Fluorogenic Rhodamine Probes with Pyrrole Substitution Enables STED and Lifetime Imaging of Lysosomes in Live Cells.

Fluorogenic dyes with high brightness, large turn-on ratios, excellent photostability, favorable specificity, low cytotoxicity, and high membrane permeability are essential for high-resolution fluorescence imaging in live cells. In this study, we endowed these desirable properties to a rhodamine derivative by simply replacing the N, N-diethyl group with a pyrrole substituent. The resulting dye, Rh-NH, exhibited doubled Stokes shifts (54 nm) and a red-shift of more than 50 nm in fluorescence spectra compared to Rhodamine B. Rh-NH preferentially exists in a non-emissive but highly permeable spirolactone form. Upon binding to lysosomes, the collective effects of low pH, low polarity, and high viscosity endow Rh-NH with significant fluorescence turn-on, making it a suitable candidate for wash-free, high-contrast lysosome tracking. Consequently, Rh-NH enabled us to successfully explore stimulated emission depletion (STED) super-resolution imaging of lysosome dynamics, as well as fluorescence lifetime imaging of lysosomes in live cells.

A Novel NIR Fluorescence Probe with AIE Property to Image Viscosity in Nystatin-Induced Cell Model.

As one of the most significant parameters in cellular microenvironment, viscosity levels could be used to determine the metabolic process of bioactive substances within cells. Abnormal viscosity levels are closely associated with a series of diseases. Therefore, the design and synthesis of fluorescent probes that can monitor changes of intracellular viscosity in real-time is of great significance for the study of disease development process. Here, a new viscosity-recognized NIR fluorescence probe W1 based on quinoline-malonitrile is synthesized, and it is not susceptible to interference substances. Besides, AIE probe W1 shows fast response, excellent photostability, low cytotoxicity, good linear relationship between fluorescence intensity value and viscosity. Based on the above advantages, probe W1 is used to image the change of viscosity level in the cell model induced by nystatin.

Detection of Tyrosinase Activity and Inhibitor Validation Based on N-GQDs Fluorescence Sensor.

Tyrosinase inhibitors have the ability to resist melanin formation and can be used for clinical and cosmetic, so it is becoming extremely crucial to search a rapid and effective method for detecting t the activity of tyrosinase. In this study, a sensing probe based on Nitrogen-doped graphene quantum dots (N-GQDs) were prepared with carbamide and citric acid. Tyrosinase can oxidize dopamine to dopamine quinone, which can quench the fluorescence of N-GQDs based on the principle of fluorescence resonance energy transfer (FRET) process, and then the detection of tyrosinase activity can be achieved. The result demonstrated that the fluorescence intensity of N-GQDs was a linear correlation with the activity of tyrosinase. Wide detection linear ranges between 0.05 and 5 U/mL and high selectivity. The detection range of tyrosinase was 0.05 to 5 U/mL and LOD of 0.005 U/mL. According to the above, the fluorescence method established in this work could be successfully used for the trace analysis of tyrosinase and it was verified that KA is an inhibitor of tyrosinase.

Construction of Cyan Blue Fluorescence Probe based on Nitrogen-Doped Carbon Dots for Detecting Nitrite Ion in Ham Sausage.

Nitrite ion is one of the materials widely used in human life, and the accurate, sensitive and stable detection of nitrite ions is of great significance to people's healthy life. In this study, nitrogen-doped fluorescent carbon dots (N-CDs) for detecting nitrite salt solutions were prepared using citric acid monohydrate and Chrysoidin as precursors through a one-pot hydrothermal method. Under the condition of pH = 3, a noticeable quenching phenomenon occurred in the carbon dot solution with the increase in nitrite ion concentration. This quenching effect might be attributed to the diazonium effect. N-CDs have been successfully used as fluorescence probes for NO2- detection. NO2- can effectively quench the fluorescence intensity of N-CDs, providing a linear response to fluorescence quenching efficiency with respect to NO2- concentration within the range of 0-10µM and 10-30µM, and a detection limit of 52nM, showing high sensitivity. In addition, the probe was applied to the determination of NO2- in ham sausage samples with a detection limit of 0.67µM and recoveries in the range of 99.5-102.3%, the fluorescent probe showed satisfactory reliability.

Investigation of the Application and Mechanism of Nitrogen and Phosphorus Co-doped Carbon Dots for Mercury Ion Detection.

In this paper, we obtained nitrogen and phosphorus co-doped carbon dots through a hydrothermal method using o-phenylenediamine and citric acid in a 40% phosphoric acid environment. The carbon dots emitted fluorescence at 476 nm under excitation at 408 nm and exhibited good selectivity and high sensitivity towards mercury ions. These carbon dots showed excellent dispersibility in water and maintained stable fluorescence even in high concentration salt environments. The interaction between mercury ions and functional groups on the carbon dots surface through electrostatic interaction resulted in static quenching. Simultaneously, by detecting the lifetime and transient absorption spectra of the carbon dots, we observed that the coordination of mercury ions with the carbon dots broadened the band structure of the carbon dots, and the existing photoinduced electron transfer process increased the non-radiative transition channel. The combined effect of dynamic quenching and static quenching significantly reduced the fluorescence intensity of the carbon dots at 476 nm. The carbon dots exhibited linear detection of mercury ions in the range of 0.01-1 µM, with a detection limit as low as 0.0245 µM. In terms of practical water environmental detection applications, these carbon dots were able to effectively detect mercury ions in tap water and lake water, demonstrating their broad application prospects in the field of environmental metal analysis.

Effective Detection of Cu(II) Ions Based on Carbon Dots@Exfoliated Layered Double Hydroxides Composites Fluorescence Probe.

A series of carbon dots@exfoliated layered double hydroxides (CDs@LDH) composites were hydrothermally fabricated by Mg/Al LDH and formamide. The results of FTIR, UV-vis, and XPS spectra in company with HRTEM images showed that crystalline nano CDs formed on the single layer of LDH by Mg-C bond. With the increase of solvothermal reaction time from 2 to 6 h, the band gap and the binding energy of aminic and graphitic N species of CDs@LDH composites decreased, whereas the crystallinity increased. The fluorescence peaks of CDs@LDH composites could be deconvoluted into short-wavelength (416 nm) and large-wavelength (443 nm) components by Gaussian function, and the fluorescence intensities of both components enhanced with the extension of the solvothermal reaction time. The simultaneous enhancements of fluorescence lifetime and quantum yield resulted from the relatively high electron density in graphitic nitrogen of CDs@LDH, whereas the reduction of nonradiative rate was due to the high crystallinity in the carbon core of CDs@LDH. A strong exciton-lattice interaction also has been validated based on the excitation and emission spectra of CDs@LDH, so the fluorescence emission of CDs@LDH composite was heavily related to its crystalline carbon core and nitrogen-containing groups. CDs@LDH with high nitrogen-containing exhibited a superior detection property for Cu2+ ion sensing with the linear range of 26.90 ~ 192.20 µM and a limit of detection of 0.1957 µM. The photo-induced electron transfer (PET) process dominated the fluorescence quenching of CDs@LDH by Cu2+ ion since the fluorescence lifetime decreased with the increase of Cu2+ ion concentration.

Meta-Phenylenediamine-Derived Silver-Containing Nanoporous Hyper-Cross-Linked Polymer: An Innovative Fluorescence Probe for S2O32- ion Detection in Aqueous Media.

The meta-phenylenediamine polymer, when hyper-cross-linked, exhibits a minimal fluorescence intensity. However, the introduction of silver ions induces a significant increase in intensity, attributed to the plasmonic effect. This heightened intensity is selectively increased more upon the addition of thiosulfate ions. Capitalizing on this property, a fluorescence probe was developed. The correlation between fluorescence intensity reduction and S2O32- concentration follows a linear and consistent pattern. The precursor's response to diverse anions such as SO42-, CO32-, HPO42-, Cr2O72-, F-, Cl-, Br-, I-, H2PO4-, CH3COO-, NO3-, ClO-, and HCO3- was also examined. Under optimal conditions, the probe exhibited a linear range of 0.5-3 µM with a detection limit of 0.01 µM. Its effectiveness was demonstrated in measuring thiosulfate concentrations in aqueous media.

A Ratiometric Fluorescence Probe Based on Silver Nanoclusters and CdSe/ZnS Quantum dots for the Detection of Hydrogen Peroxide by Aggregation and Etching.

In this study, a ratiometric fluorescence nanoprobe is developed for the analysis of hydrogen peroxide (H2O2). Silver nanoclusters (AgNCs) were synthesized by chemical reduction method using sodium borohydride (NaBH4) as reducing agent, and were coupled with CdSe/ZnS quantum dots (QDs) to form the ratiometric fluorescence nanoprobe silver nanoclusters-quantum dots (AgNCs-QDs). The effect of the volume ratio of CdSe/ZnS QDs to AgNCs on the fluorescence ratio of AgNCs-QDs was investigated. The fluorescence characterization results show that two emission peaks of AgNCs-QDs are located at 473 nm and 661 nm, respectively. Transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS) results show that H2O2 can cause the fluorescence probe to aggregate, while etching AgNCs to produce silver ions, which together cause the fluorescence of the QDs in the ratiometric fluorescent probe to be quenched. Based on this strategy, the fluorescence intensity ratio of the two emission peaks F473/F661 exhibits a strong linear correlation with the concentration of H2O2. The detection range is 3.32 µM ~ 2.65 mM with a detection limit of 3.32 µM. In addition, the ratiometric fluorescence probe can specifically recognize H2O2 and has excellent anti-interference performance and good fluorescence stability. Importantly, the probe was utilized for the detection of H2O2 in serum, showing the possibility of the probe in clinical detection applications.

A FRET-based multifunctional fluorescence probe for the simultaneous detection of sulfite and viscosity in living cells.

Viscosity and sulfur dioxide derivatives were significant indicators for the assessment of health threat and even cancers, therefore, on-site and real time detection of viscosity and sulfur dioxide derivatives has obtained considerable attentions. An FRET-based fluorescence probe JZX was designed and synthesized based on a novel energy donor of N,N-diethyl-4-(1H-phenanthro[9,10-d]imidazol-2-yl)benzamide fluorophore. JZX exhibited a large Stokes shift (230 nm), high energy transfer efficiency, wide emission channel gap (135 nm) and excellent stability and biocompatibility. JZX detected sulfur dioxide with low detection limit (55 nM), fast responding (16 min), high selectivity and sensitivity. Additionally, JZX tend to target endoplasmic reticulum of which normal metabolism will be disturbed by the abnormal levels of viscosity and sulfur dioxide derivatives. Prominently, JZX could concurrently detect viscosity and sulfur dioxide derivatives depending on different fluorescence signals in living cells for the screening of cancer cells. Hence, probe JZX will be a promising candidate for the detection of viscosity and sulfur dioxide derivatives, and even for the diagnosis of liver cancers.

A turn-on fluorescence probe for imaging tyrosinase at the wound site in broken tail of zebrafish.

Tyrosinase (TYR) is a copper-containing oxidase that affects the synthesis of melanin in the human body, which is regulate to the pigmentation of the skin. Nevertheless, abnormal expression of TYR can lead to albinism, vitiligo and other skin diseases. Excessive accumulation of TYR is a marker of melanoma cancer and an important factor leading to pigmentation during wound healing, freckles and browning of fruits and vegetables. Efficient tracking of TYR is of significance for studying its pathophysiological mechanism. Herein, we synthesized a benzindole-based fluorescent probe Pro-OH to detect TYR in living cells and zebrafish. The probe displayed a high selectivity and sensitivity in distinguishing TYR from other analytes with the low detection limit of 1.024 U/mL. Importantly, Pro-OH was successfully used to imagine TYR at the wound site of broken tail of zebrafish.

d-type peptides based fluorescent probes for "turn on" sensing of heparin.

Developing "turn on" fluorescent probes was desirable for the detection of the effective anticoagulant agent heparin in clinical applications. Through combining the aggregation induced emission (AIE) fluorogen tetraphenylethene (TPE) and heparin specific binding peptide AG73, the promising "turn on" fluorescent probe TPE-1 has been developed. Nevertheless, although TPE-1 could achieve the sensitive and selective detection of heparin, the low proteolytic stability and undesirable poor solubility may limit its widespread applications. In this study, seven TPE-1 derived fluorescent probes were rationally designed, efficiently synthesized and evaluated. The stability and water solubility were systematically estimated. Especially, to achieve real-time monitoring of proteolytic stability, the novel Abz/Dnp-based "turn on" probes that employ the internally quenched fluorescent (IQF) mechanism were designed and synthesized. Moreover, the detection ability of synthetic fluorescent probes for heparin were systematically evaluated. Importantly, the performance of d-type peptide fluorescent probe XH-6 indicated that d-type amino acid substitutions could significantly improve the proteolytic stability without compromising its ability of heparin sensing, and attaching solubilizing tag 2-(2-aminoethoxy) ethoxy) acid (AEEA) could greatly enhance the solubility. Collectively, this study not only established practical strategies to improve both the water solubility and proteolytic stability of "turn on" fluorescent probes for heparin sensing, but also provided valuable references for the subsequent development of enzymatic hydrolysis-resistant d-type peptides based fluorescent probes.

A ternary nucleotide-lanthanide coordination nanoprobe for ratiometric fluorescence detection of ciprofloxacin.

Ciprofloxacin (CIP) is a widely used broad-spectrum antibiotic and has been associated with various side effects, making its accurate detection crucial for patient safety, drug quality compliance, and environmental and food safety. This study presents the development of a ternary nucleotide-lanthanide coordination nanoprobe, GMP-Tb-BDC (GMP: guanosine 5'-monophosphate, BDC: 2-amino-1,4-benzenedicarboxylic acid), for the sensitive and ratiometric detection of CIP. The GMP-Tb-BDC nanoprobe was constructed by incorporating the blue-emissive ligand BDC into the Tb/GMP coordination polymers. Upon the addition of CIP, the fluorescence of terbium ion (Tb3+ ) was significantly enhanced due to the coordination and fluorescence sensitization properties of CIP, while the emission of the BDC ligand remained unchanged. The nanoprobe demonstrated good linearity in the concentration range of 0-10 µM CIP. By leveraging mobile phone software to analyze the color signals, rapid on-site analysis of CIP was achieved. Furthermore, the nanoprobe exhibited accurate analysis of CIP in actual drug and milk samples. This study showcases the potential of the GMP-Tb-BDC nanoprobe for practical applications in CIP detection.

Thienopyrimidine-derived multifunctional fluorescence sensor for the detection of Cu2+, Fe3+, and PPi in different solvents.

Hydrazine substituted thienopyrimidine, a new fluorophore, was used to synthesize a novel Schiff base R1 as a chemosensor via the condensation with p-formyltriphenylamine, and the structure was confirmed using nuclear magnetic resonance spectroscopy (NMR) and mass spectrometry (MS) analysis. When treated with Cu2+ in dimethylsulfoxide (DMSO)/H2O buffer, R1 showed a phenomenon of fluorescence quenching, which was reversible with the action of ethylenediaminetetraacetic acid (EDTA). When treated with Fe3+ in dimethylformamide (DMF)/H2O buffer, R1 exhibited the same phenomenon, but fluorescence was recovered with inorganic pyrophosphate (PPi) quantitatively. The complexation ratios for R1-Cu2+ and R1-Fe3+ were both 1:2, which were manifested by MS titrations and corresponding Job's plots. The limits of detection of R1 for Cu2+ and Fe3+ were 3.11 × 10-8 and 1.24 × 10-7 M, respectively. The sensing mechanism of R1 toward Cu2+ and Fe3+ was confirmed using density functional theory calculations and electrostatic potential analysis. Test strips of R1 were fabricated successfully for on-site detection of Cu2+ and Fe3+. In addition, R1 was applied to recognize Cu2+ and Fe3+ in actual water samples with satisfactory recovery.

A comparative study of two thienopyrimidine Schiff base probes for sequential monitoring of Ga3+ and Pd2.

Two Schiff base probes (S1 and S2) were prepared and synthesized by incorporating thienopyrimidine into salicylaldehyde or 3-ethoxysalicylaldehyde individually, with the aim of detecting Ga3+ and Pd2+ sequentially. Upon chelation with Ga3+, S1 and S2 exhibited fluorescence enhancement in DMSO/H2O buffer. Both S1-Ga3+ and S2-Ga3+ were quenched by Pd2+. The limit of detection for S1 in response to Ga3+ and Pd2+ was 2.86 × 10-7 and 4.4 × 10-9 M, respectively. For S2, the limit of detection for Ga3+ and Pd2+ was 4.15 × 10-8 and 3.0 × 10-9 M, respectively. Furthermore, the complexation ratios of both S1 and S2 with Ga3+ and Pd2+ were determined to be 1:2 through Job's plots, ESI-MS analysis, and theoretical calculations. Two molecular logic gates were constructed, leveraging the response behaviors of S1 and S2. Moreover, the potential utility of S1 and S2 for monitoring Ga3+ and Pd2+ in domestic water was verified.

Boron difluoride modified zinc metal-organic framework-based "off-on" fluorescence sensor for tetracycline and Al3+ detection.

A novel fluorescence "off-on" probe was developed using a boron difluoride-modified zinc metal-organic framework (Zn-MOF3) for sensitive determination of tetracycline (TC) and Al3+. The Zn-MOF3 has excellent optical property and good applicability in aqueous phase. The fluorescence recorded at 436 nm was quenched at the excitation wavelength of 336 nm. Signal-off detection of tetracycline via fluorescence quenching of Zn-MOF3 is based on the inner filter effect. Fluorescence on-off-on detection of Al3+ occurs via the specific binding between tetracycline and Al3+. The limits of detection for TC and Al3+ were 28.4 nM and 106.7 nM, respectively. This probe exhibited high selectivity which was used for the determination of TC and Al3+ with satisfied recoveries (89.8 to 105.6% for TC, 90.0 to 110.4% for Al3+) and good precision (< 5%) in milk. The developed sensor represents the first "off-on" system for fluorescence detection of TC and Al3+ based on Zn-MOF3 with a better aspect of the innovation.

Dual-mode sensing strategy based on carbon dots for sensitive and selective detection of molybdate ions.

Two kinds of carbon dots with the maximum fluorescence peak of 492 nm (named as G-CDs) and 607 nm (named as R-CDs) were synthesized. In the presence of MoO42- ions, the fluorescence of R-CDs at 607 nm can be quenched, which can probably be assigned to their aggregation caused by MoO42-, while that of G-CDs at 492 nm remained unchanged. For the first time, a ratiometric fluorescence probe was developed for MoO42- ions detection. In the range 0.25 ~ 100 µM, the fluorescence ratio (F492/F607) of the probe was linearly related to MoO42- concentration, and the detection limit was 61.5 nM, which fully meets the minimum detection requirements of MoO42- ions in drinking water. On the other hand, when MoO42- was introduced, a significant fading phenomenon of R-CDs can be observed with the naked eye; thereby, the colorimetric method can also be proposed. Based on above, the ratiometric fluorometric/colorimetric dual-mode sensing method was established for MoO42- anion quantification. Compared with the traditional analysis methods, the results obtained by multimodal sensing can be mutually verified, which effectively improves the accuracy and reliability. The dual-mode assay proposed in this work provides an alternative scheme to meet the need of sensing target compounds in complex matrices.

Fabrication of fluorescence probe based on molecularly imprinted polymers on red emissive biomass-derived carbon dots coupled with smartphone readout for tyramine determination in fermented meat products.

A fluorescence probe based on molecularly imprinted polymers on red emissive biomass-derived carbon dots (r-BCDs@MIPs) was developed to detect tyramine in fermented meat products. The red emissive biomass-derived carbon dots (r-BCDs) were synthesized by the one-step solvothermal method using discarded passion fruit shells as raw materials. The fluorescence emission peak of r-BCDs was at 670 nm, and the relative quantum yield (QY) was about 2.44%. Molecularly imprinted sensing materials were prepared with r-BCDs as fluorescent centers for the detection of trace tyramine, which showed a good linear response in the concentration range of tyramine from 1 to 40 µg L-1. The linear correlation coefficient was 0.9837, and the limit of detection was 0.77 µg L-1. The method was successfully applied to the determination of tyramine in fermented meat products, and the recovery was 87.17-106.02%. The reliability of the results was verified through high-performance liquid chromatography (HPLC). Furthermore, we combined the r-BCDs@MIPs with smartphone-assisted signal readout to achieve real-time detection of tyramine in real samples. Considering its simplicity and convenience, the method could be used as a rapid and low-cost promising platform with broad application prospects for on-site detection of trace tyramine with smartphone-assisted signal readout.

The Brown Sugar Mediated Carbon Quantum Dots as a Novel Fluorescence Sensor for Sensitive Detection of Gentamicin and Its Application in Foods.

In this work, a novel fluorescence sensing strategy was proposed for the detection of gentamicin based on fluorescent carbon quantum dots (CQDs) and gold nanoparticles (AuNPs). Herein, the CQDs were green-synthesized for the first time via a one-step hydrothermal method utilizing brown sugar as the precursor. In the presence of citrate-stabilized AuNPs, the fluorescence of CQDs was quenched efficiently. Gentamicin, on the other hand, had a higher affinity for AuNPs and was able to compete with CQDs for a preferential binding to AuNPs, which ultimately led to the aggregation of AuNPs and freeing of CQDs in solution, causing the fluorescence recovery of CQDs. Based on the above phenomenon, the concentrations of gentamicin could be ascertained by detecting the variations in fluorescence intensity of CQDs. This sensing strategy exhibited excellent selectivity in various antibiotics. At the same time, the method displayed outstanding sensitivity for gentamicin, which was successfully applied to real samples detection.

Design, Synthesis of Hydrogen Peroxide Response AIE Fluorescence Probes Based on Imidazo [1,2-a] Pyridine.

Hydrogen peroxide (H2O2), a significant member of reactive oxygen species, plays a crucial role in oxidative stress and cell signaling. Abnormal levels of H2O2 in the body can induce damage or even impair body function, leading to the development of certain diseases. Therefore, real-time monitoring of H2O2 in living cells is very important. In this work, the aggregation-induced emission fluorescence probe 2-(2-((4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl) benzyl) oxy) phenyl) imidazo [1,2-a] pyridine (B2) was designed and synthesized, which enables the long-term tracing of H2O2 in living cells. The addition of H2O2 to probe B2 results in a dramatic fluorescence enhancement around 500 nm. Notably, B2 can visualize both exogenous and endogenous H2O2 in living cells. The synthesis method for B2 is simple, has a high yield, and utilizes readily available materials. It exhibits advantages such as low toxicity, photostability, and good biocompatibility. Consequently, the developed fluorescent probe in this study has great potential as a reliable tool for determining H2O2 in living cells.

Enzyme-Activatable Near-Infrared Photosensitizer with High Enrichment in Tumor Cells Based on a Multi-Effect Design.

Enzyme-activatable near-infrared (NIR) fluorescent probes and photosensitizers (PSs) have emerged as promising tools for molecular imaging and photodynamic therapy (PDT). However, in living organisms selective retention or even enrichment of these reagents after enzymatic activation at or near sites of interest remains a challenging task. Herein, we integrate non-covalent and covalent retention approaches to introduce a novel "1-to-3" multi-effect strategy-one enzymatic stimulus leads to three types of effects-for the design of an enzyme-activatable NIR probe or PS. Using this strategy, we have constructed an alkaline phosphatase (ALP)-activatable NIR fluorogenic probe and a NIR PS, which proved to be selectively activated by ALP to switch on NIR fluorescence or photosensitizing ability, respectively. Additionally, these reagents showed significant enrichment (over 2000-fold) in ALP-overexpressed tumor cells compared to the culture medium, accompanied by massive depletion of intracellular thiols, the major antioxidants in cells. The investigation of this ALP-activatable NIR PS in an in vivo PDT model resulted in complete suppression of HeLa tumors and full recovery of all tested mice. Encouragingly, even a single administration of this NIR PS was sufficient to completely suppress tumors in mice, demonstrating the high potential of this strategy in biomedical applications.