A colorimetric titration method for quantification of millimolar glucose in a pH 7.4 aqueous phosphate buffer

A TIMS-TOF mass spectrometry study of disaccharides from in situ ESI derivatization with 3-pyridinylboronate

Mobilograms of in situ ESI 3-pyridinylboronic acid tagging of isomaltose in the positive or negative mode.

Block versus Random Amphiphilic Glycopolymer Nanopaticles as Glucose-Responsive Vehicles

To explore the effect of polymer structure on their self-assembled aggregates and their unique characteristics, this study was devoted to developing a series of amphiphilic block and random phenylboronic acid-based glycopolymers by RAFT polymerization. The amphiphilic glycopolymers were successfully self-assembled into spherically shaped nanoparticles with narrow size distribution in aqueous solution. For block and random copolymers with similar monomer compositions, block copolymer nanoparticles exhibited a more regular transmittance change with the increasing glucose level, while a more evident variation of size and quicker decreasing tendency in I/I0 behavior in different glucose media were observed for random copolymer nanoparticles. Cell viability of all the polymer nanoparticles investigated by MTT assay was higher than 80%, indicating that both block and random copolymers had good cytocompatibility. Insulin could be encapsulated into both nanoparticles, and insulin release rate for random glycopolymer was slightly quicker than that for the block ones. We speculate that different chain conformations between block and random glycopolymers play an important role in self-assembled nanoaggregates and underlying glucose-sensitive behavior.

Preparation of glucose-responsive and fluorescent micelles via a combination of RAFT polymerization and chemoenzymatic transesterification for controlled release of insulin

Polymeric micelles with glucose-responsive and fluorescent features have been synthesized using a one-pot method via a combination of RAFT polymerization and chemoenzymatic tranesterification for controlled release of insulin in vitro.

Reagentless polyol detection by conductivity increase in the course of self-doping of boronate-substituted polyaniline

We report on the novel reagentless and label-free detection principle based on electroactive (conducting) polymers considering sensors for polyols, particularly, saccharides and hydroxy acids. Unlike the majority of impedimetric and conductometric (bio)sensors, which specific and unspecific signals are directed in the same way (resistance increase), making doubtful their real applications, the response of the reported system results in resistance decrease, which is directed oppositely to the background. The mechanism of the resistance decrease is the polyaniline self-doping, i.e., as an alternative to proton doping, an appearance of the negatively charged aromatic ring substituents in polymer chain. Negative charge "freezing" at the boron atom is indeed a result of complex formation with di- and polyols, specific binding. Changes in Raman spectra of boronate-substituted polyaniline after addition of glucose are similar to those caused by proton doping of the polymer. Thermodynamic data on interaction of the electropolymerized 3-aminophenylboronic acid with saccharides and hydroxy acids also confirm that the observed resistance decrease is due to polymer interaction with polyols. The first reported conductivity increase as a specific signal opens new horizons for reagentless affinity sensors, allowing the discrimination of specific affinity bindings from nonspecific interactions.

Phenylboronate-diol crosslinked glycopolymeric nanocarriers for insulin delivery at physiological pH

Research into polymers with glucose-sensitivity in physiological conditions has expanded recently due to their therapeutic potential in diabetes. Herein, to explore the glucose-responsive properties of a new polymer under physiological conditions, we synthesized an amphiphilic block glycopolymer based on phenylboronic acid and a carbohydrate, which was named poly(d-gluconamidoethyl methacrylate-block-3-acrylamidophenylboronic acid) (p(AAPBA-b-GAMA)). Based on the cross-linking between the diol groups of the carbohydrates and phenylboronic acid, the glycopolymers self-assembled to form nanoparticles (NPs). The glucose-sensitivity was revealed by the swelling behavior of the NPs at different glucose concentrations and was found to be dependent on the glucose level. The morphology of the NPs revealed by transmission electron microscopy showed that the NPs were spherical in shape with good dispersity. The cell viability of the NPs investigated by MTT assay was more than 90%, indicating that the glycopolymers had good cytocompatibility. Insulin could be loaded onto the glycopolymer NPs with high efficiency (up to 10%), and insulin release increased with enhancement of the glucose level in the medium. Such a glucose-responsive glycopolymer is an excellent candidate that holds great potential in the treatment of diabetes.

Colorimetric Sugar Sensing Using Boronic Acid-Substituted Azobenzenes

In association with increasing diabetes prevalence, it is desirable to develop new glucose sensing systems with low cost, ease of use, high stability and good portability. Boronic acid is one of the potential candidates for a future alternative to enzyme-based glucose sensors. Boronic acid derivatives have been widely used for the sugar recognition motif, because boronic acids bind adjacent diols to form cyclic boronate esters. In order to develop colorimetric sugar sensors, boronic acid-conjugated azobenzenes have been synthesized. There are several types of boronic acid azobenzenes, and their characteristics tend to rely on the substitute position of the boronic acid moiety. For example, o-substitution of boronic acid to the azo group gives the advantage of a significant color change upon sugar addition. Nitrogen-15 Nuclear Magnetic Resonance (NMR) studies clearly show a signaling mechanism based on the formation and cleavage of the B-N dative bond between boronic acid and azo moieties in the dye. Some boronic acid-substituted azobenzenes were attached to a polymer or utilized for supramolecular chemistry to produce glucose-selective binding, in which two boronic acid moieties cooperatively bind one glucose molecule. In addition, boronic acid-substituted azobenzenes have been applied not only for glucose monitoring, but also for the sensing of glycated hemoglobin and dopamine.

Differential sensing of sugars by colorimetric arrays

While the complexes between boronic acids and diols have been studied for decades, researchers continue to design new and interesting methods to use these interactions to produce saccharide sensors that are more sensitive and selective. Herein we discuss how the use of pattern-based colorimetric arrays from a collection of crossreactive sensors have been developed as new differential sensing platforms for sugars and related saccharides.

Colorimetric detection and identification of natural and artificial sweeteners

A disposable, low-cost colorimetric sensor array has been created by pin-printing onto a hydrophilic membrane 16 chemically responsive nanoporous pigments that are comprised of indicators immobilized in an organically modified silane (ormosil). The array has been used to detect and identify 14 different natural and artificial sweeteners at millimolar concentrations, as well as commonly used individual-serving sweetener packets. The array has shown excellent reproducibility and long shelf life and has been optimized to work in the biological pH regime.

Carbohydrate recognition by boronolectins, small molecules, and lectins

Carbohydrates are known to mediate a large number of biological and pathological events. Small and macromolecules capable of carbohydrate recognition have great potentials as research tools, diagnostics, vectors for targeted delivery of therapeutic and imaging agents, and therapeutic agents. However, this potential is far from being realized. One key issue is the difficulty in the development of "binders" capable of specific recognition of carbohydrates of biological relevance. This review discusses systematically the general approaches that are available in developing carbohydrate sensors and "binders/receptors," and their applications. The focus is on discoveries during the last 5 years.

Glucose-responsive micelles from self-assembly of poly(ethylene glycol)-b-poly(acrylic acid-co-acrylamidophenylboronic acid) and the controlled release of insulin

Poly(ethylene glycol)-block-poly(acrylic acid-co-acrylamidophenylboronic acid) [PEG(114)-b-(PAA(63)-co-PAAPBA(107))] was synthesized by the modification of poly(ethylene glycol)-block-poly(acrylic acid) (PEG(114)-b-PAA(170)) with 3-aminophenylboronic acid (APBA). Glucose-responsive PEG(114)-b-(PAA(63)-co-PAAPBA(107)) self-assembled into core-shell micelles with the hydrophobic core composed of PAAPBA and hydrophilic shell composed of PEG in aqueous solution. The swelling and disaggregating behaviors of micelles responding to glucose were investigated by using light scattering in aqueous solution at pH 7.4. Characterization of insulin-loaded micelles and their drug release in solutions with various glucose concentrations were further studied. The results demonstrated that the drug release rate can be controlled by variation of glucose concentration.

Development of boronic acid grafted random copolymer sensing fluid for continuous glucose monitoring

We have previously presented a microelectromechanical system (MEMS) based viscometric sensor for continuous glucose monitoring using protein Concanavalin A (Con A). To address its drawbacks, including immunotoxicity and instability issues, we have synthesized stable, biocompatible copolymers poly(acrylamide-ran-3-acrylamidophenylboronic acid) (PAA-ran-PAAPBA) for viscosity based glucose sensing. We found that PAA-ran-PAAPBA showed very high binding specificity to glucose. Several key factors such as polymer compositions, polymer molecular weights and polymer concentrations have been investigated to optimize viscometric responses. This polymer is able to detect glucose under physiological pH conditions in a reversible manner. Therefore, it has the potential to enable a highly reliable, continuous monitoring of glucose in subcutaneous tissue using the MEMS device.

A colorimetric sensor array for detection and identification of sugars

Molecular recognition of sugars and a practical method to detect and discriminate among a large number of such similar analytes remain substantial scientific challenges. We report here a low-cost, simple colorimetric sensor array capable of identification and quantification of sugars and related compounds. Fifteen different monosaccharides, disaccharides, and artificial sweeteners were differentiated without error in 80 trials. Limits of detection at pH 7.4 for glucose were <1 mM, which is below physiologically important levels.

Effect of extended conjugation with a phenylethynyl group on the fluorescent properties of water-soluble arylboronic acids

Boronic acids that change fluorescent properties upon sugar binding are very important reporter units for the development of small molecule lectin mimics (boronolectins). Aimed at developing long wavelength fluorescent boronic acid reporter compounds, we have designed and synthesized a series of boronic acid analogs 2a-d with an extended π conjugation. Such designs are based on earlier fluorescent boronic acids that change fluorescent properties upon sugar binding. Compared with the corresponding parent chromophores, these new compounds with extended conjugations show longer excitation and emission wavelengths as designed. The patterns of fluorescent changes for the new compounds are also different from that of the corresponding parent compounds.