Lipophilic Polymer Membrane Optical Sensor with a Synthetic Receptor for Saccharide Detection

Non-Enzymatic Phenylboronic Acid-Based Optode Membrane for Glucose Monitoring in Serums of Diabetic Patients and in the Culture Medium of Human Embryos

Monitoring glucose levels is important not only for diabetics, but also for tracking embryonic development in human embryo culture media. In this study, an optochemical sensor (glucose-selective polymer membrane) was fabricated for the determination of glucose in serum from diabetic patients and the culture media of human embryos. The optode membranes were formulated using polyvinyl chloride (PVC) as the polymer matrix and 4',5'-dibromofluorescein octadecyl ester (ETH 7075) as the chromoionophore. The sensitivity of the optode membranes was optimized using two different plasticizers (tricresyl phosphate-TCP and nitrophenyloctyl ether-NOPE) and three ionophores (nitrophenylboronic acid-NPBA, trifluorophenyboronic acid-TFPBA, 4'-nitrobenzo-15-crown-5) and tested for glucose detection. The best optode membrane was formulated from 49.5% PVC, 49.5% TCP, 1% NPBA, and 1% ETH 7075. It showed a linear dynamic range of 10^-3 M to 10^-1 M, with a detection limit of 9 × 10^-4 M and a response time of 2 min. The detection mechanism involves H-bonding between NPBA and glucose, which was confirmed by Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR). The reaction also involves the formation of boronate esters in basic media with deprotonation of the chromoionophore (ETH 7075), leading to a decrease in UV-Vis absorbance at λmax = 530 nm. The membrane optode was used for glucose determination in synthetic culture medium, commercial embryo culture medium (GLOBAL^® TOTAL^® W/HEPES), and serum from normal and diabetic patients, showing good accuracy and precision of the optode.

Blood sorbitol measurement in diabetic rats treated with an aldose reductase inhibitor using an improved fiber-optic sorbitol biosensor

Sorbitol is known as a biomarker for the evaluation of the progress of diabetic complications. We have developed a sorbitol biosensor using an optical fiber for rapid diagnosis and pathological evaluation of diabetic complications. In this paper, we measured blood sorbitol in diabetic rats using an improved biosensor, and discussed the effectiveness of the developed biosensor and the significance of sorbitol measurement. In order to investigate the effectiveness of the developed biosensor, the blood sorbitol level of type II diabetic rats prepared by streptozotocin administration was measured with the developed sensor. The values of sorbitol were highly correlated with the values measured by the F-kit of food analysis and that we confirmed the sorbitol concentration could be quantified using the developed biosensor. Furthermore, the aldose reductase inhibitor "eparlrestat", which is a therapeutic drug that suppresses the accumulation of sorbitol, was administered to diabetic rats, and the blood sorbitol level was measured with the developed biosensor. As a result, the blood glucose level was high in both the treated group and the non-treated group, but the blood sorbitol level in the treated group decreased. The results suggest that the measurement of the sorbitol level with the developed biosensor in addition to the blood glucose level enables evaluation of complications like diabetic neuropathy. In the future, we expected that the developed sorbitol biosensor will be miniaturized, the pretreatment method for blood samples will be simplified, and it will be applied to the development of therapeutic agents for diabetic complications and personalized medicine.

Molecular Design of a New Diboronic Acid for the Electrohydrodynamic Monitoring of Glucose

A new dicationic diboronic acid structure, DBA2+, was designed to exhibit good affinity (K_d ≈1 mm) and selectivity toward glucose. Binding of DBA2+ to glucose changes the pK_a of DBA2+ from 9.4 to 6.3, enabling opportunities for detection of glucose at physiological pH. Proton release from DBA2+ is firmly related to glucose concentrations within the physiologically relevant range (0-30 mm), as verified by conductimetric monitoring. Negligible interference from other sugars (for example, maltose, fructose, sucrose, lactose, and galactose) was observed. These results demonstrate the potential of DBA2+ for selective, quantitative glucose sensing. The nonenzymatic strategy based on electrohydrodynamic effects may enable the development of stable, accurate, and continuous glucose monitoring platforms.

A fiber-optic sorbitol biosensor based on NADH fluorescence detection toward rapid diagnosis of diabetic complications

Accumulation of sorbitol in the tissue is known to cause microvascular diabetic complications. In this paper, a fiber-optic biosensor for sorbitol which is used as a biomarker of diabetic complications was developed and tested. The biosensor used a sorbitol dehydrogenase from microorganisms of the genus Flavimonas with high substrate specificity and detected the fluorescence of reduced nicotinamide adenine dinucleotide (NADH) by the enzymatic reaction. An ultraviolet light emitting diode (UV-LED) was used as the excitation light source of NADH. The fluorescence of NADH was detected using a spectrometer or a photomultiplier tube (PMT). The UV-LED and the photodetector were coupled using a Y-shaped optical fiber. In the experiment, an optical fiber probe with a sorbitol dehydrogenase immobilized membrane was placed in a cuvette filled with a phosphate buffer containing the oxidized form of nicotinamide adenine dinucleotide (NAD(+)). The changes in NADH fluorescence intensity were measured after adding a standard sorbitol solution. According to the experimental assessment, the calibration range of the sorbitol biosensor systems using a spectrometer and a PMT was 5.0-1000 μmol L(-1) and 1.0-1000 μmol L(-1), respectively. The sorbitol biosensor system using the sorbitol dehydrogenase from microorganisms of the genus Flavimonas has high selectivity and sensitivity compared with that from sheep liver. The sorbitol biosensor allows for point-of-care testing applications or daily health care tests for diabetes patients.

Boronic Acid Functionalized Aza-Bodipy (azaBDPBA) based Fluorescence Optodes for the Analysis of Glucose in Whole Blood

A near-infrared fluorescent dye (aza-bodipy or azaBDPBA) functionalized with boronic acid groups was synthesized for the preparation of optodes to measure glucose in 40-fold diluted whole blood. Boronic acid groups as an electron deficient group on aza-bodipy was reacted with hydrogen peroxide into an electron-rich phenolic group leading to the red-shift of emission wavelength from 682 to 724 nm. The emission in near-infrared region offered a low level of background interference from whole blood. Also, the dual-wavelength emission guaranteed our probe to measure glucose in whole blood accurately after the conversion of glucose into hydrogen peroxide using glucose oxidase. The measuring range of glucose from 0.2 to 200 mM in the buffer was achieved with high selectivity. To facilitate the blood test, the probe was immobilized into thin hydrophobic polymer films to prepare the disposal glucose optode, which could detect glucose in the solution from 60 μM to 100 mM. The concentration of glucose in 40-fold diluted whole blood was determined using our optode and the reference method, respectively. The consistence in the concentration obtained from these two assays revealed that our azaBDPBA-based optodes were promising for the clinic assay of glucose in the whole blood.

A facile channel for D-glucose detection in aqueous solution

Three facile ensembles for sensing D-glucose are designed and constructed. The ensembles are comprised of fluorescent dye (NAHBDS) and boronic acid substituted viologens (BBVs) quenchers/receptors. The sensing processes of three ensembles (NAHBDS/o-BBV, NAHBDS/m-BBV and NAHBDS/p-BBV) to D-glucose were determined by fluorescence spectra at pH 7.4 buffer solution. The results show that NAHBDS/o-BBV and NAHBDS/m-BBV ensembles embody higher sensitivity for D-glucose with reversible "on-off" fluorescence response. More importantly, the recovery of relative intensity has good linear relation to low concentration of D-glucose. The action between the ensemble with D-glucose is dynamically reversible equilibrium process. The research results provide a new mode to design highly selective probe.

Responsive materials for self-regulated insulin delivery

With diabetes mellitus becoming an important public health concern, insulin-delivery systems are attracting increasing interest from both scientific and technological researchers. This feature article covers the present state-of-the-art glucose-responsive insulin-delivery system (denoted as GRIDS), based on responsive polymer materials, a promising system for self-regulated insulin delivery. Three types of GRIDS are discussed, based on different fundamental mechanisms of glucose-recognition, with: a) glucose enzyme, b) glucose binding protein, and c) synthetic boronic acid as the glucose-sensitive component. At the end, a personal perspective on the major issues yet to be worked out in future research is provided.

Multifunctional hybrid nanogel for integration of optical glucose sensing and self-regulated insulin release at physiological pH

Optical detection of glucose, high drug loading capacity, and self-regulated drug delivery are simultaneously possible using a multifunctional hybrid nanogel particle under a rational design in a colloid chemistry method. Such hybrid nanogels are made of Ag nanoparticle (NP) cores covered by a copolymer gel shell of poly(4-vinylphenylboronic acid-co-2-(dimethylamino)ethyl acrylate) [p(VPBA-DMAEA)]. The introduction of the glucose sensitive p(VPBA-DMAEA) gel shell onto Ag NPs makes the polymer-bound Ag NPs responsive to glucose. While the small sized Ag cores (10 +/- 3 nm) provide fluorescence as an optical code, the responsive polymer gel shell can adapt to a surrounding medium of different glucose concentrations over a clinically relevant range (0-30 mM), convert the disruptions in homeostasis of glucose level into optical signals, and regulate release of preloaded insulin. This shows a new proof-of-concept for diabetes treatment that exploits the properties from each building block of a multifunctional nano-object. The highly versatile multifunctional hybrid nanogels could potentially be used for simultaneous optical diagnosis, self-regulated therapy, and monitoring of the response to treatment.

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.

Construction of optical glucose nanobiosensor with high sensitivity and selectivity at physiological pH on the basis of organic-inorganic hybrid microgels

A new class of optical glucose nanobiosensors with high sensitivity and selectivity at physiological pH is described. To construct these glucose nanobiosensors, the fluorescent CdS quantum dots (QDs), serving as the optical code, were incorporated into the glucose-sensitive poly(N-isopropylacrylamide-acrylamide-2-acrylamidomethyl-5-fluorophenylboronic acid) copolymer microgels, via both in situ growth method and "breathing in" method, respectively. The polymeric gel can adapt to surrounding glucose concentrations, and regulate the fluorescence of the embedded QDs, converting biochemical signals into optical signals. The gradual swelling of the gel would lead to the quenching of the fluorescence at the elevated glucose concentrations. The hybrid microgels displayed high selectivity to glucose over the potential primary interferents of lactate and human serum albumin in the physiologically important glucose concentration range. The stability, reversibility, and sensitivity of the organic-inorganic hybrid microgel-based biosensors were also systematically studied. These general properties of our nanobiosensors are well tunable under appropriate tailor on the hybrid microgels, in particular, simply through the change in the crosslinking degree of the microgels. The optical glucose nanobiosensors based on the organic-inorganic hybrid microgels have shown the potential for a third generation fluorescent biosensor.

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.