Boronic Acid Sensors Research Articles

A fluorescent probe for selective detection of boric acids and its application for screening the conversion of the Suzuki-Miyaura coupling reaction.

Boric acid (B(OH)3) plays an important physiological role and is widely used as a food preservative and an antiseptic. Various colorimetric, fluorescent probes have been developed to detect boric acid; however, most of them could not discriminate boric acid over boronic acids (R-B(OH)2) or are limited to boronic acid sensors. Therefore, the development of boric acid-selective probes is necessary. Herein, a salicylimine-based fluorophore, Di-OH, was designed that showed selective fluorescence response to boric acid over boronic acid. Its fluorescence response to boric acid showed a large fluorescence turn-on signal up to 140 fold and excellent selectivity with various analytes. Furthermore, since boric acid is generated in proportion to the consumed boronic acid derivatives during reactions involving oraganoboron compounds, Di-OH allowed the determination of the conversion of the Suzuki-Miyaura coupling reaction using fluorescence spectroscopy and its correlation with the GC conversion was confirmed.

Development of a switching-type fluorescence sensor for the detection of boronic acid-containing agents.

Since the therapeutic effect of boron neutron capture therapy is influenced by the intracellular distribution profile of boronoagents containing 10B atoms, it is necessary to establish a method that can determine the intracellular distribution profile of boronoagents. We aimed to develop a small molecule-based fluorescence sensor that changes its fluorescence properties upon complexation with the boronic acid moiety of a boronoagent. Thus, we designed a 2-(2-pyridyl)phenol derivative PPN-1 by introducing a N,O ligand substructure into a zinc sensor probe with excellent fluorescence properties. To investigate the effectiveness of PPN-1, we synthesized PPN-1 and evaluated its fluorescence properties compared to DAHMI, a current available boronic acid sensor. Consequently, PPN-1 showed favorable off/on fluorescence switching ability with a large Stokes shift after the addition of p-boronophenylalanine (BPA). Notably, after adding BPA, PPN-1 exhibited a rapid increase and reached a fluorescence plateau within 5min, which is much shorter than the 2h needed for DAHMI. Further, PPN-1 has excellent selectivity and detection and quantification limits similar to those of ICP-OES. These results demonstrated that PPN-1 is a practical scaffold for the detection and quantification of boronic acids and will provide essential insights for the development of boronic acid-targeted fluorescent sensors in the future.

Colorimetric discrimination of tea polyphenols based on boronic acid sensor assembled with pH indicator

Due to their analog chemical structures and trace amounts, the distinguishment of tea polyphenols has always been an important but difficult challenge. In this paper, a novel sensing strategy NapB-MR by combining boronic acid-based sensor NapB with pH indicator (methyl red, MR) was constructed to colorimetrically identify different tea polyphenols. Gallic acid (GA), methyl gallate (MG), epicatechin (EC), epicatechin gallate (ECG), epigallocatechin (EGC) and epigallocatechin gallate (EGCG) were selected as analytes, which represent the majority of the polyphenols present in green tea. Due to the pH change profile induced by boronic ester formation, methyl red was applied to reflect the difference by exhibiting a unique colorimetric response towards each tea polyphenol. In combination with the Partial Least Squares Discriminant Analysis (PLSDA) model, the discrimination of six tea polyphenols were successfully carried out. In addition, quantitatively detection of each tea polyphenol could be achieved by coupling with UV–Vis spectroscopy, and low detection limits were obtained. Most importantly, the NapB-MR was successfully applied to classify green tea samples within different categories and grades with an identification rate of 100%. Therefore, the proposed sensing strategy can be a promising method for analog detection that can meet the increasing demand from consumers for the discrimination of polyphenol-related natural products.

Binaphthalene Boronic Acid Sensor for Saccharides and d‐Fructose Determination in Beverages

AbstractThe presence of electron rich compounds such as amines added to the fluorescent methoxybinaphthalene boronic acid results in a dramatic increase in affinity of diols to the aryl boronic acid as well as in the augmented fluorescence response. This is likely the result of the change in boron geometry upon coordination with electron donor which facilitate the diols binding. Here, we demonstrate the role of amino alcohol additive in binding of saccharides by boronic acid‐based fluorescent sensor. We show that this strategy allows a poorly responsive sensor to become a highly sensitive probe for the detection of sugars, which could be used for classification of saccharides as well as for quantitative analysis in DMSO‐water solutions. The simple binaphthalene boronic acid sensor was particularly sensitive to d‐fructose (Ka=2.08×106), which allowed for identification of commercial sweetened beverages based on their d‐fructose content. The same method was successfully used for the quantitative analysis of d‐fructose in soft beverages.

A new fluorescent boronic acid sensor based on carbazole for glucose sensing via aggregation-induced emission.

A water-soluble fluorescent sensor based on carbazole pyridinium boronic acid (CPBA) was designed and synthesized. Its structure has been confirmed by CHN and 1H and 13C NMR, FT-IR, and MS spectral data. Fluorescence studies of the synthesized chemosensor CPBA showed a selective ratiometric fluorescent response for glucose among different monosaccharides. The results specified that CPBA is a pH-sensitive sensor that behaves differently in the absence and presence of glucose in the pH range 4–10. The pH, DLS, Job's plot, UV-visible, and fluorescence titration studies showed that the selectivity of CPBA towards glucose is through the aggregation-induced emission (AIE) phenomenon. The fluorescence emission intensity of CPBA changes by more than 2100 fold by adding glucose, whereas it is 2 fold for fructose. The calculated binding constant value of CPBA for glucose (K = 2.3 × 106 M−1) is 85 times greater than for fructose, indicating the high affinity of the sensor for glucose.

Novel detection method for gallic acid: A water soluble boronic acid-based fluorescent sensor with double recognition sites

As one of the widespread phenols in nature, gallic acid (GA) has attracted a subject of attention due to its extensive biological properties. It is very important and significant to develop a sensitive and selective gallic acid sensor. In recent years, owing to their reversible covalent binding with Lewis bases and polyols, boronic acid compounds have been widely reported as fluorescence sensors for the identification of carbohydrates, ions and hydrogen peroxide, etc. However, boronic acid sensors for specific recognition of gallic acid have not been reported. Herein, a novel water-soluble boronic acid sensor with double recognition sites is reported. When the concentration of gallic acid added was 1.1 × 10−4 M, the fluorescence intensity of sensor 9b decreased by 80%, followed by pyrogallic acid and dopamine. However, the fluorescence of the sensor 9b combined with other analytes such as ATP, sialic acid, and uridine was basically unchanged, indicating that the sensor 9b had no ability to recognize these analytes. Also, sensor 9b has a fast response time to gallic acid at room temperature, and has a high binding constant (12355.9 ± 156.89 M−1) and low LOD (7.30 × 10−7 M). Moreover, gallic acid content of real samples was also determined, and the results showed that this method has a higher recovery rate. Therefore, sensor 9b can be used as a potential tool for detecting biologically significant gallic acid in actual samples such as food, medicine, and environmental analysis samples.

896-P: Putting the Pieces Together: Building a Nonenzymatic Wearable Glucose Sensor Using Silicon Microneedle Arrays

We developed the technology to build a novel painless CGM that is an on-body, wirelessly transmitting device that extracts interstitial fluid with a dime-sized patch of microneedles and optically detects glucose from extremely small fluid volumes. We not only developed an innovative method for fabricating silicon microneedles, sharp and small enough to penetrate skin without pain (160 µm in height, 50 µm in diameter, and 100 µm in width), but also demonstrated that our microneedle fabrication is repeatable and reliable. Next we developed an entirely new, stable, non-enzymatic glucose-sensing method based on a variation of the well-known fluorescent-based boronic acid sensor, and further refined this sensor to allow for conductivity based sensing as well as ratiometric sensing of glucose (Figure 1, left). Finally, we built a novel integrated silicon buried dual-junction (BDJ) photodiode-based system with which to detect glucose with our sensor. The Figure attached shows our latest successes with ratiometric sensing of tartaric acid using our microfabricated device (Figure 1, right). Given our results, we believe this technology can now be transitioned to industry, and we are moving on to developing a wearable microfluidic-based patch pump that can allow for a truly affordable artificial pancreas based diabetes management solution. Disclosure S. Pennathur: Board Member; Self; Laxmi Therapeutic Devices. Employee; Self; Laxmi Therapeutic Devices. Research Support; Self; American Diabetes Association, Leona M. and Harry B. Helmsley Charitable Trust. Stock/Shareholder; Self; Laxmi Therapeutic Devices. H. Kim: None. B. Wang: None. B.N. Queenan: None. D. Huber: None. Funding American Diabetes Association/Pathway to Stop Diabetes (1-17-VSN-18 to S.P.)

A water-soluble boronic acid sensor for caffeic acid based on double sites recognition.

Due to reversibly and covalently binding with Lewis bases and polyols, boronic acid compounds as fluorescent sensors have been widely reported to recognize carbohydrates, ions, hydrogen peroxide, and so on. However, boronic acid sensors for highly selective recognition of caffeic acid rather than catechol or catechol derivatives have not been reported yet. Herein a novel water-soluble sensor 5c with double recognition sites based on a boronic acid was reported. When 2.3 × 10−4 M of caffeic acid was added, the fluorescence intensity of sensor 5c decreased by 99.6% via inner filter effect (IFE) because its excitation spectrum well overlaps with the absorption spectrum of caffeic acid under neutral condition, while the fluorescence increased or did not change obviously after binding with other analytes including carbohydrates and other catechol derivatives. In addition, the response time to caffeic acid is fast at room temperature, and a high binding constant (9245.7 ± 348.3 M−1) and low LOD (1.81 × 10−6 M) was calculated. Moreover, determination of caffeic acid content in caffeic acid tablets was studied, and the recovery rate is sufficient. Therefore, sensor 5c can be used as a potential tool for detecting biologically significant caffeic acid in real samples.

Boronic acid sensors with double recognition sites: a review.

Boronic acids reversibly and covalently bind to Lewis bases and polyols, which facilitated the development of a large number of chemical sensors to recognize carbohydrates, catecholamines, ions, hydrogen peroxide, and so on. However, as the binding mechanism of boronic acids and analytes is not very clear, it is still a challenge to discover sensors with high affinity and selectivity. In this review, boronic acid sensors with two recognition sites, including diboronic acid sensors, and monoboronic acid sensors having another group or binding moiety, are summarized. Owing to double recognition sites working synergistically, the binding affinity and selectivity of sensors can be improved significantly. This review may help researchers to sort out the binding rules and develop ideal boronic acid-based sensors.

940-P: Toward a Novel Tiny Continuous Glucose Monitor (CGM): Step 3, Building an Enhanced Ratiometric Detector Using a Buried Dual Junction Diode (BDJ)

Continuous glucose monitors (CGM) improve overall glucose control in patients with diabetes, but have many disadvantages for users. We are developing a novel CGM that will be painless to insert and wear, and easy to use. Our goal is an on-body, wirelessly transmitting CGM device that extracts interstitial fluid with a dime-sized patch of microneedles and optically detects glucose from extremely small fluid volumes. Our first step in 2016 was developing an innovative method for fabricating silicon microneedles, sharp and small enough to penetrate skin without pain (160 µm in height, 50 µm in diameter, and 100 µm in width). The next year we not only demonstrated that our microneedle fabrication is repeatable and reliable but also developed an entirely new, stable, non-enzymatic glucose-sensing method based on a variation of the well-known fluorescent-based boronic acid sensor. Since then, we have further refined our sensor for conductivity sensing as well as demonstrated a novel integrated silicon buried dual-junction (BDJ) photodiode-based system with which to detect glucose with our sensor. Specifically, we built a buried dual junction (BDJ) photodiode for color or ratiometric optical sensing. We employed a simple polycarbonate UV filter to block stray 380 nm pump light from reaching the BDJ detector, and the signal-to-background ratio is further enhanced by incorporating a yellow band filter between the LED and sample reservoir. To test the optical performance of our photosensor, cationic polymer PFP and fluorescein/coumarin are excited at 380 nm and measured at the peak 425 and 525 nm. These data prove that our device is capable of detecting ∼µM of fluorophores in a ∼7 µL of volume. Next, we demonstrated the diffusion of molecules via hollow silicon microneedles. These data show that integration if all components can enable for the first time, a compact, wearable optical biosensor. Disclosure S. Pennathur: Board Member; Self; Laxmi Therapeutic Devices. Consultant; Self; Alveo Technologies. Funding American Diabetes Association/Pathway to Stop Diabetes (1-17-VSN-18)

Pyrene-based bisboronic sensors for multichannel enantioselective recognition of tartaric acid

New chiral bisboronic receptors based on pyrene-excimer were synthesized and applied for the determination of absolute configuration and enantiomeric composition of tartaric acid. The distinction was visualized by portable UV lamp in certain concentration range. There were three ways for the sensors to enantioselectively recognize tartaric acid, including the fluorescence spectrum, UV–vis spectrum, and CD spectrum. The enantiomeric excess of tartaric acid was measured quantitatively by using fluorescence analytical technique. Compared with the previous chiral boronic acid sensors, sensor 1 showed weaker background fluorescence and excellent chiral recognition ability of D/l-tartaric acid throughout the whole pH range.

Visualization of Boronic Acid Containing Pharmaceuticals in Live Tumor Cells Using a Fluorescent Boronic Acid Sensor

Boronic acid containing compounds are regarded as a new class of pharmaceuticals, and the distribution in live cells is crucial for the development of novel drugs. However, generic detection methods for boron compounds are not suitable for live-cell imaging, and the fluorescence-labeling technique is challenging to apply for small molecules. Fluorescent boron-sensor DAHMI which is based on a boron chelating ligand was developed for a novel visualization method of boron-based pharmaceuticals in the live cell. In this study, we analyzed the distribution of boronic acid derivatives in live cells using a fluorescent boronic acid sensor.

Direct sensing of fluoride in aqueous solutions using a boronic acid based sensor.

Binding of the fluoride ion triggers aggregation of a pyreneboronic acid-catechol ensemble in acidic aqueous solutions, giving rise to intense excimer emission, allowing for sensitive fluoride ion sensing at ppm levels, with an apparent fluoride binding constant higher than 10(3) M(-1) which is unprecedented for boronic acid sensors in water.

Synthesis of three fluorescent boronic acid sensors for tumor marker Sialyl Lewis X in cancer diagnosis

Sialyl Lewis X (sLex) is a carbohydrate that is considered not only a marker for cancer, but also an antigen associated with the malignant behavior of cancerous cells. We have synthesized three fluorescent boronic acid sensors as potential sensors for sLex. Photoinduced electron transfer by a fluorescence analyzer was used to assess sensor-sLex antigen binding. The reaction was carried out in mixed aqueous solution, and Sensor 3 was identified as showing the strongest fluorescence enhancement upon binding to sLex at 10nM. In cell-line culture experiments, Sensor 1 was shown to label sLex expression positively for HepG2, Colo 205, and COS-7 cells, and negatively for MDA-MB-231 cells; Sensor 2 did so positively for HepG2, PLC/PRF/5, and Colo 205 cells, and negatively for MDA-MB-231 and COS7 cells; and Sensor 3 did so positively for PLC/PRF/5 and HepG2 cells, and negatively for MDA-MD-231 and COS7 cells. MTT cytotoxicity experiment results showed that the three sensors are nontoxic, and Hoechst 33258 experiments showed that no apoptosis occurred.

Ditopic boronic acid and imine-based naphthalimide fluorescence sensor for copper(II).

Copper ions are essential for many biological processes. However, high concentrations of copper can be detrimental to the cell or organism. A novel naphthalimide derivative bearing a monoboronic acid group (BNP) was investigated as a Cu(2+) selective fluorescent sensor in living cells. This derivative is one of the rare examples of reversible fluorescent chemosensors for Cu(2+) which uses a boronic acid group for a binding site. Moreover, the adduct BNP-Cu(2+) displays a fluorescence enhancement with fructose. The uptake of this novel compound in HeLa cancer cells was imaged using confocal fluorescence microscopy techniques including two-photon fluorescence lifetime imaging microscopy.

Boronic acid sensors for saccharides: A theoretical study

Selective detection of saccharides by fluorescent boronic acid sensors has been the object of active research over the last two decades with numerous experimental reports published. A theoretical study is presented here on pyrene- and anthracene-boronic acid systems and their fluorescent sensing of d-glucose, employing Density Functional Theory and Time-Dependent Density Functional Theory. The difficulties encountered by straight-forward computational approaches are described while it is shown that it is possible to obtain a physically correct description of the photoinduced electron transfer in these systems from diagrams of the molecular orbital energies of the separate donor and acceptor moieties.

The Progress of Selective Fluorescent Chemosensors by Boronic Acid

As a cutting-edge scientific research field, the detection of biological active substance is very important for the prevention, diagnosis and treatment of diseases. Boronic acid interacts with cis-1,2-or 1,3-diol to form five- or six-membered ring which could be used as the reporter of fluorescent sensors to probe carbohydrates and bioactive substance. This review summarizes the recent progress of boronic acid sensors for carbohydrates, L-dopamine, fluoride, copper ion, mercury ion and hydrogen peroxide. In this article, we will briefly introduce the chemistry of boronic acid, and then give a description of the fluorescence properties of each boronic acid sensor, such as fluorescence intensity change, excitation and emission wavelengths, quantum yields and water solubility. In addition, we summarize the mechanisms of fluorescent signal output for some representative sensors and discuss the strategies for developing new fluorescent probes.

Enantioselective Recognition of Mandelic Acid by a 3,6-Dithiophen-2-yl-9H-carbazole-Based Chiral Fluorescent Bisboronic Acid Sensor

We have prepared chiral fluorescent bisboronic acid sensors with 3,6-dithiophen-2-yl-9H-carbazole as the fluorophore. The thiophene moiety was used to extend the π-conjugation framework of the fluorophore in order to red-shift the fluorescence emission and, at the same time, to enhance the novel process where the fluorophore serves as the electron donor of the photoinduced electron transfer process (d-PET) of the boronic acid sensors; i.e., the background fluorescence of the sensor 1 at acidic pH is weaker compared to that at neutral or basic pH, in stark contrast to the typical a-PET boronic acid sensors (where the fluorophore serves as the electron acceptor of the photoinduced electron transfer process). The benefit of the d-PET boronic acid sensors is that the recognition of the hydroxylic acids can be achieved at acidic pH. We found that the thiophene moiety is an efficient π-conjugation linker and electron donor; as a result, the d-PET contrast ratio of the sensors upon variation of the pH is improved 10-fold when compared to the previously reported d-PET sensors without the thiophene moiety. Enantioselective recognition of tartaric acid was achieved at acid pH, and the enantioselectivity (total response K(D)I(F)(D)/K(L)I(F)(L)) is 3.3. The fluorescence enhancement (I(F)(Sample)/I(F)(Blank)) of sensor 1 upon binding with tartaric acid is 3.5-fold at pH 3.0. With the fluorescent bisboronic acid sensor 1, enantioselective recognition of mandelic acid was achieved for the first time. To the best of our knowledge, this is the first time that the mandelic acid has been enantioselectively recognized using a chiral fluorescent boronic acid sensor. Chiral monoboronic acid sensor 2 and bisboronic acid sensor 3 without the thiophene moiety failed to enantioselectively recognize mandelic acid. Our findings with the thiophene-incorporated boronic acid sensors will be important for the design of d-PET fluorescent sensors for the enantioselective recognition of α-hydroxylic acids such as mandelic acid, given that it is currently a challenge to recognize these analytes with boronic acid fluorescent molecular sensors.

Enhanced Enantioselective Recognition with Diastereoisomeric BINOL Based Chiral Fluorescent Boronic Acid Sensors

We prepared the diastereoisomers of BINOL based bisboronic acid chiral probes (the probes are with dual chirogenic centers) for enantioselective recognition of chiral analytes, such as tartaric acids, D-sorbitol, etc. We found the diastereoisomeric probes give different emission intensity-pH profiles, a phenomenon was reported, probably, for the first time. We found that with the second chirogenic center, the selectivity of the probes toward chiral analytes can be improved. For example, the diastereoisomeric probes give drastically different response to D-sorbitol, the same selectivity was not found for the BINOL bisboronic acid probes with single chirogenic center. Our result with the diastereoisomeric probes is helpful for design of new chiral molecular probes to enhance the selectivity of the boronic acid sensors toward chiral analytes.

Chiral Donor Photoinduced‐Electron‐Transfer (d‐PET) Boronic Acid Chemosensors for the Selective Recognition of Tartaric Acids, Disaccharides, and Ginsenosides

A modular approach was proposed for the preparation of chiral fluorescent molecular sensors, in which the fluorophore, scaffold, and chirogenic center can be connected by ethynyl groups, and these modules can easily be changed to other structures to optimize the molecular sensing performance of the sensors. This modular strategy to assembly chiral sensors alleviated the previous restrictions of chiral boronic acid sensors, for which the chirogenic center, fluorophore, and scaffold were integrated, thus it was difficult to optimize the molecular structures by chemical modifications. We demonstrated the potential of our new strategy by the preparation of a sensor with a larger scaffold. The photoinduced electron-transfer (PET) effect is efficient even with a large distance between the N atom and the fluorophore core. Furthermore, the rarely reported donor-PET (d-PET) effect, which was previously limited to carbazole, was extended to phenothiazine fluorophore. The contrast ratio, that is, PET efficiency of the new d-PET sensor, is increased to 8.0, compared to 2.0 with the previous carbazole d-PET sensors. Furthermore, the ethynylated phenothiazine shows longer excitation wavelength (centered at 380 nm) and emission wavelength (492 nm), a large Stokes shift (142 nm), and high fluorescence quantum yield in aqueous solution (Φ=0.48 in MeOH/water, 3:1 v/v). Enantioselective recognition of tartaric acid was achieved with the new d-PET boronic acid sensors. The enantioselectivity is up to 10 (ratio of the binding constants toward D- and L-tartaric acid, k(D)/k(L)). A consecutive fluorescence enhancement/decrease was observed, thus we propose a transition of the binding stoichiometry from 1:1 to 1:2 as the analyte concentration increases, which is supported by mass spectra analysis. The boronic acid sensors were used for selective and sensitive recognition of disaccharides and glycosylated steroids (ginsenosides).