Ultrasensitive Fluorescent Probe Research Articles

Exploring dual-channel ion detection and theoretical insights: Chromone-based colorimetric receptor for Cu2+and its Zn(II)-complex as ultrasensitive fluorescent probe for Ag+ and Fe3+

Present article delineates the design and synthesis of a chromone-appended Schiff base (1) and its complexes with Zn(II) (2) and Cu(II) (3), which have been characterized by various spectro-analytical techniques i.e., elemental analysis, FTIR, 1H & 13C NMR, ESI-MS, UV−vis and fluorescence. Structures of 1 and 3 have also been elucidated using single crystal X-ray diffraction analysis. Compounds 2 showed significant effect in vitro cytotoxicity as compared to 1 Against MDA−MB-231 cell line. Interestingly, 1 serves as a chromogenic sensor for Cu2+ with exceptional selectivity whereas, 2 serves as an ultrasensitive fluorescent probe for Ag+ and Fe3+ in mixed aqueous−ethanol. The presence of Ag+ causes ratiometric change in the fluorescence spectral feature of 2 whereas Fe3+ induces ‘turn-off’ fluorescence in 2. Probe−analyte binding stoichiometry suggested by Job's plot analysis, ESI−MS and DFT studies, has been found to be 1:1 for 1 with Cu2+ and 2 with Ag+ whereas, 1:2 between 2 and Fe3+. Based on diverse analyses and binding constants, it is observed that 2 offers higher selectivity toward Ag+ over Fe3+. Limit of detection (LoD) of 1 for Cu2+ and 2 for Ag+ and Fe3+ have been found to be 2.33 nM, 22.4 µM and 2.05 µM, respectively. Complexes 2+Ag+ and 2+Fe3+ characterized by ESI−MS whereas DFT studies have been carried out to investigate the deeper bonding insights and provide support in our experimental investigations. Further, detection of Ag+ and Fe3+ has been practically accomplished in real water samples using probe 2.

Ultra-sensitive and fast nitroreductase-responsive fluorescence probe for real-time bioimaging of hypoxia in tumor cells and zebrafish wound inflammation

Hypoxia is intertwined with the occurrence and progression of tumors and inflammation. To date, various fluorescent probes have been constructed for monitoring degrees of hypoxia in tumor cells, however, efficiently evaluating the degrees of hypoxia caused by inflammation in real-time has been rarely exhibited via fluorescence imaging technique. Hence, an ultra-sensitive and fast-response fluorescent probe R19-NTR using rhodamine 19 as the fluorescent reporter and nitro aromatic groups as the recognition unit was performed to estimate the degrees of hypoxia through assessing the changes in the level of nitroreductase. The probe R19-NTR was basically non-fluorescent on account of the intramolecular photo-induced electron transfer process. Upon selectively reacted with nitroreductase, the R19-NTR featured an ultrafast response (< 1 min), and a significant fluorescence enhancement (ca. 114-fold). Encouraged by these outstanding properties, R19-NTR has been utilized for monitoring the degree of hypoxia in tumor cells and zebrafish wound inflammation. The results revealed that tumor cells under normoxic and different degrees of hypoxic conditions can be distinguished successfully, as well as the differentiation between tumor cells and normal cells. Moreover, the in vivo visualization disclosed that the endogenous nitroreductase of 6–10 days post fertilization zebrafish embryos was mainly focused on the liver and intestine. In particularly, the elevation of hypoxia degrees in zebrafish wound inflammation caused by severed tails were successfully visualized for the first time, as well as the variation of hypoxia degrees in gradually dying zebrafish embryos. The present research may provide a promising methodology for the diagnosis of inflammation-related diseases and tumors.

Fluorescent covalent organic framework as an ultrasensitive fluorescent probe for tyrosinase activity monitoring and inhibitor screening

BackgroundAs a significant biomarker of melanocytic lesions, tyrosinase (TYR) plays an essential role in the clinical diagnosis and treatment of melanin-related diseases. Thus, it is important to develop robust methods for assessing TYR activity. Covalent organic frameworks (COFs) have garnered considerable attention owing to their unique properties, including high chemical stability, good biocompatibility, and large surface area compared with organic dyes, noble metal nanoclusters, and semiconductor quantum dots. However, most COFs are insoluble in water and exhibit weak or no fluorescence emission. Therefore, the development of a water-soluble fluorescent COF for detecting TYR activity in biological samples remains highly desired. ResultsIn this work, a sensitive and facile fluorometric method based on fluorescent COF was constructed for the detection of TYR activity in human serum samples. The water-soluble COF was fabricated through the condensation polymerization of 4′,4‴,4′′′′′,4′′′′′′′-(1,2-ethene-diylidene) tetrakis [1,1′-biphenyl]-4-carboxaldehyde and 2,4,6-tris-(4-aminophenyl)-triazine. The resulting COF displayed yellow-green fluorescence with a maximum emission peak at 560 nm. Tyrosine was catalyzed by TYR to produce melanin-like polymers which formed a coating on the surface of COF and effectively quenched its fluorescence due to fluorescence resonance energy transfer. The proposed approach demonstrated a strong linear correlation in the range of 0.5–80 U/L with a low detection limit of 0.09 U/L. Additionally, the limit of detection for kojic acid, serving as a representative TYR inhibitor, was determined to be 0.0004 μg/mL. SignificanceOur proposed fluorometric sensing platform exhibited exceptional selectivity, sensitivity, and satisfactory recoveries in human serum samples, which is of paramount importance for the clinical diagnostics of melanin-related diseases. Furthermore, the proposed approach was further employed for the screening of TYR inhibitors, suggesting the potential applications in clinical treatment and pharmaceutical research.

Propeller shaped triarylamine acid: An ultra-sensitive fluorescence probe for distinguishing propanol isomers and water sensing in organic solvents

The photophysical properties of conformationally flexible (TPA-C) and partially rigidified (Cz-C) triarylamine acids were explored in solid as well as solution state and correlated with the structure. TPA-C and Cz-C exhibited moderate solid-state fluorescence (Φf = 6.2 % (TPA-C) and 5.6 % (Cz-C)) and self-reversible mechanofluorochromism. TPA-C produced fluorescent polymorphs (TPA-C-1 and TPA-C-2) with tunable fluorescence. TPA-C-1 showed unusual carboxylic acid intermolecular interactions whereas TPA-C-2 and Cz-C showed usual carboxylic acid dimer. TPA-C exhibited strong solvent polarity dependent tunable fluorescence (Φf = 0.01 to 0.11 compared to quinine sulphate standard) but Cz-C was non-emissive in the solution state. The dual emissive TPA-C showed highly sensitive fluorescence changes in organic solvents (CH3CN, THF, DMF, EtOH) when trace amount of water was added. In CH3CN, TPA-C showed weak fluorescence at 474 nm and addition of water (1 %) exhibited significant blue shift (λmax = 416 nm). The fluorescence intensity was gradually decreased with blue shifting in DMF, THF and EtOH with water addition. Importantly, TPA-C showed drastically different fluorescence in n-propanol (n-PA) and iso-propanol (IPA). TPA-C in n-PA showed fluorescence at 408 nm that was clearly red shifted to 438 nm with 0.1 % addition of IPA. The limit of detection (LOD) of water in CH3CN, DMF, THF and EtOH by TPA-C revealed 0.02, 0.7, 0.08 and 0.77 %, respectively. The LOD of IPA sensing in n-PA is 0.05 % and indicated the very efficient sensing and distinguishing propanol isomers. Thus, simple triphenylamine acid showed excellent water sensing and propanol isomers discrimination that could be attributed to the twisted intramolecular charge transfer (TICT) formation.

Construction of an ultrasensitive hypochlorite fluorescent probe based on a novel chromophore fragmentation strategy

The excess intake of hypochlorite (ClO−) in the human body and excessive emission in wastewater can pose serious health risks and environmental pollution. Therefore, it is vital to develop an efficient method for detecting ClO− in foodstuff and water. In this work, we reported a lactam-fused aza-BODIPY (LAB1) for ultrasensitive ClO− detection based on novel chromophore fragmentation strategy for the first time. It exhibited distinct advantages of good selectivity, high sensitivity, fast response (60 s) and low detection limit of 9.65 nM. The sensing mechanism revealed LAB1 core was fragmented by ClO−, leading to significantly colorimetric and ratiometric fluorescence changes. As a result, 320 nm blue-shift in absorption maximum (from green to colorless) and 340 nm blue-shift in emission maximum (from dark to bright blue) allowed for visual detection by the naked eyes. The potential applicability of LAB1 for ClO− detection with satisfactory recovery in the real samples (tap water and lake water) and vegetables (spinach, lettuce, Chinese cabbage, bean sprouts), and fluorescence “turn on” imaging in mung bean sprout were demonstrated. In addition, LAB1-loaded test paper was suitable for semi-quantitative scanning ClO− analysis by using color recognition APP in a smartphone. Therefore, this work highlights a promising approach based on novel sensing mechanism for monitoring ClO− in food samples.

An ultra-sensitive fluorescence multi-channels and colorimetric probe based on salicylaldehyde hydrazone for Al3+ recognition with 3:1 a binding ratio

An ultra-sensitive multi-channels fluorescence probe for the detection of Al3+ in aqueous solution, 4-(diethylamino) salicylaldehyde nicotinoyl hydrazone (SBN), was synthesized. Interestingly, when 365 nm and 425 nm are the excitation...

A novel near-infrared fluorescent probe for high-sensitivity detection of butyrylcholinesterase in various pathological states

Butyrylcholinesterase (BChE) is a crucial hydrolytic enzyme predominantly synthesized in the liver, playing a significant role in conditions like liver disorders, diabetes, Alzheimer's disease, and fat metabolism regulation. This study aims to address the current limitations in visualizing BChE activity in diseases at various states by introducing an ultra-sensitive near-infrared fluorescent probe, FDCM-BChE. The probe was engineered to have several properties, such as a large Stokes shift, rapid response time, high stability, excellent selectivity, and low detection limits. We validated the efficacy of FDCM-BChE in quantifying BChE activity in human serum and leveraged its low cytotoxicity for cellular imaging. The study revealed the downregulation of BChE activity in liver cancer and hepatic injury and the upregulation in diabetes. Thus, FDCM-BChE shows promise as a tool for specific applications, providing insights into diseases associated with BChE activity.

An ultrasensitive and selective near-infrared fluorescent probe for tracking carboxylesterases with large Stokes shift in living cells and mice

Carboxylesterases (CEs) play great role in CEs-related diseases and drug metabolism. Selectively monitoring its activity is important to explore its role in CEs-related diseases and drug combination. Herein, a new “turn-on” near-infrared (NIR) fluorescent probe (CHY-1) was reported with large Stokes shift (145 nm) for CEs detection. Dicyanoisophorone-based derivative was chosen as NIR fluorophore and 4-bromobutyrate was the identifying group. What’s more, CHY-1 exhibited ultra-sensitivity (LOD ∼ 9.2 × 10−5 U/mL), high selectivity against Acetylcholinesterase (AChE), Butyrylcholinesterase (BChE) and Chymotrypsin for CEs fluorescence detection under physiological pH and temperature. Furthermore, CHY-1 showed little effect on cell viability at high concentration and featured good optical imaging character for the slight change of CEs activity induced by 5-Fu (5-Fluorouridine, anti-tumor drug) and CEs inhibitor in living cells. Moreover, CHY-1 was also used to detect the activity and distribution of CEs in mice. Taken together, CHY-1 had widely applicable value in the diagnosis of CEs-related diseases and drug combination.

Exploration of aminopeptidase N as new biomarker for early diagnosis of thyroid cancer

False-positive diagnosis and overdiagnosis are ongoing issues in clinical diagnosis of thyroid cancer. Identifying new disease markers is crucial for early diagnosis and improved treatment. Aminopeptidase N (APN) is a promising biomarker for cancer diagnosis due to its critical roles in tumor invasion, metastasis, angiogenesis, and other processes. However, its potential as biomarker for thyroid cancer diagnosis needs further investigation. This study developed an ultra-sensitive near-infrared fluorescence probe, LAN-apn, to investigate the expression level of APN in thyroid cancer and evaluate its potential as biomarker of thyroid cancer. LAN-apn could accurately and sensitively determine APN through fluorescence method (DL = 0.069 ng/mL) and colorimetric method (DL = 4.5 ng/mL). In addition, LAN-apn allowed for successful fluorescence imaging of APN in thyroid cancer cells and thyroid cancer tumors both in vivo and in vitro, and confirmed that APN was significantly upregulated in thyroid cancer. Therefore, APN may become a new biomarker for thyroid cancer diagnosis, and LAN-apn could be used as a new imaging tool for the study of APN-thyroid cancer relationship and the early diagnosis of thyroid cancer.

An ultra-sensitive fluorescent probe for recognition of aluminum ions and its application in environment, food, and living organisms

The concentration of aluminum ions (Al3+) is closely related to the ecological environment, food safety, and human health, with excessive accumulation of Al3+ causing irreversible damage to both the ecological balance and human health. Therefore, a fluorescent probe ABHS, based on aminobenzoylhydrazide Schiff-base, was designed and synthesized in one step with a high yield. ABHS can form a 1:1 coordination complex with Al3+ in a pure water system. It exhibits ultra-sensitive and accurate detection of Al3+ even at low concentration of Al3+, with the detection limit of 6.7 nM. Furthermore, ABHS demonstrated significant enhancement of specific fluorescence for Al3+, with rapid response speed, good stability, and robust resistance to interference. Importantly, ABHS has shown excellent detection and imaging capabilities even in complex real environmental samples, food samples, and living organisms.

Cuproptosis accompanied by obvious •OH generation revealed with an ultrasensitive NIR fluorescence probe

Cuproptosis is a recently discovered copper-dependent pathway of regulated cell death, and may play a role in a number of physiological and pathological processes; however, the variation of reactive oxygen species such as OH level is unclear during cuproptosis. Herein, we have developed an ultrasensitive near-infrared (NIR) fluorescence probe CDHQ for characterizing cuproptosis, which reveals an obvious hydroxyl radical (OH) generation during cuproptosis. The specific hydrogen abstraction of OH causes a large π-conjugation extension and spectral shift of CDHQ, accompanied by a high-contrast fluorescence off–on response. CDHQ can detect trace OH that is undetectable by other methods such as electron spin resonance during autoxidation of low-valent metals (Fe2+, Ti3+, V3+ and especially Cu+) in the absence of H2O2. Using CDHQ, we have found that OH is significantly generated in the copper-overloaded cells of cuproptosis, even before cell death. Moreover, CDHQ is capable of monitoring the generation of OH in living mice, and thus may be expected to be useful for studying the in vivo change of OH in more biosystems.

Achiral Sm(III)-Based Metal-Organic Framework as a Luminescence Sensor for Enantiodiscrimination of Quinine and Quinidine.

The effective discrimination and determination of the chiral antimalarial drugs quinine (QN) and quinidine (QD) are extremely important for human health. Herein, a 2D achiral Sm-based metal-organic framework (IMU-MOF1 = [Sm(tpba)(L)]n, where Htpba = 4-(2,2':6″,2'-terpyridin)-4'-ylbenzioc acid and H2L = 2,2'-biquinoline-4,4'-dicarboxylic acid) was successfully prepared by the solvothermal method. More importantly, IMU-MOF1 was designed as an ultrasensitive fluorescent probe for the identification of chiral enantiomer drugs. The limits of detection for QN and QD are 4.24 × 10-11 and 7.54 × 10-12 M, respectively. Furthermore, it was demonstrated that the stronger hydrogen-bonding interactions between IMU-MOF1 and quinine furnish a more efficient energy transfer to the ligands in the sensing process, resulting in a significant fluorescence enhancement of IMU-MOF1.

A red-emitting ultrasensitive fluorescent probe for specific detection and biological visualization of cysteine in vitro and in vivo

Developing efficient strategies for specific detection of cysteine (Cys) is of great importance for identifying complicated biological roles in physiological and pathological processes. Herein, an ultrasensitive red-emission fluorescent probe (termed 1) is constructed for specific detection and biological visualization of Cys. The linked-anthocyanin fluorophore modified with a twisted N, N-diethylamino moiety shows improved red-shifted emission (642 nm) and absolute quantum yield (0.224 in dimethyl sulfoxide), as well as minimal fluorescence background signal and good water solubility. Meanwhile, utilizing acryloyl chloride as recognition group endows the probe 1 with excellent sensitivity and selectivity towards Cys (limit of detection: 2.93 nM). More importantly, the in vitro and in vivo results confirm that the probe 1 has the capacity of fluorescence imaging of Cys and good biological safety, which holds great promise for bioanalysis and biosensing of Cys.

Exploring butyrylcholinesterase expression in diseases using a promising fluorescent imaging tool

The level of butyrylcholinesterase (BChE) in living organisms is closely linked to disease occurrence. Developing effective methods to monitor BChE levels in living systems is essential for investigating the pathogenesis of BChE-related diseases and for early screening of the diseases. However, due to the lack of intuitive imaging tools, the expression level of BChE in many diseases remains to be explored. In this study, an ultrasensitive near-infrared fluorescent probe, LAN-bche, was developed to explore BChE expression in liver cancer, liver injury, and diabetes. LAN-bche is stable, water-soluble, ultrasensitive and high selective for BChE without disturbing from AChE, can detect BChE in dual-mode using fluorescence strategy (LOD = 0.056 U/L) and colorimetric strategy (LOD = 4.92 U/L). LAN-bche was employed to investigate the BChE expression both in liver cancer and liver injury diseases and confirmed that BChE expression was downregulated in both models, which was speculated to be due to the destruction of ability to generate BChE caused by the damage and cancerization of the liver cells. Furthermore, BChE expression in diabetes was explored and confirmed the upregulation of BChE expression in diabetes. In brief, our study shed light on BChE expression in liver cancer, liver injury, and diabetes and provides support for further research on the pathogenesis of BChE-related diseases. Besides, the probe LAN-bche is a robust tool for tracking BChE that is poised to facilitate imaging studies of BChE expression in numerous disease models.

Development of a Thiophene–Thiophene π-Conjugate Ultrasensitive Fluorescent Probe for Heavy-Metal Ions via Discrete Signaling: DFT Studies and Mechanistic Insights

Development of a Thiophene–Thiophene π-Conjugate Ultrasensitive Fluorescent Probe for Heavy-Metal Ions via Discrete Signaling: DFT Studies and Mechanistic Insights

Designing a turn-on ultrasensitive fluorescent probe based on ICT-FRET for detection and bioimaging of Hypochlorous acid.

Hypochlorous acid (HClO) plays an essential role in biological systems. The characteristics of potent oxidization and short lifetime make it challenging to detect specifically from other reactive oxygen species (ROS) at cellular levels. Therefore, its detection and imaging with high selectivity and sensitivity are of great significance. Herein a turn-on HClO fluorescent probe (named RNB-OCl) with boronate ester as the recognition site was designed and synthesized. The RNB-OCl displayed good selective and ultrasensitive to HClO with a low detection limit of 1.36nM by the intramolecular charge transfer (ICT)-fluorescence resonance energy transfer (FRET) dual mechanism in reducing the fluorescence background and improving the sensitivity. In addition, the role of the ICT-FRET was further demonstrated by time-dependent density functional theory (TD-DFT) calculations. Furthermore, the probe RNB-OCl was successfully employed for imaging HClO in living cells.

A fluorescent probe of CH3NH3PbBr3 perovskite quantum dots on polystyrene nanofibres for the detection of copper ions

Recently, metal halide perovskite quantum dots (MHPQDs) have attracted considerable interest in sensing activities due to their excellent optoelectronic properties and high surface activity. Here, aiming for heavy metal detection, we proposed an ultrasensitive turn-off fluorescent probe based on MAPbBr3 MHPQDs for the measurement of copper ions in an organic solvent. A low limit of detection (LOD) of 5.6nM was achieved and the test range was recorded from 0nM to 100nM. In order to achieve this high sensitivity, a thin film layer of electrospun polystyrene(PS) nanofibre was introduced for the structural support of MHPQDs, by which the sensitivity increased two orders of magnitude. The quenching mechanism is also discussed in the paper. We believe the electron transfer effect between Cu2+ and perovskite QDs made the main contribution for turn off sensing in our prototype device.

Carbon dots doped with nitrogen as an ultrasensitive fluorescent probe for thrombin activity monitoring and inhibitor screening

A simple and sensitive fluorometric assay based on nitrogen-doped carbon dots (N-CDs) was developed for the determination of thrombin (TB) activity in human serum samples and living cells. The novel N-CDs were prepared by a facile one-pot hydrothermal method using 1,2-ethylenediamine and levodopa as precursors. Such N-CDs exhibited green fluorescence with excitation/emission peaks at 390/520 nm and a high fluorescence quantum yield of approximately 39.2%. H-D-Phenylalanyl-L-pipecolyl-Larginine-p-nitroaniline-dihydrochloride (S-2238) was hydrolyzed by TB to produce p-nitroaniline which was capable of quenching the fluorescence of N-CDs due to an inner filter effect. This assay was used to detect TB activity with a low detection limit of 11.3 fM. The proposed sensing method was then expanded to the TB inhibitor screening and exhibited excellent applicability. As a typical TB inhibitor, argatroban was determined in a concentration as low as 1.43 nM. The method has also been successfully employed for the determination of TB activity in living HeLa cells. This work showed significant potential for TB activity assay in clinical and biomedicine applications.

An ultra-sensitive ESIPT fluorescent probe for distinguishing cancerous cells and diagnosing APAP-induced liver injury via HClO fluctuation

Hypochlorous acid (HClO) has been gradually recognized as a significant reactive oxygen species (ROS) owing to its stability in organisms. ROS concentration in cancerous cells is approximately ten times that in normal cells and excessive HClO is closely associated with tissue damage. Herein, a new turn-on fluorescent probe (MOBT-Cl) based on ESIPT for sensing HClO has been synthesized. MOBT-Cl possessed a large Stokes shift (130 nm), a rapid response time (around 10 s), and ultra-sensitivity (110-folds, LOD = 0.14 nM). Moreover, MOBT-Cl was successfully applied to imaging HClO in cells, zebrafish, and mice. Importantly, MOBT-Cl effectively distinguished cancerous cells from normal cells and monitored HClO levels in APAP-treated cells and zebrafish as well as diagnosed APAP-induced liver injury. The proposed probe held great potential for investigating the precise role of HClO in multiple physiological processes.

An ultrasensitive GSH-specific fluorescent probe unveils celastrol-induced ccRCC ferroptosis

Glutathione (GSH) is closely related to the occurrence and development of tumors. The intracellular GSH levels are abnormally altered when tumor cells undergo programmed cell death. Therefore, real-time monitoring of the dynamic changes of intracellular GSH levels can better enable the early diagnosis of diseases and evaluate the effects of cell death-inducing drugs. In this study, a stable and highly selective fluorescent probe AR has been designed and synthesized for the fluorescence imaging and rapid detection of GSH in vitro and in vivo, as well as patient-derived tumor tissue. More importantly, the AR probe can be used to track changes in GSH levels and fluorescence imaging during the treatment of clear cell renal cell carcinoma (ccRCC) with celastrol (CeT) via inducing ferroptosis. These findings demonstrate that the developed fluorescent probe AR exhibits high selectivity and sensitivity, as well as good biocompatibility and long-term stability, which can be used to image endogenous GSH in living tumors and cells. Also, a significant decrease in GSH levels was observed by the fluorescent probe AR during the treatment of ccRCC with CeT-induced ferroptosis in vitro and in vivo. Overall, these findings will provide a novel strategy for celastrol targeting ferroptosis in the treatment of ccRCC and the application of fluorescent probes to help reveal the underlying mechanism of CeT in the treatment of ccRCC.