A simple and selective fluorometric assay for dopamine using a calcein blue–Fe2+ complex fluorophore

The Role of 8-Amidoquinoline Derivatives as Fluorescent Probes for Zinc Ion Determination

Mass-spectrometry-based and X-ray fluorescence-based techniques have allowed the study of the distribution of Zn²⁺ ions at extracellular and intracellular levels over the past few years. However, there are some issues during purification steps, sample preparation, suitability for quantification, and the instruments’ availability. Therefore, work on fluorescent sensors based on 8-aminoquinoline as tools to detect Zn²⁺ ions in environmental and biological applications has been popular. Introducing various carboxamide groups into an 8-aminoquinoline molecule to create 8-amidoquinoline derivatives to improve water solubility and cell membrane permeability is also a recent trend. This review aims to present a general overview of the fluorophore 8-aminoquinoline and its derivatives as Zn²⁺ receptors for zinc sensor probes. Various fluorescent chemosensor designs based on 8-amidoquinoline and their effectiveness and potential as a recognition probe for zinc analysis were discussed. Based on this review, it can be concluded that derivatives of 8-amidoquinoline have vast potential as functional receptors for zinc ions primarily because of their fast reactivity, good selectivity, and bio-compatibility, especially for biological applications. To better understand the Zn²⁺ ion fluorophores’ function, diversity of the coordination complex and geometries need further studies. This review provides information in elucidating, designing, and exploring new 8-amidoquinoline derivatives for future studies for the improvement of chemosensors that are selective and sensitive to Zn²⁺.

Optical sensors for determination of biogenic amines in food

This review presents the state-of-the-art of optical sensors for determination of biogenic amines (BAs) in food by publications covering about the last 10 years. Interest in the development of rapid and preferably on-site methods for quantification of BAs is based on their important role in implementation and regulation of various physiological processes. At the same time, BAs can develop in different kinds of food by fermentation processes or microbial activity or arise due to contamination, which induces toxicological risks and food poisoning and causes serious health issues. Therefore, various optical chemosensor systems have been devised that are easy to assemble and fast responding and low-cost analytical tools. If amenable to on-site analysis, they are an attractive alternative to existing instrumental analytical methods used for BA determination in food. Hence, also portable sensor systems or dipstick sensors are described based on various probes that typically enable signal readouts such as photometry, reflectometry, luminescence, surface-enhanced Raman spectroscopy, or ellipsometry. The quantification of BAs in real food samples and the design of the sensors are highlighted and the analytical figures of merit are compared. Future instrumental trends for BA sensing point to the use of cell phone-based fully automated optical evaluation and devices that could even comprise microfluidic micro total analysis systems.

Recent Advances in Electrochemical and Optical Sensing of Dopamine

Nowadays, several neurological disorders and neurocrine tumours are associated with dopamine (DA) concentrations in various biological fluids. Highly accurate and ultrasensitive detection of DA levels in different biological samples in real-time can change and improve the quality of a patient's life in addition to reducing the treatment cost. Therefore, the design and development of diagnostic tool for in vivo and in vitro monitoring of DA is of considerable clinical and pharmacological importance. In recent decades, a large number of techniques have been established for DA detection, including chromatography coupled to mass spectrometry, spectroscopic approaches, and electrochemical (EC) methods. These methods are effective, but most of them still have some drawbacks such as consuming time, effort, and money. Added to that, sometimes they need complex procedures to obtain good sensitivity and suffer from low selectivity due to interference from other biological species such as uric acid (UA) and ascorbic acid (AA). Advanced materials can offer remarkable opportunities to overcome drawbacks in conventional DA sensors. This review aims to explain challenges related to DA detection using different techniques, and to summarize and highlight recent advancements in materials used and approaches applied for several sensor surface modification for the monitoring of DA. Also, it focuses on the analytical features of the EC and optical-based sensing techniques available.

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.

Development of Fluorescent Reagent Based on Ligand Exchange Reaction for the Highly Sensitive and Selective Detection of Dopamine in the Serum

A new fluorescent probe (BDP-Fe2+) was developed for targeting dopamine, with a boron-dipyrromethenyl (BDP) group as the fluorophore and a Fe2+ complex as the ligand exchange site. The free form of BDP-Fe2+ in solution displayed weak fluorescence emission, while it showed strong fluorescence emission after interaction with dopamine due to the release of Fe2+ from BDP-Fe2+, confirming the binding of Fe2+ to dopamine. The increase in fluorescence intensity was concentration-dependent, and a good linear relationship was observed between the fluorescence intensity and dopamine concentration. The detection limit of dopamine by BDP-Fe2+ was 1.1 nM, indicating a 20-fold higher sensitivity than that of previously reported compounds. The reaction of BDP-Fe2+ with dopamine was not affected by the presence of foreign substances, allowing the highly selective detection of dopamine in the human serum sample. The results of this study indicate that the novel compound BDP-Fe2+ is a reliable fluorescent molecular probe for the detection of dopamine and can be widely employed in diverse scientific areas.

A selective colorimetric strategy for probing dopamine and levodopa through the mussel-inspired enhancement of Fe3O4 catalysis

Mussel-inspired enhancement of Fe₃O₄ catalysis was discovered toward the colorimetric analysis of dopamine and/or levodopa with bis-catechol structures.

Fabrication of Biocompatible, Luminescent Supramolecular Structures and Their Applications in the Detection of Dopamine

Supramolecular materials assembled by amide-functionalized surface active ionic liquid, N-dodecyl- N'-acetamido imidazolium bromide ([C₁₂ImCONH₂]Br), and europium-containing polyoxometalates (Eu-POM) were fabricated in aqueous solution by a one-step method via ionic self-assembly strategy. The [C₁₂ImCONH₂]Br/Eu-POM supramolecular structures exhibit favorable fluorescence properties and represent a 15-fold increase in quantum yield (∼13.68%) compared to Eu-POM. Besides, more fluorescence was quenched obviously with the increasing concentration of dopamine (DA) (within the range of 0-100 μM), based on which DA monitoring could be achieved. The detection limit was identified to be 0.1 μM. The supramolecular nanoparticles are highly specific for the detection of DA. In addition, the hybrid assemblies display not only low cytotoxicity but also excellent biocompatibility to MC3T3-E1 cells. As a result, as-prepared supramolecular materials with these superior properties show the promising application in some fields such as biochemistry and biomedical science.

Novel biosensing system for the simultaneous multiplex fluorescent determination of catecholamines and their metabolites in biological liquids

A novel original biosensing system for the simultaneous multiplex determination of general markers of catecholamine-producing diseases - catecholamines (dopamine, epinephrine, norepinephrine) and their metabolites (homovanillic and vanillylmandelic acids) in biological liquids without preliminary separation of analytes, in the absence of specific antibodies and receptors and with minimum pretreatment of a samples has been developed. This outstanding approach includes the unique combination of obtaining highly fluorescent derivatives of the analytes as a result of their interaction with two different amines ̶ benzylamine and 1,2-diphenylethylenediamine in the presence of peroxidase as a catalyst, with the application of first-order derivative fluorescence spectroscopy for the resolution of their spectra. Fluorescence is measured in 96-well microplates, which wells contain a bio-recognizing film consisted of horseradish peroxidase immobilized in the polymer chitosan. Spectra of the solutions are recorded in the range 400-500 nm (λ_ex ∼ 305-356 nm). The proposed procedures provide sensitive (in the range of 3-200 nM), selective, and reproducible (RSDs ≤ 1%, n = 6) multiplex determination of the catecholamines and their metabolites in biological liquids were successfully applied for the rapid simultaneous (20 samples per 15-30 min) screening of human urine and mice blood plasma. The validated results showed good linearity, precision, accuracy and selectivity of this method.

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.

A label-free platform for dopamine biosensing

AIM

This work presents a label-free platform for dopamine (DA) monitoring based on the spectroscopic properties of laccase.

RESULTS

Working in batch mode, DA ranging from 25 to 250 μM, can be determined without the interference of norepinephrine and epinephrine. Laccase immobilized in a polyacrylamide film is the basis of a platform for the label-free determination of DA. The linear range goes from 100 to 900 μM with an RSD of 5.3% and a film lifetime of more than 30 measurements. The biosensors also permit the DA + epinephrine + norepinephrine determination.

CONCLUSION

The method permits the determination of DA and the total concentration of the three neurotransmitters, and could be used for DA monitoring in urine samples.

A facile water-stable MOF-based “off–on” fluorescent switch for label-free detection of dopamine in biological fluid

An Abtz–CdI₂–MOF was developed as an “off–on” fluorescent switch for label-free detection of dopamine without any surface modification or functionalization.

Fluorescence enhancement aided by metal ion displacement

Immunosensors are one of the most common platform used in clinical laboratories, in particular the class based on Enzyme Linked Fluorescent Assays (ELFA) takes advantage of the amplification step of the enzyme, usually the alkaline phosphatase, that catalyzes the hydrolysis of a fluorescent substrate leading it to fluoresce. Anyway, they suffer in sensitivity if compared to molecular diagnostic or more modern in vitro diagnostic devices. In our work, a simple and effective mechanism to enhance the fluorescent signal, and hence the sensitivity of the system, is presented. It is based on the metal ion displacement principle in which a second fluorophore, in our case Calcein Blue, quenched by a cobalt ion is add to the first one (4-MUP), and, in presence of inorganic phosphate, it will be progressively activated by the inorganic phosphate itself leading to the metal displacement. In this way Calcein Blue, newly free to fluoresce, contributes to global fluorescent signal generated by 4-MU. We have tested our proof of principle on a currently used immunoanalyzer, that is VIDAS® system (bioMérieux, Marcy l'Etoile, France) obtaining a fluorescence enhancement of about 50% for each concentration of hydrolyzed 4-MUP tested.

A new fluorimetric method for the detection and quantification of siderophores using Calcein Blue, with potential as a bacterial detection tool

The presence of microorganisms in biological fluids like urine and blood is an indication of vulnerability to infections. Iron is one of the important micronutrients required for bacterial growth. In an iron-deficit environment, bacteria release high-affinity iron-chelating compounds called siderophores which can be used as non-invasive target molecules for the detection of such pathogens. However, only limited reagents and procedures are available to detect the presence of these organic molecules. The present study aims at detecting the presence of siderophores in the iron-depleted media, exploiting the reversible quenching of Calcein Blue and iron(III) complex. The fluorescence of Calcein Blue is known to be quenched in the presence of iron(III); if a stronger chelator removes this ion from the fluorophore, the fluorescence of the fluorophore is regained. This behaviour of the fluorophore was exploited to detect and quantify siderophores down to 50 and 800 nM equivalent of standard siderophore, deferroxamine mesylate (desferal) in Dulbecco's PBS and siderophore quantification (SPQ) medium, respectively. The siderophores released by pathogens, equivalent to standard desferal, were in the range of 1.29 to 5.00 μM and those for non-pathogens were below 1.19 μM. The simple, sensitive and cost-effective method performed in a 96-well plate was able to detect and quantify iron chelators within 7-8 h of incubation.

Selective neuronal targeting, protection and signaling network analysis via dopamine-mediated mesoporous silica nanoparticles

Mesoporous silica nanoparticle (MSN)-mediated glutathione (GSH) delivery for targeted protection of dopaminergic neuronal cells.

Luminescent ZnO quantum dots for sensitive and selective detection of dopamine

Water-soluble and luminescent ZnO quantum dots (QDs) capped by (3-aminopropyl) triethoxysilane (APTES) are environment-friendly with strong photoluminescence (max. wavelength: 530 nm). Interestingly, it was found that the fluorescence could be quenched by dopamine (DA) directly. On the basis of above, a novel ZnO QDs based fluorescent probe has been successfully designed to detect DA with high selectivity and sensitivity. Moreover, the possible fluorescence quenching mechanism was proposed, which showed that the quenching effect may be caused by the electron transfer from ZnO QDs to oxidized dopamine-quinone. Under optimum conditions, the relative fluorescence intensity was linearly proportional to the concentration of DA within the range from 0.05 to 10 μM, with the detection limit down to 12 nM (n=3). Also, the selectivity experiment indicated the probe had a high selectivity for DA over a number of possible interfering species. Finally, this method was successfully used to detect DA in serum samples with quantitative recoveries (99-110%). With excellent selectivity and high sensitivity, it is believed that the ZnO QDs based fluorescent probe has a potential for the practical application in clinical analysis.