Molecular Boronic Acid-Based Saccharide Sensors

Engineering dynamic covalent bond-based nanosystems for delivery of antimicrobials against bacterial infections

Nanodrug delivery systems (NDDS) continue to be explored as novel strategies enhance therapy outcomes and combat microbial resistance. The need for the formulation of smart drug delivery systems for targeting infection sites calls for the engineering of responsive chemical designs such as dynamic covalent bonds (DCBs). Stimuli response due to DCBs incorporated into nanosystems are emerging as an alternative way to target infection sites, thus enhancing the delivery of antibacterial agents. This leads to the eradication of bacterial infections and the reduction of antimicrobial resistance. Incorporating DCBs on the backbone of the nanoparticles endows the systems with several properties, including self-healing, controlled disassembly, and stimuli responsiveness, which are beneficial in the delivery and release of the antimicrobial at the infection site. This review provides a comprehensive and current overview of conventional DCBs-based nanosystems, stimuli-responsive DCBs-based nanosystems, and targeted DCBs-based nanosystems that have been reported in the literature for antibacterial delivery. The review emphasizes the DCBs used in their design, the nanomaterials constructed, the drug release-triggering stimuli, and the antibacterial efficacy of the reported DCBs-based nanosystems. Additionally, the review underlines future strategies that can be used to improve the potential of DCBs-based nanosystems to treat bacterial infections and overcome antibacterial resistance.

Boron-containing compounds as labels, drugs, and theranostic agents for diabetes and its complications

Diabetes is a disease with a high global burden. Current strategies have failed to limit the advancement and impact of the disease. Successful early diagnosis and treatment will require the development of new agents. In this sense, boron-containing compounds have been reported as agents with the ability to reduce glycemia and lipidemia. They have also been used for labeling and measuring carbohydrates and other molecules linked to the initial stages of diabetes and its progression. In addition, certain boron compounds bind to molecules related to diabetes development and their biological activity in the regulation of elevated glycemia. Finally, it should be noted that some boron compounds appear to exert beneficial effects on diabetes complications such as accelerating wound healing while ameliorating pain in diabetic patients.

Evaluation of digoxin-boronate ester formation through in-capillary derivatisation-large volume sample stacking-capillary zone electrophoresis

Determination of digoxin through in-capillary derivatisation based on the formation of o-tolyl- and 2-naphthyl-anionic boronate esters in combination with large volume sample stacking-capillary electrophoresis is proposed. The derivatisation reaction was performed at basic pH values to obtain compounds with a charge and chromophore group during the stacking process. After stacking, the species were separated and detected at 225 nm using p-nitrophenol as an internal standard. Stacking and derivatisation parameters such as pre-concentration time, preconcentration voltage and injection time (relation between the analyte and the derivatisation agent) were evaluated using a Box-Behnken design. Under optimal conditions, the proposed method exhibits a linear range of 1.08-50.00 μM with a limit of detection of 0.36 μM; additionally, adequate repeatability and reproducibility was obtained (%RSD ≤ 5.0%). The methodology was validated by comparing it to an HPLC-UV established methodology and was successfully applied for the determination of digoxin in pharmaceutical tablets and blood serum samples, showing a positive performance for these matrices.

A fluorescent NBD "turn-on" probe for the rapid and on-site analysis of fructose in food

High fructose intake is an important cause of metabolic disease. Due to the increasing prevalence of metabolic diseases worldwide, the development of an accurate and efficient tool for monitoring fructose in food is urgently needed to control the intake of fructose. Herein, a new fluorescent probe NBD-PQ-B with 7-nitrobenz-2-oxa-1, 3-diazole (NBD) as the fluorophore, piperazine (PQ) as the bridging group and phenylboronic acid (B) as the recognition receptor, was synthesized to detect fructose. The fluorescence of NBD-PQ-B increased linearly at 550 nm at an excitation wavelength of 497 nm with increasing fructose concentration from 0.1 to 20 mM. The limit of detection (LOD) of fructose was 40 μM. The pKa values of NBD-PQ-B and its fructose complexes were 4.1 and 10.0, respectively. In addition, NBD-PQ-B bound to fructose in a few seconds. The present technique was applied to determine the fructose content in beverages, honey, and watermelon with satisfactory results. Finally, the system could not only be applied in an aqueous solution with a spectrophotometer, but also be fabricated as a NBD-PQ-B/polyvinyl oxide (PEO) film by electrospinning for on-site food analysis simply with the assistance of a smartphone.

The Fluorescent Detection of Glucose and Lactic Acid Based on Fluorescent Iron Nanoclusters

In this paper, a novel fluorescent detection method for glucose and lactic acid was developed based on fluorescent iron nanoclusters (Fe NCs). The Fe NCs prepared using hemin as the main raw material exhibited excellent water solubility, bright red fluorescence, and super sensitive response to hydrogen peroxide (H2O2). This paper demonstrates that Fe NCs exhibit excellent peroxide-like activity, catalyzing H2O2 to produce hydroxyl radicals (•OH) that can quench the red fluorescence of Fe NCs. In this paper, a new type of glucose sensor was established by combining Fe NCs with glucose oxidase (GluOx). With the increase in glucose content, the fluorescence of Fe NCs decreases correspondingly, and the glucose content can be detected in the scope of 0-200 μmol·L-1 (μM). Similarly, the lactic acid sensor can also be established by combining Fe NCs with lactate oxidase (LacOx). With the increase in lactic acid concentration, the fluorescence of Fe NCs decreases correspondingly, and the lactic acid content can be detected in the range of 0-100 μM. Furthermore, Fe NCs were used in the preparation of gel test strip, which can be used to detect H2O2, glucose and lactic acid successfully by the changes of fluorescent intensity.

Imaging the extracellular matrix in live tissues and organisms with a glycan-binding fluorophore

All multicellular systems produce and dynamically regulate extracellular matrices (ECM) that play important roles in both biochemical and mechanical signaling. Though the spatial arrangement of these extracellular assemblies is critical to their biological functions, visualization of ECM structure is challenging, in part because the biomolecules that compose the ECM are difficult to fluorescently label individually and collectively. Here, we present a cell-impermeable small molecule fluorophore, termed Rhobo6, that turns on and red shifts upon reversible binding to glycans. Given that most ECM components are densely glycosylated, the dye enables wash-free visualization of ECM, in systems ranging from in vitro substrates to in vivo mouse mammary tumors. Relative to existing techniques, Rhobo6 provides a broad substrate profile, superior tissue penetration, nonperturbative labeling, and negligible photobleaching. This work establishes a straightforward method for imaging the distribution of ECM in live tissues and organisms, lowering barriers for investigation of extracellular biology.

Rational design of nanozyme with integrated sample pretreatment for colorimetric biosensing

Nanozymes have been widely used in the field of biosensing owing to their high stability, low cost, adjustable catalytic activity, and convenient modification. However, achieving high selectivity and sensitivity simultaneously in nanozyme-based colorimetric sensing remains a major challenge. Nanozymes are nanomaterials with enzyme-simulating activity that are often used as solid-phase adsorbents for sample pretreatment. Our design strategy integrated sample pretreatment function into the nanozyme through separation and enrichment, thereby improving the selectivity and sensitivity of nanozyme-based colorimetric biosensing. As a proof-of-concept, glucose was used as the model analyte in this study. A phenylboric acid-modified magnetic nanozyme (Cu/Fe3O4@BA) was rationally designed and synthesized. Selectivity was enhanced by boronate-affinity specific adsorption and the elimination of interference after magnetic separation. In addition, magnetic solid-phase extraction enrichment was used to improve the sensitivity. A recovery rate of more than 80% was reached when the enrichment factor was 50. The synthesized magnetic Cu/Fe3O4@BA was recyclable at least five times. The proposed method exhibited excellent selectivity and sensitivity, simple operation, and recyclability, providing a novel and practical strategy for designing multifunctional nanozymes for biosensing.

Solid-State Synthesis of B←N Adducts by the Amine-Facilitated Trimerization of the Phenylboronic Acid

Stable boroxine-amine adducts comprising dative B←N bond(s) were prepared by mechanochemically-induced reactions of phenylboronic acid (PBA) and amines (pyridine, DMAP, 1H-pyrazole, piperidine, DABCO, hexamethylenetetramine, or 4,4'-bipyridine). In-situ Raman monitoring, ex-situ PXRD and DFT calculations were used for product identification. Stoichiometry of the product (3 : 1, 3 : 2 or 6 : 1 adduct) was controlled by the amine structure and the molar ratio of the reactants. The 1 : 2 H-bonded assembly of PBA and 4,4'-bipyridine (bpy) was confirmed as an intermediate in the adduct formation for bpy. Competitive binding experiments indicated that the exchange of the amines in the 3 : 1 adducts follows the computed adduct stabilities that increase with the amine basicity. Following the DFT prediction, the first adduct with two different amines, DMAP and pip, bound to one boroxine moiety was isolated and structurally characterized. Results show that calculations can be used to predict possible and preferred product(s) and their spectral characteristics.

Regioselective Deacetylation of Peracetylated Deoxy-C-glycopyranosides by Boron Trichloride (BCl3)

A general approach for regioselective deacetylation at sugar 3-OH of peracetylated 6-deoxy-C-glucopyranosides mediated by BCl3 was developed. The approach could be extended to other sugar-derived 6-deoxy-C-glycopyranosides, such as those derived from mannose, galactose, and rhamnose, with deacetylation occurring at varied sugar hydroxyl groups, and further extended to 4-deoxy-C-glucopyranosides with deacetylation occurring at sugar 3-OH. The approach would enable access to synthetically challenging carbohydrate derivatives. A possible mechanism of the regioselectivity was proposed.

Pyrene-Appended Boronic Acids on Graphene Foam Electrodes Provide Quantum Capacitance-Based Molecular Sensors for Lactate

Molecular recognition and sensing can be coupled to interfacial capacitance changes on graphene foam surfaces linked to double layer effects and coupled to enhanced quantum capacitance. 3D graphene foam film electrodes (Gii-Sens; thickness approximately 40 μm; roughness factor approximately 100) immersed in aqueous buffer media exhibit an order of magnitude jump in electrochemical capacitance upon adsorption of a charged molecular receptor based on pyrene-appended boronic acids (here, 4-borono-1-(pyren-2-ylmethyl)pyridin-1-ium bromide, or abbreviated T1). This pyrene-appended pyridinium boronic acid receptor is employed here as a molecular receptor for lactate. In the presence of lactate and at pH 4.0 (after pH optimization), the electrochemical capacitance (determined by impedance spectroscopy) doubles again. Lactic acid binding is expressed with a Hillian binding constant (Klactate = 75 mol-1 dm3 and α = 0.8 in aqueous buffer, Klactate = 460 mol-1 dm3 and α = 0.8 in artificial sweat, and Klactate = 340 mol-1 dm3 and α = 0.65 in human serum). The result is a selective molecular probe response for lactic acid with LoD = 1.3, 1.4, and 1.8 mM in aqueous buffer media (pH 4.0), in artificial sweat (adjusted to pH 4.7), and in human serum (pH adjusted to 4.0), respectively. The role of the pyrene-appended boronic acid is discussed based on the double layer structure and quantum capacitance changes. In the future, this new type of molecular capacitance sensor could provide selective enzyme-free analysis without analyte consumption for a wider range of analytes and complex environments.

Capturing Sialyl-glycan on Live Cancer Cells by Tailored Boronopeptide

Boronic acid-containing molecules are substantially popularized in chemical biology and medicinal chemistry due to the broad spectrum of covalent conjugations as well as interaction modules offered by the versatile boron atom. Apparently, the WGA peptide (wheat germ agglutinin, 62-73), which shows a considerably low binding affinity to sialic acid, turned into a selective and >5 folds potent binder with the aid of a suitable boronic acid probe installed chemoselectively. In silico studies prompted us to install BA probes on the cysteine residue, supposedly located in close proximity to the bound sialic acid. In vitro studies revealed that the tailored boronopeptides show enhanced binding ability due to the synergistic recognition governed by selective non-covalent interactions and cis-diol boronic acid conjugation. The intense binding is observed even in 10 % serum, thus enabling profiling of sialyl-glycan on cancer cells, as compared with the widely used lectin, Sambucus nigra. The synergistic binding mode between the best boronopeptide (P3) binder and sialic acid was analyzed via 1 H and 11 B NMR.

Enantiomer Recognition Based on Chirality Transfer from Chiral Amines to Ternary Dynamic Covalent Systems

Enantiomer recognition is usually required in organic synthesis and materials and life sciences. This paper describes an enantiomer recognition method based on ternary dynamic covalent systems constructed via the complexation of chiral amines with a chiral boronate derived from 1,4-phenylenediboric acid and an L-DOPA-modified naphthalenediimide. The ternary systems aggregate into chiral assemblies driven by π-π interactions, and the chirality is transferred from the chiral amines to assemblies with high stereospecificity. Consequently, the enantiomer composition of chiral amines and the absolute configuration of the major enantiomer can be determined according to the sign of the Cotton effect of the ternary system by using circular dichroism (CD) spectroscopy. This method offers the advantage of using the long wavelength CD signals of the boronate at around 520 nm, thereby avoiding interference with those of the carbon skeleton. This ternary system provides a novel approach to the design of enantiomer recognition systems.

Stimuli-Responsive Boronate Formation to Control Nucleic Acid-Based Functional Architectures

Boronate esters, formed by the reaction of an oligonucleotide bearing a 5'-boronic acid moiety with the 3'-terminal cis-diol of another oligonucleotide, support the assembly of functional nucleic acid architectures. Reversible formation of boronate esters occurs in templated fashion and has been shown to restore the activity of split DNA and RNA enzymes as well as a split fluorescent light-up aptamer. Apart from their suitability for the design and application of split nucleic acid enzymes and aptamers in the field of biosensing, boronate esters may have played an important role in early life as surrogates of the natural phosphodiester bond. Their formation is reversible and thus fulfills an important requirement for biological self-assembly. Here we discuss the general concept of stimuli-dependent boronate formation and its application in biomolecules with implications for future research.

Enantioselective and Chemoselective Optical Detection of Chiral Organic Compounds without Resorting to Chromatography

Enantiorecognition and resolution are of essential importance in many diverse areas of science. Whenever there arises a need to analyze/investigate enantiomers in different situations chromatography stands up in our minds immediately. Nevertheless, chemoselective and enantioselective recognition/discrimination (without going for separation) constitutes a different perception and requirement. The techniques using chiroptical sensing cause detection based on molecular interactions induced in different manners. Enantioselective sensing of monosaccharides in γ-cyclodextrin assembly and by diboronic acid based fluorescent sensors, application of bi-naphthol and H8 BINOL based sensors and dendrimers, metal-to-ligand charge transfer transitions in CD, exciton-coupled circular dichroism, surface enhanced Raman spectroscopy, and enantioselective indicator displacement sensor arrays for enantioselective recognition/detection of chiral organic compounds, such as amines, amino acids/alcohols, and hydroxycarboxylic acids have been discussed in progressive manner with mechanistic explanations, wherever available. Besides, the chiroptical vs LC approach has been discussed. The present paper is focused on certain different non-chromatographic optical techniques and aims to extend an understanding and a view to consider such techniques which have been successful in selective detection, and determination of absolute configuration and enantiomeric excess, (without resorting to separation vis-à-vis LC) and that have potential use in high-throughput chiral assay and combinatorial search for asymmetric catalysts and reagents.

Polyol recognition in catalysis: toward selective modification of glycosylated polypeptides with boronic acid-rhodium(II) catalysts

Proximity-induced methodologies for peptide and protein modification have been developed using recognition elements like inhibitors, antibodies, or affinity tags on amino acids. However, the recognition of saccharides for chemical modification remains widely unexplored. Studies exploring boronic acids and their derivatives have shown their alluring capabilities as selective molecular recognition elements for saccharides, and in this study we describe the application of these ideas to the discovery of a catalytic proximity-induced methodology for covalent modification of glycopeptides using boronic acids as a saccharide recognition element.

Water-soluble fluorescent chemosensor for sorbitol based on a dicationic diboronic receptor. Crystal structure and spectroscopic studies

Selective recognition of saccharides by phenylboronic dyes capable of functioning in aqueous conditions is a central topic of modern supramolecular chemistry that impacts analytical sciences and biological chemistry. Herein, a new dicationic diboronic acid structure 11 was synthesized, structurally described by single-crystal X-ray diffraction, and studied in-depth as fluorescent receptor for six saccharides in pure water at pH = 7.4. This dicationic receptor 11 has been designed particularly to respond to sorbitol and involves two convergent and strongly acidified phenyl boronic acids, with a pKa of 6.6, that operate as binding sites. The addition of sorbitol in the micromolar concentration range to receptor 11 induces strong fluorescence change, but in the presence of fructose, mannitol, glucose, lactose and sucrose, only moderate optical changes are observed. This change in emission is attributed to a static complexation photoinduced electron transfer mechanism as evidenced by lifetime experiments and different spectroscopic tools. The diboronic receptor has a high affinity/selectivity to sorbitol (K = 31 800 M-1) over other saccharides including common interfering species such as mannitol and fructose. The results based on 1H, 11B NMR spectroscopy, high-resolution mass spectrometry and density functional theory calculations, support that sorbitol is efficiently bound to 11 in a 1 : 1 mode involving a chelating diboronate-sorbitol complexation. Since the experimental B⋯B distance (5.3 Å) in 11 is very close to the calculated distance from the DFT-optimized complex with sorbitol, the efficient binding is attributed to strong acidification and preorganization of boronic acids. These results highlight the usefulness of a new diboronic acid receptor with a strong ability for fluorescent recognition of sorbitol in physiological conditions.

Cyclodextrin Host-Guest Recognition in Glucose-Monitoring Sensors

Diabetes mellitus is a prevalent chronic health condition that has caused millions of deaths worldwide. Monitoring blood glucose levels is crucial in diabetes management, aiding in clinical decision making and reducing the incidence of hypoglycemic episodes, thereby decreasing morbidity and mortality rates. Despite advancements in glucose monitoring (GM), the development of noninvasive, rapid, accurate, sensitive, selective, and stable systems for continuous monitoring remains a challenge. Addressing these challenges is critical to improving the clinical utility of GM technologies in diabetes management. In this concept, cyclodextrins (CDs) can be instrumental in the development of GM systems due to their high supramolecular recognition capabilities based on the host-guest interaction. The introduction of CDs into GM systems not only impacts the sensitivity, selectivity, and detection limit of the monitoring process but also improves biocompatibility and stability. These findings motivated the current review to provide a comprehensive summary of CD-based blood glucose sensors and their chemistry of glucose detection, efficiency, and accuracy. We categorize CD-based sensors into four groups based on their modification strategies, including CD-modified boronic acid, CD-modified mediators, CD-modified nanoparticles, and CD-modified functionalized polymers. These findings shed light on the potential of CD-based sensors as a promising tool for continuous GM in diabetes mellitus management.

Benzoxaborole-grafted high molecular weight chitosan from prawn: Synthesis, characterization, target recognition and antibacterial properties

Boronated polymers are in the focus of dynamic functional materials due to the versatility of the B-O interactions and accessibility of precursors. Polysaccharides are highly biocompatible, and therefore, an attractive platform for anchoring boronic acid groups for further bioconjugation of cis-diol containing molecules. We report for the first time the introduction of benzoxaborole by amidation of the amino groups of chitosan improving solubility and introducing cis-diol recognition at physiological pH. The chemical structures and physical properties of the novel chitosan-benzoxaborole (CS-Bx) as well as two phenylboronic derivatives synthesized for comparison, were characterized by nuclear magnetic resonance (NMR), infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), dynamic light scattering (DLS), rheology and optical spectroscopic methods. The novel benzoxaborole grafted chitosan was perfectly solubilized in an aqueous buffer at physiological pH, extending the possibilities of boronated materials derived from polysaccharides. The dynamic covalent interaction between boronated chitosan and model affinity ligands, was studied by means of spectroscopy methods. A glycopolymer derived from poly(isobutylene-alt-anhydride) was also synthesized to study the formation of dynamic assemblies with benzoxaborole-grafted chitosan. A first approximation to apply fluorescence microscale thermophoresis for the interactions of the modified polysaccharide is also discussed. Additionally, the activity of CSBx against bacterial adhesion was studied.

Biorecognition element-free electrochemical detection of recombinant glycoproteins using metal-organic frameworks as signal tags

Accurate and sensitive determination of recombinant glycoproteins is in great demand for the treatment of anemia-induced chronic kidney disease and the illegal use of doping agents in sports. In this study, an antibody and enzyme-free electrochemical method for the detection of recombinant glycoproteins was proposed via the sequential chemical recognition of hexahistidine (His₆) tag and glycan residue on the target protein under the cooperation interaction of nitrilotriacetic acid (NTA)-Ni²⁺complex and boronic acid, respectively. Specifically, NTA-Ni²⁺ complex-modified magnetic beads (MBs-NTA-Ni²⁺) are employed to selectively capture the recombinant glycoprotein through the coordination interaction between His₆ tag and NTA-Ni²⁺ complex. Then, boronic acid-modified Cu-based metal-organic frameworks (Cu-MOFs) were recruited by glycans on the glycoprotein via the formation of reversible boronate ester bonds. MOFs with abundant Cu²⁺ ions acted as efficient electroactive labels to directly produce amplified electrochemical signals. By using recombinant human erythropoietin as a model analyte, this method showed a wide linear detection range from 0.01 to 50 ng/mL and a low detection limit of 5.3 pg/mL. With the benefits from the simple operation and low cost, the stepwise chemical recognition-based method shows great promise in the determination of recombinant glycoproteins in the fields of biopharmaceutical research, anti-doping analysis and clinical diagnosis.

Genetically Encoded Boronolectin as a Specific Red Fluorescent UDP-GlcNAc Biosensor

There is great interest in developing boronolectins that are synthetic lectin mimics containing a boronic acid functional group for reversible recognition of diol-containing molecules, such as glycans and ribonucleotides. However, it remains a significant challenge to gain specificity. Here, we present a genetically encoded boronolectin which is a hybrid protein consisting of a noncanonical amino acid (ncAA) p-boronophenylalanine (pBoF), natural-lectin-derived peptide sequences, and a circularly permuted red fluorescent protein (cpRFP). The genetic encodability permitted a straightforward protein engineering process to derive a red fluorescent biosensor that can specifically bind uridine diphosphate N-acetylglucosamine (UDP-GlcNAc), an important nucleotide sugar involved in metabolic sensing and cell signaling. We further characterized the resultant boronic acid- and peptide-assisted UDP-GlcNAc sensor (bapaUGAc) both in vitro and in live mammalian cells. Because UDP-GlcNAc in the endoplasmic reticulum (ER) and Golgi apparatus plays essential roles in glycosylating biomolecules in the secretory pathway, we genetically expressed bapaUGAc in the ER and Golgi and validated the sensor for its responses to metabolic disruption and pharmacological inhibition. In addition, we combined bapaUGAc with UGAcS, a recently reported green fluorescent UDP-GlcNAc sensor based on an alternative sensing mechanism, to monitor UDP-GlcNAc level changes in the ER and cytosol simultaneously. We expect our work to facilitate the future development of specific boronolectins for carbohydrates. In addition, this newly developed genetically encoded bapaUGAc sensor will be a valuable tool for studying UDP-GlcNAc and glycobiology.

Biosensors with Boronic Acid-Based Materials as the Recognition Elements and Signal Labels

It is of great importance to have sensitive and accurate detection of cis-diol-containing biologically related substances because of their important functions in the research fields of metabolomics, glycomics, and proteomics. Boronic acids can specifically and reversibly interact with 1,2- or 1,3-diols to form five or six cyclic esters. Based on this unique property, boronic acid-based materials have been used as synthetic receptors for the specific recognition and detection of cis-diol-containing species. This review critically summarizes the recent advances with boronic acid-based materials as recognition elements and signal labels for the detection of cis-diol-containing biological species, including ribonucleic acids, glycans, glycoproteins, bacteria, exosomes, and tumor cells. We also address the challenges and future perspectives for developing versatile boronic acid-based materials with various promising applications.

Supramolecular assemblies in the molecular complexes of 4-cyanophenylboronic acid with different N-donor ligands

Molecular complexes of 4-cyanophenylboronic acid (CB) with various N-donor compounds having different conformational features, for example, rigid (1,10-phenanthroline (110phen), 4,7-phenanthroline (47phen), 1,7-phenanthroline (17phen) and acridine (acr)) and linear (1,2-bis(4-pyridyl)ethane (bpyea), 1,2-bis(4-pyridyl)ethene (bpyee) and 4,4'-azopyridine (azopy)), have been reported. In all complexes, the -B(OH)2 moiety is found to be in a syn-anti confirmation, with the exception of structures containing 110phen, bpyee, and azopy, wherein, syn-syn conformation is observed. Further, CB molecules remain intact in all structures except in the complexes with some linear N-donor ligands, wherein -B(OH)2 transforms to monoester (-B(OH)(OCH3)) prior to the formation of corresponding molecular complexes. In such boronic monoester complexes, the conformation of -B(OH)(OCH3) is syn-anti with respect to the -OH and -OCH3 groups. Also, complexes mediated by azopy and bpyee exist in both hydrated and anhydrous forms. In these anhydrous structures, the recognition pattern is through homomeric (juxtaposed -CN and -B(OH)2) as well as heteromeric (between hetero N-atom and -B(OH)2) O-H⋯N hydrogen bonds, while only heteromeric O-H⋯N hydrogen bonds hold co-formers in all other structures. Depending upon the conformational features of both co-formers, molecules are packed in crystal lattices in the form of stacked layers, helical chains, and crossed ribbons. All structures are fully characterized by single-crystal X-ray diffraction and phase purity is established by powder X-ray diffraction. Additionally, correlation among structures is explained by calculating a similarity index and performing a Hirshfeld surface analysis to quantify the strength and effectiveness of different types of intermolecular bonds that stabilize these structures along with the presentation of energy frameworks, representing the strength of the interactions in the form gradient cylinders. Also, the morphology of each complex was computed by BFDH methodology to correlate with the actual crystal morphology and packing arrangement.

Streptavidin-Conjugated DNA for the Boronate Affinity-Based Detection of Poly(ADP-Ribose) Polymerase-1 with Improved Sensitivity

This work reports the development of a fluorescence method for the detection of poly(ADP-ribose) polymerase-1 (PARP1), in which a phenylboronic acid-modified fluorescein isothiocyanate dye (FITC-PBA) was used to recognize the formed poly(ADP-ribose) (PAR) polymer. The detection system was designed by conjugating recombinant streptavidin (rSA) with PARP1-specific double-stranded DNA (dsDNA) through streptavidin-biotin interaction. Capture of PARP1 via rSA-biotin-dsDNA allowed for the poly-ADP-ribosylation (PARylation) of both rSA and PARP1 in a homogeneous solution. The resulting rSA-biotin-dsDNA/PAR conjugates were then captured and separated via the commercialized nitrilotriacetic acid-nickel ion-modified magnetic bead (MB-NTA-Ni) through the interaction between NTA-Ni on MB surface and oligohistidine (His₆) tag in rSA. The PAR polymer could capture the dye of FITC-PBA through the borate ester interaction between the boronic acid moiety in PBA and the cis-diol group in ribose, thus causing a decrease in fluorescence signal. The PARylation of streptavidin and the influence of steric hindrance on PARylation efficiency were confirmed using reasonable detection strategies. The method showed a wide linear range (0.01~20 U) and a low detection limit (0.01 U). This work should be valuable for the development of novel biosensors for the detection of poly(ADP-ribose) polymerases and diol-containing species.

Which boronic acids are used most frequently for synthesis of bioactive molecules?

Boronic acids are essential building blocks used for the synthesis of bioactive molecules, the generation of chemical libraries and the exploration of structure-activity relationships. As a result, more than ten thousand boronic acids are commercially available. Medicinal chemists are therefore facing a challenge; which of them should they select to maximize information obtained by the synthesis of new target molecules. The present article aims to help them to make the right choices. The boronic acids used frequently in the synthesis of bioactive molecules were identified by mining several large molecular and reaction databases and their properties were analyzed. Based on the results a diverse set of boronic acids covering well the bioactive chemical space was selected and is suggested as a basis for library design for the efficient exploration of structure-activity relationships. A Boronic Acid Navigator web tool which helps chemists to make their own selection is also made available at https://bit.ly/boronics.

Metal Ion-Peptide-Intermediated Ligand Transfer for Serum Detection of the Omicron Variant of SARS-Cov-2 in Echinococcosis Patients

A method is developed to electrochemically induce target-specific covalent capturing of the spike protein of SARS-Cov-2, forming a covalent peptide-protein complex fit for working with such complicated clinical samples. Specifically, peptide-coordinated copper ions can be electrochemically controlled to induce cross-linkage between certain amino acids on the peptide probe and the target protein. Therefore, target specificity can be tuned electrochemically, realizing highly specific targeting of the omicron S protein or broader specificity toward all variants of the virus. Using this method, with electrochemically catalyzed generation of signal-enhancing molecules, the sensitivity and covalent detection allow their application in both serum and fecal samples. These results may point to their possible use in screening new variants of the virus in the near future.

Effective enantioselective recognition by steady-state fluorescence spectroscopy: Towards a paradigm shift to optical sensors with unusual chemical architecture

A series of amino acid-derived 1,2,3-triazoles presenting the amino acid residue and the benzazole fluorophore connected by a triazole-4-carboxylate spacer was studied for enantioselective recognition using only steady-state fluorescence spectroscopy in solution. In this investigation, the optical sensing was performed with D-(-) and L-(+)-Arabinose and (R)-(-) and (S)-(+)-Mandelic acid as chiral analytes. The optical sensors showed specific interactions with each pair of enantiomers, allowing photophysical responses, which were used for their enantioselective recognition. DFT calculations confirm the specific interaction between the fluorophores and the analytes corroborating the observed high enantioselectivity of these compounds with the studied enantiomers. Finally, this study investigated nontrivial sensors for chiral molecules by a mechanism different than turn-on fluorescence and has the potential to broad chiral compounds with fluorophoric units as optical sensors for enantioselective sensing.

Recent Progress in Diboronic-Acid-Based Glucose Sensors

Non-enzymatic sensors with the capability of long-term stability and low cost are promising in glucose monitoring applications. Boronic acid (BA) derivatives offer a reversible and covalent binding mechanism for glucose recognition, which enables continuous glucose monitoring and responsive insulin release. To improve selectivity to glucose, a diboronic acid (DBA) structure design has been explored and has become a hot research topic for real-time glucose sensing in recent decades. This paper reviews the glucose recognition mechanism of boronic acids and discusses different glucose sensing strategies based on DBA-derivatives-based sensors reported in the past 10 years. The tunable pK_a, electron-withdrawing properties, and modifiable group of phenylboronic acids were explored to develop various sensing strategies, including optical, electrochemical, and other methods. However, compared to the numerous monoboronic acid molecules and methods developed for glucose monitoring, the diversity of DBA molecules and applied sensing strategies remains limited. The challenges and opportunities are also highlighted for the future of glucose sensing strategies, which need to consider practicability, advanced medical equipment fitment, patient compliance, as well as better selectivity and tolerance to interferences.

Boron-Containing Compounds for Prevention, Diagnosis, and Treatment of Human Metabolic Disorders

The application of natural and synthetic boron-containing compounds (BCC) in biomedical field is expanding. BCC have effects in the metabolism of living organisms. Some boron-enriched supplements are marketed as they exert effects in the bone and skeletal muscle; but also, BCC are being reported as acting on the enzymes and transporters of membrane suggesting they could modify the carbohydrate metabolism linked to some pathologies of high global burden, as an example is diabetes mellitus. Also, some recent findings are showing effects of BCC on lipid metabolism. In this review, information regarding the effects and interaction of these compounds was compiled, as well as the potential application for treating human metabolic disorders is suggested.

Sensitive and specific detection of saccharide species based on fluorescence: update from 2016

Increasing evidence supports the critical role of saccharides in various pathophysiological steps of tumor progression, where they regulate tumor proliferation, invasion, hematogenic metastasis, and angiogenesis. The identification and recognition of these saccharides provide a solid foundation for the development of targeted drug preparations, which are however not fully understood due to their complex and similar structures. In order to achieve fluorescence sensing of saccharides, extensive research has been conducted to design molecular probes and nanoparticles made of different materials. This paper aims to provide in-depth discussion of three main topics that cover the current status of the carbohydrate sensing based on the fluorescence sensing mechanism, including a phenylboronic acid-based sensing platform, non-boronic acid entities, as well as an enzyme-based sensing platform. It also highlights efforts made to understand the recognition mechanisms and improve the sensing properties of these systems. Finally, we present the challenge of achieving high selectivity and sensitivity recognition of saccharides, and suggest possible future avenues for exploration.

Colorimetric Sensing of Gram-Negative and Gram-Positive Bacteria Using 4-Mercaptophenylboronic Acid-Functionalized Gold Nanoparticles in the Presence of Polyethylene Glycol

Gold nanoparticles (GNPs) have been used as detection probes for rapid and sensitive detection of various analytes, including bacteria. Here, we demonstrate a simple strategy for bacterial detection using GNPs functionalized with 4-mercaptophenylboronic acid (4-MPBA). 4-MPBA can interact with peptidoglycan or lipopolysaccharides present in bacterial organelles. After the addition of a high concentration of sodium hydroxide (NaOH), the functionalization of the surface of 50 nm GNPs with 4-MPBA (4-MPBA@GNPs) in the presence of polyethylene glycol results in a color change because of the aggregation of 4-MPBA@GNPs. This color change is dependent on the amount of bacteria present in the tested samples. Escherichia coli (E. coli) K-12 and Staphylococcus aureus (S. aureus) are used as Gram-negative and Gram-positive bacterial models, respectively. The color change can be detected within an hour by the naked eye. A linear relationship is observed between bacterial concentrations and the absorbance intensity at 533 nm; R ² values of 0.9152 and 0.8185 are obtained for E. coli K-12 and S. aureus, respectively. The limit of detection of E. coli K-12 is ∼2.38 × 10² CFU mL^-1 and that of S. aureus is ∼4.77 × 10³ CFU mL^-1. This study provides a promising approach for the rapid detection of target Gram-negative and Gram-positive bacteria.

Probing the Role of the Bridging Nitrogen in the Signaling Mechanism of an Anthracene-Boronic Acid Sugar Sensor and a Different Version of the PET-Based Mechanism

The N-quaternized derivative 5 of the James-Shinkai anthracene-boronic acid fluorescence sugar sensor 1 was prepared to probe the role of the bridging nitrogen in the signaling mechanism of 1. Both 5 and 1 contain positively charged bridging groups NMe⁺ or NH⁺, respectively, but 5 lacks the ability to form the intramolecular ammonium-boronate doubly ionic hydrogen bond present in 1. Receptors 1 and 5 display opposite fluorescence vs pH profiles with a small turn-on effect of the sugar binding to the zwitterion of 5 in contrast to a large effect observed with 1. It is concluded that the ammonium-boronate hydrogen bond is essential for the signaling mechanism of 1. Its possible function is enabling the PET quenching effect by shifting the NH⁺ proton toward boronate anion inside the hydrogen bond, the degree of which is modulated by the ester formation with diols affecting the basicity of boronate anion. This mechanism agrees with observed signaling selectivity of 1 toward a series of di- and polyols of variable structures as well as with the behavior of 1 in buffered D₂O and methanol solvents at controlled pH and provides an addition to the established "loose bolt" mechanism signaling mode essential for receptors with nonpolar fluorophores.

Genetically Encoded Boronolectin as a Specific Red Fluorescent UDP-GlcNAc Biosensor

There is great interest in developing boronolectins, which are synthetic lectin mimics containing a boronic acid functional group for reversible recognition of diol-containing molecules, such as glycans and ribonucleotides. However, it remains a significant challenge to gain specificity. Here, we present a genetically encoded boronolectin, which is a hybrid protein consisting of a noncanonical amino acid (ncAA) p-boronophenylalanine (pBoF), natural-lectin-derived peptide sequences, and a circularly permuted red fluorescent protein (cpRFP). The genetic encodability permitted a straightforward protein engineering process to derive a red fluorescent biosensor that can specifically bind uridine diphosphate N-acetylglucosamine (UDP-GlcNAc), an important nucleotide sugar involved in metabolic sensing and cell signaling. We further characterized the resultant boronic acid-and peptide-assisted UDP-GlcNAc sensor (bapaUGAc) both in vitro and in live mammalian cells. Because UDP-GlcNAc in the endoplasmic reticulum (ER) and Golgi apparatus plays essential roles in glycosylating biomolecules in the secretory pathway, we genetically expressed bapaUGAc in the ER and Golgi and validated the sensor for its responses to metabolic disruption and pharmacological inhibition. In addition, we combined bapaUGAc with UGAcS, a recently reported green fluorescent UDP-GlcNAc sensor based on an alternative sensing mechanism, to monitor UDP-GlcNAc level changes in the ER and cytosol simultaneously. We expect our work to facilitate the future development of specific boronolectins for carbohydrates. In addition, this newly developed genetically encoded bapaUGAc sensor will be a valuable tool for studying UDP-GlcNAc and glycobiology.

Non-enzymatic detection of glucose levels in human blood plasma by a graphene oxide-modified organic transistor sensor

We herein report an organic transistor functionalized with a phenylboronic acid derivative and graphene oxide for the quantification of plasma glucose levels, which has been achieved by the minimization of interferent effects derived from physical protein adsorption on the detection electrode.

Fluorescence Sensing of Monosaccharides by Bis-boronic Acids Derived from Quinolinium Dicarboxamides: Structural and Spectroscopic Studies

Three new diboronic acid-substituted bisquinolinium salts were synthesized, structurally described by single-crystal X-ray diffraction, and studied in-depth as fluorescent receptors for six monosaccharides and two open-chain polyols in water at physiological pH. The dicationic pyridine-2,6-dicarboxamide-based receptors contain two N-quinolinium rings as the fluorescent units covalently linked to three different isomers of phenylboronic acid (ortho, 2; meta, 3; and para, 4) as chelating binding sites for polyols. Additions of glucose/fructose in the micromolar concentration range to receptors 2 and 3 induce significant fluorescence changes, but in the presence of arabinose, galactose, mannose, and xylose, only modest optical changes are observed. This optical change is attributed to a static photoinduced electron transfer mechanism. The meta-diboronic receptor 3 exhibited a high affinity/selectivity toward glucose (K = 3800 M^-1) over other monosaccharides including common interfering species such as fructose and mannitol. Based on multiple spectroscopic tools, electrospray ionization high-resolution mass spectrometry, crystal structures, and density functional theory calculations, the binding mode between 3 and glucose is proposed as a 1:1 complex with the glucofuranose form involving a cooperative chelating diboronate binding. These results demonstrate the usefulness of a new set of cationic fluorescent diboronic acid receptors with a strong ability for optical recognition of glucose in the sub-millimolar concentration range.

Rational design of mesoporous chiral MOFs as reactive pockets in nanochannels for enzyme-free identification of monosaccharide enantiomers

Monosaccharides play significant roles in daily metabolism in living organisms. Although various devices have been constructed for monosaccharide identification, most rely on the specificity of the natural enzyme. Herein, inspired by natural ionic channels, an asymmetrical MOF-in-nanochannel architecture is developed to discriminate monosaccharide enantiomers based on cascade reactions by combining oxidase-mimicking and Fenton-like catalysis in homochiral mesoporous CuMOF pockets. The identification performance is remarkably enhanced by the increased oxidase-mimicking activity of Au nanoparticles under a local surface plasmon resonance (LSPR) excitation. The apparent steady-state kinetic parameters and nano-fluidic simulation indicate that the different affinities induced by Au-LSPR excitation and the confinement effect from MOF pockets precipitate the high chiral sensitivity. This study offers a promising strategy for designing an enantiomer discrimination device and helps to gain insight into the origin of stereoselectivity in a natural enzyme.

A New Boron-Rhodamine-Containing Carboxylic Acid as a Sugar Chemosensor

We propose a boron-rhodamine-containing carboxylic acid (BRhoC) substance as a new sugar chemosensor. BRhoC was obtained by the Friedel-Crafts reaction of 4-formylbenzoic acid and N,N-dimethylphenylboronic acid, followed by chloranil oxidation. In an aqueous buffer solution at pH 7.4, BRhoC exhibited an absorption maximum (Abs_max) at 621 nm. Its molar absorption coefficient at Abs_max was calculated to be 1.4 × 10⁵ M^-1 cm^-1, and it exhibited an emission maximum (Em_max) at 644 nm for the excitation at 621 nm. The quantum yield of BRhoC in CH₃OH was calculated to be 0.16. The borinate group of BRhoC reacted with a diol moiety of sugar to form a cyclic ester, which induced a change in the absorbance and fluorescence spectra. An increase in the D-fructose (Fru) concentration resulted in the red shift of the Abs_max (621 nm without sugar and 637 nm with 100 mM Fru) and Em_max (644 nm without sugar and 658 nm with 100 mM Fru) peaks. From the curve fitting of the plots of the fluorescence intensity ratio at 644 nm and 658 nm, the binding constants (K) were determined to be 2.3 × 10² M^-1 and 3.1 M^-1 for Fru and D-glucose, respectively. The sugar-binding ability and presence of a carboxyl group render BRhoC a suitable building block for the fabrication of highly advanced chemosensors.

Recognition of d-Glucose in Water with Excellent Sensitivity, Selectivity, and Chiral Selectivity Using γ-Cyclodextrin and Fluorescent Boronic Acid Inclusion Complexes Having a Pseudo-diboronic Acid Moiety

Fluorescence recognition of d-glucose in water with excellent sensitivity, selectivity, and chiral selectivity is desired because d-glucose is an essential component in biological and pathological processes. We report an innovative approach that exploits the 1:2 stoichiometric inclusion complexes of γ-cyclodextrin (γ-CyD) with two molecules of fluorescent monoboronic acid-based receptors, which form a pseudo-diboronic acid moiety as the recognition site for d-glucose in water. Two monoboronic acids (1F and 2N) were easily synthesized without heating or column purification. The 1:2 stoichiometric inclusion complexes (1F/γ-CyD and 2N/γ-CyD) were prepared in a mixture of dimethyl sulfoxide/water (2/98 in v/v) by mixing γ-CyD and the corresponding monoboronic acids. Both 1F/γ-CyD and 2N/γ-CyD exhibited strong turn-on response to d-glucose with excellent selectivity over nine other saccharides in the water-rich solvent at pH 7.4 owing to the ditopic recognition of d-glucose by the pseudo-diboronic acid moieties. The limits of detection of 1F/γ-CyD and 2N/γ-CyD for d-glucose were 1.1 and 1.8 μM, respectively, indicating the remarkable sensitivity for the detection of d-glucose at μM levels. 1F/γ-CyD and 2N/γ-CyD also demonstrated chiral-selective recognition of d-glucose, which is apparent from the 2.0- and 6.3-fold enhancement of fluorescence by the addition of d-glucose relative to l-glucose addition, owing to the chiral pseudo-diboronic acid moieties produced by the chiral γ-CyD cavity. To the best of our knowledge, 2N/γ-CyD has the highest d/l selectivity among hitherto reported fluorescent diboronic acid-based receptors.

Molecular Level Sucrose Quantification: A Critical Review

Sucrose is a primary metabolite in plants, a source of energy, a source of carbon atoms for growth and development, and a regulator of biochemical processes. Most of the traditional analytical chemistry methods for sucrose quantification in plants require sample treatment (with consequent tissue destruction) and complex facilities, that do not allow real-time sucrose quantification at ultra-low concentrations (nM to pM range) under in vivo conditions, limiting our understanding of sucrose roles in plant physiology across different plant tissues and cellular compartments. Some of the above-mentioned problems may be circumvented with the use of bio-compatible ligands for molecular recognition of sucrose. Nevertheless, problems such as the signal-noise ratio, stability, and selectivity are some of the main challenges limiting the use of molecular recognition methods for the in vivo quantification of sucrose. In this review, we provide a critical analysis of the existing analytical chemistry tools, biosensors, and synthetic ligands, for sucrose quantification and discuss the most promising paths to improve upon its limits of detection. Our goal is to highlight the criteria design need for real-time, in vivo, highly sensitive and selective sucrose sensing capabilities to enable further our understanding of living organisms, the development of new plant breeding strategies for increased crop productivity and sustainability, and ultimately to contribute to the overarching need for food security.

Advancements in antimicrobial nanoscale materials and self-assembling systems

Antimicrobial resistance is directly responsible for more deaths per year than either HIV/AIDS or malaria and is predicted to incur a cumulative societal financial burden of at least $100 trillion between 2014 and 2050. Already heralded as one of the greatest threats to human health, the onset of the coronavirus pandemic has accelerated the prevalence of antimicrobial resistant bacterial infections due to factors including increased global antibiotic/antimicrobial use. Thus an urgent need for novel therapeutics to combat what some have termed the 'silent pandemic' is evident. This review acts as a repository of research and an overview of the novel therapeutic strategies being developed to overcome antimicrobial resistance, with a focus on self-assembling systems and nanoscale materials. The fundamental mechanisms of action, as well as the key advantages and disadvantages of each system are discussed, and attention is drawn to key examples within each field. As a result, this review provides a guide to the further design and development of antimicrobial systems, and outlines the interdisciplinary techniques required to translate this fundamental research towards the clinic.

An extended gate field-effect transistor (EG-FET) type non-enzymatic glucose sensor with inkjet-printed copper oxide nanoparticles

Abstract

We develop a disposable and cost-effective non-enzymatic glucose sensor consisting of an extended gate field effect transistor (EG-FET) to obtain effortless operation. The sensor is fabricated by printing, gold (Au) precursor ink and copper oxide nanoparticles (CuO NPs) inks using a commercial inkjet printer on a flexible Polyimide (PI) substrate. First, sensing properties are tested electrochemically. The sensor shows a sensitivity of 728.5 μA cm−2 mM−1 and a detection limit of 0.01 mM with a correlation coefficient (R) of 0.998. The observed linear dynamic range is from 0.5 to 7 mM. After that, the sensing electrode is adapted to the EG-FET. Two linear response ranges extend from 0.1 to 4 mM of a low concentration range of glucose with a sensitivity of 1295 μA cm−2 mM−1, and from 5 to 30 mM of a high concentration range of glucose with a sensitivity of 164 μA cm−2 mM−1 are observed. The EG-FET approach can enhance the detection sensitivities using amplification for a low concentration glucose range and extending a detection range for high concentration glucose. The presented work demonstrates that simply printed CuO NPs sensors can be used at low cost for disposable wide-range glucose detection devices.

Article Highlights

Synthesis of naphthalimide-type chemsensor and its application in quality evaluation for polygonatum sibiricum Red

The premise and key of ensuring the safety and effectiveness of traditional Chinese medicine (TCM) is to construct appropriate quality evaluation system of TCM. This study aimed to establish a pre-column derivatization HPLC method for achieving the quality control of Polygonatum sibiricum by reacting synthesized 4-hydrazino-1,8-naphthalimide (HAN) with diverse monosaccharides from the hydrolytic product of P. sibiricum polysaccharides (PSPs), followed by HPLC separation. The HAN was synthesized based on a CuI-catalyzed cross-coupling reaction in water, and then employed as a novel chemosensor that reacts with reducing sugars. Good separation was achieved at a detection wavelength of 448 nm using an ZORBAX SB-C8 column under a gradient elution at a flow rate of 0.5 ml/min within 12 min. The monosaccharide compositions of PSP mainly include two hexoses [glucose (Glc), galactose (Gal)] and two hexuronic acids [glucuronic acid (GlcA) and galacturonic acid (GalA)], and the molar ratio of Glc, Gal, GlcA and GalA is 16.67:52.94:10.58:19.81. The verified HPLC method, possessing excellent precision and good accuracy, successfully achieved rapid qualitative and quantitative determination for PSP. Additionally, the HAN displayed fluorescence enhancement through “push–pull” mode, and fluorescence decreased through “pull–pull” mode after binding to monosaccharides, which is a potential for fluorescence determination of different monosaccharides.

Diboronate Fluorophore for the Measurement of l-Glucose and Other Carbohydrates and Its Interaction with Albumin

l-Glucose has recently been investigated as an artificial sweetener, but no facile method is established for the measurement of l-glucose. The commercial probe Eversense employs a fluorescent diboronate in a small device for the optical monitoring of d-glucose in people with diabetes. Being achiral, the Eversense probe should be able to detect l-glucose as well as native d-glucose, but the probe is designed for fixation under the skin, and our attempts to use the probe at laboratory conditions failed, as the probe was resetting when moved between compartments. We thus designed a water-soluble anthracene diboronate 8 similar to the fluorophore used in Eversense and found 8 to respond well to l-glucose and other carbohydrates and artificial sweeteners, thus enabling measurements of l-glucose with the limit of quantification of 12 μM. Notably, the fluorescent signal of diboronate 8 was largely quenched in buffers with the physiological concentration of albumin (0.5 mM), so the given analytical method would need more optimization to be useful for measuring l-glucose and other carbohydrates in blood samples. We suspect that other diboronate fluorophores from the literature may be similarly quenched if applied in the presence of albumin.

Applications of the Reversible Boronic Acids/Boronate Switch to Nucleic Acids

Over the last decades, boron and nucleic acids chemistries have gained a lot of attention for biological, medicinal and analytical applications. Our laboratory has a long-standing interest in both chemistries and owing to the ability of boronic acids to react with cis-diol function in aqueous media we developed over the years a variety of applications ranging from molecular recognition and sensing to the development of reversible dynamic systems in which the natural phosphodiester linkage was replaced by a boronate. In this account, we summarize research results from our group from our preliminary studies on molecular recognition of ribonucleosides to the dynamic assembly of functional DNAzymes. In particular, the various parameters influencing the dynamic nature of these reversible covalent bonds able to respond to external stimuli are discussed. Finally, current challenges and opportunities for boron-based nucleic acids are also addressed.

Printed 384-Well Microtiter Plate on Paper for Fluorescent Chemosensor Array in Food Analysis

We propose a printed 384-well microtiter paper-based fluorescent chemosensor array device (384-well microtiter PCAD) to simultaneously categorize and discriminate saccharides and sulfur-containing amino acids for food analysis. The 384-well microtiter PCAD required 1 μL/4 mm 2 of each well can allow high-throughput sensing. The device embedded with self-assembled fluorescence chemosensors displayed a fingerprint-like response pattern for targets, the image of which was rapidly captured by a portable digital camera. Indeed, the paper-based chemosensor array system combined with imaging analysis and pattern recognition techniques successfully not only categorized saccharides and sulfur-containing amino acids but also classified mono- and disaccharide groups. Furthermore, the quantitative detectability of the printed device was revealed by a spike recovery test for fructose and glutathione in a diluted freshly made tomato juice. We believe that the 384-well microtiter PCAD using the imaging analysis system will be a powerful sensor for multi-analytes at several categorized groups in real samples.

Chemical-Based Surface Plasmon Resonance Imaging of Fingerprints

Fingerprints are extremely useful in personal identification; however, they are usually based on physical rather than chemical images because it remains a challenge to reveal a clear chemical fingerprint easily and sensitively. Herein, a surface plasmon resonance imaging (SPRi) method, combined with a chemically selective stepwise signal amplification (CS³A) strategy, is proposed to chemically image fingerprints with adjustable sensitivity and clarity. High-fidelity glucose-associated fingerprint images were obtained at five to seven cycles of CS³A based on the recognition reaction of concanavalin A (ConA) with dextran. The method is also extendable to image substances that possess and/or can be tagged with ConA- or dextran-recognizable groups. For demonstration, SPRi of carboxylic substances was conducted by amidating the carboxyl group with glucosamine to enable the ConA-based CS³A. Glucose- and carboxyl-based fingerprints were simultaneously and clearly imaged, allowing us to perform quantitative analysis of the representative of either glucose or amino acid (e.g., serine) or both. The curves measured from the standard spots were linear in the ranges of 1-4000 μM for glucose and 3.2-4000 μM for serine, with linear correlated coefficients of 0.9979 and 0.9962, respectively. It was then applied to the study of metabolic secretions in fingerprints during running exercise, yielding variation tendencies similar to those measured from sweat samples in the literature. As a noninvasive tool, the CS³A-coupled SPRi reveals both clear images of fingerprints and quantitative chemical information, and it is anticipated to become a competitive new method for chemically imaging fingerprints.

2-Aminopurine Fluorescence Spectroscopy for Probing a Glucose Binding Aptamer

Glucose is the most important analyte for biosensors. Recently a DNA aptamer was reported allowing binding-based detection. However, due to a relatively weak binding affinity, it is difficult to perform binding assays to understand the property of this aptamer. In this work, we replaced the only adenine base in the aptamer binding pocket with a 2-aminopurine (2AP) and used fluorescence spectroscopy to study glucose binding. In the selection buffer, glucose increased the 2AP fluorescence with a Kd of 15.0 mM glucose, which was comparable with the 10 mM Kd previously reported using the strand displacement assay. The binding required two Na+ ions or one Mg2+ that cannot be replaced by Li+ or K+. The binding was weaker at higher temperature and its van't Hoff plot indicated enthalpy-driven binding. While monosaccharides failed to achieve saturated binding even at high concentrations, two glucose-containing disaccharides, namely trehalose and sucrose, reached a similar fluorescence level as glucose although with over 10-fold higher Kd's. Detection limits in both the selection buffer (0.9 mM) and in artificial interstitial fluids (6.0 mM) were measured.