Molecular two-point recognition of fructosyl valine and fructosyl glycyl histidine in water by fluorescent Zn(II)-terpyridine complexes bearing boronic acids

Selective recognition of fructosyl amino acids in water by arylboronic acid-based receptors is a central field of modern supramolecular chemistry that impacts biological and medicinal chemistry. Fructosyl valine (FV) and fructosyl glycyl histidine (FGH) occur as N-terminal moieties of human glycated hemoglobin; therefore, the molecular design of biomimetic receptors is an attractive, but very challenging goal. Herein, we report three novel cationic Zn-terpyridine complexes bearing a fluorescent N-quinolinium nucleus covalently linked to three different isomers of strongly acidified phenylboronic acids (ortho-, 2Zn; meta-, 3Zn and para-, 4Zn) for the optical recognition of FV, FGH and comparative analytes (D-fructose, Gly, Val and His) in pure water at physiological pH. The complexes were designed to act as fluorescent receptors using a cooperative action of boric acid and a metal chelate. Complex 3Zn was found to display the most acidic -B(OH)2 group (pKa = 6.98) and exceptionally tight affinity for FV (K = 1.43 × 105 M-1) with a strong quenching analytical response in the micromolar concentration range. The addition of fructose and the other amino acids only induced moderate optical changes. On the basis of several spectroscopic tools (1H, 11B NMR, UV-Vis, and fluorescence titrations), ESI mass spectrometry, X-ray crystal structure, and DFT calculations, the interaction mode between 3Zn and FV is proposed in a 1 : 1 model through a cooperative two-point recognition involving a sp3 boronate-diol esterification with simultaneous coordination bonding of the carboxylate group of Val to the Zn atom. Fluorescence quenching is attributed to a static complexation photoinduced electron transfer mechanism as evidenced by lifetime experiments. The addition of FGH to 3Zn notably enhanced its emission intensity with micromolar affinity, but with a lower apparent binding constant than that observed for FV. FGH interacts with 3Zn through boronate-diol complexation and coordination of the imidazole ring of His. DFT-optimized structures of complexes 3Zn-FV and 3Zn-FGH show a picture of binding which shows that the Zn-complex has a suitable (B⋯Zn) distance to the two-point recognition with these analytes. Molecular recognition of fructosyl amino acids by transition-metal-based receptors has not been explored until now.

Optoelectronic Response to the Fluor Ion Bond on 4-(4,4,5,5-Tetramethyl-1,3,2-dioxoborolan-2-yl)benzaldehyde

Boronate esters are a class of compounds containing a boron atom bonded to two oxygen atoms in an ester group, often being used as precursors in the synthesis of other materials. The characterization of the structure and properties of esters is usually carried out by UV-visible, infrared, and nuclear magnetic resonance (NMR) spectroscopic techniques. With the aim to better understand our experimental data, in this article, the density functional theory (DFT) is used to analyze the UV-visible and infrared spectra, as well as the isotropic shielding and chemical shifts of the hydrogen atoms 1H, carbon 13C and boron 11B in the compound 4-(4,4,5,5-tetramethyl-1,3,2-dioxoborolan-2-yl)benzaldehyde. Furthermore, this study considers the change in its electronic and spectroscopic properties of this particular ester, when its boron atom is coordinated with a fluoride anion. The calculations were carried out using the LSDA and B3LYP functionals in Gaussian-16, and PBE in CASTEP. The results show that the B3LYP functional gives the best approximation to the experimental data. The formation of a coordinated covalent B-F bond highlights the remarkable sensitivity of the NMR chemical shifts of carbon, oxygen, and boron atoms and their surroundings. Furthermore, this bond also highlights the changes in the electron transitions bands n → π* and π → π* during the absorption and emission of a photon in the UV-vis, and in the stretching bands of the C=C bonds, and bending of BO2 in the infrared spectrum. This study not only contributes to the understanding of the properties of boronate esters but also provides important information on the interactions and responses optoelectronic of the compound when is bonded to a fluorine atom.

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.

Electrochemistry in sensing of molecular interactions of proteins and their behavior in an electric field

Electrochemical methods can be used not only for the sensitive analysis of proteins but also for deeper research into their structure, transport functions (transfer of electrons and protons), and sensing their interactions with soft and solid surfaces. Last but not least, electrochemical tools are useful for investigating the effect of an electric field on protein structure, the direct application of electrochemical methods for controlling protein function, or the micromanipulation of supramolecular protein structures. There are many experimental arrangements (modalities), from the classic configuration that works with an electrochemical cell to miniaturized electrochemical sensors and microchip platforms. The support of computational chemistry methods which appropriately complement the interpretation framework of experimental results is also important. This text describes recent directions in electrochemical methods for the determination of proteins and briefly summarizes available methodologies for the selective labeling of proteins using redox-active probes. Attention is also paid to the theoretical aspects of electron transport and the effect of an external electric field on the structure of selected proteins. Instead of providing a comprehensive overview, we aim to highlight areas of interest that have not been summarized recently, but, at the same time, represent current trends in the field.

Electrochemical detection of glycoproteins using boronic acid-modified metal-organic frameworks as dual-functional signal reporters

The sensitive analysis of glycoproteins is of great importance for early diagnosis and prognosis of diseases. In this work, a sandwich-type electrochemical aptasensor was developed for the detection of glycoproteins using 4-formylphenylboric acid (FPBA)-modified Cu-based metal-organic frameworks (FPBA-Cu-MOFs) as dual-functional signal probes. The target captured by the aptamer-modified electrode allowed the attachment of FPBA-Cu-MOFs based on the interaction between boronic acid and glycan on glycoproteins. Large numbers of Cu2+ ions in FPBA-Cu-MOFs produced an amplified signal for the direct voltammetric detection of glycoproteins. The electrochemical aptasensor showed a detection limit as low as 6.5 pg mL-1 for prostate specific antigen detection. The method obviates the use of antibody and enzymes for molecular recognition and signal output. The dual-functional MOFs can be extended to the design of other biosensors for the determination of diol-containing biomolecules in clinical diagnosis.

Construction of a Dendritic Nanoassembly-Based Fluorescent Biosensor for Electrostatic Interaction-Independent and Label-Free Measurement of Human Poly(ADP-ribose) Polymerase 1 in Lung Tissues

Poly(ADP-ribose) polymerase 1 (PARP-1) is responsible for catalyzing the creation of poly(ADP-ribose) polymer and involved in DNA replication and repair. Sensitive measurement of PARP-1 is critical for clinical diagnosis. However, the conventional electrostatic attraction-based PAPR-1 assays usually involve laborious procedures, poor sensitivity, and false positives. Herein, we demonstrate the construction of a dendritic nanoassembly-based fluorescent biosensor for electrostatic interaction-independent and label-free measurement of human PARP-1 in lung tumor tissues. When PARP-1 is present, the specific double-stranded DNA (dsDNA)-activated PARP-1 transfers the ADP-ribosyl group from nicotinamide adenine dinucleotide (NAD+)/biotinylated NAD+ to the PARP-1 itself, resulting in the formation of biotinylated dsDNA-PARP-1-PAR polymer bioconjugates that can be captured by magnetic beads. Upon the addition of TdT, APE1, and NH2-modified T-rich probe, the captured dsDNAs with dual 3'-OH termini initiate TdT-activated APE1-mediated hyperbranched amplification to produce abundant dendritic DNA nanoassemblies that can be stained by SYBR Green I to generate a high fluorescence signal. This biosensor is characterized by a template-free, electrostatic interaction-independent, high sensitivity, and label-free assay. It enables rapid (less than 3 h) measurement of PARP-1 with a limit of detection of 4.37 × 10-8 U/μL and accurate measurement of cellular PARP-1 activity with single-cell sensitivity. Moreover, it is capable of screening potential inhibitors and discriminating the PARP-1 level in normal person tissues and lung cancer patient tissues, with great potential in PARP-1-related clinical diagnosis and drug discovery.

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.

Diboronic-Acid-Based Electrochemical Sensor for Enzyme-Free Selective and Sensitive Glucose Detection

A diboronic acid anthracene-based fluorescent system for detecting blood glucose could be used for 180 days. However, there has not yet been a boronic acid immobilized electrode to selectively detect glucose in a signal-increased way. Considering malfunctions of sensors at high sugar levels, the electrochemical signal should be increased proportionally to the glucose concentration. Therefore, we synthesized a new diboronic acid derivative and fabricated the derivative-immobilized electrodes for the selective detection of glucose. We performed cyclic voltammetry and electrochemical impedance spectroscopy with an Fe(CN)₆^3-/4- redox pair for detecting glucose in the range of 0-500 mg/dL. The analysis revealed increased electron-transfer kinetics such as increased peak current and decreased semicircle radius of Nyquist plots as the glucose concentration increased. The cyclic voltammetry and impedance spectroscopy showed that the linear detection range of glucose was 40 to 500 mg/dL with limits of detection of 31.2 mg/dL and 21.5 mg/dL, respectively. We applied the fabricated electrode to detect glucose in artificial sweat and obtained 90% of the performance of the electrodes in PBS. Cyclic voltammetry measurements of other sugars such as galactose, fructose, and mannitol also showed linear increased peak currents proportional to the concentrations of the tested sugars. However, the slopes of the sugars were lower than that of glucose, indicating selectivity for glucose. These results proved the newly synthesized diboronic acid is a promising synthetic receptor for developing a long-term usable electrochemical sensor system.

Direct Electrochemical Signaling in Organic Electrochemical Transistors Comprising High-Conductivity Double-Network Hydrogels

In composite hydrogels, the high electrical performance of poly(3,4-ethylenedioxythiophene) complexed with poly(styrenesulfonate) (PEDOT:PSS) is integrated with complementary structural and electrochemical functions via a rationally designed poly(acrylamide) second network incorporating phenylboronic acid (PBA). Free-standing double-network hydrogels prepared by a simple one-pot radical polymerization exhibit state-of-the-art electrical conductivity (∼20 S cm^-1 in phosphate buffered saline) while retaining a degree of hydration similar to that of biological soft tissues. Low resistance contacts to Au electrodes are formed via facile thermo-mechanical annealing and demonstrate stability over a month of continuous immersion, thus enabling hydrogels to serve as channels of organic electrochemical transistors (OECTs). Despite thicknesses of ∼100 μm, gating of hydrogel OECTs is efficient with transconductances g_m ∼ 40 mS and on/off ratios of 10³ in saturation mode operation, whereas sufficiently high conductivity enables linear mode operation (g_m ∼ 1 mS at -10 mV drain bias). This drives a shift of sensing strategy toward detection of electrochemical signals originating within the bulky channel. A kinetic basis for glucose detection via diol esterification on PBA is identified as the coupling of PBA equilibrium to electrocatalyzed O₂ reduction occurring on PEDOT in cathodic potentials. Hydrogel OECTs inherently amplify this direct electrochemical signal, demonstrating the viability of a new class of soft, structural biosensors.

Synthesis of Novel One-Walled meso-Phenylboronic Acid-Functionalized Calix[4]pyrrole: A Highly Sensitive Electrochemical Sensor for Dopamine

Facile access to new one-walled meso-substituted phenylboronic acid-functionalized calix[4]pyrrole (C4P) has been revealed for the first time, starting from cost-effective and easily accessible materials. The structures of both the intermediate dipyrromethane (DPM) and the targeted functionalized C4P have been confirmed by means of ¹H-NMR, ¹³C-NMR, IR, and HRMS spectral data. The voltammetric investigations of the functionalized C4P films cast over a glassy carbon electrode (C4P-GCE) clearly establish the redox stability and redox accessibility of the boronic acid functional moiety present in the C4P framework. We demonstrate that the presence of the unique boronic acid functionality in the C4P endows it with an excellent potential for the highly sensitive electrochemical sensing of the neurotransmitter dopamine (DA). A linear correlation between the strength of the Faradaic signals corresponding to the electro-oxidation of DA over C4P-GCE and the concentration of DA was observed in a concentration range as wide as 0.165-2.302 μM. The C4P-GCE has revealed exceptional stability and reproducibility in the electrochemical sensing of DA, with a nanomolar level limit of detection as low as 15 nM.

Polymer indicator displacement assay: electrochemical glucose monitoring based on boronic acid receptors and graphene foam competitively binding with poly-nordihydroguaiaretic acid

A poly-nordihydroguaiaretic acid film is employed as a voltammetric indicator for bound/unbound boronic acid sites to report on glucose and fructose concentration.

The modern role of boron as a 'magic element' in biomedical science: chemistry perspective

Boron was misconstrued as a toxic element for animals, which retarded the growth of boron-containing drug discovery in the last century. Nevertheless, modern applications of boronic acid derivatives are attractive in biomedical applications after the declaration that boron is a 'probable essential element' for humans by the WHO. Additionally, the approval of five boronic acid-containing drugs by the FDA has vastly impacted the use of boron in medicinal chemistry, chemical biology, drug delivery, biomaterial exploration, pharmacological improvements, and nutrition. This review article focuses on the chemistries attributed to boronic acids at physiological pH, enticing chemists to multidisciplinary applications. Prospective uses of boronic acid in pharma and chemical biology, along with prospects and challenges, are also part of the deliberation. Understanding these fundamental chemistries and interactions of boronic acid in biological systems will enable solving future challenges in drug discovery and executing space-age applications.

SERS imaging analyses of bacteria cells among plant tissues

A chemical imaging method to mass surveil bacteria cells among plant tissues in situ is reported. Bacteria cells were pre-labeled with 3-mercaptophenylboronic acid for complexation with gold nanoparticles. Surface-enhanced Raman spectra were collated en masse to generate panoramic chemical images of bacteria populations. The approach was successfully employed to study the distribution of mass bacteria populations directly on and in selected plant tissues. This study demonstrates the great potential with which SERS imaging can be utilized for the study of bacterial cells among complex matrices, in some ways that are superior to electron and fluorescent microscopies.

Boronate-appended polymers with diol-functionalized ferrocene: an effective and selective method for voltammetric glucose sensing

In this research, three types of poly(amidoamine) dendrimers doped with a phenylboronic derivative at different ratios of -B(OH)₂ groups to amino groups (-NH₂) and one polyethyleneimine (PEI) polymer doped with a phenylboronic acid derivative were used as molecular receptors. The voltammetric glucose detection was based on the difference in the affinity of the tested systems in relation to 2-((ferrocenylmethyl)amino)propane-1,3-diol (Fc-1,3-diol) and glucose. Polymeric phenylboronic compounds were introduced to the electrode surface through an electrodeposition process at a constant potential. The obtained calibration curves were characterized by a wide range of linearity (0.005-100 μM) and low values of the limit of detection reaching even 0.0012 μM. Moreover, the influence of interferents (ascorbic acid, uric acid and fructose) was investigated at two different concentrations. Only fructose had a significant influence on the oxidation signal of ferrocene units, but solely in the case of R-Ph-B(OH)₂ (where R = PEI or PAMAM; Ph - phenyl ring) systems with a low content of boron groups, and these systems form complexes with glucose in a stoichiometric ratio of 1 : 1. The reliability of the results was confirmed by determining the percentage of recovery (added glucose vs. labeled glucose). Most of the results met the acceptance criteria (95%-105%), allowing the developed electrochemical sensors to be successfully used for the analysis of real-life samples.

Electrochemical Assay for Extremely Selective Recognition of Fructose Based on 4-Ferrocene-Phenylboronic Acid Probe and β-Cyclodextrins Supramolecular Complex

The aim of the present paper is to highlight a novel electrochemical assay for an extremely-selective detection of fructose thanks to the use of a supramolecular complex between β-cyclodextrins (β-CDs) and a chemically modified ferrocene with boronic acid named 4-Fc-PB/natural-β-CDs. Another kind of β-CDs, the 4-Fc-PB/3-phenylboronic-β-CDs, is proposed for the detection of glucose. The novel electrochemical probe is fully characterized by ¹ H nuclear magnetic resonance, mass spectroscopy, and elemental analysis, while the superior electrochemical performance is assessed in terms of sensitivity and detection limit. The novelty of the present work consists in the role of CDs that for the first time are employed in electrochemistry with a unique detection mechanism based on specific chemical interactions with the target molecule by the introduction of proper binding groups. A highly selective detection of fructose is obtained and it is believed that the proposed mechanism of detection represents a new way to electrochemically sense other molecules by varying the combination of specific groups of the supramolecular complex. The findings are of impactful importance since a quick, easy, cheap, and extremely selective detection of fructose is not yet available in the market, here achieved by using electrochemical methods which are a very growing field.

Fluorescent molecularly imprinted nanoparticles with boronate affinity for selective glycoprotein detection

Specific recognition and sensing of glycoproteins are of great importance in clinical diagnostics considering their frequent utilization as biomarkers and therapeutic targets. In this work, a biomimetic fluorescent sensor for the selective and sensitive detection of glycoprotein was developed, which was based on late-model boronate fluorescent molecularly imprinted nanoparticles (B-FMIP NPs). The B-FMIP NPs were fabricated via the macromolecular assembly of a fluorescent photo-crosslinkable amphiphilic copolymer containing boronic acid with glycoprotein in aqueous solution and in situ photo-crosslinking. Due to the synergism of boronate affinity and the molecular imprinting effect, the resultant B-FMIP NPs demonstrated specific recognition and remarkable selectivity toward the template glycoprotein (ovalbumin, OVA) with a high imprinted factor (α) of 6.0 and gave rise to obvious fluorescence quenching after binding with OVA in water. Under optimized experimental conditions, the as-prepared B-FMIP NPs exhibited linearity over the OVA concentration range of 10^-13 to 10^-3 mg mL^-1 with a detection limit of 3.3 × 10^-14 mg mL^-1, as well as a rapid response time (about 10 min), which was superior to that of other previously reported OVA sensors. Finally, these B-FMIP NPs have been applied for the determination of OVA in real samples.

Construction and Evaluation of a Self-Calibrating Multiresponse and Multifunctional Graphene Biosensor

Recently, many studies have been focused on the development of graphene-based biosensors. However, they rely on one type of signal and need to be calibrated by other techniques. In this study, a nonenzymatic graphene-based biosensor has been designed and constructed. Its ability to detect glucose and Escherichia coli by three different types of signals has been investigated. For its preparation, dopamine-functionalized polyethylene glycol and 2,5-thiophenediylbisboronic acid were conjugated onto the surface of graphene sheets by nitrene [2 + 1] cycloaddition and condensation reactions, respectively. Multivalent interactions between boronic acid segments and biosystems consequently increased the quantifiable fluorescence emission and UV absorption of dopamine segments. Additionally, changing the electrochemical behavior of the functionalized graphene sheets was possible and resulted in a measurable output signal. Conjugation of mannose onto the surface of the biosensor improved its magnitude of signals and specificity for sensing E. coli in a complex medium. The efficiency and accuracy of each signal was monitored by others, which resulted in a real-time self-calibrating biosensor. Taking advantage of the versatility of the three different indicators, including florescence, UV, and electrochemistry, the functionalized graphene sheets have been used as self-regulating biosensors to detect a variety of biosystems with a high accuracy and specificity in a short time.

Electrochemical preparation of surface molecularly imprinted poly(3-aminophenylboronic acid)/MWCNTs nanocomposite for sensitive sensing of epinephrine

A nanocomposite with multi-walled carbon nanotubes (MWCNTs) coated with surface molecularly imprinted polymers (MIPs) poly(3-aminophenylboronic acid) (PAPBA) was successfully prepared via potentiodynamic electropolymerization and tested as an effective electrochemical material for epinephrine (EP) detection. The morphology and properties of the sensing material were characterized with scanning electron microscopy and electrochemical impedance spectroscopy. Compared with MWCNTs or non-imprinted polymers PAPBA modified MWCNTs electrodes, the PAPBA(MIPs)/MWCNTs modified electrode showed a lower charge transfer resistance and enhanced electrochemical performance for EP detection. The improved performance can be attributed to the large amount of specific imprinted cavities with boric acid group which can selectively adsorb EP molecule and the synergistic effect between MWCNTs and PAPBA(MIPs). The effects of pH, the molar ratio between monomer and template molecule, the cycle number of electropolymerization, and the accumulation time of the modified electrode on the sensing performance were investigated. It was found that under the optimal conditions, the PAPBA(MIPs)/MWCNTs sensor could effectively recognize EP from many possible interferents of higher concentration within a wide linear range of 0.2-800 μmol·L^-1, with low detection limit of 35 nmol·L^-1, high sensitivity and good discrimination. The detection of EP in human serum and real injection samples using the PAPBA(MIPs)/MWCNTs sensor also gave satisfactory results.

Boronic acid as an efficient anchor group for surface modification of solid polyvinyl alcohol

We report the use of boronic acid as an anchor group for surface modification of solid polyvinyl alcohol (PVA); the surfaces of PVA microparticles, films, and nanofibers were chemically modified with boronic acid-appended fluorescent dyes through boronate esterification using a simple soaking technique in a short time under ambient conditions.

Recent development of boronic acid-based fluorescent sensors

As Lewis acids, boronic acids can bind with 1,2- or 1,3-diols in aqueous solution reversibly and covalently to form five or six cyclic esters, thus resulting in significant fluorescence changes. Based on this phenomenon, boronic acid compounds have been well developed as sensors to recognize carbohydrates or other substances. Several reviews in this area have been reported before, however, novel boronic acid-based fluorescent sensors have emerged in large numbers in recent years. This paper reviews new boron-based sensors from the last five years that can detect carbohydrates such as glucose, ribose and sialyl Lewis A/X, and other substances including catecholamines, reactive oxygen species, and ionic compounds. And emerging electrochemically related fluorescent sensors and functionalized boronic acid as new materials including nanoparticles, smart polymer gels, and quantum dots were also involved. By summarizing and discussing these newly developed sensors, we expect new inspiration in the design of boronic acid-based fluorescent sensors.

As Lewis acids, boronic acids can bind with 1,2- or 1,3-diols in aqueous solution reversibly and covalently to form five or six cyclic esters, thus resulting in significant fluorescence changes.

Boronic acids as molecular inks for surface functionalization of polyvinyl alcohol substrates

Boronic acids are proposed to be used as molecular inks for surface functionalization of polyvinyl alcohol substrates using marker pen applicators.

Hyper-Cross-Linked Polypyrene Spheres Functionalized with 3-Aminophenylboronic Acid for the Electrochemical Detection of Diols

A sensor for the determination of diols using 3-aminophenylboronic acid (APBA)-functionalized hyper-cross-linked polypyrene (PPy) (APBA@PPy) is presented. The uniform (∼1 μm in diameter) and highly porous (628 m2 g-1 in specific surface area) PPy spheres are fabricated via a one-pot protocol that consists of ZnBr2-catalyzed alkylation of pyrene, a subsequent cross-linking reaction, and concomitant self-assembly. The PPy spheres formed within a few minutes at mild conditions are featured by an excellent structural integrity and inertness to organic solvents. Thus, the APBA@PPy composites (∼1 μm in diameter; 458 m2 g-1 in specific surface area) are prepared simply by substituting unreacted bromomethyl groups on the surface of PPy spheres for APBA. The APBA@PPy composites are successfully applied for the electrochemical sensing of d-glucose and dopamine. A dye displacement assay is also performed using alizarin red dye conjugated to boronic acid in glucose buffer solution.

Boronic acid recognition of non-interacting carbohydrates for biomedical applications: increasing fluorescence signals of minimally interacting aldoses and sucralose

To address carbohydrates that are commonly used in biomedical applications with low binding affinities for boronic acid based detection systems, two chemical modification methods were utilized to increase sensitivity. Modified carbohydrates were analyzed using a two component fluorescent probe based on boronic acid-appended viologen-HPTS (4,4'-o-BBV). Carbohydrates normally giving poor signals (fucose, l-rhamnose, xylose) were subjected to sodium borohydride (NaBH₄) reduction in ambient conditions for 1 h yielding the corresponding sugar alcohols from fucose, l-rhamnose and xylose in essentially quantitative yields. Compared to original aldoses, apparent binding affinities were increased 4-25-fold. The chlorinated sweetener and colon permeability marker sucralose (Splenda), otherwise undetectable by boronic acids, was dechlorinated to a detectable derivative by reactive oxygen and hydroxide intermediates by the Fenton reaction or by H₂O₂ and UV light. This method is specific to sucralose as other common sugars, such as sucrose, do not contain any carbon-chlorine bonds. Significant fluorescence response was obtained for chemically modified sucralose with the 4,4'-o-BBV-HPTS probe system. This proof of principle can be applied to biomedical applications, such as gut permeability, malabsorption, etc.

A Novel Fiber Optic Surface Plasmon Resonance Biosensors with Special Boronic Acid Derivative to Detect Glycoprotein

We proposed and demonstrated a novel tilted fiber Bragg grating (TFBG)-based surface plasmon resonance (SPR) label-free biosensor via a special boronic acid derivative to detect glycoprotein with high sensitivity and selectivity. TFBG, as an effective sensing element for optical sensing in near-infrared wavelengths, possess the unique capability of easily exciting the SPR effect on fiber surface which coated with a nano-scale metal layer. SPR properties can be accurately detected by measuring the variation of transmitted spectra at optical communication wavelengths. In our experiment, a 10° TFBG coated with a 50 nm gold film was manufactured to stimulate SPR on a sensor surface. To detect glycoprotein selectively, the sensor was immobilized using designed phenylboronic acid as the recognition molecule, which can covalently bond with 1,2- or 1,3-diols to form five- or six-membered cyclic complexes for attaching diol-containing biomolecules and proteins. The phenylboronic acid was synthetized with long alkyl groups offering more flexible space, which was able to improve the capability of binding glycoprotein. The proposed TFBG-SPR sensors exhibit good selectivity and repeatability with a protein concentration sensitivity up to 2.867 dB/ (mg/mL) and a limit of detection (LOD) of 15.56 nM.

A sensitive signal-off electrogenerated chemiluminescence biosensing method for the discrimination of DNA hydroxymethylation based on glycosylation modification and signal quenching from ferroceneboronic acid

In this study, a new and sensitive signal-off electrogenerated chemiluminescence (ECL) biosensing method for the quantification of 5-hydroxymethylcytosine in DNA (5-hmC-DNA) was developed. The method achieved simple and sensitive detection of 5-hmC-DNA based on the glycosylation of 5-hmC, combining both the amplification function of gold nanoparticles (AuNPs) and the high quenching efficiency of the tris(2, 2'-ripyridine) dichlororuthenium(II) (Ru(bpy)₃²⁺)-ferrocene (Fc) system. First, the electrode modified with a mixture of Nafion and AuNPs was utilized as the platform for electrostatically adsorbing Ru(bpy)₃²⁺(an ECL-emitting species) and assembling 5-hmC-DNA. The 5-hmC-DNA was glycosylated by T4 β-glucosyltransferase, yielding β-glucosyl-5-hydroxymethyl-cytosine in DNA (5-ghmC-DNA). Finally, quencher-FcBA was further covalently bound to 5-ghmC-DNA through formation of boronate ester covalent bonds between boronic acid and cis-diols of 5-ghmC, resulting in a decrease in ECL intensity. The results indicated that the decreased ECL intensity was directly linear to the concentration of 5-hmC-DNA in the range from 1.0×10^-8 to 5.0×10^-11M with a low detection limit of 1.63×10^-11M. In addition, this ECL method was demonstrated to be useful for the quantification of 5-hmC in clinical serum samples. Moreover, the method allowed good discrimination among cytosine (5-C), 5-methylcytosine (5-mC), and 5-hmC in DNA.