A water-soluble near-infrared fluorescent probe for sensitive and selective detection of cysteine

Near-Infrared Fluorescent Probe for the Detection of Cysteine

Hemicyanine dyes are an ideal structure for building near-infrared fluorescent probes due to their excellent emission wavelength properties and biocompatibility in biological imaging field. Developing a near-infrared fluorescent probe capable of detecting cysteine (Cys) was the aim of this study. A novel developed fluorescent probe P showed high selectivity and sensitivity to Cys in the presence of various analytes. The detection limit of P was found to be 0.329 μM. The MTT assay showed that the probe was essentially non-cytotoxic. Furthermore, the probe was successfully used as cysteine imaging in living cells and mice.

Long-Term Imaging of Cys in Cells and Tumor Mice by a Solid-State Fluorescence Probe

Cysteine is an important biological thiol and is closely related to cancer. It remains a challenge to develop a probe that can provide long-term fluorescence detection and imaging of Cys in cells as well as in living organisms. Here, a solid-state fluorophore HTPQ is combined with an acrylate group to construct a solid-state fluorescent probe HTPQC for Cys recognition. The fluorescence of the probe is quenched when the photoinduced electron transfer (PET) process is turned on and the excited-state intramolecular proton transfer (ESIPT) process is turned off. In the presence of Cys, an obvious solid-state fluorescence signal can be observed. The double quenching mechanism makes the probe HTPQC have the advantages of high sensitivity, good selectivity, and high contrast of biological imaging. Due to low cytotoxicity, the probe HTPQC can be used to detect exogenous and endogenous Cys in living cells and is capable of imaging over long periods of time. By making full use of long wavelengths, the probe can be applied for the detection of Cys levels in tumor mice and equipped with the ability to conduct long-term imaging in vivo.

A New Lysosome-Targeted NIR Fluorescent Probe for Specific Detection of Cysteine over Homocysteine and Glutathione

In this paper, by modifying the thioxanthene-benzothiozolium fluorophore, BCy-Cys, a lysosome-targeted near-infrared (NIR) fluorescent probe was synthesized for the detection of cysteine (Cys) from homocysteine (Hcy)/glutathione (GSH). As expected, BCy-Cys exhibited high selectivity and high sensitivity for detection of Cys over Hcy/GSH, with an extremely low limit of detection at 0.31 μM, marked by obvious color changes. HRMS was conducted to confirm that the fluorescence intensity at 795 nm was significantly enhanced by the enhancement of intramolecular charge transfer (ICT). Importantly, BCy-Cys could be used to visualize both exogenous and endogenous lysosomal Cys, signifying its potential application in complex organismal systems.

Near-Infrared Probes for Biothiols (Cysteine, Homocysteine, and Glutathione): A Comprehensive Review

Biothiols (cysteine, homocysteine, and glutathione) are an important class of compounds with a free thiol group. These biothiols plays an important role in several metabolic processes in living bodies when present in optimum concentration. Researchers have developed several probes for the detection and quantification of biothiols that can absorb in UV, visible, and near-infrared (NIR) regions of the electromagnetic spectrum. Among them, NIR organic probes have attracted significant attention due to their application in in vivo and in vitro imaging. In this review, we have summarized probes for these biothiols, which could work in the NIR region, and discussed their sensing mechanism and potential applications. Along with focusing on the pros and cons of the reported probes we have classified them according to the fluorophore used and summarized their photophysical and sensing properties (emission, response time, limit of detection).

A novel aggregation-induced emission fluorescent probe with large Stokes shift for sensitive detection of pH changes in live cells

The detection of intracellular pH is crucial for elucidating the pathological process of cancers, as well as for medical diagnostic applications. Here, we developed an aggregation-induced emission active pH-responsive fluorescent probe (TPE-DCP) for sensitively detecting cell pH changes. The probe shows obvious pH-sensing properties at ~615 nm, with a pKa value of 6.82 and a good linear pH response ranging from 8.5 to 4.5. TPE-DCP holds advantages such as excellent anti-interference performance, good photostability, and low cytotoxicity, and has been successfully used to image intracellular pH changes in cells.

An indanone-based fluorescent probe for detection and imaging of Cys/Hcy in living cells

Effective detection of Cys and Hcy plays an important role in the diagnosis of diseases. In this work, a novel indanone-based fluorescent probe INIAc-CN for sensitively and effectively detecting Cys and Hcy was developed. The probe exhibited weak fluorescence, but obvious fluorescent enhancement after reacted with Cys/Hcy. Moreover, the good anti-interference and low cytotoxicity of the probe made it successfully applied for monitoring Cys and Hcy of in living cells.

A NIR fluorescence probe for monitoring Cys upregulation induced by balsam pear polysaccharide and imaging in zebrafish

In this work, we introduced the acrylate recognition group into dicyanoisophorone derivative DCI-C-OH to construct the NIR fluorescent probe DCI-C-Cys with a large Stokes shift (240 nm). DCI-C-Cys could specifically respond to Cys, resulting in a 22-fold increase in fluorescence intensity at 702 nm. Meanwhile, the probe has the advantages of good water solubility, high sensitivity (93 nM), and excellent biocompatibility. Moreover, DCI-C-Cys successfully monitored endogenous and exogenous Cys in HepG2 cells and zebrafish. Most importantly, we found that balsam pear polysaccharide could lead to the increase of intracellular Cys levels, which might be conducive to the further study of the antioxidant mechanism of balsam pear polysaccharide.

A simple "turn-on" fluorescent probe capable of recognition cysteine with rapid response and high sensing in living cells and zebrafish

Cysteine (Cys), an essential biological amino acid, participates several crucial functions in various physiological and pathological processes. The sensitive and specific detection of Cys is of great significance for understanding its biological function to disease diagnosis. Herein, we designed and synthesized a simple fluorescence sensor 2-(benzothiophen-2-yl)-4-oxo-4H-chromen-3-yl acrylate (BTCA) composed of a flavonol skeleton as the fluorophore and acrylic ester group as the recognition receptor. Probe BTCA displayed high selectivity and extremely fast response toward Cys in phosphate buffer solution in the presence of other competitive species even Homocysteine (Hcy) and Glutathione (GSH) owing to a specific conjugate addition-cyclization reaction between the acrylate moiety and Cys. The photoluminescence mechanism of probe BTCA toward Cys was modulated by excited state intramolecular proton transfer (ESIPT) process. The sensing property for Cys was studied by UV-Visible, fluorescence spectrophotometric analyses and time-dependent density functional theory (TD-DFT) calculations, those results indicated that probe BTCA possessed excellent sensitivity, higher specificity, dramatically "naked-eye" fluorescence enhancement (30-fold), high anti-interference ability, especially immediate response speed (within 40 s). Additionally, the practicability of sensor BTCA in exogenous and endogenous Cys imaging in living cells and zebrafish was elucidated as well, suggesting that it has remarkedly diagnostic significance in physiological and pathological process.

Rapid determination of cysteine and chiral discrimination of D-/L-cysteine via the aggregation-induced emission enhancement of gold nanoclusters by Ag. ANAL SCI 2022;38:541-551. [PMID: 35359272 DOI: 10.2116/analsci.21p207]

Cysteine (Cys) plays vital roles in various physiological and pathological functions. Either a deficiency or excess of Cys could lead to severe ailments in human. The identification and determination of Cys are the key issues for the early diagnosis of relevant diseases. This contribution has presented a promising potential of fluorescent gold nanoclusters (AuNCs) for Cys determination and D-/L-Cys enantiomer discrimination. Cys determination and discrimination are involved three steps. First, as a reducing and capping ligand, glutathione was applied to fabricate weak fluorescent AuNCs. Second, Ag+ was introduced to lead the aggregation-induced emission (AIE) to form well-dispersed aggregates. The fluorescence intensity of AuNCs was monitored at excitation/emission wavelengths of 396/620 nm. Third, Cys was found to quickly bind with Ag+ to form a grid network to light up the system via aggregation-induced emission enhancement (AIEE). A novel sensor for a sensitive and a visually selective detection of Cys was established on the basis of the AIEE mechanism. Rapid quantitative determination of Cys was achieved in 2 min via AIEE within the range of 0.5-100 μmol L-1 and a detection limit of 0.365 μmol L-1. Moreover, due to the specific interactions of D-/L-Cys with mandelic acid and tartaric acid, the visual discrimination of D-/L-Cys enantiomers with naked eyes was realized by replacing the organic acid buffer.

A turn-on fluorescent probe via substitution-rearrangement for highly sensitive and discriminative detection of cysteine and its imaging in living cells

Biothiols play an important role in many physiological and pathological processes, especially in the occurrence of oxidative stress caused by abnormal cysteine (Cys) concentration. Therefore, it is particularly critical to develop a method that can specifically identify Cys to avoid interference from other biological analytes. However, most Cys-specific fluorescent probes are difficult to distinguish between homocysteine (Hcy) and glutathione (GSH). In this work, to avoid the interference of Hcy and GSH, we developed a fluorescent probe triarylimidazole-naphthalimide-piperazine-sulfonyl benzoxadiazole (TNP-SBD-Cl) based on fluorescence resonance energy transfer (FRET) on platform of naphthalimide-sulfonyl benzoxadiazole (SBD), the main SBD 4-chlorine groups have mild reactivity to undergo substitution and rearrangement to distinguish Hcy and GSH. The TNP-SBD-Cl response to Cys would turn on FRET and generate a new yellow fluorescence with a large Stokes shift (157 nm), and with excellent selectivity and low detection limit (0.87 μM). Moreover, TNP-SBD-Cl can be used to monitor Cys in living HeLa cells with low cytotoxicity, suggesting that it has markedly diagnostic significance in physiological and pathological processes.

Three-fold interpenetrated metal–organic framework as a multifunctional fluorescent probe for detecting 2,4,6-trinitrophenol, levofloxacin, and l-cystine

A robust Zn(ii) MOF with good chemical and thermal stability, was prepared as an effective fluorescent probe for 2,4,6-trinitrophenol (TNP), levofloxacin (LVX) and l-cystine (l-Cys) with recyclability.

A coumarin-based fluorescent probe for specific detection of cysteine in the lysosome of living cells

Cysteine (Cys), the only amino acid in the 20 natural amino acids that contains a reduced sulfhydryl group, plays important roles in the balance of redox homeostasis in biological systems. Lysosome is an important organelle containing a variety of hydrolases and has been proved to be the decomposition center of a variety of exogenous and endogenous macromolecular substances. In this research, a coumarin-based fluorescent probe MCA for the detection of Cys in lysosomes of living cells was developed. Due to the acrylate moiety, this probe exhibited high sensitivity (detection limit = 6.8 nM) and selectivity towards Cys superior to other analytes. Moreover, the probe was proved to be lysosome-targetable and showed good cell imaging ability and low cell toxicity.

Amphiphilic copolymer fluorescent probe for mitochondrial viscosity detection and its application in living cells

The mitochondrial viscosity measurement with the amphiphilic copolymer fluorescent probe (PP) has been successfully revealed for the first time. PP was synthesized, starting from a hydrophobic rhodamine derivative fluorophore and hydrophilic 2-hydroxyethyl acrylate (HEA) by radical polymerization, which could be used to detect mitochondrial viscosity specifically. The systematic investigation demonstrated that the fluorescence emission of PP with a deep red emission increased about 9-fold when the medium is changed from methanol to 99% glycerol, indicating high viscosity dependence. Moreover, PP could self-assemble into nanospheres with the particle size of about 140 nm in water and the nano-structure enabled PP to enter living cells quickly. Cytotoxicity test showed that the cells survival rate remained above 70% at 70 μg·mL^-1 of PP. Good biocompatibility and low cytotoxicity of PP are promising to provide a high contrast fluorescence imaging. Taken together, the results point the way to development of novel amphiphilic copolymer fluorescent probes-based the detection in solutions, physiology and pathology.

Ratiometric fluorescent sensors for sequential on-off-on determination of riboflavin, Ag+ and l-cysteine based on NPCl-doped carbon quantum dots

The fluorescent sensor, especially ratiometric fluorescent sensor, is one of the most important applications for CQDs, which is becoming a research hotspot. Herein, carbon quantum dots co-doped with nitrogen, phosphorus and chlorine (NPCl-CQDs) were synthesized by acid-base neutralization reaction exothermic carbonization method. The as-fabricated NPCl-CQDs could emit blue fluorescence and possess excellent fluorescence properties. Based on the FRET, multifunctional and ratiometric fluorescent sensors for "on-off-on" sequential determination of riboflavin, Ag⁺, and Cys with good selectivity and high sensitivity were established. The linear range of riboflavin, Ag⁺, and Cys are 0.50-10.18 μM and 15.89-27.76 μM, 0.66-1.46 mM and 1.50-4.20 mM, and 0.01-0.15 μM and 0.15-0.36 μM with the limit of detection of 3.50 nM, 26.38 μM, and 0.96 nM, respectively. Furthermore, the sensors were successfully used to determine riboflavin, Ag⁺, and Cys in tablets, river water, and human urine with the recoveries of 95.2-104.0%, 95.6-102.0%, and 94.8-106.4%, respectively. More importantly, the as-constructed "on-off-on" NPCl-CQDs-based ratiometric fluorescent sensors were applied for detecting riboflavin, Ag⁺, and Cys in HeLa cells with satisfying results. The finding of this study shows the feasibility and effectiveness of the NPCl-CQDs as the available ratiometric fluorescent sensors for the determination of riboflavin, Ag⁺, and Cys in real samples and living cells.

Colorimetric determination of cysteine by a paper-based assay system using aspartic acid modified gold nanoparticles

A method is described for cysteine (Cys) determination on paper-based analytical devices using aspartic acid modified gold nanoparticles (Asp-AuNPs). The Asp-AuNPs were characterized by their size, zeta potential, and UV-visible absorption spectrum. After the addition of Cys, it will interact with Asp-AuNPs selectively and leads to the aggregation of Asp-AuNPs. A color change from red to blue can be observed on the paper-based analytical devices. The results were recorded using a cell phone and subsequently analyzed using the Photoshop software. The ratiometric color intensity at red channel and blue channel (Red/Blue) increased linearly in the range 99.9-998.7 μM for Cys (R = 0.9984), and the limit of detection was 1.0 μM. The effects of assay conditions have been investigated and are discussed. The Cys concentration was determined as (0.27 ± 0.02 mM) in human plasma, and the recovery was from 99.2 to 101.1%. Graphical abstract Schematic representation of the paper-based assay system using aspartic acid modified gold nanoparticles (Asp-AuNPs). The ratiometric color intensity method was used for the cysteine (Cys) determination.

Introducing ortho-methoxyl group as a fluorescence-enhancing and bathochromic-shift bi-functional strategy for typical cysteine sensors

A practical strategy of introducing ortho-methoxyl group was explored to achieve the fluorescence-enhancing and bathochromic-shift bi-functional optimization. It was tested in the Cys sensing ISOPH-X series, thus the successful case, ISOPH-2, was obtained. It realized the optimization in a simple and compatible way. The corresponding strategy was basically established during the confirmation of checkpoints including applicable steadiness (over 24 h), wide pH range (7.0-9.0), rapid response (20 min), good biocompatibility, high sensitivity (LOD = 0.072 nm), high selectivity and biological monitoring of Cys in living cells as well as C. elegans. In this work, the o-methoxyl introduction strategy led to a 15 nm red shift and a near 4-fold fluorescence enhancement. This strategy could be combined with the double bond-introducing approach. Compared with reported strategies, by breaking the dilemma between red shift and strong fluorescent intensity, this strategy might offer beneficial information for exploiting better sensors with more fluorophores and mechanisms for their targets.

A paper-based colorimetric assay system for sensitive cysteine detection using a fluorescent probe

Sensitive analysis of Cys on a paper-based platform via colorimetric detection which abandons sophisticated instruments.