Rationally designed chromogenic chemosensor that detects cysteine in aqueous solution with remarkable selectivity

A Hydrogen Bonded Non-Porous Organic-Inorganic Framework for Measuring Cysteine in Blood Plasma and Endogenous Cancer Cell

An imbalance in cysteine (Cys) levels in the cells and plasma has been identified as the risk indicator for various human diseases. The structural similarity of cysteine with its congener homocysteine and glutathione offers challenges in its measurement. Herein, we report a hydrogen-bonded organic-inorganic framework of Cu(II) (HOIF) for the selective detection of cysteine over other biothiols. The non-fluorescent HOIF showed 12-fold green emission in the presence of cysteine. The monomeric unit of HOIF is stabilized via intermolecular hydrogen bonds, resulting in a non-porous network structure. Non-interference from homocysteine, glutathione, and other competitive bio-analytes revealed explicit affinity of HOIF for cysteine. Fluorimetric titration showed a wide working concentration window (650 nM-800 μM) for measuring cysteine in an aqueous medium. The mechanistic investigation involving HRMS, EPR, and UV-vis spectroscopic studies revealed the decomplexation of HOIF with Cys, resulting in a fluorescence turn-on response from the luminescent ligand. Validation using a commercial dye, "Cysteine Green", confirmed the prospect of HOIF for early diagnostic purposes. Utilizing the fluorescence turn-on property of HOIF in the presence of cysteine, we measured cysteine quantitatively in the blood plasma samples. Bio-imaging of endogenous cysteine in cancer cells indicated the ability of HOIF to monitor the intracellular cysteine.

Rapid detection of the biomarker for cystinuria by a metal-organic framework fluorescent sensor

Arginine (Arg) is considered a valuable biomarker for various diseases, including cystinuria, and its concentration level holds significant implications for human health. To achieve the purposes of food evaluation and clinical diagnosis, it is imperative to develop a rapid and facile method for selective and sensitive determination of Arg. In this work, a novel fluorescent material (Ag/Eu/CDs@UiO-66) was synthesized by encapsulating carbon dots (CDs), Eu³⁺ and Ag ⁺ into UiO-66. This material can serve as a ratiometric fluorescent probe for detecting Arg. It exhibits a high sensitivity with a detection limit of 0.74 μM and a relatively broad linear range from 0-300 μM. After dispersing the composite Ag/Eu/CDs@UiO-66 in an Arg solution, the red emission of Eu³⁺ center at 613 nm was significantly enhanced, while the characteristic peak of CDs center at 440 nm remained unchanged. Therefore, a ratio fluorescence probe could be constructed based on the peak height ratio of the two emission peaks to achieve selective detection of Arg. In addition, the remarkable ratiometric luminescence response induced by Arg results in a significant color transition from blue to red under UV-lamp for Ag/Eu/CDs@UiO-66, which was convenient for visual analysis.

Coumarin-Ensembled Vanadium(V) Compounds and Their Affinity Studies Toward Biological Thiols Probed by Fluorescence Spectroscopy

Fluorescence spectroscopic studies of a pair of new oxido-vanadium(V) compounds with biological thiols, such as homocysteine (Hcy), cysteine (Cys), and glutathione (GSH), have been investigated in this article. Despite notable progress in vanadium-thiol chemistry, no attention has been paid to exploring vanadium-based optical probes to study their interaction with biothiols. For this purpose, two oxido-vanadium(V) compounds, 1 and 2, have been prepared involving a tridentate ONO donor-based luminescent coumarin-derived ligand. Single crystal X-ray diffraction analysis, NMR (¹ H, ¹³ C, and ⁵¹ V) spectroscopy, XPS, and DFT calculations have been used to establish their identities. The vanadium center in these compounds has a distorted octahedral environment. In compound 2, a methanol molecule is coordinated to the vanadium(V) center in the trans position of the terminal oxido moiety. The latter exerts a strong trans-labilizing influence on the coordinating methanol. Both 1 and 2 are weakly fluorescent. Photophysical investigations of the vanadium complexes in aqueous media at physiological pH (7.4) in the presence of various biothiols and amino acids showed significant fluorescence enhancement (83-fold) of the vanadium complexes, specifically with Hcy. The specific affinity of the complexes for Hcy remained unchanged even in the presence of other biothiols and amino acids. Kinetic investigation reveals pseudo-first order behavior of the compound with Hcy. Mechanistic studies have manifested that Hcy-induced reduction triggers the decomplexation of the vanadium compound, followed by hydrolysis and subsequent cyclization. Time-correlated single photon counting suggested that the radiative rate constant (k_r ) of 1 and 2 in the presence of Hcy serves as the prime factor for the fluorescence enhancement of the medium. Compound 1 has been tested efficiently for Hcy measurement in blood plasma rendering it suitable for practical applications.

Selective chiroptical sensing of D/L-cysteine

A chromophoric bifunctional probe design that allows selective chiroptical sensing of cysteine in aqueous solution is introduced. The common need for chiral HPLC separation is eliminated which expedites and simplifies the sample analysis while reducing solvent waste. Screening of the reaction between six phenacyl bromides and the enantiomers of cysteine showed that cyclization to an unsaturated thiomorpholine scaffold coincides with characteristic UV and CD effects, in particular when the reagent carries a proximate auxochromic nitro group. The UV changes and CD inductions were successfully used for determination of the absolute configuration, enantiomeric composition and total concentration of 18 test samples. This assay is highly selective for free cysteine while other amino acids, cysteine derived small peptides and biothiols do not interfere with the chiroptical signal generation.

Synthesis of BINOL-xylose-conjugates as "Turn-off" fluorescent receptors for Fe3+ and secondary recognition of cysteine by their complexes

A novel chiral fluorescence "turn-off" sensor was synthesised using the click reaction. The sensor was a BINOL-xylose derivative, modified at the 2-position and linked by 1,2,3-triazole. It was structurally characterized by ¹HNMR, ¹³CNMR, ESI-MS and IR analysis. The selectivity of R-β-d-2 in methanol solution has been studied. Among the 19 transition metal ions, alkaline metal ions and alkaline earth metal ions studied, R-β-d-2 had a selective fluorescence quenching reaction for Fe³⁺. The detection limit of R-β-d-2 for Fe³⁺ was 0.91 μmol L^-1. Complexation between R-β-d-2 and Fe³⁺ was investigated by ESI-MS and ¹HNMR. The stoichiometric ratio of R-β-d-2 was 1 : 1. In addition, the R-β-d-2-Fe³⁺ complex was titrated with 20 naturally occurring amino acids and Hcy with GSH. It was found that the complex R-β-d-2-Fe³⁺ had a secondary recognition effect on Cys by switching to fluorescence.

Fluorescent probe for Cu2+ and the secondary application of the resultant complex to detect cysteine

A special fluorescent probe has been developed, one that demonstrated excellent "off-on-type" change in fluorescence with high selectivity toward Cu2+. Interestingly, the probe-Cu2+ complex could detect cysteine due to the ability of this amino acid to strongly coordinate Cu2+, and no obvious interference was observed from other amino acids and anions. According to the proposed mechanism, addition of cysteine induced decomplexation of the probe-Cu2+ form. Furthermore, the results of confocal microscopy experiments demonstrated the potential of using the probe to image Cu2+ in living cells and mice.

Development of a two-photon turn-on fluorescent probe for cysteine and its bio-imaging applications in living cells, tissues, and zebrafish

A two-photon fluorescent probe Co-Cys for detecting cysteine has been designed to monitor cysteine in cells, tissues and zebrafish.

Colorimetric chemosensor for multiple targets, Cu2+, CN−and S2−

New Schiff-base was developed as colorimetric sensor for Cu²⁺, CN⁻and S²⁻with the detection limits lower than the given guidelines.

Thiol-addition reactions and their applications in thiol recognition

Because of the biological importance of thiols, the development of probes for thiols has been an active research area in recent years. In this review, we summarize the results of recent exciting reports regarding thiol-addition reactions and their applications in thiol recognition. The examples reported can be classified into four reaction types including 1,1, 1,2, 1,3, 1,4 addition reactions, according to their addition mechanisms, based on different Michael acceptors. In all cases, the reactions are coupled to color and/or emission changes, although some examples dealing with electrochemical recognition have also been included. The use of thiol-addition reactions is a very simple and straightforward procedure for the preparation of thiol-sensing probes.

Designing a thiol specific fluorescent probe for possible use as a reagent for intracellular detection and estimation in blood serum: kinetic analysis to probe the role of intramolecular hydrogen bonding

A new and simple chemodosimetric probe L1 is utilized for the selective detection of biothiols in the presence of other relevant amino acids under physiological conditions (pH = 7.4). This eventually led to a turn-off luminescence response due to an effective photoinduced electron transfer based signaling mechanism. A comparison of the results of the fluorescence kinetic analysis and (1)H NMR studies of the reaction between thiol and L1 or the analogous compound L2 revealed the role of intramolecular hydrogen bonding in activating the imine functionality towards nucleophilic addition. Such an example is not common in contemporary literature. Conventional MTT assay studies revealed that this probe (L1) has low cytotoxicity. Results of the cell imaging studies revealed that this probe was cell membrane permeable and could detect the intracellular distribution of biothiols within living HeLa cells. Furthermore, our studies with human blood plasma demonstrated the possibility of using this reagent for the quantitative optical detection of total biothiols in biological fluid. Such an example for the detection of biothiols in real biological samples is rare in the contemporary literature. These results clearly demonstrate the possibility of using this reagent in medicinal biology and diagnostic applications.

Enantio- and chemoselective differentiation of protected α-amino acids and β-homoamino acids with a single copper(II) host

The association between an achiral copper(II)-containing host 1 and chiral carboxylates has been expanded beyond previous studies to new chiral carboxylate guests, both α-amino acids and β-homoamino acids. The observed exciton-coupled circular dichroism (ECCD) signals for the enantiomers of each carboxylate were equal and opposite, and these signals differed in size and shape between the individual amino acids. Linear discriminant analysis (LDA) was applied as a statistical analysis technique to differentiate the amino acids, both enantioselectively and chemoselectively, giving the absolute configuration and identity of the amino acid. The identity of each of the α-amino acids and β-homoamino acids were determined independently by LDA, and then the two were considered together. Each of these analyses showed good differentiation of the amino acid guests with the use of only one host molecule.

Spectrophotometric determination of cysteine with gold nanoparticles stabilized with single-stranded oligonucleotides

A sensitive and selective spectrophotometric detection method for cysteine has been established in this paper. The assay is based on the displacement of single-stranded oligonucleotide (ssDNA) adsorbed on the surface of citrate-capped gold nanoparticles (AuNPs) by cysteine in 2-[4-(2-hydroxyethyl)-1-piperazinyl]ethanesulfonic acid buffer solution (pH 7.2) and on the phenomenon of salt-induced AuNPs aggregation. Upon addition of cysteine, the red-to-blue color changes of the ssDNA-stabilized AuNPs associated with aggregation under high-salt conditions were easily observed with the naked eye. The absorption ratio at 520 and 600 nm was herein employed to quantify the AuNPs aggregation process. The calibration curve showed that the absorption ratio increased linearly over the concentration range of 0.1-1.3 microM with a limit of detection of 100 nM. Subsequently, the assay was successfully employed to determine cysteine in artificial and pharmaceutical injection samples.

Fluorescent and colorimetric probes for detection of thiols

Due to the biological importances of thiols, such as cysteine, homocysteine and glutathione, the development of optical probes for thiols has been an active research area in recent few years. This critical review focuses on the fluorescent or colorimetric sensors for thiols according to their unique mechanisms between sensors and thiols, including Michael addition, cyclization with aldehyde, cleavage of sulfonamide and sulfonate ester by thiols, cleavage of selenium-nitrogen bond by thiols, cleavage of disulfide by thiols, metal complexes-oxidation-reduction, metal complexes-displace coordination, nano-particles and others (110 references).

A thiol-specific fluorescent probe and its application for bioimaging

A fluorescent probe based on fluorescein displays an excellent selectivity and sensitivity for thiols and its application for bioimaging is described.