Highly sensitive cell imaging "Off-On" fluorescent probe for mitochondria and ATP

Integrating commercial personal glucose meter with peroxidase-mimic DNAzyme to develop a versatile point-of-care biosensing platform

The development of point-of-care testing (POCT) methods is highly desirable in molecular detection, as they enable disease diagnosis and biomarker monitoring on-site or at home. Repurposing existing POCT devices to detect diverse biomarkers is an economical way to develop new devices for POCT use. Personal glucose meter (PGM) is one of the most used off-the-shelf POCT devices that has been reused to detect non-glucose targets. However, developing a label-free, user-friendly, and cost-effective general PGM-based sensing platform remains a great challenge, primarily due to the reliance on protein enzymes in most existing signal transducing strategies. To overcome the challenges, we herein developed a DNAzyme-based signal transduction strategy that bridges non-glucose signals to PGM readouts. By integrating this strategy with CRISPR/Cas12a-mediated target sensing, we successfully established a simple and versatile platform (CaG-PGM) for biosensing. The utility of CaG-PGM in the detection of nucleic acid targets was successfully validated by detecting Monkeypox virus DNA and SARS-CoV-2 RNA with high sensitivity and specificity. We further demonstrated its generality in detecting non-nucleic acid targets including protein and small molecule. In conclusion, this study provides a cheap and effective strategy for repurposing PGM as a general biosensing platform and sheds new light on translating functional nucleic acids for POCT applications.

Boron-Salphen Conjugate based Molecular Probe Exhibiting Fluorescence On-Off-On Response in Detection of Cu2+ and ATP through Displacement Approach

Synthesis and photophysical properties of a fluorescent probe HBD is described. Probe upon interaction with metal ions, anions and nucleoside pyrophosphates (NPPs) showed fluorescence quenching with Cu2+ due to chelation enhanced quenching effect (CHEQ). Moreover, interaction of ensemble HBD.Cu2+ with anions and NPPs showed fluorescence "turn-On" response with ATP selectively. "On-Off-On" responses observed with Cu2+ and ATP is attributed to an interplay between ESIPT and TICT processes. Cyclic voltammogram of probe exhibited quasi-reversible redox behaviour with three oxidation and two reduction potentials and the change in band gaps of probe suggested the interaction with Cu2+ and ATP. The 2 : 1 and 1 : 1 binding stoichiometry for an interaction between probe and Cu2+ (LOD, 62 nM) and ensemble, HBD.Cu2+ with ATP (LOD, 0.4 μM) respectively are realised by Job's plot and HRMS data. Cell imaging studies carried out to detect Cu2+ and ATP in HeLa cells. Also, the output emission observed with Cu2+ and ATP is utilized to construct an implication (IMP) logic gate. Test paper strips showed naked-eye visible color responses to detect Cu2+ and ATP. In real water samples probe successfully detected copper (0.03 μM) between 5-6.5 ppb level (ICP-MS method).

Highly-ordered assembled organic fluorescent materials for high-resolution bio-sensing: a review

Organic fluorescent materials (OFMs) play a crucial role in the development of biosensors, enabling the extraction of biochemical information within cells and organisms, extending to the human body. Concurrently, OFM biosensors contribute significantly to the progress of modern medical and biological research. However, the practical applications of OFM biosensors face challenges, including issues related to low resolution, dispersivity, and stability. To overcome these challenges, scientists have introduced interactive elements to enhance the order of OFMs. Highly-ordered assembled OFMs represent a novel material type applied to biosensors. In comparison to conventional fluorescent materials, highly-ordered assembled OFMs typically exhibit robust anti-diffusion properties, high imaging contrast, and excellent stability. This approach has emerged as a promising method for effectively tracking bio-signals, particularly in the non-invasive monitoring of chronic diseases. This review introduces several highly-ordered assembled OFMs used in biosensors and also discusses various interactions that are responsible for their assembly, such as hydrogen bonding, π-π interaction, dipole-dipole interaction, and ion electrostatic interaction. Furthermore, it delves into the various applications of these biosensors while addressing the drawbacks that currently limit their commercial application. This review aims to provide a theoretical foundation for designing high-performance, highly-ordered assembled OFM biosensors suitable for practical applications. Additionally, it sheds light on the evolving trends in OFM biosensors and their application fields, offering valuable insights into the future of this dynamic research area.

Macrocyclic Conformational Switch Coupled with Pyridinium-Induced PET for Fluorescence Detection of Adenosine Triphosphate

The binding of nucleotides is crucial for signal transduction as it induces conformational protein changes, leading to downstream cellular responses. Synthetic receptors that bind nucleotides and transduce the binding event into global conformational rearrangements are highly challenging to design, especially those that operate in an aqueous solution. Much work is focused on evaluating functionalized dyes to detect nucleotides, whereas coupling of a nucleotide-induced conformational switching to a sensing event has not been reported to date. We disclose synthetic receptors that undergo a global conformational rearrangement upon nucleotide binding. Integrating naphthalimide and the pyridinium ion into the structure enables stabilization of the folded conformation and efficient fluorescence quenching. The binding of a nucleotide rearranges the receptor conformation and alters the strong fluorescence enhancement. The methylpyridinium-containing receptor demonstrated high sensing selectivity for adenosine 5'-triphosphate (ATP) and a record 160-fold fluorescence enhancement. It can detect fluctuations of ATP in HeLa cells and possesses low cytotoxicity. The developed systems present an attractive approach for designing ATP-responsive artificial molecular switches that operate in water and integrate a strong fluorescence response.

Improving the Sensitivity of a Mn(II)-Specific DNAzyme for Cellular Imaging Sensor through Sequence Mutations

Detection of Mn2+ in living cells is important in understanding the roles of Mn2+ in cellular processes and investigating its potential implications in various diseases and disorders. Toward this goal, we have previously selected a Mn2+-specific 11-5 DNAzyme through an in vitro selection method and converted it into a fluorescence sensor for intracellular Mn2+ sensing. Despite the progress, the nucleotides responsible for the activity are unclear, and the performance of the DNAzyme needs to be improved in order for more effective applications in biological systems. To address these issues, we herein report site-specific mutations within the catalytic domain of the selected 11-5 DNAzyme. As a result, we successfully identified a variant DNAzyme, designated as Mn5V, which exhibited a twofold increase in activity compared to the original 11-5 DNAzyme. Importantly, Mn5V DNAzyme maintained its high selectivity for Mn2+ over other competing metal ions. Upon the addition of Mn2+, Mn5V DNAzyme exhibited a higher fluorescence signal within the tumor cells compared to that of the 11-5 DNAzyme. This study therefore provides a better understanding of how the DNAzyme functions and a more sensitive probe for investigating Mn2+ in biological systems.

Detection of Biomarker Using Aptasensors to Determine the Type of Diabetes

Diabetes mellitus (DM) is a metabolic disorder characterized by elevated blood glucose levels. This disease is so serious that many experts refer to it as the "silent killer". The early detection of diabetes mellitus, whether type 1, type 2 or mitochondrial, is crucial because it can improve the success of treatment and the quality of life for patients. Aptamer-based biosensor diagnosis methods have been widely developed because they have high sensitivity and selectivity in detecting biomarkers of various diseases. Aptamers are short sequences of oligonucleotides or proteins that recognize specific ligands and bind to various target molecules, ranging from small ions to large proteins. They are promising diagnostic molecules due to their high sensitivity and selectivity, ease of modification, low toxicity, and high stability. This article aims to summarize the progress of detection methods, including detection principles, sensitivity, selectivity, and the performance of detection devices, to distinguish between types of diabetes mellitus using electrochemical aptasensors with biomarkers such as glucose, insulin, HbA1c, GHSA, and ATP.

Supramolecular Recognition of Cytidine Phosphate in Nucleotides and RNA Sequences

Supramolecular recognition of nucleotides would enable manipulating crucial biochemical pathways like transcription and translation directly and with high precision. Therefore, it offers great promise in medicinal applications, not least in treating cancer or viral infections. This work presents a universal supramolecular approach to target nucleoside phosphates in nucleotides and RNA. The artificial active site in new receptors simultaneously realizes several binding and sensing mechanisms: encapsulation of a nucleobase via dispersion and hydrogen bonding interactions, recognition of the phosphate residue, and a self-reporting feature-"turn-on" fluorescence. Key to the high selectivity is the conscious separation of phosphate- and nucleobase-binding sites by introducing specific spacers in the receptor structure. We have tuned the spacers to achieve high binding affinity and selectivity for cytidine 5' triphosphate coupled to a record 60-fold fluorescence enhancement. The resulting structures are also the first functional models of poly(rC)-binding protein coordinating specifically to C-rich RNA oligomers, e.g., the 5'-AUCCC(C/U) sequence present in poliovirus type 1 and the human transcriptome. The receptors bind to RNA in human ovarian cells A2780, causing strong cytotoxicity at 800 nM. The performance, self-reporting property, and tunability of our approach open up a promising and unique avenue for sequence-specific RNA binding in cells by using low-molecular-weight artificial receptors.

Conjugated structures based on quinazolinones and their application in fluorescent labeling

As an alkaloid, quinazolinone exhibits excellent biological properties; structurally, it also has the potential to construct fluorescent probes with conjugated structures. In this work, probes 5a-c and 6b were obtained by introducing quinazolone into aldehydes with different numbers of double bonds. Their absorption maxima were located at 420-540 nm and their emission maxima were at 500-600 nm in solvents of different polarities. In particular, probe 5c showed significant fluorescence enhancement with the increase in viscosity due to the limited intramolecular rotation, and its fluorescence intensity in glycerol was 37.8 times higher than that in water. Moreover, probes 5a-c and 6b containing the NH structure showed sensitive response to pH, and their fluorescence intensity in alkaline solution (pH 9-11) was suddenly enhanced, which was elucidated with the help of theoretical calculation. In addition, the cell experiments showed that probes 5a and 5b had the ability to target mitochondria and probes 5c and 6b targeted lysosomes in HeLa cells. Furthermore, the viscosity-sensitive probe 5c could be used for monitoring changes in lysosomal viscosity in HeLa cells, which had important guiding significance for designing multi-response fluorogenic probes and promoting the advancement of cancer diagnosis.

Near-infrared fluorescent probes based on a quinoxaline skeleton for imaging nucleic acids in mitochondria

In this paper, two cationic probes 1a and 1b and a neutral dye 1c were successfully designed and synthesized according to the Knoevenagel condensation reaction, which combines the good optical properties of hemocyanine and the biocompatibility of nitrogen-containing heterocyclic rings based on a quinoxaline skeleton. Probes 1a and 1b showed an OFF-ON fluorescence response to nucleic acids with excellent selectivity. Specifically, the fluorescence intensity of probe 1a was enhanced by 18 and 133 times, respectively, along with the increase of DNA or RNA concentrations (0-600 μg mL^-1). Furthermore, a good linear correlation between the fluorescence intensity of probes 1a and 1b and the concentrations of DNA or RNA (0-350 μg mL^-1) was obtained. In particular, the maximum emission wavelengths of probes 1a and 1b reached the near-infrared region (660-664 nm) when DNA or RNA was detected, which might reduce the light damage to cells and facilitate cell experiments. Fluorescence imaging revealed that all three dyes could be localized in the mitochondria of HeLa cells. The difference was that probes 1a and 1b could stain the nucleic acid in the mitochondria, while dye 1c was only a neutral mitochondrial biomarker. The results indicated that probes 1a and 1b are promising in the development of low toxicity mitochondrial nucleic acid probes and are expected to be used in monitoring the normal state of mitochondrial nucleic acids for living cells, which will help improve the situation in that currently reported studies of fluorescent probes are mainly focused on the nucleic acids in the nucleus, but less so on DNA in the mitochondria.

A double-decker cage for allosteric encapsulation of ATP

In this work, we describe the preparation of double-decker cage [1-H₆]⁶⁺ comprising two binding pockets, each with three ammonium and three amide hydrogen bonding sites. This novel host possesses a high affinity for trapping two molecules of ATP in an allosteric fashion, with both experiments and theory suggesting the synergistic action of charged hydrogen bonds and π-π stacking in the encapsulation.

Intracellular biosensor-based dynamic regulation to manipulate gene expression at the spatiotemporal level

The use of intracellular, biosensor-based dynamic regulation strategies to regulate and improve the production of useful compounds have progressed significantly over previous decades. By employing such an approach, it is possible to simultaneously realize high productivity and optimum growth states. However, industrial fermentation conditions contain a mixture of high- and low-performance non-genetic variants, as well as young and aged cells at all growth phases. Such significant individual variations would hinder the precise controlling of metabolic flux at the single-cell level to achieve high productivity at the macroscopic population level. Intracellular biosensors, as the regulatory centers of metabolic networks, can real-time sense intra- and extracellular conditions and, thus, could be synthetically adapted to balance the biomass formation and overproduction of compounds by individual cells. Herein, we highlight advances in the designing and engineering approaches to intracellular biosensors. Then, the spatiotemporal properties of biosensors associated with the distribution of inducers are compared. Also discussed is the use of such biosensors to dynamically control the cellular metabolic flux. Such biosensors could achieve single-cell regulation or collective regulation goals, depending on whether or not the inducer distribution is only intracellular.

Optical/electrochemical methods for detecting mitochondrial energy metabolism

This review highlights the biological importance of mitochondrial energy metabolism and the applications of multiple optical/electrochemical approaches to determine energy metabolites. Mitochondria, the main sites of oxidative phosphorylation and adenosine triphosphate (ATP) biosynthesis, provide the majority of energy required by aerobic cells for maintaining their physiological activity. They also participate in cell growth, differentiation, information transmission, and apoptosis. Multiple mitochondrial diseases, caused by internal or external factors, including oxidative stress, intense fluctuations of the ionic concentration, abnormal oxidative phosphorylation, changes in electron transport chain complex enzymes and mutations in mitochondrial DNA, can occur during mitochondrial energy metabolism. Therefore, developing accurate, sensitive, and specific methods for the in vivo and in vitro detection of mitochondrial energy metabolites is of great importance. In this review, we summarise the mitochondrial structure, functions, and crucial energy metabolic signalling pathways. The mechanism and applications of different optical/electrochemical methods are thoroughly reviewed. Finally, future research directions and challenges are proposed.

Visual Detection of Adenosine Triphosphate by Taylor Rising: A Simple Point-of-Care Testing Method Based on Rolling Circle Amplification

Rapid and sensitive point-of-care testing (POCT) is an extremely critical mission in practical applications, especially for rigorous military medicine, home health care, and in the third world. Here, we report a visual POCT method for adenosine triphosphate (ATP) detection based on Taylor rising in the corner of quadratic geometries between two rod surfaces. We discuss the principle of Taylor rising, demonstrating that it is significantly influenced by contact angle, surface tension, and density of the sample, which are controlled by ATP-dependent rolling circle amplification (RCA). In the presence of ATP, RCA reaction effectively suppresses Taylor-rising behavior, due to the increased contact angle, density, and decreased surface tension. Without addition of ATP, untriggered RCA reaction is favorable for Taylor rising, resulting in a significant height. With this proposed method, visual sensitive detection of ATP without the aid of other instruments is realized with only a 5 μL droplet, which has good selectivity and a low detection limit (17 nM). Importantly, this visual method provides a promising POCT tool for user-friendly molecular diagnostics.

Recent progress in developing fluorescent probes for imaging cell metabolites

Cellular metabolites play a crucial role in promoting and regulating cellular activities, but it has been difficult to monitor these cellular metabolites in living cells and in real time. Over the past decades, iterative development and improvements of fluorescent probes have been made, resulting in the effective monitoring of metabolites. In this review, we highlight recent progress in the use of fluorescent probes for tracking some key metabolites, such as adenosine triphosphate, cyclic adenosine monophosphate, cyclic guanosine 5'-monophosphate, Nicotinamide adenine dinucleotide (NADH), reactive oxygen species, sugar, carbon monoxide, and nitric oxide for both whole cell and subcellular imaging.

AIEgen-based nanoprobe for the ATP sensing and imaging in cancer cells and embryonic stem cells

A turn-on fluorescent nanoprobe (named AAP-1), based on an aggregation-induced emission luminogen (AIEgen), is disclosed for the detection of adenosine triphosphate (ATP), which is an essential element in the biological system. Organic fluorophore (named TPE-TA) consists of tetraphenylethylene (TPE, sensing and signaling moiety) and mono-triamine (TA, sensing moiety), and it forms an aggregated form in aqueous media as a nanoprobe AAP-1. The nanoprobe AAP-1 has multiple electrostatic interactions as well as hydrophobic interactions with ATP, and it displays superior selectivity toward ATP, reliable sensitivity, with a detection limit around 0.275 ppb, and fast responsive (signal within 10 s). Such a fluorescent probe to monitor ATP has been actively pursued throughout fundamental and translational research areas. In vitro assay and a successful cellular ATP imaging application was demonstrated in cancer cells and embryonic stem cells. We expect that our work warrants further ATP-related studies throughout a variety of fields.

MOF@COFs with Strong Multiemission for Differentiation and Ratiometric Fluorescence Detection

Aggregation-caused quenching (ACQ) is often observed in covalent organic frameworks (COFs) for their low emission. Here, we propose that limited COF layers form on UiO-66 to eliminate the ACQ by the formation of UiO@COF composites. UiO-66 is selected because this metal-organic framework (MOF) is easily prepared in nanosize with Zr⁴⁺ ion and 2-aminoterephthalic acid (BDC-NH₂). The high affinity of the Zr⁴⁺ ion to phosphate species improves sensing selectivity. The surface -NH₂ reacts with 2,4,6-triformylphloroglucinol (Tp) to integrate COF1 and COF2, which are prepared with Tp and phenylenediamine or tetraamino-tetraphenylethylene, respectively. The hydrogen bond formed between the hydroxyl group in Tp and imine nitrogen realizes excited-state intramolecular proton transfer; therefore, multiemission is observed from the enol and keto states of the COFs and UiO-66 at 360, 470, and 613 nm for UiO@COF1 and at 370, 470, and 572 nm for UiO@COF2. When phosphate ion is added in the composites, the emissions from the COFs keep stable, while that from UiO-66 is enhanced. However, adenosine-5'-triphosphate (ATP) improves the emissions from UiO-66 and COF's enol state, but that from the keto state keeps stable. The differentiation and ratiometric fluorescence detection of ATP and phosphate ion are therefore realized with the multiemission, the affinity of Zr⁴⁺ ions, and the structural selectivity of the COFs. Thus, UiO@COF is a novel strategy to integrate multiemission, affinity, and structural selectivity to improve the sensing performance for differentiation and ratiometric detection.

Adenine-based small molecule fluorescent probe for imaging mitochondrial nucleic acid

A small molecule fluorescent probe (probe 1) based on adenine-coumarin derivative was designed and synthesized in this paper. Probe 1 exhibited a significant fluorescence-enhancing response to nucleic acids at 495 nm (for DNA) and 487 nm (for RNA). The fluorescence enhancement of probe 1 for DNA and RNA was 5.68 and 9.73 times respectively, the fluorescence quantum yield was changed from 2.5% to 11.7% and 22.5% accordingly. Meanwhile, an excellent linear relationship of fluorescence intensity at 495 nm or 487 nm versus the nucleic acid concentration (1 μM for probe 1, 0-350 μg/mL for DNA and 0-300 μg/mL for RNA) was obtained. Co-staining and nucleic acid digestion experiments showed that probe 1 could selectively image nucleic acids in mitochondria and nucleoli in HeLa cells.

Multifunctional Single-Layered Graphene Quantum Dots Used for Diagnosis of Mitochondrial Malfunction-Related Diseases

Mitochondria are critical organelles in eukaryotes that efficiently generate adenosine 5'-triphosphate (ATP) for various biological activities, and any defect in the process of ATP synthesis may lead to mitochondrial dysfunction and directly link to a variety of medical disorders. Monitoring the ATP variations in cells is key for innovative early diagnosis of mitochondrial diseases. Herein, multifunctional single-layered graphene quantum dots (s-GQDs) with bright green emission were constructed, which exhibit strong binding affinity for ATP and good mitochondria targeting ability. Using the proposed s-GQDs, we successfully discriminated the primary smooth muscle cells isolated from the transgenic mouse (heterozygote sarco/endoplasmic reticulum Ca²⁺ ATPase (SERCA) 2 C674S knock-in mouse) with mitochondrial disorders or their littermate controls, indicating s-GQDs as promising probes for the study of cell metabolism and mitochondrial malfunction-related diseases, and targeting endoplasmic reticulum stress is an effective way to modulate metabolic pathways relevant to SERCA 2 inactivity mitochondrial dysfunction.

A label-free hairpin aptamer probe for colorimetric detection of adenosine triphosphate based on the anti-aggregation of gold nanoparticles

A facile and rapid colorimetric approach was described for selective and sensitive determination of adenosine triphosphate (ATP) based on a hairpin aptamer probe and the anti-aggregation of AuNPs. Poly(diallyldimethylammonium chloride) (PDDA) can induce the aggregation of AuNPs due to the electrostatic interaction causing a red to blue color change. Upon the addition of ATP, aptamer-based hairpin probe is opened and releases flexible ssDNA ends. The released flexible ssDNA ends can interact with PDDA and prevent PDDA-induced AuNPs aggregation. Thus, a visible color change from blue to red and a decrease in the absorption ratio (A₆₁₀/A₅₂₀) are observed. Under the optimal conditions, the hairpin aptamer-based colorimetric assay exhibits high sensibility and selectivity for the detection of ATP with a detection limit of 1.7nM. Moreover, this assay is successfully used in the rapid determination of ATP in spiked human serum samples with good recoveries in the range of 102.88 to 104.07%.

Molecular Receptors for Recognition and Sensing of Nucleotides

Nucleotides are constituents of nucleic acids and they have a variety of functions in cellular metabolism. Synthetic receptors and sensors are required to reveal the role of nucleotides in living organisms and mechanisms of signal transduction events. In recent years, a large number of nucleotide-selective synthetic receptors have been devised, which utilize different molecular designs and sensing mechanisms. This Minireview presents recent progress in the design of synthetic molecular receptors for selective recognition of nucleotides in aqueous solution. The binding properties of receptors and the origins of their selectivity for a particular nucleotide are discussed.

A mitochondria-targeted fluorescent probe for imaging endogenous malondialdehyde in HeLa cells and onion tissues

The mitochondria-targeted turn-on fluorescent probe (Mito-FMP) based on a benzoxadiazole platform was developed for detection of malondialdehyde (MDA). Mito-FMP performed with large enhancement of the optical signal (774-fold) in response to MDA in an aqueous system and has the capability of monitoring endogenous MDA in HeLa cells and onion tissues.

Biological perspectives of a FRET based pH-probe exhibiting molecular logic gate operation with altering pH

A FRET probe for applications in pH sensing, CT-DNA/BSA interactions and logic gate/circuit construction with H⁺/OH⁻ions.

Target-triggered transcription machinery for ultra-selective and sensitive fluorescence detection of nucleoside triphosphates in one minute

Nucleoside triphosphates (NTPs) play important roles in living organisms. However, no fluorescent assays are currently available to simply and rapidly detect multiple NTPs with satisfactory selectivity, sensitivity and low cost. Here we demonstrate for the first time a target-triggered in-vitro transcription machinery for ultra-selective, sensitive and instant fluorescence detection of multiple NTPs. The machinery assembles RNA polymerase, DNA template and non-target NTPs to convert the target NTP into equivalent RNA signal sequences which are monitored by the fluorescence enhancement of molecular beacon. The machinery offers excellent selectivity for the target NTP against NDP, NMP and dNTP. Notably, to accelerate the kinetics of the machinery while maintain its high specificity, we investigated the sequence of DNA templates systematically and established a set of guidelines for the design of the optimum DNA templates, which allowed for instant detection of the target NTP at fmol level in less than 1min. Furthermore, the machinery could be transformed into logic gates to study the coeffects of two NTPs in biosynthesis and real-time monitoring systems to reflect the distribution of NTP in nucleotide pools. These results provide very useful and low-cost tools for both biochemical tests and point-of-care analysis.

Water-Soluble Conjugated Polymer as a Fluorescent Probe for Monitoring Adenosine Triphosphate Level Fluctuation in Cell Membranes during Cell Apoptosis and in Vivo

Adenosine triphosphate (ATP) is used as the energy source in cells and plays crucial roles in various cellular events. The cellular membrane is the protective barrier for the cytoplasm of living cells and involved in many essential biological processes. Many fluorescent probes for ATP have been successfully developed, but few of these probes were appropriate for visualizing ATP level fluctuation in cell membranes during the apoptotic cell death process. Herein, we report the synthesis of a new water-soluble cationic polythiophene derivative that can be utilized as a fluorescent sensor for detecting ATP in cell membranes. Poly((3-((4-methylthiophen-3-yl)oxy)propyl)triphenylphosphonium chloride) (PMTPP) exhibits high sensitivity and good selectivity to ATP, and the detection limit is 27 nM. The polymer shows low toxicity to live cells and excellent photostability in cell membranes. PMTPP was practically utilized for real-time monitoring of ATP levels in the cell membrane through fluorescence microscopy. We have demonstrated that the ATP levels in cell membranes increased during the apoptotic cell death process. The probe was also capable of imaging ATP levels in living mice.

A Toolbox of Chromones and Quinolones for Measuring a Wide Range of ATP Concentrations

A series of 26 3-hydroxychromones, three bis-flavonols and four 3-hydroxyquinolones were studied to evaluate their fluorescence response to interaction with ATP in buffer. The dyes differ by the total charge, the size and number of their aromatic units, as well as the position or electron-donating ability of their substituents. All of them were suggested to form complexes with ATP of 1:1 and 1:2 stoichiometry, which can be evidenced by their bright fluorescence and their 3000-6000 cm^-1 red-shifted excitation band. These fluorescent complexes allow detection of ATP concentrations over 3 orders of magnitude, whereas most other known probes cover no more than two orders. In total, the dyes allow ATP detection from 0.001 to 57 mm. In addition, most of the dye-ATP complexes can be excited in the visible and monitored in the red region of the spectrum. The response amplitude of the described dyes to ATP is as high as for the best known probes. Considering that complexation takes place at neutral pH, the studied dyes form a toolbox of fluorescent probes for intensiometric and ratiometric measurements of ATP concentration in a broad concentration range. Finally, the obtained results stimulate the idea that most of natural 3-hydroxyflavones in living cells may form complexes with ATP.

A self-assembled amphiphilic imidazolium-based ATP probe

A novel amphiphilic imidazolium-based probe containing a dansyl fluorophore and a long cetyl chain has been developed for ATP recognition. The probe forms self-assembled micelle-like aggregates at low concentration in its aqueous solution and can selectively recognize ATP among other bioactive anions with a significant enhancement in fluorescence emission.

Real-Time Monitoring ATP in Mitochondrion of Living Cells: A Specific Fluorescent Probe for ATP by Dual Recognition Sites

Adenosine triphosphate (ATP) is mainly produced in the mitochondrion and used as a universal energy source for various cellular events. Various fluorescent probes for ATP have been established successfully, but most of them are not appropriate for monitoring the fluctuation of the mitochondrial ATP level. Herein, a fluorescent probe named Mito-Rh is first synthesized and used to recognize ATP in mitochondrion. In the probe, rhodamine, diethylenetriamine, and triphenylphosphonium are selected as fluorophore, reaction site, and mitochondrion-targeting group, respectively. Probe Mito-Rh shows high sensitivity to ATP with 81-fold fluorescence enhancement, and the detection range (0.1-10 mM) can match the concentration level of ATP in the mitochondrion. Moreover, Mito-Rh provides excellent selectivity toward ATP over other biological anions (ADP, AMP, GTP, CTP, UTP) owing to a concurrent effect of dual recognition sites (hydrogen bond and π-π stacking). In particular, the probe can localize in mitochondrion specifically and demonstrates utility in the real-time detection of mitochondrial ATP concentration changes.

Study of Fluorescent Imaging of Se (IV) in Living Cells Using a Turn-on Fluorescent Probe Based on a Rhodamine Spirolactame Derivative

A highly selective fluorescent probe 2-(2-(2-aminoethylamino)ethyl)-3',6'-bis(ethylamino)-2',7'-dimethylspiro[isoindoline-1,9'-xanthen]-3-one (ABDO) for Se (IV) had been synthesized in our earlier report. In this study, this fluorescent sensor is applied on analysis fluorescent imaging of Se (IV) in Hela cells. The experiment conditions, such as the MTT assay, different concentration of saline, incubated time of Hela cells with ABDO and Se (IV), and intracellular action position of Se (IV), are investigated. Through a series of experiments, the fluorescent image of Se (IV) in Hela cells can be observed when the cells cultured by 2 μM ABDO and 2 μM Se (IV) for 210 min. And the intracellular action position of Se (IV) is verified after the co-localization experiments are done. It is mitochondria. These experimental results show that ABDO will be an eagerly anticipated sensor for fluorescent imaging analysis of selenium ion in living cells. Besides, we also can use the complexes of ABDO-Se to observe morphology and distribution of mitochondria in cells like JG-B.

Lysosomal ATP imaging in living cells by a water-soluble cationic polythiophene derivative

Lysosomes in astrocytes and microglia can release ATP as the signaling molecule for the cells through ca(2+)-dependent exocytosis in response to various stimuli. At present, fluorescent probes that can detect ATP in lysosomes have not been reported. In this work, we have developed a new water-soluble cationic polythiophene derivative that can be specifically localized in lysosomes and can be utilized as a fluorescent probe to sense ATP in cells. PEMTEI exhibits high selectivity and sensitivity to ATP at physiological pH values and the detection limit of ATP is as low as 10(-11)M. The probe has low cytotoxicity, good permeability and high photostability in living cells and has been applied successfully to real-time monitoring of the change in concentrations of ATP in lysosomes though fluorescence microscopy. We also demonstrated that lysosomes in Hela cells can release ATP through Ca(2+)-dependent exocytosis in response to drug stimuli.

A Multisite-Binding Switchable Fluorescent Probe for Monitoring Mitochondrial ATP Level Fluctuation in Live Cells

Adenosine triphosphate (ATP), commonly produced in mitochondria, is required by almost all the living organisms; thus fluorescent probes for monitoring mitochondrial ATP levels fluctuation are essential and highly desired. Herein, we report a multisite-binding switchable fluorescent probe, ATP-Red 1, which selectively and rapidly responds to intracellular concentrations of ATP. Live-cell imaging indicated that ATP-Red 1 mainly localized to mitochondria with good biocompatibility and membrane penetration. In particular, with the help of ATP-Red 1, we successfully observed not only the decreased mitochondrial ATP levels in the presence of KCN and starvation state, but also the increased mitochondrial ATP levels in the early stage of cell apoptosis. These results indicate that ATP-Red 1 is a useful tool for investigating ATP-relevant biological processes.

In situ amplified electrochemical aptasensing for sensitive detection of adenosine triphosphate by coupling target-induced hybridization chain reaction with the assembly of silver nanotags

Biomolecular immobilization and construction of the sensing platform are usually crucial for the successful development of a high-efficiency detection system. Herein we report on a novel and label-free signal-amplified aptasensing for sensitive electrochemical detection of small molecules (adenosine triphosphate, ATP, used in this case) by coupling with target-induced hybridization chain reaction (HCR) and the assembly of electroactive silver nanotags. The system mainly consisted of two alternating hairpin probes, a partial-pairing trigger-aptamer duplex DNA and a capture probe immobilized on the electrode. Upon target ATP introduction, the analyte attacked the aptamer and released the trigger DNA, which was captured by capture DNA immobilized on the electrode to form a newly partial-pairing double-stranded DNA. Thereafter, the exposed domain at trigger DNA could be utilized as the initator strand to open the hairpin probes in sequence, and propagated a chain reaction of hybridization events between two alternating hairpins to form a long nicked double-helix. The electrochemical signal derived from the assembled silver nanotags on the nicked double-helix. Under optimal conditions, the electrochemical aptasensor could exhibit a high sensitivity and a low detection limit, and allowed the detection of ATP at a concentration as low as 0.03 pM. Our design showed a high selectivity for target ATP against its analogs because of the high-specificity ATP-aptamer reaction, and its applicable for monitoring ATP in the spiking serum samples. Improtantly, the distinct advantages of the developed aptasensor make it hold a great potential for the development of simple and robust sensing strategies for the detection of other small molecules by controlling the apatmer sequence.

A polynuclear hetero atom containing molecular organic scaffold to detect Al3+ ion through a fluorescence turn-on response

A simple polynuclear hetero atom (N and O) containing molecular organic scaffold/probe, 3 has been designed and synthesized and explored as a potential chemosensor to detect Al³⁺ (22 nM; ∼0.6 ppb) ion in a HEPES buffer.

Smart excimer fluorescence probe for visual detection, cell imaging and extraction of Hg2+

Smart pyrene-based simple fluorescent probes 2 and 4 were designed, synthesized and characterized by different spectroscopic methods.