A novel fluorescence probe based on triphenylamine Schiff base for bioimaging and responding to pH and Fe 3+

A benzothiophene-based fluorescent probe with dual-functional to polarity and cyanide for practical applications in living cells and real water samples

Polarity is a significant intracellular environmental parameter associated with cancer, while cyanide (CN-) is known to be highly toxic to humans. In this work, we designed a dual-functional fluorescent probe (TPABT) for simultaneous detection of polarity and CN-. As a polarity sensor, the probe exhibits NIR emission at 766 nm in 1,4-dioxane (non-polar solvent), whose emission intensity is 71-fold stronger than that in water (polar solvent). Meanwhile, the fluorescence intensity and quantum yield are linearly related to solvent polarity, confirming the polarity response ability of TPABT. For cell polarity detection, low cytotoxicity and polarity sensitivity of probe enable the applications for differentiating cancer cells (HeLa, 4TI) from normal cells (HUV, 3 T3) and monitoring the polarity changes of 4TI cells. As a CN- sensor, TPABT displays a turn-on fluorescence at 640 nm upon the addition of CN-, with advantages of anti-interference, response in aqueous media and low detection limit (22 nM). Additionally, we further explored the practical applications of TPABT for CN- determination in three types of real water samples (drinking water, tap water and lake water) and living cells. Notably, TPABT responses to polarity and CN- in two independent fluorescence channels of 766 and 640 nm, respectively, ensuring the dual functions for polarity and CN- sensing. Consequently, this multi-responsive fluorescent probe TPABT is promising to diagnose polarity-related diseases and detect CN- in real environments.

Novel biocompatible N-rich AIE fluorescent probe for live cell imaging and visual onsite detection of uranium

A sensitive and biocompatible N-rich probe for rapid visual uranium detection was constructed by grafting two trianiline groups to 2,6-bis(aminomethyl)pyridine. Possessing excellent aggregation-induced emission (AIE) property and the advantages to form multidentate chelate with U selectively, the probe has been applied successfully to visualize uranium in complex environmental water samples and living cells, demonstrating outstanding anti-interference ability against large equivalent of different ions over a wide effective pH range. A large linear range (1.0 × 10-7-9.0 × 10-7 mol/L) and low detection limit (72.6 nmol/L, 17.28 ppb) were achieved for the visual determination of uranium. The recognition mechanism, photophysical properties, analytical performance and cytotoxicity were systematically investigated, demonstrating high potential for fast risk assessment of uranium pollution in field and in vivo.

Spectroscopic Investigation of Coumarin Based Novel Fluorescent TURN OFF Sensor for the Selective Detection of Fe3+: In-vitro Live Cell Imaging Application

The novel TURN-OFF fluorescent sensors 4-(Benzo[1,3]dioxol-5-yloxymethyl)-7-hydroxy-chromen-2-one (4BHC) and 4-(6-Bromo-benzo[1,3]dioxol-5-yloxymethyl)-7-hydroxy-chromen-2-one (4BBHC) are designed and synthesized for the spectrofluorometric detection of the biologically important Fe3+ ions, which has sensitive and selective fluorescence quenching over other competitive metal ions. The effectiveness of the sensors and rapid response are validated through UV-Visible, and fluorescence spectral changes. These spectral changes could be due to the formation of coordination bond between ligand and metal ion. The binding stoichiometry of both sensors with Fe3+ ions is studied with the help of Job's plot, which gives a 1:2 coordination ratio; this is further confirmed through DFT, IR and NMR studies. The association constants of 4BHC and 4BBHC are calculated through Benesie-Hildebrand plots, and they are found to be 6 × 104 M-1 and 11.2 × 104 M-1 respectively. Following, LOD is calculated to define the range of sensitivity of the proposed sensors and is found to be 3.43 μM and 2.14 μM respectively. The chemical hardness parameter suggested that both sensors are soft molecules. In addition, low cytotoxicity levels of 4BHC and 4BBHC led to the demonstration of their efficacy in In-Vitro imaging of Fe3+ ions inside living cells, which ensures that these sensors are promising candidates for bioimaging.

Recent advances of lanthanide nanomaterials in Tumor NIR fluorescence detection and treatment

Lanthanide nanomaterials have garnered significant attention from researchers among the main near-infrared (NIR) fluorescent nanomaterials due to their excellent chemical and fluorescence stability, narrow emission band, adjustable luminescence color, and long lifetime. In recent years, with the preparation, functional modification, and fluorescence improvement of lanthanide materials, great progress has been made in their application in the biomedical field. This review focuses on the latest progress of lanthanide nanomaterials in tumor diagnosis and treatment, as well as the interaction mechanism between fluorescence and biological tissues. We introduce a set of efficient strategies for improving the fluorescence properties of lanthanide nanomaterials and discuss some representative in-depth research work in detail, showcasing their superiority in early detection of ultra-small tumors, phototherapy, and real-time guidance for surgical resection. However, lanthanide nanomaterials have only realized a portion of their potential in tumor applications so far. Therefore, we discuss promising methods for further improving the performance of lanthanide nanomaterials and their future development directions.

Colorimetric and fluorescent dual-signals probes for naked-eye detection of hydrogen peroxide and applications in milk samples and in vivo

Excessive residual hydrogen peroxide (H₂O₂) disinfectant in food is harmful to human health. Therefore, it is necessary to develop efficient detection methods for H₂O₂ detection. In this work, we designed and synthesized five D-A molecules 3a-3e by introducing electron-donor substituents (-OCH₃ and -CH₃) to the electron-acceptor dicyanoisophorone skeleton in order to find out the suitable probes for H₂O₂ detection. Among them, two promising probes, 3a and 3c, are screened out according to structure-property relationships. Based on the principle of intramolecular charge transfer (ICT), 3a and 3c express colorimetric and fluorescent dual-signals towards H₂O₂ with low detection limits (0.20 μM and 0.14 μM) and rapid response (within 20 mins). The reaction mechanism between probes and H₂O₂ is determined by ¹H NMR and HRMS. Density functional theory (DFT) calculations are measured to study the regulation mechanism of structure adjustment on probs performance. Furthermore, a smartphone RGB analysis is utilized as a portable platform for the quantitative detection of H₂O₂ without complicated instruments, indicating a high efficiency and on-site detection method for H₂O₂. In addition, probes are applied to detect H₂O₂ in milk samples, HepG-2 cells and zebrafish, suggesting the promising applications in food samples and physiological systems.

Schiff base compounds as fluorimetric pH sensor: a review

With the recent progress of biological and environmental research, detection of pH values has become one of the most indispensable requirements. To determine the pH values of a certain medium, organic Schiff base compounds and their derivatives have been observed to play pivotal roles because of their smooth synthetic roots, easily tuneable structural architecture, non-destructive signals of emission, visually differentiable colour generation and capability of real sample analysis. Therefore with the revolutionary upgradation of wavelength radiometric techniques, the construction of molecular structures which can exhibit dual emission and absorption characteristics and which can be regulated by the change in pH values, has been a stimulating challenge. Generally a pH sensor molecule has a chromophoric or fluorophoric portion. Normally heteroatoms attached to these chromophore units either get protonated or deprotonated in acidic or basic media which gives rise to changes in absorption and emission properties of the molecule.

Real time sensor for Fe3+, Al3+, Cu2+ & PPi through quadruple mechanistic pathways using a novel dipodal quinoline-based molecular probe

A quinoline-based small molecular probe, H₂L was designed, synthesized and characterized by different spectroscopic methods. It was utilized as a multi-responsive probe for the detection of Fe³⁺, Al³⁺, Cu²⁺ and PPi. It showed very selective instant turn-on fluorimetric response towards Fe³⁺and Al³⁺ with a detection limit in nanomolar range. Solutions of H₂L containing Fe³⁺ or Al³⁺ could sequentially sense PPi by a turn-off mechanism. Also, H₂L could determine the presence of Cu²⁺ very selectively among a series of other metal ions by a sharp change in colour. Detection of Cu²⁺ through colorimetry was further investigated by systematic UV-Vis studies and the potential of H₂L to act as a potential colorimetric sensor for Cu²⁺ was suitably established. Filter-paper strip experiments were conducted to demonstrate the practical utility of the proposed sensor. Potential applications of H₂L as a sensor for pH in the acidic range has also been explored.

Triphenylamine-based small-molecule fluorescent probes

Ammonia with the three hydrogens substituted by phenyls is known as triphenylamine (TPA), and is one of the most useful compounds because of its vast practical applications. Chemists have produced thousands of TPA derivatives to date. Because of its biocompatibility and structural features, it has been widely used in the fields of molecular recognition, molecular imaging, materials chemistry, and also in biology and medical science. Its strong electron-donating ability encourages scientists to produce different types of probes for molecular recognition. This review is based on recent developments and advances in TPA-based small molecular fluorescent probes within the time period 2010-2021. This extensive review may expedite improvements in more advanced fluorescent probes for vast and stimulating applications in the future.

Sensing and imaging of exosomal CD26 secreted from cancer cells and 3D colorectal tumor model using a novel near-infrared fluorogenic probe

Cancer-derived exosomes or their specific components hold great promise for early diagnosis and precise staging of cancers. This work aimed to construct a novel enzyme-activatable fluorescent substrate for real-time detection and in situ imaging of a key exosomal surface protein CD26 in various biological systems, as well as to reveal the relevance of exosomal CD26 to the tumorigenesis. For these purposes, a group of Gly-Pro amides deriving from several near-infrared fluorophores were designed on the basis of the unique prolyl-cleaving dipeptidease activity of CD26, while molecular docking simulations were applied to assess the possibility of the designed amides as CD26 specific substrates. Following virtual screening and experimental validation, it was observed that GP-ACM displayed the best combination of high sensitivity and excellent specificity to CD26. The sensing and imaging ability of GP-ACM towards CD26 were examined in a range of biological systems, such as living cells, in situ tissues, and the exosomes secreted from cancer cells. Under physiological conditions, GP-ACM can be readily hydrolyzed by CD26 to release the fluorescent product ACM. The fluorescent product emits strong near-infrared fluorescence signals around 660 nm, which can be easily captured by the devices equipped with a fluorescence detector. GP-ACM prolyl-cleaving reaction shows excellent specificity and rapid response towards CD26, while its fluorescent product ACM displays good chemical stability and outstanding photostability. With the help of GP-ACM, CD26 in living cells, tissues and the tumor-secreted exosomes can be real-time monitored and in-situ imaged, while further investigations reveal that the exosomal CD26 activities are abnormally elevated with the progression of colon tumor. Collectively, the present study offers a practical optical assay for real-time monitoring CD26 activities in multiple complex biological systems including the exosomes secreted by tumor cells. The simplicity and effectiveness of this assay hold great potential for facilitating fundamental researches and clinical diagnosis of exosomal CD26 associated diseases.

Novel triphenylamine-based fluorescent chemo-sensors for fast detection of thiophenols in vitro and in vivo

A novel chemo-sensor based on triphenylamine derivative Probe-TPA for thiophenols (C₆H₅SH, p-NH₂-C₆H₄SH, p-OH-C₆H₄SH) detection was presented in this work. The target dye Probe-TPA displayed high selectivity and extremely fast response toward thiophenols in DMSO/PBS buffer (5/5, v/v) solution in the presence of other competitive species (such as K⁺, Na⁺, Ni²⁺, Fe³⁺, S^2-, HS^-, SO₄^2-, SO₃^2-, NaClO, H₂O₂, GSH, Cys, Hcy, etc.). The sensing property for thiophenols was studied by UV-Visible, fluorescence spectrophotometric analyses and DFT/TD-DFT calculations, those results indicated that the sensor Probe-TPA possessed high anti-interference ability, excellent sensitivity, higher specifity, dramatically "naked-eye" fluorescence enhancement (almost 200-folds) under 365 nm UV lamp, especially immediate response speed (within 15 s). In extended application aspect, the fluorescent chemo-sensor Probe-TPA could provide a new method of analysis to detect of thiophenol in real water samples and visualize monitoring in live cells with remarkable fluorescence variation.

Application of rare earth-doped nanoparticles in biological imaging and tumor treatment

Rare earth-doped nanoparticles have been widely used in disease diagnosis, drug delivery, tumor therapy, and bioimaging. Among various bioimaging methods, the fluorescence imaging technology based on the rare earth-doped nanoparticles can visually display the cell activity and lesion evolution in living animals, which is a powerful tool in biological technology and has being widely applied in medical and biological fields. Especially in the band of near infrared (700–1700 nm), the emissions show the characteristics of deep penetration due to low absorption, low photon scattering, and low autofluorescence interference. Furthermore, the rare earth-doped nanoparticles can be endowed with the water solubility, biocompatibility, drug-loading ability, and the targeting ability for different tumors by surface functionalization. This confirms its potential in the cancer diagnosis and treatment. In this review, we summarized the recent progress in the application of rare earth-doped nanoparticles in the field of bioimaging and tumor treatment. The luminescent mechanism, properties, and structure design were also discussed.

A novel triphenylamine-based bis-Schiff bases fluorophores with AIE-Activity as the hydrazine fluorescence turn-off probes and cell imaging in live cells

Developing a specific and sensitive method for endogenous hydrazine detection in living systems is valuable to understand its various pathological events. In this work, two novel fluorescent chemosensors (C1, C3) based on triphenylamine Schiff-base derivative and reference dyes (C2, C4) were prepared in relatively high yield (more than 72% yield). The aggregation induced emission (AIE) properties of sensors were investigated through UV-Visible, dynamic light scattering, X-ray diffraction, fluorescence spectrophotometric analyses as well as scanning electron microscope images (SEM). The results indicated that probes C1 and C3 exhibited strong AIE property in DMF/H₂O (1:1, v/v) mixture system with brilliant yellow fluorescence emission (560 nm) observed under 365 nm UV lamp. The experiments of sensing indicated that probes C1 and C3 possessed the sequentially detecting abilities for hydrazine with high sensitivity, specificity as well as an extremely low detection limit (55.1 nM), which was due to blocking of AIE process of probes C1 and C3 by special chemical reaction (-CHN- moiety transformed into -CH₂-NH- group) after hydrazine addition, resulting in the increase in water solubility and a weak emission in aqueous media. Furthermore, ¹H NMR, SEM and fluorescence titration experiment was also conducted to confirm the sensing mechanism. For biological application, probes C1 and C3 presented a good bio-imaging performance and showed the similar fluorescence quenching after adding hydrazine. Therefore, the probes are suitable for the fluorescence imaging of exogenous hydrazine in HeLa cells.

Insight into triphenylamine and coumarin serving as copper (II) sensors with "OFF" strategy and for bio-imaging in living cells

Chemosensing is one of the widest and powerful techniques for response to anions and cations in living systems serving as bio-probes. Meanwhile, copper(II) (Cu(II)) widely exists in the environment and the human body as a common trace element, which plays an necessary role in most physiological processes. Thus, it is extremely urgent to explore means for effective, rapid and convenient detection of Cu(II) in living cells. Herein, we introduce a novel strategy for designing triphenylamine (TS) and coumarin-based (CS) functional sensors for Cu(II) detection with fluorescence "OFF" switching mechanism by blocking intramolecular charge transfer (ICT). Based on this design strategy, we have demonstrated two kinds of fluorophores sensors with aunique new fluorescent dye and excellent photophysical properties, which have shown rapid recognition of Cu(II) via a stoichiometric ratio of 2:1 and the proposed binding mode was confirmed by the single-crystal structure of CS-Cu(II) complex. In addition, we have carried out density functional theory (DFT) calculation with the B3LYP exchange functional employing RB3LYP/6-31G basis sets to get insight into the mechanism of Cu(II)-sensors alongside their optical properties. Furthermore, the sensors were capable of bio-imaging Cu(II) in living cancer cells (HepG2, A549 and Hela) with low cytotoxicity and good biocompatibility shown. Taken together, We expect that this novel strategy would provide new insight into the development of Cu(II) detection techniques and could be used more for biomedical applications.

Highly sensitive oligothiophene-phenylamine-based dual-functional fluorescence "turn-on" sensor for rapid and simultaneous detection of Al3+ and Fe3+ in environment and food samples

Developing low-cost and efficient sensors for rapid, selective and sensitive detection of the transition metal ions in environmental and food science is very important. In this study, a novel dual-functional fluorescent "turn-on" sensor 3TP based on oligothiophene-phenylamine Schiff base has been synthesized for discrimination and simultaneous detection of both Al³⁺ and Fe³⁺ ions with high selectivity and anti-interference over other metal ions. Sensor 3TP displayed a very fast fluorescence-enhanced response towards Al³⁺ and Fe³⁺ ions with low detection limits (0.177μM for Al³⁺ and 0.172μM for Fe³⁺) and wide pH response range (4.0-12.0). The Al³⁺/Fe³⁺ sensing mechanisms were investigated by fluorescence experiments, ¹H NMR titrations, FT-IR and ESI-MS spectra. Importantly, sensor 3TP was served as an efficient solid material for the highly sensitive and selective detection of Fe³⁺ on TLC plates. Moreover, the sensor 3TP has been successfully used to detect trace Al³⁺ and Fe³⁺ in environment and food samples with satisfactory results and good recoveries, revealing a convenient, reliable and accurate method for Al³⁺ and Fe³⁺ analysis in real samples.

Exploring the hidden potential of a benzothiazole-based Schiff-base exhibiting AIE and ESIPT and its activity in pH sensing, intracellular imaging and ultrasensitive & selective detection of aluminium (Al3+)

The hidden potential of an AIE-ESIPT active, simple substituted benzothiazole compound has been explored.