODIPY-based fluorescent probes A, B and C for zinc(ii) ions. Fluorescent probes A and B display sensitive fluorescent responses with significant fluorescence enhancement to zinc(ii) ions at pH 7.0 while fluorescent probe C shows two distinct measurable fluorescent signals at 521 nm and 661 nm, and displays ratiometric responses to zinc(ii) ions with fluorescence quenching at 661 nm and fluorescence enhancement at 521 nm. These three fluorescent probes exhibit excellent sensitive and selective responses to zinc(ii) ions. Intracellular zinc(ii) concentration could be monitored in cancer cells with fluorescent probe C.

BODIPY-based ratiometric fluorescent probes for the sensitive and selective sensing of cyanide ions

Three BODIPY-based ratiometric fluorescent probes (1, 2 and 3), with two being highly soluble in aqueous solution, were prepared by the condensation of 2-formyl-BODIPY dyes with 2,3,3-trimethyl-1-propyl-3H-indolium iodide and 2,3,3-trimethyl-1-(3-sulfonatepropyl)-3H-indolium for the selective and sensitive ratiometric fluorescent responses to cyanide ions.

Highly Water-Soluble BODIPY-Based Fluorescent Probe for Sensitive and Selective Detection of Nitric Oxide in Living Cells

A highly water-soluble BODIPY dye bearing electron-rich o-diaminophenyl groups at 2,6-positions was prepared as a highly sensitive and selective fluorescent probe for detection of nitric oxide (NO) in living cells. The fluorescent probe displays an extremely weak fluorescence with fluorescence quantum yield of 0.001 in 10 mM phosphate buffer (pH 7.0) in the absence of NO as two electron-rich o-diaminophenyl groups at 2,6-positions significantly quench the fluorescence of the BODIPY dye via photoinduced electron transfer mechanism. The presence of NO in cells enhances the dye fluorescence dramatically. The fluorescent probe demonstrates excellent water solubility, membrane permeability, and compatibility with living cells for sensitive detection of NO.

Glycosylation of Quinone-Fused Polythiophene for Reagentless and Label-Free Detection of E. coli

In this report, a new polythiophene interface is fabricated containing fused quinone moieties which are then glycosylated to form a carbohydrate platform for bacterial detection. Very importantly, this interface can be used for label-free and reagentless detection, both by electrochemical and Quartz Crystal Microbalance (QCM) transducers and by using the direct pili-mannose binding as well as Concanavalin A (Con A) mediated lipopolysaccharides (LPS)-mannose binding. The conductive polymers unique collective properties are very sensitive to very minor perturbations, which result in significant changes of electrical conductivity and providing amplified sensitivity and improved limits of detection (i.e., 25 cell/mL for electrochemical sensor and 50 cells/mL for QCM sensor), a widened logarithmic range of detection (i.e., 3-7 for pili-mannose binding and 2-8 for Con A mediated binding), high specificity and selectivity, and an extraordinary reliability by a mechanism of internal validation. With these analytical performances, the described biosensor is envisaged for being capable of differentiating Gram-negative bacterial strain and species, for many important applications.

Controlled Knoevenagel reactions of methyl groups of 1,3,5,7-tetramethyl BODIPY dyes for unique BODIPY dyes

Formyl groups at 6- and 2,6-positions initiated Knoevenagel reactions of the methyl groups at the 7, and 1,7-positions of 1,3,5,7-tetramethyl BODIPY dyes with aromatic aldehydes. Formation of vinyl bonds at the 7-, and 1,7-positions facilitates further Knoevenagel reactions of the methyl groups at the 3,5-positions. This approach offers fast, facile and versatile ways to prepare potential novel building blocks of BODIPY dyes for conjugated oligomers, dendrimers, and highly water-soluble, near-infrared emissive sensing materials.

Highly water-soluble neutral near-infrared emissive BODIPY polymeric dyes

Three highly water-soluble near-infrared emissive polymeric BODIPY dyes (polymers A–C) were prepared by the palladium-catalyzed Suzuki polymerization of highly water-soluble 2,6-diiodo-3,5-distyryl-BODIPY dyes with 1,4-phenyldiboronic acid and 2,7-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-9,9-di[1-[2-(2-methoxyethoxy)ethoxy]ethyl]fluorene, respectively. Partial replacement of fluorine subunits of BODIPY cores at 4,4-positions of polymer C with ethynyl subunits resulted in a highly water-soluble BODIPY polymeric dye (polymer D). Polymers A–D show solubility of at least 20 mg mL−1 in aqueous solution. For comparison purposes, polymers E and F were prepared by palladium-catalyzed Sonogashira polymerization of highly water-soluble 2,6-diiodo-3,5-distyryl-BODIPY dye with highly water-soluble 1,4-diethynylbenzene and 2,6-diethynyl BODIPY dye bearing branched oligo(ethylene glycol)methyl ether residues, respectively. Upon comparison, polymer E shows low solubility in aqueous solution (0.1 mg mL−1), whereas polymer F is almost insoluble in aqueous solution (less than 0.05 mg mL−1), but both are soluble in organic solvents such as chloroform, DMSO and DMF (at least 10 mg mL−1).

Highly Water-soluble, Near-infrared Emissive BODIPY Polymeric Dye Bearing RGD Peptide Residues for Cancer Imaging

Near-infrared emissive BODIPY polymeric dye bearing cancer-homing cyclic arginine-glycine-aspartic acid (RGD) peptide residues (polymer B) was prepared by post-polymerization functionalization of BODIPY polymeric dye bearing bromo groups through tetra(ethylene glycol) tethered spacers (polymer A) with thiol-functionalized RGD cancer-homing peptide through thioether bonds under a mild basic condition. Polymer B possesses excellent water solubility, good photostability, biocompatibility and resistance to nonspecific interactions to normal endothelial cells, and can efficiently detect breast tumor cells through specific cooperative binding of cancer-homing RGD peptides to αvβ3 integrins of cancer cells while its parent polymer A without RGD residues fails to target cancer cells.

BODIPY-Based Fluorescent Probes for Sensing Protein Surface-Hydrophobicity

Mapping surface hydrophobic interactions in proteins is key to understanding molecular recognition, biological functions, and is central to many protein misfolding diseases. Herein, we report synthesis and application of new BODIPY-based hydrophobic sensors (HPsensors) that are stable and highly fluorescent for pH values ranging from 7.0 to 9.0. Surface hydrophobic measurements of proteins (BSA, apomyoglobin, and myoglobin) by these HPsensors display much stronger signal compared to 8-anilino-1-naphthalene sulfonic acid (ANS), a commonly used hydrophobic probe; HPsensors show a 10- to 60-fold increase in signal strength for the BSA protein with affinity in the nanomolar range. This suggests that these HPsensors can be used as a sensitive indicator of protein surface hydrophobicity. A first principle approach is used to identify the molecular level mechanism for the substantial increase in the fluorescence signal strength. Our results show that conformational change and increased molecular rigidity of the dye due to its hydrophobic interaction with protein lead to fluorescence enhancement.

Functionalization of BODIPY dyes at 2,6-positions through formyl groups

A 2,6-diformyl-BODIPY dye has been modified by transforming its formyl groups at the 2,6-positions into different functional groups such as hydroxyl, carboxylic acid, cyano, nitro and oxime groups, resulting in a series of new BODIPY dyes. The optical properties of the resulting BODIPY dyes significantly depend on the functional groups at the 2,6-positions.

Photoelectrochemical properties and interfacial charge transfer kinetics of BODIPY-sensitized TiO2 electrodes

We present studies of the photoelectrochemical characteristics and interfacial charge transfer dynamics of two (4,4′-difluoro-4-bora-3a,4a-diaza-s-indacene) BODIPY dyes (BODIPY-1 and 2) attached to nanostructured TiO2 electrodes. BODIPY-1 bears two carboxylic acid groups at its 2 and 6 positions and BODIPY-2 is modified with two cyanoacetic acid groups at these positions. Photoelectrochemistry measurements show that BODIPY-2 has better photostability and device short-circuit current density than BODIPY-1 because of its broader light absorption and efficient charge injection as shown by ultrafast transient absorption spectroscopy and steady-state photoelectrochemical studies. The more efficient photocurrent generation by BODIPY-2 is also attributed to the improved redox reaction kinetics with its hole transport media, I−/I3−, in comparison with BODIPY-1.