A novel near-infrared turn-on fluorescent probe for the detection of Fe3+ and Al3+ and its applications in living cells imaging

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.

A colorimetric and fluorescent probe of lignocellulose nanofiber composite modified with Rhodamine 6G derivative for reversible, selective and sensitive detection of metal ions in wastewater

Heavy metal ions have extremely high toxicity. As the top of food chain, human beings certainly will accumulate them by ingesting food and participating other activities, which eventually result in the damage to our health. Therefore, it is very meaningful and necessary to design a simple, portable, stable and efficient material for heavy metal ions detection. Based on the spirolactam Rhodamine 6G (SRh6G) fluorescent probe, we prepared two types of nanocomposite materials (membrane and aerogel) by vacuum filtration and freeze-drying methods with lignocellulose nanofiber (CNF) as a carrier, polyvinyl alcohol (PVA) and glutaraldehyde (GA) as the cross-linkers. Then the microstructure, chemical composition, wetting property, fluorescence intensity and selectivity of as-prepared SRh6G/PVA/CNF would be characterized and analyzed. Results showed that SRh6G/PVA/CNF nanocomposites would turn red in color under strong acidic environment and produced orange fluorescence under ultraviolet light. Besides, they were also to detect Al3+, Cu2+, Hg2+, Fe3+ and Ag+ through color and fluorescence variations. We had further tested its sensitivity, selectivity, adsorption, fluorescence limits of detection (LOD) to Fe3+ and Cu2+. The test towards real water samples (hospital wastewater, Songhua River and tap water) proved that SRh6G/PVA/CNF nanocomposites could detect the polluted water with low concentrations of Fe3+ and Cu2+. In addition, SRh6G/PVA/CNF nanocomposites have excellent mechanical property, repeatability, superhydrophilicity and underwater superoleophobicity, which may offer a theoretical reference for the assembly strategy and detection application of cellulose-based fluorescent probe.

Nanocellulose-based sensors in medical/clinical applications: The state-of-the-art review

In recent years, the considerable importance of healthcare and the indispensable appeal of curative issues, particularly the diagnosis of diseases, have propelled the invention of sensing platforms. With the development of nanotechnology, the integration of nanomaterials in such platforms has been much focused on, boosting their functionality in many fields. In this direction, there has been rapid growth in the utilisation of nanocellulose in sensors with medical applications. Indeed, this natural nanomaterial benefits from striking features, such as biocompatibility, cytocompatibility and low toxicity, as well as unprecedented physical and chemical properties. In this review, different classifications of nanocellulose-based sensors (biosensors, chemical and physical sensors), alongside some subcategories manufactured for health monitoring, stand out. Moreover, the types of nanocellulose and their roles in such sensors are discussed.

A novel water-soluble flavonol-based fluorescent probe for highly specific and sensitive detection of Al3+ and its application in onion and zebrafish

A novel and simple turn-on fluorescence probe (HD) for Al³⁺ detection was successfully developed based on flavonol derivatives. This probe exhibited a significantly enhanced fluorescence response toward Al³⁺ in aqueous solution which could be observed by naked-eye from poor fluorescence to strong light green emission. The probe HD displays highly specific detection for Al³⁺ over other competitive metal ions, and the detection limit of probe HD for Al³⁺ was determined to be 2.57 × 10^-8 M, which are much lower than the World Health Organization (WHO) guideline value for drinking food/water. The binding stoichiometry of probe HD with Al³⁺ was determined to be 1:1 according to Job's plot and ESI-HRMS analysis, and the binding constant was calculated to be 2.01 × 10⁴ M^-1. The probe HD exhibited high selectivity, high sensitivity, good anti-interface ability, and wide pH application range as well as the quantitative determination in the detection of Al³⁺. The coordination mechanism of probe HD with Al³⁺ was supported by density functional theory (DFT) calculations and HRMS analysis. In addition, the probe HD was found to have good cell permeability and could be applied for live-cell imaging to detect Al³⁺ in onions and zebrafish.

Nanocellulose-based sensing platforms for heavy metal ions detection: A comprehensive review

Increase in industrial activities has been arising a severe concern about water pollution caused by heavy metal ions (HMIs), such us lead (Pb²⁺), cadmium (Cd²⁺) or mercury (Hg²⁺). The presence of substantial amounts of these ions in the human body is harmful and can cause serious diseases. Hence, the detection of HMIs in water is of great importance. As technological advances have developed, some conventional methods have become obsolete due to some methodological disadvantages, giving way to a second generation that uses novel sensors. Recently, nanocellulose, as a biocompatible material, has drawn a remarkable attraction for developing sensors owing to its extraordinary physical and chemical properties. This review pays a special attention to the different dimensional nanocellulose-based sensors devised for HMIs recognition. What is more, different sensing techniques (optical and electrochemical), sensing mechanisms and the roles of nanocellulose in such sensors are discussed.

Multifunctional fluorescence sensor as a potential theranostic agent against Alzheimer's disease

Metal ions play an important role in the pathogenesis of Alzheimer's disease (AD). Metal dyshomeostasis, β-amyloid (Aβ) accumulation and oxidative stress, etc. are related to metal ions. So, metal therapeutics has aroused increasingly more attention, especially the research of metal-involved theranostic agents. In this work, a highly selective and sensitive multifunctional fluorescence sensor 1 with a naphthol unit based on photoinduced electron transfer (PET) and excited state proton transfer (ESPT) mechanism was synthesized, and its synergistic biological effects on regulating metal dyshomeostasis, modulating Aβ accumulation and scavenging reactive oxygen species (ROS) was evaluated. The results demonstrated that 1 exhibited significant fluorescence enhancement towards Al³⁺ (the limit was as low as 0.01 ppm), superior chelating abilities with metal ions, even better modulation effect of Cu²⁺-induced Aβ_1-42 accumulation than curcumin, good elimination effect of ROS, clear fluorescence image in living cells, low cytotoxic and appropriate blood brain barrier (BBB) permeability. Overall, these findings revealed that 1 could be used as a potential theranostic agent against AD for further research.

A NIR fluorescent sensor based on thiazoline-isophorone with low cytotoxicity in living cells for Hg2+ detection through ICT associated hydrogen bonding effect

Mercury (Hg) is a toxic pollutant and may cause serious health and environmental threats even at low concentrations. Thus, sensitive, efficient, and accurate techniques for the detection of Hg²⁺ ions in biological systems are in particular demand. In the current paper, a new, red emitting fluorescence probe (THI) based on electron deficient dicyanovinyl, electron-rich diethylamino, and receptor thiazoline toward Hg²⁺ has been developed. It has been determined that the recognition behavior of the probe toward Hg²⁺ is reversible with S^2-. The probe not only shows perfect selectivity toward Hg²⁺ with a low detection limit over a series of metal ions, but it also displays positive solvato-chromism among the tested solvents via modulation of intramolecular energy transfer from the diethylamino to a dicyanovinyl moiety. Furthermore, it has been shown that the probe can be applied as a fluorescent probe for visualizing Hg²⁺ in living HeLa cells through a confocal laser scanning microscope. Also, the probe THI has not shown any toxic effect in cervical cancer and epithelial cells. Thus, the probe demonstrates high promise for Hg²⁺ detection in biomarker screening, disease diagnosis, and clinical medicine with low cytotoxicity.

A dual-response fluoran-phenothiazine hybrid fluorescent probe for selective sensing of Fe3+ and ClO- and cell imaging application

Bifunctional fluorescent probes with dual-emission response attract extensive attention. A novel fluorescent probe FP, a hybrid of fluoran and phenothiazine, has been designed and synthesized for selective sensing of Fe³⁺ and ClO^- with dual-emission changes, which involes mechanisms of Fe³⁺-promoted spirolactone ring opening and ClO^--induced oxidation of phenothiazine moiety, respectively. In addition, the detection limits for Fe³⁺ and ClO^- were estimated to be 49.1 and 35.9 nM, respectively. Significantly, FP can be employed as an tracer for the detection of Fe³⁺ ions within living HeLa cells by fluorescence imaging.

Monitoring of Fe (II) ions in living cells using a novel quinoline-derived fluorescent probe

Physiologically, Fe(III) and Fe(II) is the most important redox pairs in a variety of biological and environmental procedures with its capability of transition. The detection of physiological iron, especially Fe(II), has become the recent research focus of investigations on revealing the mechanism of iron-related metabolism. In this work, we exploited a novel quinoline-derived fluorescent probe, YTP, for the detection of Fe(II). It could monitor the level of Fe(II) with a linear range of 0-2.0 equivalent and the detection limit of 0.16 µM. High selectivity from other analytes including Fe(III) and steadiness for over 24 h confirmed the practicability of YTP. YTP was further applied in real buffer systems and in cellular imaging. The probe could achieve the semi-quantitative monitoring of Fe(II) in living cells. This work provided a potential implement for the detection of Fe(II), and raised important information for further researches on the redox pairs of iron, in mechanism and in practice.

Highly sensitive and selective fluorescence sensing and imaging of Fe3+ based on a novel nitrogen-doped graphene quantum dots

A novel nitrogen-doped graphene quantum dots (N-GQDs) with a green fluorescence emission was synthesized through microwave method using citric acid and semicarbazide hydrochloride as reactants. The as-synthesized N-GQDs exhibited good stability, excellent water solubility, and negligible cytotoxicity. Due to intermolecular charge transfer, ferric ion (Fe³⁺ ) has a strong quenching effect on the N-GQDs. Fluorescence quenching has a linear relationship with the Fe³⁺ concentration in the range 0.02-12 μM. The detection limit was 1.43 nM. What is more, it is worth mentioning that the obtained N-GQDs showed high selectivity and sensitivity towards Fe³⁺ . Under the optimum conditions, the addition of 10-fold copper ions and 100-fold other metal ions had no influence on the detection of Fe³⁺ (0.8 μM), which indicated a higher sensitivity compared with that of the reported methods. Due to their excellent properties, the obtained N-GQDs was successfully applied for sensing and imaging Fe³⁺ in water samples and HeLa cells.

A purine based fluorescent chemosensor for the selective and sole detection of Al3+ and its practical applications in test strips and bio-imaging

A novel purine Schiff base fluorescent probe (WYW), (E)-4-methyl-2-((2-(9-(naphthalen-1-yl)-8-(thiophen-2-yl)-9H-purin-6-yl)hydrazono)methyl)phenol, was designed and prepared as an excellent reversible fluorescent chemosensor for monitoring Al³⁺. The fluorogenic "turn-on" sensor WYW exhibited high selectivity towards Al³⁺ over other coexistent metal ions, accompanying with an obvious visual color change in DMSO/H₂O (9/1, v/v, pH = 7.4) media. The enhancement fluorescence of WYW could be attributed to the inhibition of PET and ESIPT process induced by Al³⁺. Notably, the WYW-Al³⁺ complex exhibited a fluorescence "turn-off" response towards F^- with exceptional selectivity via the displacement approach. The detection limit of WYW for Al³⁺ was calculated to be as low as 82 nM. The formation of complex WYW-Al³⁺ (1:1 stoichiometry) was confirmed by Job's methods and further verified by density functional theory (DFT) calculations. Furthermore, the probe WYW with low cytotoxicity and excellent membrane-permeable property has also been successfully applied for detecting low concertation Al³⁺ in living HeLa cells.

Multiple stimulus-responsive behavior of a triphenylamine-substituted acylhydrazone derivative

A triphenylamine-based acylhydrazone derivative (TBHM) was synthesized, and its emission properties either in solution or in the solid state were studied.