Highly selective fluorescent probe based on AIE for identifying cysteine/homocysteine

A novel AIE fluorescent probe for the detection and imaging of hydrogen peroxide in living tumor cells and in vivo

Hydrogen peroxide (H2O2), a key reactive oxygen species (ROS), plays crucial roles in redox signaling pathways and immune responses associated with cell proliferation, differentiation, migration, and disease progression. The selective monitoring of overproduced H2O2 is important for understanding the diagnosis and pathogenesis of diseases such as cardiovascular disease, cancers, diabetes, Parkinson's disease, Alzheimer's disease, and inflammation. In this paper, an AIE fluorescent probe BQM-H2O2 was developed by connecting phenyl borate with the fluorophore BQM-PNH for selective detection of H2O2. In the presence of H2O2 at fw = 99% (pH = 7.4, 1% DMSO), the probe BQM-H2O2 could generate strong fluorescent signals due to the oxidation of the borate ester. The probe exhibited high selectivity and a low detection limit toward H2O2 with the calculated LOD of 112.6 nM. Importantly, it was employed in the detection of exogenous and endogenous hydrogen peroxide in 4T1 cells with low cytotoxicity. This probe has also been successfully applied to imaging of H2O2 in Blab/c mice bearing 4T1 graft tumors.

A Near-Infrared Fluorescent Dye with Tunable Emission Wavelength and Stokes Shift as a High-Sensitivity Cysteine Nanoprobe for Monitoring Ischemic Stroke

Sulfur-substituted dicyanomethylene-4H-chromene (DCM) derivatives based on the intramolecular charge transfer (ICT) mechanism were designed as near-infrared (NIR) fluorescent dyes. Using the Knoevenagel condensation method, the S-DCM-OH(835) fluorescence dye was synthesized, which had an emission wavelength exceeding 800 nm and 220 nm of a Stokes shift. Compared to commercial ICG, S-DCM-OH(835) was not only synchronized in emission wavelength but also far superior in Stokes shifts. These advantages made the design of S-DCM-NIR(835) based on this dye potentially valuable for biological applications. Based on this chemical structure, a fluorescent S-DCM-NIR(835) nanoprobe with a mean diameter of 17.69 nm was fabricated as the NIR imaging nanoprobe. Results showed that the nanoprobe maintained the high-specificity identification of cysteine (Cys) via the Michael addition reaction, with the detection limitation of 0.11 μM endogenous Cys. More importantly, in an ischemic stroke mouse model, the S-DCM-NIR(835) nanoprobe could monitor the Cys concentration change at stroke lesion due to the disruption of Cys metabolism under the ischemic stroke condition. Such a S-DCM-NIR(835) nanoprobe could not only differentiate the severity of the ischemic stroke using response time but also quantify the concentration of Cys in real-time in vivo.

Phosphorescent iridium (III) complex with covalent organic frameworks as scaffolds for highly selective and sensitive detection of homocysteine

Introduction: Developing a convenient and cost-effective platform for detecting homocysteine (Hcy) is of great interest as Hcy has been found to be a biomarker for Alzheimer's disease, gastric cancer, and other diseases. Methods: In this study, we synthesized five phosphorescent Ir(C∧N)2(N∧N)+ compounds (Irn, n = 1-5) with various substituents (-CHO or -CHO/-NH2), which were then doped into a covalent organic framework (COF) host via covalent bonding. Results and Discussion: The resulting optimal composites (denoted as Ir4/5@EBCOF) with -CHO/-NH2 substituents not only overcame the self-quenching issue of the bare Ir4/5 complexes but also showed rapid, highly selective, and sensitive detection of Hcy, with a limit of detection (LOD) of 0.23 μM and reaction time of 88 s. The sensing mechanism was revealed as the unique cyclization reaction between Ir(III) and Hcy that forms a six-membered ring. During the process, the color changes in the composites can be observed visually. It is expected that these phosphorescent Iridium (III) complexes with COFs will have the potential to serve as promising platforms for detecting thiols.

A new lysosome-targeted Cys probe and its application in biology and food samples

Cysteine (Cys) is a sulfur-containing amino acid that plays an important role in living systems. The most common way to supplement the body with exogenous Cys is through the consumption of Cys-rich foods. Therefore, it is important to detect and analyze Cys in living systems and food samples. However, most of the Cys fluorescent probes developed so far are limited to the detection of the cellular environment only, and very few probes can take into account the detection of Cys in plant roots and food samples. In this paper, a novel fluorescent probe LN-NCS targeting the detection of Cys in lysosomes was designed and synthesized by modifying the naphthalimide fluorophore. The probe LN-NCS has a large Stokes shift (140 nm), low cytotoxicity, low detection limit (16.3 nM), and high selectivity, and probe LN-NCS reacts with Cys to produce the compound LN-NH2 with good fluorescence quantum yield (Ф = 0.81). Probe LN-NCS can be used to detect Cys in cells, zebrafish, plant roots, food samples, and environmental water samples. In addition, by modeling cellular inflammation, we have demonstrated that probe LN-NCS can detect changes in Cys concentration induced by cellular inflammation, providing a potential tool to better study the cellular inflammatory environment.

A novel fluorescent probe for rapid detection of sulfatase in vitro and in living cells

Sulfatase participates in a variety of physiological processes in organisms including hormone regulation, cell signaling, and bacterial pathogenesis. Current sulfatase fluorescent probes can be used to track sulfate esterase overexpression in cancer cells for diagnostic purposes and to understand the pathological activity of sulfate esterase. However, some sulfatase fluorescent probes based on the hydrolysis of the sulfate bond were easily disturbed by the catalytic activity of sulfatase. Herein, we developed the fluorescent probe BQM-NH2 for sulfatase detection, which was based on the quinoline-malononitrile. The probe BQM-NH2 showed a fast response to sulfatase within 1 min and satisfactory sensitivity with a calculated LOD of 1.73 U/L. Importantly, it was successfully used to monitor endogenous sulfate in tumor cells, indicating BQM-NH2 has the potential to monitor sulfatase under physiological and pathological conditions.

Construction of a novel ESIPT and AIE-based fluorescent sensor for sequentially detecting Cu2+ and H2S in both living cells and zebrafish

The development of effective methods for tracking Cu²⁺ and H₂S in living organisms is urgently required due to their vital function in a variety of pathophysiological processes. In this work, a new fluorescent sensor BDF with excited-state intramolecular proton transfer (ESIPT) and aggregation-induced emission (AIE) features for the successive detection of Cu²⁺ and H₂S was constructed by introducing 3,5-bis(trifluoromethyl)phenylacetonitrile into the benzothiazole skeleton. BDF showed a fast, selective and sensitive fluorescence "turn off" response to Cu²⁺ in physiological media, and the situ-formed complex can serve as a fluorescence "turn on" sensor for highly selective detection of H₂S through the Cu²⁺ displacement approach. In addition, the detection limits of BDF for Cu²⁺ and H₂S were determined to be 0.05 and 1.95 μM, respectively. Encouraged by its favourable features, including strong red fluorescence from the AIE effect, large Stokes shift (285 nm), high anti-interference ability and good function at physiological pH as well as a low toxicity, BDF was successfully applied for the consequent imaging of Cu²⁺ and H₂S in both living cells and zebrafish, making it an ideal candidate for detecting and imaging of Cu²⁺ and H₂S in live systems.

Aggregation-Induced emission photosensitizer with lysosomal response for photodynamic therapy against cancer

Photosensitizers play a key role in bioimaging and photodynamic therapy (PDT) of cancer. However, conventional photosensitizers usually do not achieve the desired efficacy in PDT due to their poor photostability, targeting ability, and responsiveness. Herein, we designed a series of photosensitizers with aggregation-induced emission (AIE) effect using benzothiazole- triphenylamine (BZT-triphenylamine) as the parent nucleus. The synthesized compound SIN ((E)-2-(4-(diphenylamino)styryl)-3-(4-iodobutyl)benzo[d]thiazol-3-ium) exhibits good biocompatibility, photostability, and bright emission in the near-infrared range (600-800 nm). The fluorescence emission intensity is responsive to viscosity, with significant fluorescence enhancement (48 times) and high fluorescence quantum yield (4.45 %) at high viscosity. Moreover, SIN has particular lysosome targeting properties with a Pearson correlation coefficient (PCC) of 0.97 and has good ¹O₂ generation ability under white light irradiation, especially in a weak acidic environment. Thus, SIN can realize good bioimaging ability and photodynamic therapeutic efficacy under the highly viscous and weakly acidic environment of lysosomes in the tumor cells. This study indicates that SIN has potential as a multifunctional organic photosensitizer for bioimaging and PDT of tumor.

A novel AIRE-based fluorescent ratiometric probe with endoplasmic reticulum-targeting ability for detection of hypochlorite and bioimaging

Hypochlorite (ClO^-) plays an important role in the human immune defense system, but high concentrations of ClO^- in the endoplasmic reticulum (ER) damage cellular proteins, causing ER stress, cell death, and various diseases. Herein, we developed a simple hydrazone probe (1) featuring aggregation-induced ratiometric emission, which would quickly (within 20 s) and sensitively (detection limit of 15.4 μM) respond to ClO^- in an almost pure aqueous solution via a fluorescent ratiometric output. Furthermore, the probe was employed to track the level of ClO^- in the ER of HeLa cells and zebrafish.

Development of a colloidal gold strip assay for the detection of total homocysteine in serum samples

A highly sensitive anti-SAH mAb was produced and an LFIA strip was developed to detect tHcy in serum samples after enzymatic hydrolysis.