Direct detection of homocysteine

BODIPY-based fluorometric sensor for the simultaneous determination of Cys, Hcy, and GSH in human serum

Cysteine (Cys), homocysteine (Hcy), and glutathione (GSH) are interconnected and play essential roles for regulating the redox balance of biological processes. However, finding a simple and effective method for the simultaneous determination for these three biothiols in biological systems is always a challenge. In this work, we report a method for the simultaneous quantitative determination of three biothiols in a mixture using a monochlorinated boron dipyrromethene (BODIPY)-based fluorometric sensor. At a specified period of time, after reacting with excess sensor, Hcy and GSH form predominantly sulfur-substituted BODIPY, while Cys generates sulfur-amino-diBODIPY due to a fast substitution-rearrangement-substitution reaction. A significant difference in polarities of these respective major products simplifies their separation by TLC, thus leading to the simultaneous determination of Cys, Hcy, and GSH readily. The sensor was successfully applied for the simultaneous quantitative detection of three biothiols in human serum, and the results were in good agreement with those obtained via high performance liquid chromatography (HPLC).

A recyclable carbon nanoparticle-based fluorescent probe for highly selective and sensitive detection of mercapto biomolecules

Hg²⁺quenched CNPs (CNP-Hg²⁺) as a highly sensitive and selective reversible probe for the detection of mercapto biomolecules in aqueous solutions and in living cells.

A miniaturized electrochemical assay for homocysteine using screen-printed electrodes with cytochrome c anchored gold nanoparticles

Electrochemical point-of-care analysis of homocysteine in a drop of the blood plasma samples.

A new turn-on chemosensor for bio-thiols based on the nanoaggregates of a tetraphenylethene-coumarin fluorophore

In this work, a tetraphenylethene-coumarin hybrid fluorophore (TPE-Cou) that contains a Schiff base form is designed and synthesized. A combination of plentiful optical properties and chemical reactivity towards thiols allows TPE-Cou to work as an excellent turn-on probe of thiols with a wide linear range, revealing the great potential of this dye as a quantitative fluorescence indicator. By means of NMR and optical spectrum analyses, a mechanistic picture at the molecular level has been drawn to illustrate how this dye works as a bio-thiol-sensitive fluorescent probe.

Recent advances in thiol and sulfide reactive probes

Because of the biological relevance of thiols and sulfides such as cysteine, homocysteine, glutathione and hydrogen sulfide, their detection has attracted a great deal of research interest. Fluorescent probes are emerging as a new strategy for thiol and hydrogen sulfide analysis due to their high sensitivity, low cost, and ability to detect and image thiols in biological samples. In this short review, we have summarized recent advances in the development of thiol and hydrogen sulfide reactive fluorescent probes. These probes are compared and contrasted with regard to their designing strategies, mechanisms, photophysical properties, and/or reaction kinetics. Biological applications of these probes are also discussed.

The application of a chemical determination of N-homocysteinylation levels in developing mouse embryos: implication for folate responsive birth defects

Elevated homocysteine levels have long been associated with various disease states, including cardiovascular disease and birth defects, including neural tube defects (NTDs). One hypothesis regarding the strong correlation between these various disorders and high levels of homocysteine is that a reactive form of this small molecule can attach to mammalian proteins in a phenomenon known as homocysteinylation. These posttranslational modifications may become antigenic or may even directly disrupt certain protein function. It remains to be determined whether dietary influences that can cause globally increased levels of circulating homocysteine confer negative effects maternally, or may otherwise negatively and materially impact the metabolic balance in developing embryos. Herein we present the application of a chemical method of determination of N-homocysteinylation to a set of neural tube closure stage mouse embryos and their mothers. We explore the uses of this newly described technique to investigate levels of maternal and embryonic N-homocysteinylation using dietary manipulations of one-carbon metabolism with two known folate-responsive NTD mouse models. The data presented reveal that although diet appeared to have significant effects on the maternal metabolic status, those effects did not directly correlate to the embryonic folate or N-homocysteinylation status. Our studies indicate that maternal diet and embryonic genotype most significantly affected the embryonic developmental outcome.

Plasmonic nanoparticle-film calipers for rapid and ultrasensitive dimensional and refractometric detection

In this study, we develop an ultrasensitive nanoparticle (NP)-film caliper that functions with high resolution (angstrom scale) in response to both the dimensions and refractive index of the spacer sandwiched between the NPs and the film. The anisotropy of the plasmonic gap mode in the NP-film caliper can be characterized readily using spectroscopic ellipsometry (SE) without the need for further optical modeling. To the best of our knowledge, this paper is the first to report the use of SE to study the plasmonic gap modes in NP-film calipers and to demonstrate that SE is a robust and convenient method for analyzing NP-film calipers. The high sensitivity of this system originates from the plasmonic gap mode in the NP-film caliper, induced by electromagnetic coupling between the NPs and the film. The refractometric sensitivity of this NP-film caliper reaches up to 314 nm per RIU, which is superior to those of other NP-based sensors. The NP-film caliper also provides high dimensional resolution, down to the angstrom scale. In this study, the shift in wavelength in response to the change in gap spacing is approximately 9 nm Å(-1). Taking advantage of the ultrasensitivity of this NP-film caliper, we develop a platform for discriminating among thiol-containing amino acids.

A photochemical method for determining plasma homocysteine with limited sample processing

The photolytic formation of thiyl radicals allows for the selective detection of total homocysteine (tHcy) in plasma after reduction and filtering. The mechanism is based on the reduction of viologens by the α-amino carbon centred radical of Hcy generated by intramolecular hydrogen atom transfer (HAT) of its thiyl radical.

A dual emission fluorescent probe enables simultaneous detection of glutathione and cysteine/homocysteine

Many studies have shown that glutathione (GSH) and cysteine (Cys) / homocysteine (Hcy) levels are interrelated in biological systems. To unravel the complicated biomedical mechanisms by which GSH and Cys/Hcy are involved in various disease states, probes that display distinct signals in response to GSH and Cys/Hcy are highly desirable. In this work, we report a rhodol thioester (1) that responds to GSH and Cys/Hcy with distinct fluorescence emissions in neutral media. Probe 1 reacts with Cys/Hcy to form the corresponding deconjugated spirolactam via a tandem native chemical ligation (NCL) reaction. This intramolecular spirocyclization leads to the "quinone - phenol" transduction of rhodol dyes, and an excited-state intramolecular proton transfer (ESIPT) process between the phenolic hydroxyl proton and the aromatic nitrogen in the benzothiazole unit occurs upon photoexcitation, thus affording 2-(2'-hydroxyphenyl) benzothiazole (HBT) emission (454 nm). In the case of the tripeptide GSH, only transthioesterification takes place removing the intramolecular photo-induced electron transfer (PET) process caused by the electron deficient 4-nitrobenzene moiety giving rise to a large fluorescence enhancement at the rhodol emission band (587 nm). The simultaneous detection of GSH and Cys/Hcy is attributed to the significantly different rates of intramolecular S,N-acyl shift of their corresponding thioester adducts derived from 1. The utility of probe 1 has been demonstrated in various biological systems including serum and cells.

Sensitive and regenerable organochalcogen probes for the colorimetric detection of thiols

Isothiazolone and isoselenazolone based colorimetric probes for the detection of thiols have been reported. A regenerable probe for the detection of organothiols is developed from isoselenazolone. Both of these probes possess higher selectivity for aromatic thiols, cysteine and glutathione.

A dioxadithiaazacrown ether–BODIPY dyad Hg2+ complex for detection of l-cysteine: fluorescence switching and application to soft material

A Hg²⁺ coordinate complex of a 1,4-dioxa-7,13-dithia-10-azacyclopentadecane–BODIPY dyad recognises l-cysteine (cys) via reversible complexation/decomplexation and show switching of fluorescence upon sequential addition of Hg²⁺ and cys in solution as well as in hydrogel.

A turn-on NIR fluorescent probe for the detection of homocysteine over cysteine

A BODIPY-based turn-on NIR fluorescent probe containing a partially exposed aldehyde group at the meso position for the detection of homocysteine over cysteine was developed. Such a probe is potentially useful for the discrimination of Hcy from Cys.

The selective electrochemical detection of homocysteine in the presence of glutathione, cysteine, and ascorbic acid using carbon electrodes

The detection of homocysteine, HCys, was achieved with the use of catecholvia1,4-Michael addition reaction using carbon electrodes: a glassy carbon electrode and a carbon nanotube modified glassy carbon electrode.

Nitrogen-doped graphene quantum dots-based fluorescent probe for the sensitive turn-on detection of glutathione and its cellular imaging

Fluorescence turn-on sensor based on nitrogen-doped graphene quantum dots can be used for glutathione detection in living cells.

Redox-based selective fluorometric detection of homocysteine

Homocysteine, an important biomarker, could be selectively quantified with a redox-sensitive fluorescent probe.

Extremely selective fluorescence detection of cysteine or superoxide with aliphatic ester hydrolysis

A novel fluorescence probe modality demonstrated with fluorescein affords a highly selective aqueous-based detection of cysteine over other biothiols,e.g.homocysteine, with a limit of detection of 11.3 μM.

Thiol reactive probes and chemosensors

Thiols are important molecules in the environment and in biological processes. Cysteine (Cys), homocysteine (Hcy), glutathione (GSH) and hydrogen sulfide (H₂S) play critical roles in a variety of physiological and pathological processes. The selective detection of thiols using reaction-based probes and sensors is very important in basic research and in disease diagnosis. This review focuses on the design of fluorescent and colorimetric probes and sensors for thiol detection. Thiol detection methods include probes and labeling agents based on nucleophilic addition and substitution, Michael addition, disulfide bond or Se-N bond cleavage, metal-sulfur interactions and more. Probes for H₂S are based on nucleophilic cyclization, reduction and metal sulfide formation. Thiol probe and chemosensor design strategies and mechanism of action are discussed in this review.

New chemodosimetric reagents as ratiometric probes for cysteine and homocysteine and possible detection in living cells and in blood plasma

In this work, we have rationally designed and synthesized two new reagents (L(1) and L(2)), each bearing a pendant aldehyde functionality. This aldehyde group can take part in cyclization reactions with β- or γ-amino thiols to yield the corresponding thiazolidine and thiazinane derivatives, respectively. The intramolecular charge-transfer (ICT) bands of these thiazolidine and thiazinane derivatives are distinctly different from those of the molecular probes (L(1) and L(2)). Such changes could serve as a potential platform for using L(1) and L(2) as new colorimetric/fluorogenic as well as ratiometric sensors for cysteine (Cys) and homocysteine (Hcy) under physiological conditions. Both reagents proved to be specific towards Cys and Hcy even in the presence of various amino acids, glucose, and DNA. Importantly, these two chemodosimetric reagents could be used for the quantitative detection of Cys present in blood plasma by using a pre-column HPLC technique. Such examples are not common in contemporary literature. MTT assay studies have revealed that these probes have low cytotoxicity. Confocal laser scanning micrographs of cells demonstrated that these probes could penetrate cell membranes and could be used to detect intracellular Cys/Hcy present within living cells. Thus, the results presented in this article not only demonstrate the efficiency and specificity of two ratiometric chemodosimeter molecules for the quantitative detection of Cys and Hcy, but also provide a strategy for developing reagents for analysis of these vital amino acids in biological samples.

A colorimetric and fluorescent dual probe for specific detection of cysteine based on intramolecular nucleophilic aromatic substitution

4-Nitro-1,8-naphthalic anhydride (NNA) was used to distinguish cysteine from homocysteine and other potentially interfering thiols through a novel sequential substitution mechanism. The discrimination involves a blue-fluorescent thioether formation via nucleophilic aromatic substitution of the nitro group by thiol, followed by a second intramolecular nucleophilic aromatic substitution of alkylthio with the amino group to give the green-fluorescent 4-amino derivative. NNA is highly selective towards Cys, and the detection limit of Cys by this method is 0.3 μM.

A silica nanoparticle-based sensor for selective fluorescent detection of homocysteine via interaction differences between thiols and particle-surface-bound polymers

Biothiols play crucial roles in maintaining biological systems; among them, homocysteine (Hcy) has received increasing attention since elevated levels of Hcy have been implicated as an independent risk factor for cardiovascular disease. Hence, the selective detection of this specific biothiol, which is a disease-associated biomarker, is very important. In this paper, we demonstrate a new mesoporous silica nanoparticle-based sensor for selective detection of homocysteine from biothiols and other common amino acids. In this fluorescent sensing system, an anthracene nitroolefin compound was placed inside the mesopores of mesoporous silica nanoparticles (MSNs) and used as a probe for thiols. The hydrophilic polyethylene glycol (PEG 5000) molecules were covalently bound to the MSN surface and used as a selective barrier for Hcy detection via different interactions between biothiols and the PEG polymer chains. The sensor can discriminate Hcy from the two low-molecular mass biothiols (GSH and Cys) and other common amino acids in totally aqueous media as well as in serum, with a detection limit of 0.1 μM. This strategy may offer an approach for designing other MSN-based sensing systems by using polymers as diffusion regulators in sensing assays for other analytes.

A Zn2+ specific triazole based calix[4]arene conjugate (L) as a fluorescence sensor for histidine and cysteine in HEPES buffer milieu

A highly fluorescent Zn(2+) complex of the triazole linked salicyl-imino-thiophenyl conjugate of calix[4]arene, [ZnL] has been demonstrated to be a chemo-sensing ensemble for the recognition of His and Cys among the naturally occurring amino acids in HEPES buffer milieu. The recognition behaviour of the [ZnL] towards these amino acids has been shown on the basis of fluorescence, absorption and visual fluorescent colour changes. The species of recognition were shown by ESI MS titrations, AFM & TEM microscopy and cell studies.

A fluorescein-based probe with high selectivity to cysteine over homocysteine and glutathione

A fluorescent probe based on fluorescein displays excellent selectivity and sensitivity for cysteine and its application for bio-imaging is described.

A cysteine-selective fluorescent probe for the cellular detection of cysteine

A series of coumarin fluorophores (1-3), each bearing a double bond conjugated quinoline unit that can undergo a Michael-type reaction with thiol-containing compounds, is reported. These systems, designed to provide so-called turn-on changes in fluorescence response when exposed to thiols, act as fluorescent chemical sensors for cysteine (Cys), homocysteine (Hcy), and glutathione (GSH). In the case of 1, selectivity for Cys over Hcy and GSH is observed, both in terms of analyte-induced signal enhancement and response time. On the basis of fluorescence spectroscopic analyses, DFT calculations, and pH dependent studies this substrate selectivity is ascribed to steric interactions between the substituents on the quinolone units present in 1 and the targeted thiols, as well as to the comparatively lower pK(a) value of Cys relative to Hcy and GSH. In aqueous solution, probe 1 was found capable of detecting Cys with a detection limit of 10(-7) m. This system was successfully applied to the fluorescence imaging of intracellular Cys in HepG2 cells.

Chromogenic and fluorogenic chemosensors and reagents for anions. A comprehensive review of the year 2009

This critical review is focused on examples reported in the year 2009 dealing with the design of chromogenic and fluorogenic chemosensors or reagents for anions (264 references).