An Emission-Based Probe for the Detection and Quantification of DNA and RNA

Sequence-independent detection of low concentrations of nucleic acids is important for applications in forensics and diagnostics. An emission-based probe for detecting and quantifying DNA and RNA utilizing a water-soluble dicationic tetraphenylethene (TPE) derivative was developed. The recognition is based on the electrostatic and other non-covalent interactions between the phosphate backbone of nucleic acids and the cationic probe, which cause the restriction of rotation of the aryl units of the probe, ensuing in the enhancement of the fluorescence signal. The binding was validated by different spectroscopic techniques and also by electrophoretic mobility shift assay. The probable mode of binding with the nucleic acids was studied by blind-docking studies that correlated well with the experimental results.

Delineating a tailor-made fluorescent probe designed for the selective detection of tyrosinase

A dicyanoisophorone based fluorescent probe (E)-2-(3-(4-hydroxystyryl)-5,5-dimethylcyclohex-2-en-1-ylidene)malononitrile (DCIP-OH) was developed for the selective sensing of tyrosinase in apple extract and live cells. The probe was obtained by the condensation of 2-(3,5,5-trimethylcyclohex-2-en-1-ylidene)malononitrile with 4-hydroxybenzaldehyde. Upon interaction with tyrosinase, the probe exhibited absorbance switching from 417 nm to 357 nm, accompanied by a slight increase in absorption value and an isosbestic point observed at 373 nm. Additionally, a reduction in emission intensity at 592 nm was observed. Furthermore, we successfully employed the probe for sensing of tyrosinase in apple extract and conducted inhibition studies by using kojic acid. LOD was determined to be ~0.4 nM. Moreover, the biocompatible nature of DCIP-OH enabled its effective localization in epithelial-like melanoma cells, B16F10, where it demonstrated successful fluorescent probing of intracellular tyrosinase.

Fluorescence and Lifetime Imaging of Endoplasmic Reticulum Polarity Change During Ferroptosis

As a new form of regulated cell death, ferroptosis is closely related to various diseases. Tracing ferroptosis related biological behavior is helpful to better understand this process and its related biology. Considering that ferroptosis is featured with remarkable lipid peroxidation which can easily change the membranes' compositions and structures, it is potential to detect intracellular environmental changes for direct assessment of ferroptosis. In view of the close relationship between endoplasmic reticulum (ER) and ferroptosis, we designed an ER-targeted and polarity-sensitive fluorescent probe SBD-CH, which has superior photostability and can respond to polarity with high selectivity without the affection of viscosity. SBD-CH can monitor the trend of ER polarity during ferroptosis by confocal laser scanning microscopy (CLSM), and analyze the distribution of polarity in ferroptosis by fluorescence lifetime imaging microscopy (FLIM). During Erastin induced ferroptosis, the polarity of ER in HT-1080 cells increased and the polarity distribution in ER was more dispersed. Our work provides an effective strategy for evaluating the process of ferroptosis by monitoring the changes of ER polarity.

Chemical Approaches to Optimize the Properties of Organic Fluorophores for Imaging and Sensing

Organic fluorophores are indispensable tools in cells, tissue and in vivo imaging, and have enabled much progress in the wide range of biological and biomedical fields. However, many available dyes suffer from insufficient performances, such as short absorption and emission wavelength, low brightness, poor stability, small Stokes shift, and unsuitable permeability, restricting their application in advanced imaging technology and complex imaging. Over the past two decades, many efforts have been made to improve these performances of fluorophores. Starting with the luminescence principle of fluorophores, this review clarifies the mechanisms of the insufficient performance for traditional fluorophores to a certain extent, systematically summarizes the modified approaches of optimizing properties, highlights the typical applications of the improved fluorophores in imaging and sensing, and indicates existing problems and challenges in this area. This progress not only proves the significance of improving fluorophores properties, but also provide a theoretical guidance for the development of high-performance fluorophores.

A Enhanced Fluorescent Probe for Simultaneous Detection and Discrimination of Hydrogen Bisulfite Anions and Glutathione

Bisulfite (HSO3-) and biological thiols molecules, such as glutathione (GSH), cysteine (Cys), and homocysteine (Hcy), play important roles in organisms. Developing a fluorescent probe that can simultaneously detect and distinguish HSO3- and biological thiols is of great significance. In this study, ethyl(2E,4Z)-5-chloro-2-cyano-5-(7-(diethylamino)-2-oxo-2 H-chromen-3-yl)penta-2,4-dienoate (CCO) as a novel enhanced fluorescence probe was synthesized by integrating coumarin derivatives and ethyl cyanoacetate, which can simultaneous detection and discrimination of hydrogen bisulfite anions and glutathione. The sensing mechanism was elucidated through spectral analysis and some control experiments. In weakly alkaline environments, the probe not only has good selectivity for HSO3- and GSH, but also has a lower detection limits of 0.0179 µM and 0.2034 µM. The probe exhibited fuorescent turn-on for distinguishing with 296 and 28 fold the fluorescent intensity increase at 486 and 505 nm, respectively, through diferent excitation wavelengths. This provides a new method for simultaneous detection and discrimination of HSO3- and biological thiol cell levels and further applications.

NeuM: A Neuron-Selective Probe Incorporates into Live Neuronal Membranes via Enhanced Clathrin-Mediated Endocytosis in Primary Neurons

The development of a small-molecule probe designed to selectively target neurons would enhance the exploration of intricate neuronal structures and functions. Among such probes, NeuO stands out as the pioneer and has gained significant traction in the field of research. Nevertheless, neither the mechanism behind neuron-selectivity nor the cellular localization has been determined. Here, we introduce NeuM, a derivative of NeuO, designed to target neuronal cell membranes. Furthermore, we elucidate the mechanism behind the selective neuronal membrane trafficking that distinguishes neurons. In an aqueous buffer, NeuM autonomously assembles into micellar structures, leading to the quenching of its fluorescence (Φ=0.001). Upon exposure to neurons, NeuM micelles were selectively internalized into neuronal endosomes via clathrin-mediated endocytosis. Through the endocytic recycling pathway, NeuM micelles integrate into neuronal membrane, dispersing fluorescent NeuM molecules in the membrane (Φ=0.61). Molecular dynamics simulations demonstrated that NeuM, in comparison to NeuO, possesses optimal lipophilicity and molecular length, facilitating its stable incorporation into phospholipid layers. The stable integration of NeuM within neuronal membrane allows the prolonged monitoring of neurons, as well as the visualization of intricate neuronal structures.

Acylhydrazone Functionalized Triphenylamine-Based Fluorescent Probe for Cu2+: Tunable Structures of Conjugated Bridge and Its Practical Application

Novel fluorescent probes were constructed for the convenient and rapid analysis of Cu2+ ions, taking advantages of the the triphenylamine backbone as chromophore and acylhydrazone group as the Cu2+ recognition site. Especially, probe T2 could act as a dual-channel probe towards Cu2+ through both fluorescent and colorimetric method. Through the fluorescent method, the detection limit of probe T2 was calculated to be as low as 90 nmol/L and there was a good linear relationship between the intensity change and the concentration of Cu2+ ions. By virtue of the two-phase liquid-liquid extraction method, probe T2 could be successfully applied in practical extraction and separation of Cu2+. Furthermore, by applying a "turn-off-turn-on" circle, compound T2 could act as a sensitive probe towards S2- anions through the indirect approach and the detection limit of complex T2-Cu2+ for S2- anion was found to be 110 nmol/L.

An Aggregation-induced Emission Probe to Detect the Viscosity Change in Lipid Droplets during Ferroptosis

Ferroptosis is a recently identified form of cell death characterized by iron-dependent lipid peroxidation. Understanding the effects of lipid peroxidation on cellular processes during ferroptosis requires insights into lipid droplets (LDs) and their viscosity changes. To gain further insights into the intricacies of ferroptosis, it is crucial to have a fluorescent probe that targets LDs and responds to changes in viscosity. In this study, we introduce a novel LD-targeting viscosity fluorescent probe named TQE, based on the principles of aggregation-induced emission (AIE). The probe displayed AIE characteristics in tetrahydrofuran, possessing a partition coefficient (logP) of 5.87. With increased viscosity, intramolecular rotation was restricted, leading to a remarkable 3.3-fold enhancement in emission. Notably, TQE exhibited robust resistance to photo-bleaching during cellular imaging, maintaining approximately 75% of its emission intensity even after 30 min of laser irradiation. Importantly, the AIEgen could not generate hydroxyl radicals when exposed to light for up to 3 h, suggesting the low photo-toxicity of TQE to cells. Leveraging these properties, we successfully employed the probe for fluorescent imaging of the viscosity change in LDs during ferroptosis.

The Green Synthesis of Carbon Quantum Dots through One-step Hydrothermal Approach by Orange Juice for Rapid, and Accurate Detection of Dopamine

In the current study, the fluorescent Carbon quantum dots (CDs) were synthesized through one-step hydrothermal approach by orange juice without any additional agents. The as-prepared green-CDs (GCDs) were quasi-spherical shape ranged from 2 to 8 nm with an average diameter of 5 nm, and emitted bright blue fluorescent (FL) under ultraviolet light irradiation (Uv). Different detailed analyses proved that the as-prepared GCDs had good morphologies, various functional groups, high water solubility, great optical features, and excellent stability towards diverse environmental conditions. The results indicated that the as-prepared GCDs can detect different concentrations of dopamine from 1 to 100 µM based on the quenching of their native fluorescent. Furthermore, the good linear relationship was obtained for dopamine in the broad range of concentrations from 1 to 100 µM with the limit of detection (LOD) of 0.81 µM. In addition, the as-prepared GCDs can be applied as a fluorescent probe for detection of dopamine in the different real samples.

Bilayer-Coating Strategy for Hydrophobic Nanoparticles Providing Colloidal Stability, Functionality, and Surface Protection in Biological Media

The surface chemistry of nanoparticles is a key step on the pathway from particle design towards applications in biologically relevant environments. Here, a bilayer-based strategy for the surface modification of hydrophobic nanoparticles is introduced that leads to excellent colloidal stability in aqueous environments and good protection against disintegration, while permitting surface functionalization via simple carbodiimide chemistry. We have demonstrated the excellent potential of this strategy using upconversion nanoparticles (UCNPs), initially coated with oleate and therefore dispersible only in organic solvents. The hydrophobic oleate capping is maintained and a bilayer is formed upon addition of excess oleate. The bilayer approach renders protection towards luminescence loss by water quenching, while the incorporation of additional molecules containing amino functions yields colloidal stability and facilitates the introduction of functionality. The biological relevance of the approach was confirmed with the use of two model dyes, a photosensitizer and a nitric oxide (NO) probe that, when attached to the surface of the UCNPs, retained their functionality to produce singlet oxygen and detect intracellular NO, respectively. We present a simple and fast strategy to protect and functionalize inorganic nanoparticles in biological media, which is important for controlled surface engineering of nanosized materials for theranostic applications.

A Quencher-Based Blood-Autofluorescence-Suppression Strategy Enables the Quantification of Trace Analytes in Whole Blood

Precise quantification of trace components in whole blood via fluorescence is of great significance. However, the applicability of current fluorescent probes in whole blood is largely hindered by the strong blood autofluorescence. Here, we proposed a blood autofluorescence-suppressed sensing strategy to develop an activable fluorescent probe for quantification of trace analyte in whole blood. Based on inner filter effect, by screening fluorophores whose absorption overlapped with the emission of blood, a redshift BODIPY quencher with an absorption wavelength ranging from 600-700 nm was selected for its superior quenching efficiency and high brightness. Two 7-nitrobenzo[c] [1,2,5] oxadiazole ether groups were introduced onto the BODIPY skeleton for quenching its fluorescence and the response of H2 S, a gas signal molecule that can hardly be quantified because of its low concentration in whole blood. Such detection system shows a pretty low background signal and high signal-to-back ratio, the probe thus achieved the accurate quantification of endogenous H2 S in 20-fold dilution of whole blood samples, which is the first attempt of quantifying endogenous H2 S in whole blood. Moreover, this autofluorescence-suppressed sensing strategy could be expanded to other trace analytes detection in whole blood, which may accelerate the application of fluorescent probes in clinical blood test.

Fluorescent Probes Based on AIEgen-Mediated Polyelectrolyte Assemblies for Manipulating Intramolecular Motion and Magnetic Relaxivity

Uniting photothermal therapy (PTT) with magnetic resonance imaging (MRI) holds great potential in nanotheranostics. However, the extensively utilized hydrophobicity-driven assembling strategy not only restricts the intramolecular motion-induced PTT, but also blocks the interactions between MR agents and water. Herein, we report an aggregation-induced emission luminogen (AIEgen)-mediated polyelectrolyte nanoassemblies (APN) strategy, which bestows a unique "soft" inner microenvironment with good water permeability. Femtosecond transient spectra verify that APN well activates intramolecular motion from the twisted intramolecular charge transfer process. This de novo APN strategy uniting synergistically three factors (rotational motion, local motion, and hydration number) brings out high MR relaxivity. For the first time, APN strategy has successfully modulated both intramolecular motion and magnetic relaxivity, achieving fluorescence lifetime imaging of tumor spheroids and spatio-temporal MRI-guided high-efficient PTT.

An effective fluorescent probe for detection of phosgene based on naphthalimide dyes in liquid and gaseous phases

A fluorescent probe was developed for the detection of phosgene based on 1,8-naphthalimide, of which o-diaminobenzene was used as the recognition moiety. The probe does not fluoresce due to nonradiative decay. The probe reacts rapidly with phosgene via an intramolecular cyclization reaction, which induces large fluorescence due to increased rigidity in the resulting molecule and a low detection limit (0.23 nM). This probe has excellent selectivity for phosgene against competing interference analytes and, in the form of probe-loaded test paper, is an extremely sensitive method for phosgene sensing in the gas phase below 1 ppm concentrations.

Tuning the Cellular Uptake and Retention of Rhodamine Dyes by Molecular Engineering for High-Contrast Imaging of Cancer Cells

Probes allowing high-contrast discrimination of cancer cells and effective retention are powerful tools for the early diagnosis and treatment of cancer. However, conventional small-molecule probes often show limited performance in both aspects. Herein, we report an ingenious molecular engineering strategy for tuning the cellular uptake and retention of rhodamine dyes. Introduction of polar aminoethyl leads to the increased brightness and reduced cellular uptake of dyes, and this change can be reversed by amino acetylation. Moreover, these modifications allow cancer cells to take up more dyes than normal cells (16-fold) through active transport. Specifically, we further improve the signal contrast (56-fold) between cancer and normal cells by constructing activatable probes and confirm that the released fluorophore can remain in cancer cells with extended time, enabling long-term and specific tumor imaging.

Advances in Multifunctional Chemotherapeutic Prodrugs for Near-infrared Fluorescence Imaging-guided Therapy

Conventional chemotherapy (CT) is associated with severe side effects and inducible resistance, making it difficult to meet clinical requirements, forcing the development of new multifunctional prodrugs for precision medicine. In recent decades, researchers and clinicians have focused on developing of multifunctional chemotherapeutic prodrugs with tumor-targeting capability, activatable and traceable chemotherapeutic activity, as a powerful tool to improve theranostic outcomes in cancer treatment. The conjugates of near-infrared (NIR) organic fluorophores and chemotherapy reagents create an exciting avenue for real-time monitoring of drug delivery and distribution, as well as the combination of chemotherapy and photodynamic therapy (PDT). Therefore, there are great opportunities for researchers to conceive and exploit multifunctional prodrugs that can visualize chemo-drugs release and tumor treatment in vivo. In this review, the design strategy and the recent progress of multifunctional organic chemotherapeutic prodrugs for activating NIR fluorescence imaging-guided therapy are described and discussed in detail. Finally, the prospects and challenges of multifunctional chemotherapeutic prodrugs for NIR fluorescence imaging-guided therapy are provided.

Unravelling the Turn-On Fluorescence Mechanism of a Fluorescein-Based Probe in GABAA Receptors

GABAA (γ-aminobutyric acid type A) receptors are ligand-gated ion channels mediating fast inhibitory transmission in the mammalian brain. Here we report the molecular and electronic mechanism governing the turn-on emission of a fluorescein-based imaging probe able to target the human GABAA receptor. Multiscale calculations evidence a drastic conformational change of the probe from folded in solution to extended upon binding to the receptor. Intramolecular ππ-stacking interactions present in the folded probe are responsible for quenching fluorescence in solution. In contrast, unfolding within the GABAA receptor changes the nature of the bright excited state triggering emission. Remarkably, this turn-on effect only manifests for the dianionic prototropic form of the imaging probe, which is found to be the strongest binder to the GABAA receptor. This study is expected to assist the design of new photoactivatable screening tools for allosteric modulators of the GABAA receptor.

A Simple Fluorescence Affinity Assay to Decipher Uranyl-Binding to Native Proteins

Determining the affinity of proteins for uranyl is key to understand the toxicity of this cation and to further develop decorporation strategies. However, usual techniques to achieve that goal often require specific equipment and expertise. Here, we propose a simple, efficient, fluorescence‐based method to assess the affinity of proteins and peptides for uranyl, at equilibrium and in buffered solution. We first designed and characterized an original uranyl‐binding fluorescent probe. We then built a reference scale for uranyl affinity in solution, relying on signal quenching of our fluorescent probe in presence of high‐affinity uranyl‐binding peptides. We finally validated our approach by re‐evaluating the uranyl‐binding affinity of four native proteins. We envision that this tool will facilitate the reliable and reproducible assessment of affinities of peptides and proteins for uranyl.

Experimental and Theoretical Studies of the Pyrazoline Derivative 5-(4-methylphenyl)-3-(5-methylfuran-2-yl)-1-phenyl-4,5-dihydro-1H-Pyrazole and its Application for Selective Detection of Cd2+ ion as Fluorescent Sensor

A simple fluorescent chemosensor 5-(4-methylphenyl)-3-(5-methylfuran-2-yl)-1-phenyl-4, 5-dihydro-1H-pyrazole (PY) has been synthesized for the detection of Cd²⁺ ion.The fluorescent probe PY shows high selectivity for Cd²⁺in the presence of othermetal ions (Co²⁺, Cu²⁺, Hg²⁺, Mn²⁺, Zn²⁺, Fe³⁺, Pb²⁺, Ni²⁺, and Al³⁺). The fluorescence intensity of the PY has been strongly quenched with increasing concentration of Cd²⁺ (0-0.9 μM)via photoinduced electron transfer mechanism. The binding constant of Cd²⁺ to PY for the 1:1 complex isfound to be 5.3 × 10⁵ M^-1with a detection limit of 0.09 μM. The chemosensor was successfully applied for determination of Cd²⁺ in different water samples (tap, river, and bottled water) showing good recovery values in the range of 94.8-101.7% with RSD less than 3%. Density functional theory (DFT) calculations were also performed to investigate electronic and spectral characteristics which are quite agreeable with the experimental value. The results show that the synthesized fluorescent chemosensor shows good selectivity towards Cd²⁺ and can be readily applied for the detection of Cd²⁺ in real samples including water samples.

A fluorescent molecular rotor for the selective detection of the hybrid-conformation 22AG G-Quadruplex

G-quadruplex (G4) DNA plays a vital role in myriad biological process and is linked to several human diseases, including Alzheimer's disease. Probing G4s with fluorescent probes can provide a better understanding their mechanisms of action and of their roles in Nature. In this study we developed a quinolinium-vinylaniline molecular rotor probe, featuring a diethylaminosalicylaldehyde unit that could discriminate the hybrid-22AG G4 sequence selectively amongst other G4 sequences. This probe underwent a significant red-shift upon binding to the target G4 (broad 575 nm → sharp 630 nm) with enhanced fluorescence (up to 14-fold). We suspect that the vinylaniline unit of the molecular rotor, when bound to the hybrid-22 A G4, experienced restricted rotation, thereby undergoing enhanced intramolecular charge transfer. The presence of the diethylaminosalicylaldehyde moiety appeared to play a major role in the enhanced selectivity toward the 22AG G4.

A time-dependent density functional theory study of a fluorescent probe to detect hydroxyl radicals: Inhibiting the twisted intramolecular charge-transfer process

Due to the relevance to excited-state processes, sensing mechanisms of fluorescent probes were difficult to study directly by experimental methods. This work investigated theoretically the sensing mechanism of a reported bifunctional fluorescent probe to detect intracellular hydroxyl radicals and their environmental viscosity (J. Am. Chem. Soc. 2019, 141, 18301). Calculations were performed at the B3P86/TZVP/SMD level using density functional theory and time-dependent density functional theory. The transition from the ground-state (S₀) to the first singlet excited state (S₁) was calculated to have the largest oscillation strength for the probe. The wavelength that corresponded to the S₀-S₁ vertical excitation energy (427 nm) agreed well with the maximum absorption band at 400 nm in the ultraviolet-visible spectra. Theoretical results showed that the probe had two distinct geometries in the S₀ and S₁ states, respectively. This difference was caused by the different distributions of frontier molecular orbitals that were involved in the S₀-S₁ transition and corresponds to a twisted intramolecular charge transfer. The S₁-state potential energy curve of the probe molecule confirmed that the twisted intramolecular charge transfer could proceed spontaneously with a potential barrier of only 12.20 kJ/mol. This result provided an irradiative approach for the probe molecule to dissipate the S₁-state energy, which explained its fluorescence quenching. In contrast, the hydroxyl oxidation reaction changed frontier molecular orbitals of the probe molecule, which made its S₁ state a local S₁ state with a strong fluorescence emission. Precisely due to the mechanism, the hydroxyl radicals could be detected by changes in the fluorescence signal of the probe molecule.

Cobalt (II) complex as a fluorescent sensing platform for the selective and sensitive detection of triketone HPPD inhibitors

4-Hydroxyphenylpyruvatedioxygenase (HPPD) is a Fe(II)/Co(II)-dependent enzyme which has become one of the most effective herbicide targets. HPPD inhibitors have been developed as efficient herbicides for resistant weed control. Developing a method for efficient and rapid HPPD inhibitors detection is still challenging. N-n-butyl-4-methylhydrazinecarbothioamide-1,8-naphthalimide (NMN) was synthesized and used to detect Co²⁺ efficiently with the limit of detection (LOD) of 7.82 nM with a turn-on fluorescence. Herein a novel fluorescent complex, NMN‒Co²⁺ was employed to determine HPPD inhibitors which performed a turn-off effect in the sensing process based on the competitive coordination between the probe and HPPD with Co²⁺. The LODs for three commercial triketone HPPD inhibitors (mesotrione, tembotrione and NTBC) were 6.60 nM, 7.37 nM and 10.22 nM with good sensitivity and selectivity. Furthermore, the present probe has potentials to quantitatively detect mesotrione and tembotrione in real samples.

Multiporous Terbium Phosphonate Coordination Polymer Microspheres as Fluorescent Probes for Trace Anthrax Biomarker Detection

Lanthanide coordination polymers have been recently regarded as attractive sensing materials because of their selectivity, high sensitivity, and rapid response ability. In this research, the multiporous terbium phosphonate coordination polymer microspheres (TbP-CPs) were prepared as a novel fluorescent probe, which showed a fluorescence turn-on response capability for the detection of the trace anthrax biomarker dipicolinate acid (DPA). The morphology and chemical composition of as-prepared TbP-CPs were characterized in detail. The TbP-CPs have the vegetable-flower-like structure and microporous surface. In addition, the as-prepared TbP-CPs not only possess the merits of convenience and simple preparation with high yield but also have the excellent characters as fluorescent probes, such as high stability, good selectivity, and rapid detection ability within 30 s. This proposed sensor could detect DPA with a linear relationship in concentrations ranging from 0 to 8.0 μM and a high detection sensitivity of 5.0 nM. Furthermore, the successful applications of DPA detection in urine and bovine serum were demonstrated. As a result, the recovery ranged from 93.93-101.6%, and the relative standard deviations (RSD) were less than 5%.

Preparation of a Two-Photon Fluorescent Probe for Imaging H2O2 in Lysosomes in Living Cells and Tissues

Hydrogen peroxide (H₂O₂) plays important roles in many physiological and pathological processes. At the cellular organelle level, the abnormal concentrations of H₂O₂ in the lysosomes may cause redox imbalance and the loss of the critical functions of the lysosomes. Herein, we describe the preparation of a potent lysosome-targeted two-photon fluorescent probe (Lyso-HP) for the detection of H₂O₂ in the lysosomes in the living cells. This unique fluorescent probe can also be employed to effectively detect H₂O₂ in the living tissues using two-photon fluorescence microscopy.