A Bisboronic Acid Sensor for Ultra-High Selective Glucose Assay by 19F NMR Spectroscopy

A difunctional NMR&CD probe for specific detection and enantiomeric recognition of biothiols in complex mixtures

BACKGROUND

Biothiols are important for numerous cellular processes, such as resisting oxidative stress and protecting cell health. Their abnormal levels and molecular configurations have been associated with various diseases. So, establishing an effective and reliable method for the specific detection and enantiomeric discrimination of diverse biothiols is highly meaningful.

RESULTS

We have developed a new NMR and CD probe using 1,4-dinitroimidazole, specifically targeting the thiol group. This probe allows for the specific detection and enantiomeric recognition of biothiols in complex mixtures. We achieved this by identifying the distinguishable 1H NMR signals of 2nd in imidazole-ring of the resulting 4NI-biothiols in the downfield region at 7-8 ppm and newly discovered induced CD signals within 290-430 nm. Using this probe, the limits of detection of Cys, GSH, and Hcy, the recovery rates, and the concentration of GSH extracted from HEK293T cells were determined by measuring the unique downfield 1H NMR signals. Moreover, Cys, GSH, and Hcy can be discriminated simultaneously in complicated samples at a pH range of 2-3.5. Furthermore, this probe can also be utilized to sense chiral thiol-drugs.

SIGNIFICANCE

This method offers a cost-effective and accurate sensing solution for the specific detection of biothiols in complex mixtures, with stereochemical recognition.

Novel Pseudo-Two-Dimensional 19F NMR Spectroscopy for Rapid Simultaneous Detection of Amines in Complex Mixture

Rapid detection of amines in complex mixtures presents a significant challenge. Here, we introduce a novel nuclear magnetic resonance (NMR) method for amine detection utilizing a probe with two fluorine atoms in distinct chemical environments. Upon interaction with an amine, the probe generates two atomic resonance peaks, which are used to create coordinates, revealing fluorine chemical shifts on the 19F NMR spectroscopy. This innovative approach allows for the clear distinction of amine signals in a two-dimensional plane. This method has been effectively employed in analyzing amines in pharmaceuticals and amino acids in Ophiopogon japonicus and dry white wine, providing a robust and general approach for amine analysis.

BODIPYs α-appended with distyryl-linked aryl bisboronic acids: single-step cell staining and turn-on fluorescence binding with D-glucose

Small-molecule sensors that are selective for particular sugars are rare. The synthesis of BODIPYs appended with two boronic acid units is reported, alongside cellular staining/labelling and turn-on fluorescence binding data for carbohydrates. The structural frameworks were designed using computational methods, leaning on the chelation characteristics of bis(boronic acids) and the photophysical properties of BODIPYs. Selective binding to glucose is demonstrated via emission and absorption methods, and the challenges of using NMR data for studying carbohydrate binding are discussed. Furthermore, crystal structures, cell permeability and imaging properties of the BODIPYs appended with two boronic acid units are described. This work presents boronic-acid-appended BODIPYs as a potential framework for tunable carbohydrate sensing and chemical biology staining.

19F NMR Probes: Molecular Logic Material Implications for the Anion Discrimination and Chemodosimetric Approach for Selective Detection of H2O2

Detection and discrimination of similar solvation energies of bioanalytes are vital in medical and practical applications. Currently, various advanced techniques are equipped to recognize these crucial bioanalytes. Each strategy has its own benefits and limitations. One-dimensional response, lack of discrimination power for anions, and reactive oxygen species (ROS) generally limit the utilized fluorescent probe. Therefore, a cutting-edge, refined method is expected to conquer these limitations. The use of 19F NMR spectroscopy for detecting and discriminating essential analytes in practical applications is an emerging technique. As an alternative strategy, we report two fluorinated boronic acid-appended pyridinium salts 5-F-o-BBBpy (1) and 5-CF3-o-BBBpy (2). Probe (1) acts as a chemosensor for identifying and discriminating inorganic anions with similar solvation energies with strong bidirectional 19F shifts in the lower ppm range. Probe (2) turns as a chemo dosimeter for the selective detection and precise quantification of hydrogen peroxide (H2O2) among other competing ROS. To demonstrate real-life applicability, we successfully quantified H2O2 via probe (2) in different pharmaceutical, dental, and cosmetic samples. We found that tuning the -F/-CF3 moiety to the arene boronic acid enables the π-conjugation, a crucial prerequisite for the discrimination of anions and H2O2. Characteristic 19F NMR fingerprints in the presence of anions revealed a complementary implication (IMP)/not implication (NIMP) logic function. Finally, the 16 distinct binary Boolean operations on two logic values are defined for "functional completeness" using the special property of the IMP gate. Boolean logic's ability to handle information by utilizing characteristic 19F NMR fingerprints has not been seen previously in a single chemical platform for detecting and differentiating such anions.

Bioinspired Fluorine Labeling for 19F NMR-Based Plasma Amine Profiling

Metabolite profiling serves as a powerful tool that advances our understanding of biological systems, disease mechanisms, and environmental interactions. In this study, we present an approach employing 19F-nuclear magnetic resonance (19F NMR) spectroscopy for plasma amine profiling. This method utilizes a highly efficient and reliable fluorine-labeling reagent, 3,5-difluorosalicylaldehyde, which effectively emulates pyridoxal phosphate, facilitating the formation of Schiff base compounds with primary amines. The fluorine labeling allows for distinct resolution of 19F NMR signals from amine mixtures, leading to precise identification and quantification of amine metabolites in human plasma. This advancement offers valuable tools for furthering metabolomics research.

Highly sensitive surface plasmon resonance sensor with surface modified MoSe2/ZnO composite film for non-enzymatic glucose detection

The rapid and accurate assessment of glucose concentration has been demonstrated to play a significant role in human health, such as the diagnosis and treatment of diabetes, pharmaceutical research and quality monitoring in the food industry, necessitating further development of the performance for glucose sensor especially at low concentrations. However, glucose oxidase-based sensors suffer from crucial restriction in bioactivity because of their poor environmental tolerance. Recently, catalytic nanomaterials with enzyme-mimicking activity, known as nanozymes, have gained considerable interest to overcome the drawback. In this scenario, we report an inspiring surface plasmon resonance (SPR) sensor for non-enzymatic glucose detection employing ZnO nanoparticles and MoSe2 nanosheets composite (MoSe2/ZnO) as sensing film, featuring desirable advantages of high sensitivity and selectivity, lab-free and low cost. The ZnO was used to specifically recognize and bind glucose, and further signal amplification was realized by incorporating of MoSe2 owing to its larger specific surface area and favorable bio-compatibility, as well as high electron mobility. These unique features of MoSe2/ZnO composite film result in an obvious improvement of sensitivity for glucose detection. Experimental results show that the measurement sensitivity of the proposed sensor could reach 72.17 nm/(mg/mL) and a detection limit of 4.16 μg/mL by appropriately optimizing the componential constitutions of MoSe2/ZnO composite. In addition, the favorable selectivity, repeatability and stability are demonstrated as well. This facile and cost-effective work provides a novel strategy for constructing high-performance SPR sensor for glucose detection and a prospective application in biomedicine and human health monitoring.

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.

Portable smartphone-assisted ratiometric fluorescence sensor for visual detection of glucose

Fluorescence-based visual assays have sparked tremendous attention in on-site detection due to their obvious color gradient changes and high sensitivity. In this study, a novel emission wavelength shift-based visual sensing platform is constructed to detect glucose based on the oxidation of Rhodamine B (RhB). MnO₂ nanosheets (MnO₂ NS) with strong oxidizing properties were introduced to oxidize RhB, which resulted in a blue shift in the emission wavelength, and a visual color changed of the fluorescence from orange-red to green. The oxidation reaction could be inhibited via reducing and destroying MnO₂ NS by H₂O₂, which was produced by the oxidizing procedure of glucose in the presence of glucose oxidase (GOx). A series of wavelength shifts and fluorescence color variations appeared with the addition of various amounts of glucose. A ratiometric fluorescence glucose sensor with a lowest recorded concentration of 0.25 μM was developed. Meanwhile, test paper-based assays integrated with the smartphone platform were established for the sensing of glucose by means of the significant fluorescence color changes, offering a reliable, sensitive, and portable on-site assay of glucose.

Rapid and Selective 19F NMR-Based Sensors for Fingerprint Identification of Ribose

Ribose plays an important role in the process of life. Excessive ribose in the human cerebrospinal fluid or urine can be used as an early diagnostic marker of leukoencephalopathy. Fluorinated phenylboronic acid combined with ¹⁹F NMR spectroscopy was a powerful method for molecular recognition. However, phenylboronic acid-based sensors for selective detection of ribose are rarely reported in the literature. In this study, the rapid and highly selective recognition of ribose was studied by ¹⁹F NMR and 2-fluorophenylboric acid. It was found that 2-fluoro-phenylboric acid was an appropriate ¹⁹F NMR-based sensor molecule for the determination of ribose under physiological conditions with high selectivity and robust anti-interference ability. When 2-fluorophenylboric acid was used for the detection of ribose in human urine without any sample pretreatment, a limit of detection of 78 μM was obtained at room temperature under given ¹⁹F NMR experimental conditions (400 MHz, 512 scans, ca. 12 min), which can well meet the needs of practical application.

Diol responsive viscosity increase in a cetyltrimethylammonium bromide/sodium salicylate/3-fluorophenylboronic acid micelle system

We report a novel smart micellar system utilising a phenylboronic acid (PBA) derivative whose viscosity increases on adding diol compounds such as sugar or sugar alcohol. We prepared a typical worm-like micelle (WLM) system in 100 mM cetyltrimethylammonium bromide (CTAB)/70 mM sodium salicylate (NaSal), which showed high zero-shear viscosity (η 0). Upon the addition of 20 mM 3-fluorophenylboronic acid (3FPBA) to the WLM system, η 0 decreased by 1/300 that of the system without 3FPBA. Furthermore, upon the addition of 1.12 M fructose (Fru) and 1.12 M sorbitol (Sor) to the CTAB/NaSal/3FPBA system, η 0 increased by 50-fold and 30-fold, respectively. 19F NMR spectral results of the systems using 4-fluorosalicylic acid (FSal) instead of NaSal demonstrated that the FSal/3FPBA-complex interacts with CTAB. Moreover, the addition of sugar or sugar alcohol to the micellar system leads to a decrease in the amount of FSal/3FPBA-complex interacting with CTA+ and an increase in the amount of 3FPBA/Fru or Sor-complex, which does not interact with CTA+. These changes in molecular interactions induce the elongation of the WLMs and increase the viscosity of the system. This system utilises the competitive cyclic ester bond between the NaSal/3FPBA and 3FPBA/sugar or sugar alcohol to induce viscosity changes.