FRET-based ratiometric fluorescent probe for Cu 2+ with a new indolizine fluorophore

A near-infrared "turn-on" fluorescent probe for selective detection of copper(II) ions in aqueous media and its application in cell imaging

Copper (II) is considered the third most essential trace element for life, following iron and zinc, and plays a vital role in various physiological and pathological processes. The fluorescent probe has become an important method for the detection of heavy metal ions. This investigation involved the development and synthesis of a near-infrared "turn-on" fluorescent probe, DCX-Cu, with a significant Stokes shift (156 nm), specifically to identify Cu2+ compared other ions. A detection limit (LOD) of 19.47 nM for Cu2+ was demonstrated by probe DCX-Cu. A strong linear correlation was observed between the fluorescence intensities measured at 746 nm and the concentrations of Cu2+. Furthermore, the current probe successfully visualized Cu2+ in water samples and HepG2 cells.

Novel förster resonance energy transfer (FRET)-based ratiometric fluorescent probe for detection of cyanides by nucleophilic substitution of aromatic hydrogen (SNArH)

The development of novel fluorescent probes for real-time detection of cyanides (CN-) in environmental and biological systems has become a significant focus in chemical sensing. Particularly, ratiometric fluorescence sensing offers a unique method for precise and quantitative detection of cyanides, even under complex conditions. We report herein the design of a new ratiometric fluorescent probe for cyanides based on modulation of Förster resonance energy transfer (FRET) coupled with novel cyanide-induced nucleophilic substitution of aromatic hydrogen (SNArH). The target probe (R1) is developed by introducing coumarin fluorophores as FRET donors into a 3-nitro-naphthalimide acceptor, which is easily synthesized and exhibits a colorimetric change from colorless to faint yellow and a significant ratiometric fluorescence shift (Δλ = 114 nm) upon cyanide binding. A clear ratiometric signal at I582/I468 was obtained, with a limit of detection of 5.69 μM. The sensing mechanism was confirmed through 1H NMR titration and LC-MS analysis. Additionally, R1-loaded strips were easily prepared, serving as a portable device for detecting CN- with visible color changes. The probe R1 has been successfully utilized for real-time monitoring of cyanide in food materials and water samples. Importantly, fluorescence bioimaging studies in HeLa cells were conducted, demonstrating the probe's capability for ratiometric detection of exogenous CN- in living systems.

A dual-response ratiometric near-infrared fluorescence probe based on cyanine platform for Cu2+ detection and its imaging in vitro and vivo

A near-infrared fluorescent probe (NUST-Cy-1) was disclosed here, which displays ratiometric and dual-channel response for Cu2+ (λex1 = 450 nm, λex2 = 750 nm) with large Stokes shifts (143 nm, 375 nm, 75 nm respectively). This probe demonstrates high sensitivity with low detection limit (1.4 μM) and selectivity for Cu2+ detection. Furthermore, fluorescent imaging of Cu2+ in vitro and vivo were successfully achieved.

Development of a Coumarin-Based Schiff Base Fluorescent Probe and its Application in Detection of Cu²⁺

A highly practical Schiff base fluorescent probe, (E)-3-amino-N'-((7-(diethylamino)-2-oxo-2 H-chromen-3-yl)methylene)thiophene-2-carbohydrazide (M), with a facile synthetic route has been successfully developed. M has been utilized for the specific detection of Cu2+ in THF/H2O Tris buffer solution (v/v = 9:1, 0.01 M, pH = 7.4) via the fluorescence quenching mechanism. The detection of Cu2+ by M has been largely unaffected by interfering ions and has demonstrated a distinct dual-channel response in both colorimetry and fluorescence. The response time of M towards Cu2+ is remarkably fast, taking only 30 s. Additionally, M exhibits exceptional sensitivity with a limit of detection (LOD) as low as 1.76 × 10- 7 M. The stoichiometric ratio between M and Cu2+ has been determined to be 1:1 through Job's Plot, while the binding constant has been calculated as 1.19 × 104 M- 1 using the Benesi-Hildebrand equation. The structure of M has been elucidated by 1H NMR and ESI-MS analyses, thereby confirming the binding mode between M and Cu2+. Further validation has been achieved through DFT calculations. The test paper based on M has finally been prepared for the rapid and convenient detection of Cu2+. The M has also been utilized for the detection of Cu2+ in real samples, including lake water, onions, and coffee, demonstrating favorable recovery rates. Moreover, successful visual detection has been achieved in food samples such as bean sprouts and rice. The aforementioned examples have collectively illustrated the practical applicability of M in authentic samples.

A novel peptide fluorescent chemical sensor capable of detecting Cu2+, Zn2+, and S2

A novel peptide-based chemical fluorescence sensor L (Dansyl-His-Pro-Thr-Cys-NH2) was designed and synthesized. This sensor exhibits an "On-Off-On" detection cycle to detect Cu2+, Zn2+, and S2- in solution. According to the chelation-enhanced fluorescence (CHEF) mechanism, when Zn2+ is present, the fluorescence is significantly enhanced and a blue shift occurs, representing a "Turn-On" phase of the fluorescence detection mode. Because copper ions (Cu2+) have a paramagnetic quenching sensing mechanism, the fluorescence of L quenches rapidly with the formation of the L-Cu system, representing the "Turn-Off" phase. The subsequent introduction of S2- to the L-Cu system results in the recovery of the L-fluorescence, thereby representing the second "Turn-On" phase. As a peptide molecule, the sensor L has several advantages over other types of sensors, including water solubility, high sensitivity, and good biocompatibility, with a very low detection limit. The detection lines of Zn2+ and Cu2+ are 97 nM (R = 0.993) and 75 nM (R = 0.995), respectively. Additionally, the sensor does not exhibit any obvious cell toxicity. These results indicate that this peptide chemiluminescent sensor has the potential to be applied in in vivo detection.

Small-Molecule Fluorescent Probes for Binding- and Activity-Based Sensing of Redox-Active Biological Metals

Although transition metals constitute less than 0.1% of the total mass within a human body, they have a substantial impact on fundamental biological processes across all kingdoms of life. Indeed, these nutrients play crucial roles in the physiological functions of enzymes, with the redox properties of many of these metals being essential to their activity. At the same time, imbalances in transition metal pools can be detrimental to health. Modern analytical techniques are helping to illuminate the workings of metal homeostasis at a molecular and atomic level, their spatial localization in real time, and the implications of metal dysregulation in disease pathogenesis. Fluorescence microscopy has proven to be one of the most promising non-invasive methods for studying metal pools in biological samples. The accuracy and sensitivity of bioimaging experiments are predominantly determined by the fluorescent metal-responsive sensor, highlighting the importance of rational probe design for such measurements. This review covers activity- and binding-based fluorescent metal sensors that have been applied to cellular studies. We focus on the essential redox-active metals: iron, copper, manganese, cobalt, chromium, and nickel. We aim to encourage further targeted efforts in developing innovative approaches to understanding the biological chemistry of redox-active metals.

Recent Progress in Fluorescent Probes for Real-Time Monitoring of Glioblastoma

Treating glioblastoma (GBM) by resecting to a large extent can prolong a patient's survival by controlling the tumor cells, but excessive resection may produce postoperative complications by perturbing the brain structures. Therefore, various imaging procedures have been employed to successfully diagnose and resect with utmost caution and to protect vital structural or functional features. Fluorescence tagging is generally used as an intraoperative imaging technique in glioma cells in collaboration with other surgical tools such as MRI and navigation methods. However, the existing fluorescent probes may have several limitations, including poor selectivity, less photostability, false signals, and intraoperative re-administration when used in clinical and preclinical studies for glioma surgery. The involvement of smart fluorogenic materials, specifically fluorescent dyes, and biomarker-amended cell-penetrable fluorescent probes have noteworthy advantages for precise glioma imaging. This review outlines the contemporary advancements of fluorescent probes for imaging glioma cells along with their challenges and visions, with the anticipation to develop next-generation smart glioblastoma detection modalities.

Simple and Commercially Available 6-chloroimidazo[1,2-a]pyridine-2-carboxylic Acid-based Fluorescent Probe for Monitoring pH Changes

Commercially available compounds that can be directly used as fluorescent probes will greatly promote the development of fluorescent imaging. Based on our previously work related to nitrogen bridgehead heterocycles, herein, a commercially available compound, 6-chloroimidazo[1,2-a]pyridine-2-carboxylic acid, has been detected for monitoring pH value (3.0-7.0). The probe proves to have high selectivity and sensitivity, brilliant reversibility, and extremely short response time. The real-time imaging of pH changes in yeast was also conducted.

Rational design of a FRET-based ratiometric fluorescent probe with large Pseudo-Stokes shift for detecting Hg2+ in living cells based on rhodamine and anthracene fluorophores

The development of fluorescent dyes has been a continuing attractive research topic in the field of fluorescence sensing and bioimaging technologies, most of them were subject to a single signal change. In this work, a novel colorimetric and ratiometric fluorescent probe 1 based on rhodamine and anthracene groups was designed and synthesized via the fluorescence resonance energy transfer (FRET) mechanism. Probe 1 showed excellent selectivity, higher sensitivity and ratiometric response to Hg²⁺ in the CH₃CN/H₂O (1/1, v/v) system, with a fast response time (less than 30 s); The fluorescent color changed from purple to orange and the solution visible to the naked-eye changed from colorless to pink. The Pseudo-Stokes shift was 174 nm upon addition of Hg²⁺. The limit of detection (LOD) was calculated to be 0.81 μM and 0.38 μM according to fluorescence and UV/vis measurements, respectively. Furthermore, a possible mechanism for the detection of Hg²⁺ by probe 1 was verified by using ¹H NMR, ESI-MS, and HPLC spectra. Meanwhile, probe 1 was successfully used for cell imaging for the detection of Hg²⁺ in living cells.

Acetic Acid-Catalyzed Regioselective C(sp2)-H Bond Functionalization of Indolizines: Concomitant Involvement of Synthetic and Theoretical Studies

An atom economical and environmentally benign protocol has been developed for the regioselective C(sp²)-H bond functionalization of indolizines. The acetic acid-catalyzed cross-coupling reaction proceeds under metal-free conditions, producing a wide range of synthetically useful indolizine derivatives. The present protocol showed good functional group tolerance and broad substrate scope in good to excellent yields. Quantum mechanical investigation using density functional theory (DFT) has played a crucial role in understanding that acetic acid is the key player in determining the actual pathway as the catalyst and its ultrafast nature. Different pathways involving inter- and intramolecular proton transfer, with or without acetic acid, were investigated. Calculated results revealed that a proton shuttle mechanism is involved for the least energetic, most favorable acetic acid-catalyzed pathway. Furthermore, regioselectivity has also been explained theoretically.

Recent development in fluorescent probes for copper ion detection

Abstract:

Copper is the third most common heavy metal and an indispensable component of life. Variations of body copper levels, both structural and cellular, are related to a number of disorders; consequently, pathophysiological importance of copper ions demands the development of sensitivity and selective for detecting these organisms in biological systems. In recent years, the area of fluorescent sensors for detecting copper metal ions has seen revolutionary advances. Consequently, closely related fields have raised awareness of several diseases linked to copper fluctuations. Further developments in this field of analysis could pave the way for new and innovative treatments to combat these diseases. This review reports on recent progress in the advancement of three fields of fluorescent probes; chemodosimeters, near IR fluorescent probes, and ratiometric fluorescent probes. Methods used to develop these fluorescent probes and the mechanisms that govern their reaction to specific analytes and their applications in studying biological systems, are also given.

A turn-on fluorescent probe based on indolizine for the detection of sulfite

Numerous SO32−/HSO3− fluorescent probes have been reported based on various mechanisms.

A novel 1,8-naphthalimide-based Cu2+ ion fluorescent probe and its bioimaging application

A new 1,8-naphthalimide-based Schiff base compound, named as (Z)-2-butyl-6-(((2-hydroxyphenyl)imino)methyl)-1H-benzo[de]isoquinoline-1,3(2H)-dione (BHBD), has been simply synthesized with high yields. BHBD can be employed as a "turn-on" fluorescent probe for Cu²⁺ ion with high sensitivity, high selectivity and relatively low detection limit (0.48 × 10^-6 M). The fluorescence emission of BHBD is very weak in H₂O/THF (v/v: 7/3) mixture, which is significantly enhanced after addition of Cu²⁺ ion. The proposed mechanism is verified by ¹H NMR, Job's plot and TOF-MS experiments. Anti-interference experiment, cytotoxicity assay and pH influence results indicated that BHBD meets the requirements of bioimaging. Therefore, BHBD has been successfully applied in detecting Cu²⁺ ion in HeLa cells.

Interest of novel N-alkylpyridinium-indolizine hybrids in the field of Alzheimer's disease: Synthesis, characterization and evaluation of antioxidant activity, cholinesterase inhibition, and amyloid fibrillation interference

A small library of molecules combining indolizine and N-alkyl pyridinium was synthesized and evaluated in a multi-target-directed-ligand strategy for Alzheimer's disease (AD) treatment. The new compounds were classified in three series depending on the number of methylene residues linking the two heterocycles (Ind-PyCx with x = 0, 2 or 3). The molecules were synthesized from the corresponding bis-pyridines by two-step formation of the indolizine core including mono-alkylation of pyridine and 1,3-dipolar cycloaddition with an alkylpropiolate. Their activities against AD's key-targets were evaluated in vitro: acetyl- and butyrylcholinesterase (AChE and BChE) inhibition, antioxidant properties and inhibition of amyloid fibril formation. None of the three series showed significant activities against all the targets. The Ind-PyC2 and Ind-PyC3 series are active on eeAChE and hAChE (µM IC₅₀ values). Most of the positively charged molecules from these two series also appeared active against eqBChE, however they lost their activity on hBChE. Comparative molecular modeling of 13 and 15 docked in hAChE and hBChE highlighted the importance of the substituent (p-methoxybenzoyl or methyloxycarbonyl, respectively) located on the indolizine C-3 for the binding. The larger molecule 13 fits more tightly at the active site of the two enzymes than 15 that shows a larger degree of freedom. The Ind-PyC2 and Ind-PyC3 hybrids displayed some antioxidant activity when tested at 750 µg/mL (up to 95% inhibition of DPPH radical scavenging for 10). In both series, most hybrids were also able to interact with amyloid fibers, even if the inhibitory effect was observed at a high 100 µM concentration. The Ind-PyC0 molecules stand out completely due to their spectroscopic properties which prevent their evaluation by Ellman's and ThT assays. However, these molecules showed interesting features in the presence of preformed fibers. In particular, the strong increase in fluorescence of 3 in the presence of amyloid fibers is very promising for its use as a fibrillation fluorescent reporter dye.

Recent advances (2017-20) inthe detection of copper ion by using fluorescence sensors working through transfer of photo-induced electron (PET), excited-state intramolecular proton (ESIPT) and Förster resonance energy (FRET)

An essential trace element copper plays several physiological roles in living systems. But at excess concentration, it exerts toxicity and becomes associated with numerous disorders. In this article, we have reviewed the recent developments (from 2017 to 2020) in the field of fluorescence-based chemosensors for the detection of Cu²⁺ ion. The sensing probes which were built to work through transfer of photo-induced electron (PET), excited-state intramolecular proton (ESIPT) and Förster resonance energy (FRET) mechanisms have been included in this review. Emphasis is given on the design, sensitivity and response of the probe molecules for the detection of Cu²⁺ ion. Using suitable examples, applications of these three recognition mechanisms for the probing of copper ion have been addressed.

A novel chemosensor for the distinguishable detections of Cu2+ and Hg2+ by off-on fluorescence and ratiometric UV-visible absorption

A novel dual-functional chemosensor, derived from the conjugation of rhodamine B with a quinoline derivative (RHQ), was firstly synthesized with high efficiency and cost-effectiveness for the distinguishable detections of Cu²⁺ and Hg²⁺ via ring-opening and ring-forming mechanism. The chemosensor exhibits highly selective and distinguishable responses for Cu²⁺ and Hg²⁺ in CH₃CN-H₂O (4:1, v/v) with off-on fluorescence and ratiometric ultraviolet-visible (UV-Vis) absorption changes. Additionally, Cu²⁺ is identified by opening a rhodamine spirocycle with a UV-Vis absorption band, at around 560 nm and fluorescence turn-on. Interestingly, Hg²⁺ is discerned by opening the rhodamine spirocycle and by generating a new special cycle for the quinoline unit. Resultantly, there were two UV-Vis absorption bands at around 365 nm and 560 nm, which were accompanied by fluorescence turn-on. Moreover, the chemosensor can quantitatively detect Cu²⁺ and Hg²⁺ by off-on fluorescence and ratiometric UV-Vis absorption changes, respectively. Furthermore, the chemosensor with low cytotoxicity could be successfully administered to monitor Cu²⁺ and Hg²⁺ in living cells. This work may pay the way for the development of dual-functional chemosensor for quantificationally detecting metal ions in environmental and biological systems.

Access to 6-hydroxy indolizines and related imidazo[1,5-a]pyridines through the SN2 substitution/condensation/tautomerization cascade process

A simple and efficient cascade reaction was developed for the construction of hydroxy substituted indolizines from pyrrole-2-carbaldehydes and commercially available 4-halogenated acetoacetic esters.

A dual-channel chemosensor based on 8-hydroxyquinoline for fluorescent detection of Hg2+ and colorimetric recognition of Cu2

A novel dual-channel chemosensor, 7-allylquinolin-8-ol (AQ), was synthesized based on 8-hydroxyquinoline for selective fluorescence detection of Hg²⁺ and colorimetric recognition of Cu²⁺. The chemosensor reacted with Hg²⁺ and generated a new Hg-containing compound with significantly enhanced fluorescence, which turned from faint blue to strong green. Further experiments indicated that AQ could be used to quantitatively detect Hg²⁺ via fluorescence spectroscopy with a low detection limit (2.1 nM). The good reversibility of the synthesized chemosensor was also demonstrated using NaBH₄. Moreover, AQ was successfully used for the detection of Cu²⁺ through the formation of a stable coordination compound, which exhibited an ultraviolet-visible (UV-Vis) ratiometric change, while its color changed from colorless to pale yellow under natural light. Additional experiments using various Cu²⁺ concentrations showed that the developed chemosensor could be further employed for the quantitative ratiometric estimation of Cu²⁺ by UV-Vis.

Heterocyclization Reagents for Rapid Assembly of N-Fused Heteroarenes from Alkenes

N-Fused heterocycles are of particular use and upmost importance in multiple fields. Herein, we disclose a conceptually new approach for the rapid assembly of N-fused heteroarenes from alkenes. A portfolio of strategically designed heterocyclization reagents are readily prepared for the cascade reaction. A plethora of N-fused heteroarenes including seven types of heterocyclic core are furnished. The protocol features a broad functional-group compatibility and high product diversity, and provides a practical tool for late-stage heteroarene elaboration.

Synthetic ratiometric fluorescent probes for detection of ions

Metal cations and anions are essential for versatile physiological processes. Dysregulation of specific ion levels in living organisms is known to have an adverse effect on normal biological events. Owing to the pathophysiological significance of ions, sensitive and selective methods to detect these species in biological systems are in high demand. Because they can be used in methods for precise and quantitative analysis of ions, organic dye-based ratiometric fluorescent probes have been extensively explored in recent years. In this review, recent advances (2015-2019) made in the development and biological applications of synthetic ratiometric fluorescent probes are described. Particular emphasis is given to organic dye-based ratiometric fluorescent probes that are designed to detect biologically important and relevant ions in cells and living organisms. Also, the fundamental principles associated with the design of ratiometric fluorescent probes and perspectives about how to expand their biological applications are discussed.

Enhanced chemical sensing for Cu2+ based on composites of ZIF-8 with small molecules

Two organic molecules, pyridoxal hydrazide (PAH) and salicylaldehyde based Rhodamine B hydrazone (RBS) were integrated into zeolitic imidazolate framework-8 (ZIF-8) to give composites, namely PAH/ZIF-8 and RBS/ZIF-8. The organic molecules and ZIF-8 are proposed to be assembled via hydrogen bonds and π–π stacking in the composites. The mass fraction of PAH and RBS in the composites was calculated to be 21.86% and 29.3%. The fluorescence of PAH/ZIF-8 is quenched regularly by Cu²⁺. The detection limit for Cu²⁺ was calculated to be 1.42 nM for PAH/ZIF-8, which is one order of magnitude lower than that of PAH. The detection limit for Cu²⁺ was determined to be 0.8 μM for RBS/ZIF-8, which is three times lower than that of RBS. The two composites both display high selectivity to Cu²⁺ over competing metal ions. The PAH/ZIF-8 fluorescent sensor was successfully applied to Cu²⁺ determination in environmental water. PAH/ZIF-8 exhibits excellent cell membrane permeability and low cytotoxicity in cellular imaging. The enhanced chemical sensor was designed by introducing small molecules into ZIF-8 for the specific recognition of Cu²⁺.

An enhanced chemical sensor was designed by introducing small molecules into ZIF-8 for the specific recognition of Cu²⁺.

A pyrazolo[1,5-a]pyridine-based ratiometric fluorescent probe for sensing Cu2+ in cell

Ratiometric fluorescent probes based on FRET mechanism have attracted great attention due to their large pseudo-Stokes shifts and built-in correction for environmental effects. However, most donors failed to meet the requirement that the emission of the donor must overlap well with the absorption of the acceptor. Therefore, searching for new fluorophore to construct FRET system is in great need. In this paper, a new fluorescent dye pyrazolo[1,5-a]pyridine was synthesized and used as a donor in the FRET system for ratiometric sensing of Cu²⁺. The probe is based on FRET and PET mechanism. It shows high selectivity and sensitivity toward Cu²⁺ (detection limit 30 nM). Furthermore, it was successfully used to detect Cu²⁺ in Glioma cells.

Near-infrared fluorescent probe for selective detection of Cu2+ in living cells and in Vivo

A NIR-rhodamine fluorescent probe was designed and successfully synthesized. The structure of the probe NRh-Cu was characterized by ¹H NMR, ¹³C NMR and HRMS. The probe was found to show high sensitivity and high selectivity. The detection limit was calculated to be as low as 0.95 ppb. The sensing mechanism was proposed and confirmed by HRMS spectra. Furthermore, it could be used for imaging Cu²⁺ in living cells and in vivo.

A ratiometric and colorimetric probe for detecting Hg2+ based on naphthalimide-rhodamine and its staining function in cell imaging

In this work, a rhodamine derivative was developed as a colorimetric and ratiometric fluorescent probe for Hg2+. It exhibited a highly sensitive fluorescence response toward Hg2+. Importantly, studies revealed that the probe could be used for ratiometric detection of Hg2+, with a low detection limit of 0.679 μM. The mechanism of Hg2+ detection using compound 1 was confirmed by ESI-MS, 1H NMR, and HPLC. Upon the addition of Hg2+, the rhodamine receptor was induced to be in the ring-opening form via an Hg2+-promoted hydrolysis of rhodamine hydrazide to rhodamine acid. In addition to Hg2+ detection, the naphthalimide-rhodamine compound was proven to be effective in cell imaging.

A reversible and highly selective two-photon fluorescent "on-off-on" probe for biological Cu2+ detection

A two-photon active probe for physiological copper (Cu2+) detection is expected to play an important role in monitoring biological metabolism. Herein, a novel Schiff base derivative (E)-2,2'-((4-((4-(diethylamino)-2-hydroxybenzylidene)amino)phenyl)azanediyl)bis(ethan-1-ol) (L) with remarkable two-photon activity was developed and synthetically investigated. L presents high selectivity and sensitivity for Cu2+ sensing in ethanol/HEPES buffer (v/v, 1 : 1), which is accompanied by the fluorescence switching "off" and subsequently "on" with the addition of EDTA. The mechanism for the detection of Cu2+ is further analyzed using 1H NMR titration, mass spectra and theoretical calculations. Furthermore, since the probe L possesses good photophysical properties, excellent biocompatibility and low cytotoxicity, it is successfully applied to track Cu2+ in the cellular endoplasmic reticulum by two-photon fluorescence imaging, showing its potential value for practical applications in biological systems.

A new turn-on fluorescent probe for the detection of palladium(0) and its application in living cells and zebrafish

A new “turn-on” fluorescent probe 1 for the detection of Pd⁰ has been designed and synthesized.

Synthesis of a crystallochromic indolizine dye by a base- and catalyst-free photochemical route

Irradiation of 2-benzoyl-N-benzylpyridinium derivatives and dimethyl acetylene dicarboxylate resulted in the formation of inolizine derivatives, one which was found to be the first example of a crystallochromic indolizine.

A FRET based ratiometric fluorescent probe for detection of sulfite in food

A new fluorophore pyrido[1,2-a]benzimidazole based ratiometric fluorescent probe for the selective detection of sulfite ions in water was investigated.

A ratiometric fluorescent probe for detection of exogenous mitochondrial SO2 based on a FRET mechanism

A novel imidazo[1,5-a]pyridine-hemicyanine based ratiometric fluorescent probe for detection of mitochondrial SO₂ was designed and synthesized. The probe is based on a fluorescence resonance energy transfer (FRET) mechanism. It exhibits high selectivity and sensitivity towards SO₃²⁻ with a fast response time (3 min) and detection limit of 0.13 μM. Further, it showed low cytotoxicity and was successfully applied to image exogenous mitochondrial SO₂ in cells.

A novel imidazo[1,5-a]pyridine-hemicyanine based ratiometric fluorescent probe for detection of mitochondrial SO₂ was designed and synthesized.

Dual-functional probe based on rhodamine for sequential Cu2+ and ATP detection in vivo

A rhodamine-based fluorescent probe for Cu²⁺ and ATP has been designed. The fluorescence intensity/absorbance was significantly enhanced upon the addition of Cu²⁺ owning to the opening of the spiro-ring of rhodamine, which quickly returned to the original level due to the reconstruction of the probe by the reacting with ATP. Cu²⁺/ATP-induced fluorescent intensity/aborbance changes showed a good linear relationship with the concentration of Cu²⁺/ATP in the range of 2-20 μM/0-10 μM with a detection limit of 0.1 μM/1.0 μM. The proposed method is simple in design and fast in operation, and is suitable for the reversible monitoring of Cu²⁺ and ATP in bioanalytical applications.