Probe with large Stokes shift for effective cysteine imaging in living cells

A D-π-A-based near-infrared fluorescent probe with large Stokes shift for the detection of cysteine in vivo

D-π-A dyes are an ideal strategy for building near-infrared fluorescent probes that have a large Stokes shift due to their excellent properties of adjustable emission wavelength and Stokes shift. Developing a near-infrared (NIR) fluorescent probe (JTPQ-Cys) capable of detecting cysteine (Cys) was the aim of this study. In JTPQ-Cys, julolidine served as the electron donor (D) and quinoline as the electron acceptor (A), with 3,4-ethylenedioxythiophene as the π-bridge. The π-conjugation and vibrational/rotational activity of the molecule were increased by the introduction of 3,4-ethylenedioxythiophene, causing the molecule to exhibit NIR emission and a large Stokes shift. When JTPQ-Cys was used to detect Cys, a clear fluorescence turn-on signal was observed at 741 nm, together with a Stokes shift of 268 nm. The limit of detection of JTPQ-Cys for Cys is 24 nM. Moreover, JTPQ-Cys has been utilized successfully for imaging studies of Cys in cells and zebrafish because it has good photostability, low cytotoxicity, and a high signal-to-noise ratio. Overall, our findings demonstrate the potential of JTPQ-Cys to be one of the best choices for detecting Cys in biological systems, and JTPQ is an ideal fluorophore to construct fluorescence dyes for bioimaging.

A highly chromogenic selective Rhodamine-chloride-based fluorescence probe activated by cysteine and application in living cells and zebrafish

Cysteine (Cys), one of the biological thiols, which plays critical roles in biological system regulating the balance of redox homeostasis. In order to monitor the level of Cys in the living cells and organisms, a chromogenic fluorescence probe Rhocl-Cys based on Rhodamine chloride exhibiting the preferable performance of fluorescence turn-on response reacting with Cys was presented. Rhocl-Cys responded rapidly to Cys within 20 min, and had stable fluorescence intensity within pH 6.0-10.0, high selectivity towards Cys and the anti-inference capability with a low detection limit of 0.80 μM. In particular, Rhocl-Cys could qualitatively and quantitatively monitor the level of endogenous and exogenous Cys in living cells and successfully apply to zebrafish detecting Cys. Therefore, these results might further provide the basis exploring the role of Cys in biological system and facilitate as clinical diagnostic molecular tools.

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 novel cysteine fluorescent probe with large stokes shift for imaging in living cells, zebrafish and living mice

The small molecule biological thiols, such as Cysteine (Cys), homocysteine (Hcy), and glutathione (GSH), play crucial roles in maintaining various cellular vital activities. In the organism, abnormal levels of small-molecule biological thiols have been associated with a variety of diseases. Therefore, quantitative determination of biological thiols, especially Cys, is significant for understanding their functions in various biological processes. Thus, in this work we designed a new fluorescent probe Ty-Cys1 with a large Stokes shift of 207 nm to monitor Cysteine. The maximum absorption wavelength of Ty-Cys1 was 418 nm, and the maximum emission wavelength was 625 nm. Significantly, the novel probe Ty-Cys1 was effectively in detecting of Cys changes in living cells, zebrafishes, and living mice.

Unveiling the effects of atomic electronegativity on the ESIPT mechanism and luminescence property of new coumarin benzothiazole Fluorophore: A TD-DFT exploration

The excited-state intramolecular proton transfer (ESIPT) mechanism, photophysical properties of 8-(benzo[D] thiazole-2-yl)-7-hydroxy-2H-benzopyran-2-one (L-HKS) and the effect of O/Se atomic substitution on L-HKS have been studied in detail based on density functional theory (DFT) and time-dependent DFT (TD-DFT) methods. The S atom in the thiazole ring of L-HKS has been replaced by O/Se atom (denoted to L-HKO/L-HKSe) to analyze the effects of atomic electronegativity on the intramolecular H-bond, absorption/emission spectrum and ESIPT process. Through the analysis of series of calculated results, it can be found that the intramolecular H-bonds at normal form and tautomer form are enhanced and weakened in the S₁ state, respectively, which is favorable to ESIPT process. The potential energy curves revealed that the ESIPT process is much easier to occur gradually from L-HKO to L-HKS and L-HKSe, as the electron-withdrawing ability of atom (from O to S and Se) is weakened. The atomic substitution also has an effect on the photophysical properties. From L-HKO to L-HKS, the emission peak at tautomer form red-shifts 70 nm. The energy gaps of the three compounds follow the decreased order of L-HKO (4.866 eV) > L-HKS (4.753 eV) > L-HKSe (4.371 eV) with the weakened electron-withdrawing ability of atom (from O to S and Se), which leads to the gradual red-shift of the absorption spectra from L-HKO to L-HKS and L-HKSe.

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.

Specific two-photon fluorescent probe for cysteine detection in vivo

Cysteine (Cys), an essential amino acid, plays several crucial functions in numerous biological processes. Notably, the detection of Cys is critical to disease diagnosis. Fluorescent probes that can quickly detect Cys will help to study the mechanism of certain diseases. Herein, a new fluorescent probe, ANP, which is based on 6-acetyl-N-methyl-2-naphthyl amine, has been developed for Cys detection over Hcy and GSH in vivo. The addition of thiol on α,β-unsaturated ketone promotes 87-fold fluorescence turn-on response with a 65 nM limit of detection. The high two-photon efficiency of the probe ANP (cross-section = 22.3) makes it a suitable probe for evaluating Cys in living cells without background fluorescence interference. Its application was extended to monitor the Cys distribution in live cells and tissues.