Search

Long-wavelength fluorescent sensors with large Stokes shifts show useful applications in chemical biology and clinical laboratory diagnosis. We have recently reported [4-(4-{[3-(4-boronobenzamido)propyl]carbamoyl}quinolin-2-yl)phenyl]boronic acid that can selectively recognize d -ribose in a buffer solution of pH 7.4. However, the short emission wavelength (395 nm) and aggregation-caused quenching effect are not conducive to applications as a sensor. Novel diboronic acid compounds are synthesized using 2-(4-boronophenyl)quinoline-4-carboxylic acid as the building block and p -phenylenediamine as the linker. These compounds show aggregation-induced emission and fluorescence emission at about 500 nm. In addition, after binding to most carbohydrates, the aggregated state of the boronic acid–containing compounds is dissociated, resulting in fluorescence quenching. Using [4-(4-{[4-(3-borono-5-methoxybenzamido)phenyl]carbamoyl}quinoline-2-yl)phenyl]boronic acid as an example, addition of 55 mM of d -ribose resulted in the strongest quenching of 83% for all the tested carbohydrates, indicating selectively recognizing d -ribose. The reciprocal of the fluorescence intensity change showed a good linear relationship with the reciprocal of d -ribose concentration (R 2 ⩾ 0.99), indicating sensor binding to d -ribose in a ratio of 1:1 to form an inclusion complex. The fluorescence emission is red-shifted compared to 2-(4-boronophenyl)quinoline-4-carboxylic acid and its common derivatives, which provides a new method for the development of long-wavelength fluorescent sensors. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Fig. 2 The recognition mechanism of sensor 9b and gallic acid. [Display omitted] • Gallic acid is involved in many important biological events and has a variety of biological properties. • Boronic acid-based fluorescence sensors can specifically recognize compounds with 1, 2-diol structure. • Guanidine group synergizes with boronic acid group to enhance the binding affinity, selectivity and water solubility of sensor 9b. • We discussed the fluorescence response characteristics of sensor 9b with gallic acid and its application in actual samples. 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. [ABSTRACT FROM AUTHOR]

Three simple fluorescence turn-on sensors have been designed for the selective detection of adenosine (AD) based on a boronic acid receptor and a coumarin fluorophore (NLC, NJC, NDC). In the absence of AD, the fluorescence emission intensity of the sensors was relatively weak due to the effective electronic transfer from the to the coumarin to the boronic acid moiety. When the AD was introduced into the system, an obvious fluorescence enhancement was observed. It was attributed to the boronic acid covalently binding to the cis -diol unit of the AD resulting in the electronic transfer process being inhibited. Under the optimal conditions, these fluorescent sensors not only could perform good selectivity and fast response (< 30 s), but also show good water solubility. Finally, the proposed sensor NLC has been utilized for the AD determination in urine without any complicated pretreatment and the recovery was in the range of 95–103%. As a result, it is promising for application on the AD detection in complex biological samples. Moreover, there are no small molecular sensors detecting AD have been reported, yet, it is promising for providing a new platform to detect AD by small molecular sensor. [Display omitted] • Fluorescence turn on sensors for specific detection of adenosine (AD) in urine. • The first synthesized small molecular sensor for detecting AD. • The sensors operated by phenylboronic acid as the recognition group and coumarin as the luminescent group. • Sensor NLC has a low detection limit when detecting AD (6.87 μM). [ABSTRACT FROM AUTHOR]

Small-molecule reactive species, such as reactive oxygen species, catecholamines, ions, sialic acid and gas signal molecules, are involved in many important biological events. For example, abnormal reactive oxygen species levels can lead to a range of cell dysfunctions and eventually cancer and neurodegenerative diseases. Therefore, the development of sensors for detecting small-molecule reactive species is of great significance for disease prevention, diagnosis and treatment. Boronic acid has been widely used for the selective recognition of sugars due to their obvious fluorescence change after combining with sugar, easily structure modification and good light stability. In recent years, a large number of boronic acid-based sensors that can selectively recognize small-molecule reactive species have been reported, however, there are few systematic reviews in this field, and lack of in-depth understanding of the identification mechanism and structure-activity relationship. In this review, boronic acid-based sensors detecting small-molecule reactive species (such as reactive oxygen species (H 2 O 2 , ONOO−, CLO−), catecholamines (dopamine, norepinephrine), sialic acid and sialic acid derivatives (sialic acid, sialic Lewis X, sialic Lewis Y) and ions (F−, Fe3+, Cu2+)) over the recent years (2015–2020) will be discussed, focusing on the fluorescence characteristics of the sensors and their potential in disease detection, and we are aiming to provide researchers with better inspiration. • Small-molecule reactive species are involved in many important biological events. • Boronic acid-based fluorescent sensors are widely used to detect small-molecule reactive species in organisms. • We review boronic acid-based sensors for small-molecule reactive species imaging. • We discuss the characteristic and response mechanism of the sensors. [ABSTRACT FROM AUTHOR]