New Diketopyrrolopyrrole-Based Ratiometric Fluorescent Probe for Intracellular Esterase Detection and Discrimination of Live and Dead Cells in Different Fluorescence Channels

Construction of a novel aminofluorene-based ratiometric near-infrared fluorescence probe for detecting carboxylesterase activity in living cells

Herein, we constructed a novel aminofluorene-based fluorescence probe (FEN-CE) for the detection of carboxylesterase (CE) in living cells by a ratiometric near-infrared (NIR) fluorescence signal. FEN-CE with NIR emission (650 nm) could be hydrolyzed specifically by CE and transformed to FENH with the release of the self-immolative group, which exhibited a red-shifted emission peak of 680 nm. In addition, FEN-CE showed high selectivity for CE and was successfully used in the detection of CE activity in living cells through its ratiometric NIR fluorescence signals.

Design of donor-acceptor conjugated polymers based on diketopyrrolopyrrole for NIR-II multifunctional imaging

Diketopyrrolopyrrole (DPP) is an excellent photosensitizer and photothermal agent with the advantages of good planarity, strong electron affinity, high electron mobility, easy purification, easy structural modification and high molar absorption coefficient. It is regarded as one of the ideal choices for the design and synthesis of efficient organic photovoltaic materials. Therefore, two kinds of donor-acceptor (D-A) conjugated polymers were designed and synthesized with DPP as the acceptor, and their optical properties and applications in the near-infrared region were studied. The quantum yield (QY) of PBDT-DPP is 0.46%, and the highest temperature reached within 10 minutes after irradiation with a 660 nm laser is 60 °C. Another polymer, EDOT-DPP, has a QY of 0.48%, and its semiconductor polymer nanoparticle aqueous solution can reach 60 °C within 12 minutes under laser irradiation, achieving photothermal treatment of nude mice tumors. Both polymer NPs have good biocompatibility and promising applications in bioimaging and photothermal therapy.

Precisely Constructing Renal-Clearable and LAP-Activatable Ratiometric Molecular Probes for Early Diagnosis of Acute and Chronic Kidney Injury Via Optimizing Asymmetric DPP Dyes

Fluorescence analysis is an increasingly important contributor to the early diagnosis of kidney diseases. To achieve precise visualization of the kidneys and early diagnosis of related diseases, an asymmetric pyrrolopyrrolidone (DPP) dye platform with C-aromatic substituents and N-lipophilic/hydrophilic modification was constructed. Based on these, we developed the renal-clearable, water-soluble, and kidney injury biomarker leucine aminopeptidase (LAP) activated ratiometric fluorescent probe DPP-S-L. In the mouse model of cisplatin-induced acute kidney injury and during the development of type 2 diabetes to diabetic kidney disease, we visualized for the first time the upregulation of LAP in the kidney and urine by dual-channel ratiometric fluorescence signal and diagnosed the kidney injury earlier and more sensitively than blood/urine enzyme detection and tissue analysis. This study showcases an excellent asymmetric DPP dye platform and renal-clearable ratiometric fluorescent probe design strategy that is extended to determination and visualization of other biomarkers for early disease diagnosis.

Diketopyrrolopyrrole-based fluorescent probe for visualizing over-expressed carboxylesterase in fever via ratiometric imaging

Fever is the result of inflammation and the innate self-defense response of organisms, can cause abnormal changes in the activity of many enzymes in organisms, including the important carboxylesterase (CE). Monitoring the activity changes of CE in vivo during a fever will help to understand heat-related pathological mechanisms. In this paper, we designed diketopyrrolopyrrole-based ratiometric fluorescent probes DPP-FBC-P and DPP-FBO-P containing alkyl chain and diethylene glycol monomethyl ether chain respective for detection of CE. Both probes could realized fast response to CE and displayed good selectivity and high sensitivity. Compared with DPP-FBO-P, DPP-FBC-P had better biocompatibility, larger signal to noise ratio (225-fold vs 125-fold) and lower detection limit (1.6 × 10-5 U/mL vs 4.2 × 10-5 U/mL). Moreover, the probe DPP-FBC-P had been successfully applied to image the endogenous CE in HepG2 cells and solid tumors, and also visualized the over expressed CE in fever cells. Most importantly, the changes of CE level in the liver of fever mice model induced by LPS were monitored with the assistance of DPP-FBC-Pvia dual channel ratio imaging for the first time. In addition, fluorescence color signal in solution was captured by smart phone, and the linear relationship between RGB ratio (G/R) and CE concentration was established. This work will provide a potential approach for investigating the physiological and pathological processes of heat related diseases.

New Advances in the Exploration of Esterases with PET and Fluorescent Probes

Esterases are hydrolases that catalyze the hydrolysis of esters into the corresponding acids and alcohols. The development of fluorescent probes for detecting esterases is of great importance due to their wide spectrum of biological and industrial applications. These probes can provide a rapid and sensitive method for detecting the presence and activity of esterases in various samples, including biological fluids, food products, and environmental samples. Fluorescent probes can also be used for monitoring the effects of drugs and environmental toxins on esterase activity, as well as to study the functions and mechanisms of these enzymes in several biological systems. Additionally, fluorescent probes can be designed to selectively target specific types of esterases, such as those found in pathogenic bacteria or cancer cells. In this review, we summarize the recent fluorescent probes described for the visualization of cell viability and some applications for in vivo imaging. On the other hand, positron emission tomography (PET) is a nuclear-based molecular imaging modality of great value for studying the activity of enzymes in vivo. We provide some examples of PET probes for imaging acetylcholinesterases and butyrylcholinesterases in the brain, which are valuable tools for diagnosing dementia and monitoring the effects of anticholinergic drugs on the central nervous system.

An endoplasmic reticulum-specific ratiometric fluorescent probe for imaging esterase in living cells

Esterase is primarily distributed in the endoplasmic reticulum (ER) and often overexpressed in cancer cells. Therefore, the detection of esterase in ER is significant for monitoring the metabolic process of various esters and evaluating the efficacy of chemotherapeutic prodrugs. However, only few fluorescent probes can detect esterase in the ER due to the lack of ER-specificity. More seriously, these probes are often limited by low pearson's colocalization coefficient and one single wavelength emission. To solve those problems, an ER-specific ratiometric fluorescent probe (ER-EST) is designed for detecting esterase in living cells. The ER-EST shows a ratiometric and red-shifted emission (125 nm) from 435 to 560 nm after hydrolysis by esterase. The fluorescence intensity ratio of ER-EST displays quantitative response to the esterase activity (0-0.5 U/mL) with low detection limit of 1.8 × 10^-4 U/mL. Importantly, the ER-EST with good biocompatibility and excellent ER-targeted ability was successfully employed to ratiometric image the endogenous endoplasmic reticulum esterase in living cells.

A Turn-On Lipid Droplet-Targeted Near-Infrared Fluorescent Probe with a Large Stokes Shift for Detection of Intracellular Carboxylesterases and Cell Viability Imaging

Carboxylesterases (CEs) play important physiological roles in the human body and are involved in numerous cellular processes. Monitoring CEs activity has great potential for the rapid diagnosis of malignant tumors and multiple diseases. Herein, we developed a new phenazine-based "turn-on" fluorescent probe DBPpys by introducing 4-bromomethyl-phenyl acetate to DBPpy, which can selectively detect CEs with a low detection limit (9.38 × 10^-5 U/mL) and a large Stokes shift (more than 250 nm) in vitro. In addition, DBPpys can also be converted into DBPpy by carboxylesterase in HeLa cells and localized in lipid droplets (LDs), emitting bright near-infrared fluorescence under the irradiation of white light. Moreover, we achieved the detection of cell health status by measuring the intensity of NIR fluorescence after co-incubation of DBPpys with H₂O₂-pretreated HeLa cells, indicating that DBPpys has great potential applications for assessing CEs activity and cellular health.

Monitoring cell viability in N-nitrosodiethylamine induced acute hepatitis and detection of hydrazine in solution and gas phase with Dual-function fluorescent probes

The highly toxic N-nitrosodiethylamine (NDEA) and hydrazine (N₂H₄) caused severe environmental contamination and serious health risks. Herein, we designed the two-photon ratiometric fluorescent probe (Nap-2), emission maximum shifted from 466 nm to 571 nm, to monitor cell viability of NDEA induced acute hepatitis via esterase activity detection. Furthermore, the probe Nap-2 evaluate the hydrazine (N₂H₄) content in the solution and gas phase. It is worth mentioning that we used NDEA induced acute hepatitis in the mice and evaluated the negative correlation of esterase activity in the tissue cells and serum with Nap-2. The probe Nap-2 exhibited that acute hepatitis induced by NDEA decreased cell viability. Furthermore, we made convenient test papers using Nap-2 to detect N₂H₄ in solution and gas phase. After adding N₂H₄, the fluorescence color changed from blue to yellow and was visible to the naked eye. This work provides a convenient tool and method for evaluating the toxicity of NDEA induced acute hepatitis and detecting N₂H₄ in the environment.

Esterase-Responsive Polymeric Micelles Containing Tetraphenylethene and Poly(ethylene glycol) Moieties for Efficient Doxorubicin Delivery and Tumor Therapy

Enzyme-responsive drug delivery systems have drawn much attention in the field of cancer theranostics due to their high sensitivity and substrate specificity under mild conditions. In this study, an amphiphilic polymer T1 is reported, which contains a tetraphenylethene unit and a poly(ethylene glycol) chain linked by an esterase-responsive phenolic ester bond. In aqueous solution, T1 formed stable micelles via self-assembly, which showed an aggregation-induced emission enhancement of 32-fold at 532 nm and a critical micelle concentration of 0.53 μM as well as esterase-responsive activity. The hydrophobic drug doxorubicin (DOX) was efficiently encapsulated into the micelles with a drug loading of 21%. In the presence of the esterase, the selective decomposition of drug-loaded T1 micelles was observed, and DOX was subsequently released with a half-life of 5 h. In vitro antitumor studies showed that T1@DOX micelles exhibited good therapeutic effects on HeLa cells, while normal cells remained mostly intact. In vivo anticancer experiments revealed that T1@DOX micelles indeed suppressed tumor growth and had reduced side effects compared to DOX·HCl. The present work showed the potential clinical application of esterase-responsive drug delivery in cancer therapy.

A carboxylesterase-activatable near-infrared phototheranostic probe for tumor fluorescence imaging and photodynamic therapy

Phototheranostic probes have been proven to be a promising option for cancer diagnosis and treatment. However, near-infrared phototheranostic probes with specific tumor microenvironment responsiveness are still in demand. In this paper, a carboxylesterase (CES)-responsive near-infrared phototheranostic probe was developed by incorporating 6-acetamidohexanoic acid into a hemicyanine dye through an ester bond. The probe exhibits highly sensitive and selective fluorescence enhancement towards CES because CES-catalyzed cleavage of the ester bond leads to the release of the fluorophore. By virtue of its near-infrared analytical wavelengths and high sensitivity, the probe has been employed for endogenous CES activatable fluorescence imaging of tumor cells. Moreover, under 660 nm laser irradiation, the probe can generate toxic reactive oxygen species and efficiently kill tumor cells, with low cytotoxicity in dark. As far as we know, the probe was the first CES-responsive phototheranostic probe with both near-infrared analytical wavelengths and photosensitive capacity, which may be useful in the real-time and in situ imaging of CES as well as imaging-guided photodynamic therapy of tumors. Therefore, the proposed probe may have wide application prospect in cancer theranostics.

Stereolithographic Visible-Light Printing of Poly(l-glutamic acid) Hydrogel Scaffolds

Bioprinting is a promising fabrication technique aimed at developing biologically functional, tissue-like constructs for various biomedical applications. Among the different bioprinting approaches, vat polymerization-based techniques offer the highest feature resolution compared to more commonly used extrusion-based methods and therefore have greater potential to be utilized for printing complex hierarchical tissue architectures. Although significant efforts have been directed toward harnessing digital light processing techniques for high-resolution bioprinting, the use of stereolithography (SLA) setups for producing distinct hydrogel filaments smaller than 20 μm has received less attention. Improving the bioprinting resolution is still a technical challenge that must consider both the practical limitations of the bioprinter apparatus and the formulation of the cytocompatible bioresin. In this study, we developed a novel bioresin compatible with SLA and capable of printing high-resolution features. This resin, composed of a biosynthetic polypeptide poly(l-glutamic acid) functionalized with tyramine moieties (PLGA-Tyr), was crosslinked using a visible-light photoinitiator system. Varying concentrations of PLGA-Tyr and the co-photoinitiator were evaluated for the hydrogel system's gelation ability, swelling characteristics, degradation profiles, mechanical properties, and cell viability post-encapsulation. This study introduces a custom-built, cost-effective, visible-light SLA bioprinting system named the "MicroNC". Using the newly developed visible-light bioresin, we demonstrated for the first time the ability to fabricate hydrogel scaffolds with well-resolved filaments (less than 8 μm in width) capable of supporting cell viability and proliferation and directing cellular morphology at the single-cell level for up to 14 days. Overall, these experiments have underscored the exciting potential of using the visible-light-photoinitiated PLGA-Tyr material system for developing physiologically relevant in vitro hydrogel scaffolds with feature resolutions comparable to the dimensions of individual human cells for a wide range of biomedical applications.

Development of an esterase fluorescent probe based on naphthalimide-benzothiazole conjugation and its applications for qualitative detection of esterase in orlistat-treated biosamples

Esterase is a large hydrolysis family, and widely distributed in many kinds of cells. It is responsible for multiple physiological and pathological functions including metabolism, gene expression. While abnormality of esterase is associated with many pathological activities in obesity, Wolman's disease, and cancer. Thereby, it is essential to design an effective tool for esterase in situ detection in biological systems. Herein, a novel fluorescent probe Y-1 for monitoring esterase in living cells was rationally designed. Probe Y-1 was synthesized by the conjugation between an acetylation of 4-hydroxy naphthalimide and benzothiazole group. Benzothiazole moiety is a typical Excited-state intramolecular proton transfer (ESIPT) controller. Acetate group was selected as the responsive site and ESIPT initiator. As the acetate group could block the ESIPT effect, the probe emits no fluorescence under the excitation of 455 nm. When binding with esterase, Y-1 shows distinct fluorescence with the peak at 560 nm with short time when ESIPT is on. Y-1 displays high sensitivity (LOD is 0.216 × 10^-3 U/mL), fast response (within 5 min), high selectivity and photostability towards esterase. Furthermore, the %RSD (relative standard deviation) of within-day and day-to-day precision was no more than 13.0% and the accuracy ranged from -6.5 to -12.3%. Kinetics performance of Y-1 indicates that esterase has high affinity and hydrolysis to Y-1. For biological applications, our probe is a time-dependent visualizing esterase in living HepG2 and CoLo205 cells within 15 min. After the treatment of orlistat (1 and 5 μM) for inhibiting the activity of esterase, the bright fluorescence has also been detected using our probe. Furthermore, it has been successful in monitoring the esterase in zebrafish, the data were consistent with cellular phenomena. Therefore, all these findings indicate that the robust probe Y-1 is a useful qualitative tool for detecting esterase in biological systems.

Ultrasensitive fluorescent probe for visual biosensing of esterase activity in living cells and its imaging application

Esterase activity is often used as an index to evaluate the health status of cells and plays an important role in cell metabolism and apoptosis. Herein, we develop two fluorescent probes for visual biosensing of esterase activity and imaging in living cells. In vitro, after the introduction of esterase, enzymolysis destroys the ester bond of the probe, causing the fluorescent color of probe changes from yellow to red, thus realizing the visual strategy for determination of esterase activity, with high sensitivity and selectivity. Especially, probe VA, 2-(4-acetoxystyryl)-3-ethyl-1,1-dimethyl- 1H-benzo[e]indol-3-ium, exhibits higher sensitivity with a lower detection limit (up to 7.15 × 10^-6 U/mL). In the cell experiment, the fluorescent probe VA also shows good biocompatibility and high spatial resolution, and is successfully applied to the intracellular fluorescent imaging and biosensing of esterase in living cells. More importantly, the probe VA can judge the unhealthy state of H₂O₂-induced HeLa cells using dual-fluorescence signals. The results confirm that the fluorescence method is a reliable tool for detecting endogenous esterase in living biological system.

A diketopyrrolopyrrole-based ratiometric fluorescent probe for endogenous leucine aminopeptidase detecting and imaging with specific phototoxicity in tumor cells

Leucine aminopeptidase (LAP) is a vital proteolytic enzyme, and its overexpression is often associated with many physiological diseases, such as liver dysfunction and breast cancer. Therefore, the accurate measurement of LAP concentrations in cells is critical for the diagnosis and prevention of related diseases. Herein, a new ratiometric fluorescent probe, DPP-Leu, based on diketopyrrolopyrrole (DPP) was designed and synthesized for LAP detection based on the specific enzymatic cleavage of the N-terminal leucine residue. The fluorescence intensity ratio of DPP-Leu (I₅₄₈/I₆₅₁) showed a remarkable change in the presence of LAP, with a limit of detection of 0.011 U L^-1, and DPP-Leu was successfully applied to detect LAP in fetal bovine serum (FBS) and artificial urine. Cell imaging experiments revealed that DPP-Leu could target mitochondria and distinguish tumor cells with high LAP content from normal cells. Importantly, benefiting from the structural transformation of DPP-Leu to the photosensitizer 4 under LAP catalysis, the probe could kill tumor cells under light irradiation without damaging normal cells.

Nanomolar determination of nitrofurans in water via excited-state inter-ligand proton transfer

Qualification and quantification of trace organic contaminants necessitates development of highly efficient sensing system, where excited-state inter-ligand proton transfer (ESILPT) provides a feasible pathway to construct efficient chemo-sensors. Herein, a strategically synthesized lanthanide complex, Eu(DBM)₃(MeOH)₃ (briefly as Eu-DBM-MeOH; DBM = dibenzoylmethane), features two-step ESILPT processes, along with modification on molecular structure and energy band. As a result, Eu-DBM-MeOH exhibits excellent photophysical properties with characteristic luminescence of Eu³⁺ ion. Benefiting from these merits, the Eu-DBM-MeOH complex acts as ultra-sensitive chemo-sensor toward nanomolar-level nitrofuran antibiotics (nitrofurazone and nitrofurantoin) in water, by disrupting ESILPT processes. Combining the advantages on photophysical property and luminescent sensitivity, ESILPT-active compounds are expected to widen and deepen the research on complex-based luminophores, being potentially useful in trace detection and biological imaging.

A Convenient Synthesis of Diketopyrrolopyrrole Dyes

Diketopyrrolo[3,4-c]pyrroles (DPP) are high-performance organic optoelectronic materials. They have applications in solar cells, fluorescent probes, bioimaging, photodynamic/photothermal therapy, and in many other areas. This article reports a convenient two-step synthesis of various DPP dyes from Pigment Red 254, an inexpensive commercial pigment. The synthesis includes a Suzuki-Miyaura cross-coupling reaction of a bis(4-chlorophenyl)DPP derivative with aryl and hetaryl boronic acids under mild reaction conditions. The new dyes show large Stokes shifts and high fluorescence quantum yields, important features for their potential use in technical and biological applications.

Microbicidal effect of 405-nm blue LED light on Candida albicans and Streptococcus mutans dual-species biofilms on denture base resin

This study investigated: (1) the microbicidal effect of 405-nm blue LED light irradiation on biofilm formed by Candida albicans hyphae and Streptococcus mutans under dual-species condition on denture base resin, (2) the generation of intracellular reactive oxygen species (ROS) induced by irradiation, and (3) the existence of intracellular porphyrins, which act as a photosensitizer. Denture base resin specimens were prepared and C. albicans and S. mutans dual-species biofilms were allowed to form on the specimens. The biofilms were irradiated with 405-nm blue LED light and analyzed using the colony-forming unit assay, fluorescence microscopy, and scanning electron microscopy (SEM). Single-species biofilms of C. albicans and S. mutans formed on the specimens were irradiated with 405-nm blue LED light. After the irradiation, the intracellular ROS levels in C. albicans and S. mutans cells were measured. In addition, the level of intracellular porphyrins in C. albicans and S. mutans were measured. Irradiation for more than 30 min significantly inhibited the colony formation ability of C. albicans and S. mutans. Fluorescence microscopy revealed that almost all C. albicans and S. mutans cells were killed by irradiation. SEM images showed various cell damage patterns. Irradiation led to the generation of intracellular ROS and porphyrins were present in both C. albicans and S. mutans cells. In conclusion, irradiation with 405-nm blue light-emitting diode light for 40 min effectively disinfect C. albicans hyphae and S. mutans dual-species biofilms and possibly react with intracellular porphyrins resulting in generation of ROS in each microorganism.

Design, synthesis and evaluation of enzyme-responsive fluorogenic probes based on pyridine-flanked diketopyrrolopyrrole dyes

The ever-growing demand for fluorogenic dyes usable in the rapid construction of analyte-responsive fluorescent probes, has recently contributed to a revival of interest in the chemistry of diketopyrrolopyrrole (DPP) pigments. In this context, we have explored the potential of symmetrical and unsymmetrical DPP derivatives bearing two or one 4-pyridyl substituents acting as optically tunable group(s). The unique fluorogenic behavior of these molecules, closely linked to N-substitution/charge state of their pyridine unit (i.e., neutral pyridine or cationic pyridinium), has been used to design DPP-based fluorescent probes for detection of hypoxia-related redox enzymes and penicillin G acylase (PGA). In this paper, we describe synthesis, spectral characterization and bioanalytical validations of these probes. Dramatic differences in terms of aqueous stability and enzymatic fluorescence activation were observed. This systematic study enables to delineate the scope of application of pyridine-flanked DPP fluorophores in the field of enzyme biosensing.

Synthesis of fully asymmetric diketopyrrolopyrrole derivatives

Diaryl-diketopyrrolopyrroles (DPP) are a widely studied class of chromophore that possesses unique properties which have been of great interest for use in conjugated polymers and as small molecules in optoelectronic devices. While previously only partially asymmetric DPP derivatives have been reported, here a novel methodology towards fully asymmetric DPP derivatives is demonstrated via the synthesis and condensation of novel alkylated thienyl pyrrolinone esters with aromatic nitriles followed by N-alkylation. Two fully asymmetric DPP structural isomers T-DPP-P and P-DPP-T were synthesised demonstrating the full customizability of the DPP core. A further two fully asymmetric DPP derivatives incorporating an ethylene glycol chain and a furan moiety were also synthesised, demonstrating the scope of this powerful methodology and it's potential to largely broaden the library of available DPP derivatives.

A sensitive and rapid "off-on" fluorescent probe for the detection of esterase and its application in evaluating cell status and discrimination of living cells and dead cells

The discrimination of living and dead cells shows great importance in the development of biology, pathology, medicine, and pharmacology research. Herein, we synthesized a simple benzothiazole-based probe, EP, which was characterized via1H NMR (hydrogen nuclear magnetic resonance) spectroscopy, 13C NMR (carbon nuclear magnetic resonance) spectroscopy and HRMS (high-resolution mass spectroscopy). The fluorescence changes in response to esterase were characterized via fluorescence spectroscopy. EP exhibited a 70-fold fluorescence enhancement in the presence of esterase and possessed a very low limit of detection (4.73 × 10-5 U mL-1). EP also showed high selectivity to esterase compared to other biological species. Bright fluorescence appeared in living cells, which was activated by esterase when incubated with EP. In paraformaldehyde or H2O2 pretreated cells, the fluorescence became very weak since esterase became inactive in these cells. In summary, the EP probe can monitor esterase activity both in vitro and in living cells and can be used to evaluate the health status of cells and discriminate living and dead cells effectively.

Multifunctional Near-Infrared Fluorescent Probes with Different Ring-Structure Trigger Groups for Cell Health Monitoring and In Vivo Esterase Activity Detection

A series of multifunctional ratiometric near-infrared fluorescent probes (CYOH-3, CYOH-4, CYOH-5, and CYOH-6) for esterase detection are designed by gradually changing the deflection of the plane twist in the molecule. These probes are composed of different ring-structure trigger groups (from three-membered ring to six-membered ring) and the same luminescent group CYOH. These probes show maximum absorption at ∼585 nm and a fluorescence emission peak at ∼655 ± 5 nm. In the presence of esterase, the probes were hydrolyzed to expose the fluorophore CYOH (λ_abs = 690 nm, λ_em = 710 ± 5 nm), thus exhibiting ratiometric near-infrared fluorescence. The probe CYOH-6 has lower plane deflection angle and better ratiometric (R = I_710±5nm/I_657±4nm) fluorescence properties than probes CYOH-3, CYOH-4, and CYOH-5. CYOH-6 (six-membered ring) has been successfully used to target esterase in mitochondria and distinguish between dead cells (esterase inactivation) and live cells. In addition, CYOH-6 has been well used for monitoring of esterase activity in zebrafish and mice, which proves that these probes have good prospects for clinical biomedical applications.

An ESIPT-based ratiometric fluorescent probe for the discrimination of live and dead cells

Cell death can destroy homeostasis and is a hallmark of many pathological conditions. Discrimination of live and dead cells is a crucial task for the biological, medical and pharmaceutical studies. Herein, we constructed an ESIPT-based fluorescent probe (BTE) on the basis of the different esterase activity in live and dead cells. Under excitation, the probe BTE showed the blue emission peaked at 465 nm, while it mainly displayed green emission peaked at 543 nm after it was hydrolyzed by esterase. Imaging of the cells treated by H₂O₂ and ultraviolet (UV) radiation demonstrated that the probe BTE is effective in the detection of the health of cells, could help us to better understand cell death and its effects in a range of diseases and treatments.

Establishment of a Customizable Fluorescent Probe Platform for the Organelle-Targeted Bioactive Species Detection

A customizable fluorescent probe platform that can be used to detect various bioactive analytes offers significant potential for engineering a wide range of bioprobes with diverse sensing and imaging functions. Here, we show a facile and innovative strategy for introducing cis-amino-proline as a carrier scaffold, which is appended with three specific functional groups: a target group, a water-soluble group, and fluorophores with triggers. The potency of the designed strategy could be customized to generate variable multifunctional fluorescent probes for detecting bioactive species of interest, including reactive oxygen species (ROS), reactive nitrogen species (RNS), reactive sulfur species (RSS), ROS/RSS, and even enzymes. We designed and synthesized five representative water-soluble and organelle-targeted compounds, PMB, PMN, PMD, PRB, and PME, with emission wavelengths of these fluorescent probes varying from blue to red (465, 480, 535, 550, 565, and 640 nm). This strategy could be exemplified by its application to develop a mitochondria-/lysosome-targeting multifunctional fluorescent probe capable of imaging bioactive species of interest in live cells and nude mice.

Porphyrin–diketopyrrolopyrrole conjugates and related structures: Synthesis, properties and applications

A large diversity of porphyrin–diketopyrrolopyrrole conjugates and related structures formed by diketopyrrolopyrrole units and pyrrole-based moieties such as phthalocyanine, porphycene, calix[4]pyrrole or BODIPY have been reported since 2010. The new compounds, whether small molecules or polymeric materials, exhibit very interesting photophysical properties and have been tested in a range of technical or biological applications. This review summarizes the advances in the synthesis of such compounds. Their photophysical properties and potential applications are also briefly discussed.

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

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

Biosensors for epigenetic biomarkers detection: A review

Epigenetic inheritance is a heritable change in gene function independent of alterations in nucleotide sequence. It regulates the normal cellular activities of the organisms by affecting gene expression and transcription, and its abnormal expression may lead to the developmental disorder, senile dementia, and carcinogenesis progression. Thus, epigenetic inheritance is recognized as an important biomarker, and the accurate quantification of epigenetic inheritance is crucial to clinical diagnosis, drug development and cancer treatment. Noncoding RNA, DNA methylation and histone modification are the most common epigenetic biomarkers. The conventional biosensors (e.g., northern blotting, radiometric, mass spectrometry and immunosorbent biosensors) for epigenetic biomarkers assay usually suffer from hazardous radiation, complicated manipulation, and time-consuming procedures. To facilitate the practical applications, some new biosensors including colorimetric, luminescent, Raman scattering spectroscopy, electrochemical and fluorescent biosensors have been developed for the detection of epigenetic biomarkers with simplicity, rapidity, high throughput and high sensitivity. In this review, we summarize the recent advances in epigenetic biomarkers assay. We classify the biosensors into the direct amplification-free and the nucleotide amplification-assisted ones, and describe the principles of various biosensors, and further compare their performance for epigenetic biomarkers detection. Moreover, we discuss the emerging trends and challenges in the future development of epigenetic biomarkers biosensors.

Fluorescent Probes for the Visualization of Cell Viability

Monitoring cell viability is a crucial task essential for the fundamental studies in apoptosis, necrosis, and drug discovery. Cell apoptosis and necrosis are significant to maintain the cell population, and their abnormality can lead to severe diseases including cancer. During cell death, significant changes occur in the intracellular contents and physical properties, such as decrease of esterase activity, depolarization of the mitochondrial membrane potential (ΔΨ_m), increase of caspase content, dissipation of membrane asymmetry, and loss of membrane integrity. To detect cell viability, the fluorescent probes have been developed by taking advantage of these biological parameters and using various fluorescence mechanisms. These fluorescent probes can serve as powerful tools to facilitate the research in biology and pathology. In this Account, the representative examples of the fluorescent probes for cell viability during the past decades have been summarized and classified into five types based on the biological changes. The basic principle, design strategy, fluorescence mechanisms, and molecular construction of these fluorescent probes have been discussed. Furthermore, the intrinsic characteristics and merits of these probes have been illustrated. Particularly, this Account describes our recent works for the design and synthesis of the fluorescent probes to detect cell viability in the dual-color and reversible modes. The dual-color and reversible fluorescent probes are highlighted owing to their unique benefits in accurate and dynamic detection of cell viability. In general, the dual-color fluorescent probes were constructed based on the loss of esterase activity during cell death. Excited-state intramolecular proton transfer (ESIPT) and intramolecular charge transfer (ICT) process were exploited for the probe design. The construction of such dual-color probes were realized by the acetate of the phenyl group on fluorophores. Esterases in healthy cells hydrolyze the acetate and bring a spectral shift to the probes. Moreover, reversible fluorescent probes for cell viability were designed based on the depolarization of ΔΨ_m, with relocalization properties dependent on ΔΨ_m. The probes target mitochondria in healthy cells with high ΔΨ_m, while they are relocalized into the nucleus in unhealthy cells with depolarized ΔΨ_m. As ΔΨ_m is reversibly changed according to the cell viability, these probes reversibly detect cell viability. The reversible and simultaneously dual-color fluorescent probes were developed based on the relocalization mode and aggregation-induced emission shift. The probes target mitochondria to form aggregates with deep-red emission, while they migrate into the nucleus to present in monomers with green fluorescence. In this manner, the probes enable dual-color and reversible detection of cell viability. Fluorescent probes for cell viability based on sensing the membrane integrity, caspase activity, and membrane symmetry are also presented. High-polarity and large-size fluorescent probes impermeable to the intact lipid bilayer selectively target apoptotic cells with a destructive plasma membrane. Fluorescent probes sensing caspases in a turn-on manner exclusively light up apoptotic cells with caspase expression. Membrane-impermeable probes with high affinity to phosphatidylserine (PS) specifically stain the plasma membrane of dead cells, since PS flip-flops to the outer leaflet of the membrane during cell death. In summary, this Account illustrates the basic principles, design strategies, characteristics, and advantages of the fluorescent probes for cell viability, and it highlights the dual-color and reversible probes, which can promote the development of fluorescent probes, apoptosis studies, drug discovery, and other relative areas.

A Nucleus-Targeting DNA Aptamer for Dead Cell Indication

Dead cells always accompany with live cells in vivo and in cell culture. It is important to distinguish dead cells from live cells in various biological studies. Currently, the probes for dead cells are mainly nucleic acid-intercalators, most of which have low affinity and potential toxicity to live cells. In this work, we report a novel aptameric probe (Ch4-1) for the first time, which binds cell nuclei with high affinity (apparent K_d = 6.65 ± 3.40 nM). Ch4-1 was generated by Cell-SELEX process, it was identified to target nucleoproteins in cell nuclei. As an oligonucleotide, Ch4-1 cannot penetrate the integrated cell membrane; therefore, it only binds to dead cells rather than live cells. Compared with traditional DNA-targeting nuclear dyes, Ch4-1 possesses a high affinity to the nucleus, no toxicity to live cells, and can be easily labeled with different fluorescent dyes. It was demonstrated to serve as a probe for distinguishing dead cells from live cells in apoptosis assay, as well as for the nuclear staining of tissue sections.

Significant improvement of photocatalytic hydrogen evolution of diketopyrrolopyrrole-based donor–acceptor conjugated polymers through side-chain engineering

The hydrogen evolution rate of PDPP3B-O4 with butoxy chain was 5.53 mmol h⁻¹ g⁻¹ with 1% Pt loading (λ > 400 nm), increased 110 times than PDPP3B-C8 with octyl chain due to wider absorption spectrum and better wettability via side chain engineering.

A coumarin chalcone ratiometric fluorescent probe for hydrazine based on deprotection, addition and subsequent cyclization mechanism

A coumarin chalcone derivative with a levulinic acid terminal group acts as a ratiometric fluorescent probe for hydrazine based on deprotection, addition and a subsequent cyclization reaction mechanism.