Fluorescent Probes for Sugar Detection

Design and Synthesis of Novel Di-Boronic Acid-Based Chemical Glucose Sensors

Chemical-based fluorescent sensors with the capability of long-term stability and low cost are promising agents in clinical diagnosis and medical research. Measuring glucose levels inside cells and their surroundings provides insight into cellular metabolic homeostasis and may be employed as an indicator for potential pathological conditions. Anthracene-based diboronic acid (BA) derivatives offer a reversible and covalent binding mechanism for glucose recognition, which enables robust and continuous glucose monitoring. To improve its poor solubility and biological applicability, a diboronic acid chemical structure design was explored. To date, several anthracene-based ortho-amino methylphenyl boronic acid glucose-sensors have been developed. Most recently, the structure of Mc-CDBA (((((2-(methoxycarbonyl) anthracene-9,10-diyl) bis (methylene)) bis(methylazanediyl)) bis(methylene)) bis(4-cyano-2,1-phenylene)) diboronic acid was disclosed. Mc-CDBA exhibits suitable water-solubility and sensitivity toward glucose, with limited modification sites and suitability to extra-cellular applications. Here, we present a palette of Mc-CDBA derivatives: carboxylic (BA), amid (BA 5) and acryl (BA 21)-based Mc-CDBA sensors for extra- and intracellular glucose monitoring, respectively. The developed chemical glucose sensors were designed to obtain a final product with fewer synthetic steps, allowing easier scale-up capacity. Moreover, we showed that ortho-amino site modifications do not interfere with the sensor activity, allowing alternative water solubility solutions without chemically modifying the chromophore/aromatic subunits within the molecule. Among these probes, we also developed an extracellular hydrogel-embedded sensor (BA 21) to monitor extracellular glucose levels under persistent solution flow, a feature that is lacking in other glucose sensors. The synthesized derivatives could serve as diverse fluorescent sensors for glucose monitoring in medical applications.

Surface-enhanced Raman spectroscopy as effective tool for detection of sialic acid as cancer biomarker

Sialic acid, a negatively charged nine-carbon monosaccharide, is mainly located at the terminal end of glycan chains on glycoproteins and glycolipids of cell surface and most secreted proteins. Elevated levels of sialylated glycans have been known as a hallmark in numerous cancers. As a result, sialic acid acts as a useful and accessible cancer biomarker for early cancer detection and monitoring the disease development during cancer treatment which is crucial in elevating the survival rate. The detection of sialic acid has been done by many tools including surface-enhanced Raman spectroscopy (SERS) which gained incredible attention due to its high selectivity and sensitivity. However, currently, comprehensive reviews of sialic acid detection and imaging as a cancer biomarker using SERS are still lacking. Here, we present the significant breakthroughs in SERS-based detection of sialic acid levels on cells, tissues, and body fluids due to the presence of cancer, different cancer metastasis stages, and in response to the external stimuli. This review covers the SERS substrate and novel SERS strategies, using lectin, boronic acid, metabolic glycan labelling and label-free methods, for sialic acid detection as cancer biomarker. The remaining challenges to detect sialic acid and prospect of future development of SERS for other carbohydrate-based cancer biomarker, for instance fucose, are also discussed.

Effective enrichment of glycated proteome using ultrasmall gold nanoclusters functionalized with boronic acid

Glycated proteins play a crucial role in various biological pathways and the pathogenesis of human diseases. A comprehensive analysis of glycated proteins is essential for understanding their biological significance. However, their low abundance and heterogeneity in complex biological samples necessitate an enrichment procedure prior to their detection. Current enrichment strategies primarily rely on the boronic acid (BA) affinity method combined with functional nanoparticles; however, the effectiveness of these approaches is often suboptimal. In this study, a novel nanocluster (NC)-based enrichment material was synthesized for the first time, characterized as Au22SG18 functionalized with 24 BA groups, in which SG is glutathione. The functionalized BA established a reversible covalent bond with the cis-dihydroxy group through pH adjustment, enabling selective enrichment of glycated peptides. After the optimization of the enrichment protocol, we demonstrated highly sensitive and selective enrichment of standard glycopeptides using the NC-based enrichment material, exhibiting excellent reusability. Efficient enrichment was also demonstrated for the glycated proteome from human serum. These results highlight the potential of the atomically well-defined ultrasmall Au NCs as a powerful tool for high-throughput analysis of glycated peptides.

Construction of Pt/Ni/NiFe2O4/C nanocomposite with one dimensional hollow structure for portable glucose sensing application

Designing portable electrochemical sensors combined with highly efficient glucose oxidation electrodes offers a significant opportunity for convenient glucose detection. In this report, we present the design and preparation of platinum deposited Ni/NiFe2O4/Carbon composite (Pt/Ni/NiFe2O4/C) derived from Ni/Fe metal-organic frameworks (MOFs) followed by Pt deposition. Energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and electron microscopy (EM) were utilized to analyze the crystal structure, morphology, and chemical composition of the resulting materials. The glucose sensing capabilities of the optimal Pt/Ni/NiFe2O4/C-3 were assessed using amperometry methods on a smartphone-based portable device. Acting as a nonenzymatic glucose sensor, the Pt/Ni/NiFe2O4/C-3 electrode demonstrated notable sensitivity and a low limit of detection for glucose. The portable sensor exhibits high sensitivities of 131.88 μM mM cm-2 at low glucose concentration (3-500 μM) and 29.52 μA mM cm-2 at high glucose concentration (700-4000 μM), achieving a low detection limit of 1.1 μM (S/N = 3). The sensor also demonstrates enhanced selectivity and stability for detecting glucose. Furthermore, the portable sensor exhibits a clear step-ampere response in the detection of serum samples with satisfactory recovery ranging from 99.30 to 101.32%. This suggests the significant potential of portable glucose sensing applications.

ortho-Boronic Acid Carbonyl Compounds and Their Applications in Chemical Biology

Iminoboronates and diazaborines are related classes of compounds that feature an imine ortho to an arylboronic acid (iminoboronate) or a hydrazone that cyclizes with an ortho arylboronic acid (diazaborine). Rather than acting as independent chemical motifs, the arylboronic acid impacts the rate of imine/hydrazone formation, hydrolysis, and exchange with competing nucleophiles. Increasing evidence has shown that the imine/hydrazone functionality also impacts arylboronic acid reactivity toward diols and reactive oxygen and nitrogen species (ROS/RNS). Untangling the communication between C=N linked functionalities and arylboronic acids has revealed a powerful and tunable motif for bioconjugation chemistries and other applications in chemical biology. Here, we survey the applications of iminoboronates and diazaborines in these fields with an eye toward understanding their utility as a function of neighboring group effects.

Polarimetric and fluorescence spectroscopic based classification of mono and disaccharide solutions

In this article, we demonstrate the potential application of polarimetry and fluorescence spectroscopy for classifying mono and disaccharides (sugar) both qualitatively and quantitatively. A phase lock-in rotating analyzer (PLRA) polarimeter has been designed and developed for real time quantification of sugar concentration in a solution. Polarization rotation in the form of phase shift in sinusoidal photovoltages of reference and sample beams occurred when incident on the two spatially distinct photodetectors. Monosaccharide (fructose and glucose) and disaccharide (sucrose) have been quantitatively determined with sensitivities of 122.06 deg ml g^-1, 272.84 deg ml g^-1 and 163.41 deg ml g^-1 respectively. Calibration equations have been obtained from the respective fitting functions to estimate the concentration of each individual dissolved in deionized (DI) water. In comparison to the predicted results, the absolute average errors of 1.47 %, 1.63 % and 1.71 % are calculated for the readings of sucrose, glucose and fructose, respectively. Furthermore, the performance of the PLRA polarimeter has been compared with fluorescence emission results acquired from the same set of samples. The Limit of detections (LODs) attained from both experimental setups are comparable for mono and disaccharides. A linear detection response is observed by both polarimeter and fluorescence spectrometer in a wide range 0-0.28 g/ml of sugar. These results depict that PLRA polarimeter is novel, remote, precise and cost-effective for quantitative determination of optically active ingredient in the host solution.

A Rainbow Structural Color by Stretchable Photonic Crystal for Saccharide Identification

Photonic crystals (PCs) with fascinating structural color nanomaterials present effectively spontaneous emission modulation and selectively optical signal amplification. Stretchability or elasticity could enable the feasible tunability for structural colors. Aimed at the regulation of structural colors, we endeavored to achieve the PC nanomatrix evolution and optical property during stretching. In this work, a rainbow structural color by stretchable PCs was exploited to provide abundant optical information for multianalyte recognition. The finite element analysis proved the electric field distribution in the PC matrix, which completely matched with the phenomenon of the measured PC spectra. By simply employing analysis of the multistate PC during stretching, the mono PC matrix chip can differentially enhance fluorescence signals in broad spectral regions, resulting in diverse sensing information for high-efficiency multianalysis. The stretchable PC chip can facilely discriminate 14 similar structured saccharides with a minimum concentration of 10^-7 M using only one fluorescence complex. Furthermore, saccharides in different concentrations, mixtures, and real samples (beverages and sweets) also can be successfully distinguished. The exploration on fluorescent stretch dependence behavior of the photonic crystal contributes the biomatching optical platform for wearable devices, dynamic environment, clinical, or health monitoring auxiliary.

A selective hybrid fluorescent sensor for fructose detection based on a phenylboronic acid and BODIPY-based hydrophobicity probe

Fructose is widely used in the food industry. However, it may be involved in diseases by generating harmful advanced glycation end-products. We have designed and synthesized a novel fluorescent probe for fructose detection by combining a phenylboronic acid group with a BODIPY-based hydrophobicity probe. This probe showed a linear fluorescence response to d-fructose concentration in the range of 100-1000 μM, with a detection limit of 32 μM, which is advantageous for the simple and sensitive determination of fructose.

Photo- and Electrochemical Dual-Responsive Iridium Probe for Saccharide Detection

Dual detection systems are of interest for rapid, accurate data collection in sensing systems and in vitro testing. We introduce an IrIII complex with a boronic acid receptor site attached to the 2-phenylpyridine ligand as an ideal probe with photo- and electrochemical signals that is sensitive to monosaccharide binding in aqueous solution. The complex displays orange luminescence at 618 nm, which is reduced by 70 and 40 % upon binding of fructose and glucose, respectively. The electro-chemiluminescent signal of the complex also shows a direct response to monosaccharide binding. The IrIII complex shows the same response upon incorporation into hydrogel matrices as in solution, thus demonstrating the potential of its integration into a device, as a nontoxic, simple-to-use tool to observe sugar binding over physiologically relevant pH ranges and saccharide concentrations. Moreover, the complex's luminescence is responsive to monosaccharide presence in cancer cells.

3D Printed Sugar-Sensing Hydrogels

The ability of boronic acids (BAs) to reversibly bind diols, such as sugars, has been widely studied in recent years. In solution, through the incorporation of additional fluorophores, the BA-sugar interaction can be monitored by changes in fluorescence. Ultimately, a practical realization of this technology requires a transition from solution-based methodologies. Herein, the first example of 3D-printed sugar-sensing hydrogels, achieved through the incorporation of a BA-fluorophore pair in a gelatin methacrylamide-based matrix is presented. Through optimization of monomeric cocktails, it is possible to use extrusion printing to generate structured porous hydrogels which show a measurable and reproducible linear fluorescence response to glucose and fructose up to 100 mm.