Interaction of an Iridium(III) Complex with G-Quadruplex DNA and Its Application in Luminescent Switch-On Detection of Siglec-5

A robust luminescent assay for screening alkyladenine DNA glycosylase inhibitors to overcome DNA repair and temozolomide drug resistance

Temozolomide (TMZ) is an anticancer agent used to treat glioblastoma, typically following radiation therapy and/or surgical resection. However, despite its effectiveness, at least 50% of patients do not respond to TMZ, which is associated with repair and/or tolerance of TMZ-induced DNA lesions. Studies have demonstrated that alkyladenine DNA glycosylase (AAG), an enzyme that triggers the base excision repair (BER) pathway by excising TMZ-induced N3-methyladenine (3meA) and N7-methylguanine lesions, is overexpressed in glioblastoma tissues compared to normal tissues. Therefore, it is essential to develop a rapid and efficient screening method for AAG inhibitors to overcome TMZ resistance in glioblastomas. Herein, we report a robust time-resolved photoluminescence platform for identifying AAG inhibitors with improved sensitivity compared to conventional steady-state spectroscopic methods. As a proof-of-concept, this assay was used to screen 1440 food and drug administration-approved drugs against AAG, resulting in the repurposing of sunitinib as a potential AAG inhibitor. Sunitinib restored glioblastoma (GBM) cancer cell sensitivity to TMZ, inhibited GBM cell proliferation and stem cell characteristics, and induced GBM cell cycle arrest. Overall, this strategy offers a new method for the rapid identification of small-molecule inhibitors of BER enzyme activities that can prevent false negatives due to a fluorescent background.

The Research Advances of Aptamers in Hematologic Malignancies

Currently, research for hematological malignancies is very intensive, with many breakthroughs. Among them, aptamer-based targeted therapies could be counted. Aptamer is a targeting tool with many unique advantages (easy synthesis, low toxicity, easy modification, low immunogenicity, nano size, long stability, etc.), therefore many experts screened corresponding aptamers in various hematological malignancies for diagnosis and treatment. In this review, we try to summarize and provide the recent progress of aptamer research in the diagnosis and treatment of hematologic malignancies. Until now, 29 aptamer studies were reported in hematologic malignancies, of which 12 aptamers were tested in vivo and the remaining 17 aptamers were only tested in vitro. In this case, 11 aptamers were combined with chemotherapeutic drugs for the treatment of hematologic malignancies, 4 aptamers were used in combination with nanomaterials for the diagnosis and treatment of hematologic malignancies, and some studies used aptamers for the targeted transportation of siRNA and miRNA for targeted therapeutic effects. Their research provides multiple approaches to achieve more targeted goals. These findings show promising and encouraging future for both hematological malignancies basic and clinical trials research.

DNA G-quadruplex-stabilizing metal complexes as anticancer drugs

Guanine quadruplexes (G4s) are important targets for cancer treatments as their stabilization has been associated with a reduction of telomere ends or a lower oncogene expression. Although less abundant than purely organic ligands, metal complexes have shown remarkable abilities to stabilize G4s, and a wide variety of techniques have been used to characterize the interaction between ligands and G4s. However, improper alignment between the large variety of experimental techniques and biological activities can lead to improper identification of top candidates, which hampers progress of this important class of G4 stabilizers. To address this, we first review the different techniques for their strengths and weaknesses to determine the interaction of the complexes with G4s, and provide a checklist to guide future developments towards comparable data. Then, we surveyed 74 metal-based ligands for G4s that have been characterized to the in vitro level. Of these complexes, we assessed which methods were used to characterize their G4-stabilizing capacity, their selectivity for G4s over double-stranded DNA (dsDNA), and how this correlated to bioactivity data. For the biological activity data, we compared activities of the G4-stabilizing metal complexes with that of cisplatin. Lastly, we formulated guidelines for future studies on G4-stabilizing metal complexes to further enable maturation of this field.

Ruthenium(II) Polypyridyl Complexes and Their Use as Probes and Photoreactive Agents for G-quadruplexes Labelling

Due to their optical and electrochemical properties, ruthenium(II) polypyridyl complexes have been used in a wide array of applications. Since the discovery of the light-switch ON effect of [Ru(bpy)2dppz]2+ when interacting with DNA, the design of new Ru(II) complexes as light-up probes for specific regions of DNA has been intensively explored. Amongst them, G-quadruplexes (G4s) are of particular interest. These structures formed by guanine-rich parts of DNA and RNA may be associated with a wide range of biological events. However, locating them and understanding their implications in biological pathways has proven challenging. Elegant approaches to tackle this challenge relies on the use of photoprobes capable of marking, reversibly or irreversibly, these G4s. Indeed, Ru(II) complexes containing ancillary π-deficient TAP ligands can create a covalently linked adduct with G4s after a photoinduced electron transfer from a guanine residue to the excited complex. Through careful design of the ligands, high selectivity of interaction with G4 structures can be achieved. This allows the creation of specific Ru(II) light-up probes and photoreactive agents for G4 labelling, which is at the core of this review composed of an introduction dedicated to a brief description of G-quadruplex structures and two main sections. The first one will provide a general picture of ligands and metal complexes interacting with G4s. The second one will focus on an exhaustive and comprehensive overview of the interactions and (photo)reactions of Ru(II) complexes with G4s.

Electrochemiluminescence aptasensor for Siglec-5 detection based on MoS2@Au nanocomposites emitter and exonuclease III-powered DNA walker

Lectins are highly specific binding proteins for glycoproteins which widely exist in living organisms, playing a vital role in exploring the biological evolution process, such as cellular proliferation, differentiation, carcinogenesis and apoptosis. Therefore, the content monitoring of lectin becomes particularly significant and urgent in the bioanalytical application. In this work, we fabricated an aptasensor, majorly capitalizing the eminent affinity between sialic acid-binding immunoglobulin (Ig)-like lectin 5 (Siglec-5) and nucleic acids aptamer (K19), with nontoxic MoS₂@Au nanocomposites as electrochemiluminescence (ECL) emitters based on exonuclease III (Exo III)-powered DNA walker for the bioassays of Siglec-5. The DNA track was constructed on the emitters' surface, providing a reliable platform for the DNA walker's autonomous move. In the assay, the primer DNA in the DNA duplex was replaced by Siglec-5 due to the aptamer interactions and repeatedly released to participate in the movement of the DNA walker, further triggering cascade signal amplification. Finally, our aptasensor indicates significant potential for assays of Siglec-5 with a detection limit of 8.9 pM.

A highly sensitive method for simultaneous detection of hAAG and UDG activity based on multifunctional dsDNA probes mediated exponential rolling circle amplification

DNA glycosylase is an indispensable DNA damage repair enzyme which can recognize and excise the damaged bases in the DNA base excision-repair pathway. The dysregulation of DNA glycosylase activity will give rise to the dysfunction of base excision-repair and lead to abnormalities and diseases. The simultaneous detection of multiple DNA glycosylases can help to fully understand the normal physiological functions of cells, and determine whether the cells are abnormal in pre-disease. Regrettably, the synchronous detection of functionally similar DNA glycosylases is a great challenge. Herein, we developed a multifunctional dsDNA probe mediated exponential rolling circle amplification (E-RCA) method for the simultaneously sensitive detection of human alkyladenine DNA glycosylase (hAAG) and uracil-DNA glycosylase (UDG). The multifunctional dsDNA probe contains the hypoxanthine sites and the uracil sites which can be recognized by hAAG and UDG respectively to generate apyrimidinic (AP) sites in the dsDNA probe. Then the AP sites will be recognized and cut by endonuclease Ⅳ (Endo IV) to release corresponding single-stranded primer probes. Subsequently, two padlock DNA templates are added to initiate E-RCA to generate multitudinous G-quadruplexes and/or double-stranded dumbbell lock structures, which can combine N-methyl mesoporphyrin IX (NMM) and SYBR Green Ⅰ (SGI) for the generation of respective fluorescent signals. The detection limits are obtained as low as 0.0002 U mL^-1 and 0.00001 U mL^-1 for hAAG and UDG, respectively. Notably, this method can realize the simultaneous detection of two DNA glycosylases without the use of specially labeled probes. Finally, this method is successfully applied to detect hAAG and UDG activities in the lysates of HeLa cells and Endo1617 cells at single-cell level, and to detect the inhibitors of DNA glycosylases.

Exploring the trans-cleavage activity of CRISPR-Cas12a for the development of a Mxene based electrochemiluminescence biosensor for the detection of Siglec-5

Sialic acid-binding immunoglobulin (Ig)-like lectins (Siglecs) is a type I transmembrane receptor on the cell surface. Siglec-5, as one of the Siglecs family, play an important role as an inhibitory receptor for leukocytes in the human body. The development of novel siglec-5 assays can help to study the pathogenesis of related diseases as well as to develop novel therapeutic drugs. We use catalytic hairpin assembly (CHA) amplification strategy combined with CRISPR-Cas12a's side-cutting feature to build a 2D ultra-thin Ti3C2Tx (MXene) based electrochemiluminescence (ECL) biosensor for the detection of Siglec-5. By using this ECL biosensor, the cleavage of CRISPR-Cas12a is reasonably combined with CHA-mediated isothermal amplification, thereby realizing the sensitive amplification assay Siglec-5 with 20.22 fM sensitivity. By introducing pairs of sites that are not in the same double-stranded DNA into the DNA duplex, the hybridization sequence of CRISPR-Cas12a complements the targeting mechanism to enhance indirect Siglec-5 amplification assay. Also, the double-strand DNA (dsDNA) design based on CRISPR-Cas12a amplification allows the same CRISPR RNA (crRNA, also known as guide RNA (gRNA)) to detect the output of DNA duplexes from different intermediate DNAs, which provides a common way for biomarker detection based on the conversion of protein analytes to intermediate DNA strategy. This work extends the application scope of CRISPR-Cas12a to the construction of ECL biosensors, evaluates the role of lectins, which can be used for the biochemical research and clinical diagnosis of protein markers. This is the first investigative work exploring the Trans-Cleavage activity of CRISPR-Cas12a for Mxene-based ECL biosensor establishment to the best of our knowledge.

Chiroptical property enhancement of chiral Eu(III) complex upon association with DNA-CTMA

DNA-based materials have attracted much attention due to their unique photo-functional properties and potential applications in various fields such as luminescent and biological systems, nanodevices, etc. In this study, the photophysical properties of a chiral Eu(III) complex, namely (Eu(D-facam)₃), within DNA films were extensively investigated. The enhancement of photoluminescence (more than 25-folds increase of luminescence quantum yield) and degree of circularly polarization in luminescence (g_lum = − 0.6) was observed upon interaction with DNA. Various photophysical analyses suggested that the emission enhancement was mainly due to an increase of the sensitization efficiency (high η_sens) from the ligands to Eu(III) and suppression of the vibrational deactivation upon immobilization onto the DNA molecule. From CD and VCD measurements, it was suggested that the coordination structure of Eu(D-facam)₃ was affected by the interaction with DNA, suggesting that the structural change of Eu(D-facam)₃ contributed to the improvement of its luminescent properties.

β-Lactoglobulin amyloid fibril-templated gold nanoclusters for cellular multicolor fluorescence imaging and colorimetric blood glucose assay

β-Lactoglobulin amyloid fibril (BLGF)-capped gold nanoclusters (Au NCs) with red, green and blue emissions were fabricated via pH-dependent reduction strategy. The BLGF-Au NCs exhibited 3.2 times enhancement of fluorescence (λex = 500 nm, λem = 684 nm), a significant 42 nm red shift, a 11.57% quantum yield and a 1.4 μs decay time compared with native β-lactoglobulin (BLG)-stabilized Au NCs. Meanwhile, the multicolor Au NCs were employed for cell imaging via incubation with A549 cells for 14 h. According to the Michaelis-Menten equation, the kinetic parameters of the BLGF-Au NCs showed a lower Km value (66 μmol L-1) for 3,3,5,5-tetramethylbenzidine (TMB) and a higher vmax (3.74 × 10-8 M s-1) for H2O2, which are comparable with other artificial nanoenzymes and natural peroxidases. Based on the highly intrinsic peroxidase-like activity of the BLGF-Au NCs, a colorimetric method was developed for glucose determination with a detection limit of 1.5 μmol L-1 by determining the variation of the absorption at 652 nm, ranging from 5 to 100 μmol L-1. In addition, the glucose assay method also revealed a 101.02 to 104.16% recovery in a real human serum sample.

Recent Progress and Development of G-Quadruplex-Based Luminescent Assays for Ochratoxin A Detection

Ochratoxin A (OTA) is a mycotoxin that is widespread throughout the world. It contaminates foods such as vegetables, fruits, and rice. It harms human health and has potential carcinogenic effects. The G-quadruplex (G4) is a tetraplexed DNA structure generated from guanine-rich DNA that has found emerging use in aptamer-based sensing systems. This review outlines the status of OTA contamination and conventional detection methods for OTA. Various G4-based methods to detect OTA developed in recent years are summarized along with their advantages and disadvantages compared to existing approaches.

Switch-on effect on conformation-specific arylamine-DNA adduct by cyclometalated Ir(III) complexes

Arylamines are known to form covalent-DNA adducts upon metabolic activation. These covalent adducts adopt different conformational attributes, viz., major groove (B), stacked (S), and minor groove (W), and lead to different types of mutations. The conformation depends on the flanking and next flanking bases at the 3' position of the adduct. Early detection of these conformations by simple probes is an ideal and challenging task. Here, we have reported two Ir(III)-based cyclometalated complexes, viz., [Ir(ppy)₂(imiphen)]⁺ (1) (ppy: 2-phenylpyridine; imiphen: 2-(1H-imidazol-2-yl)-1H-imidazo[4,5-f][1,10]phenanthroline) and [Ir(ppy)₂(furphen)]⁺ (2) (furphen: 2-(furan-2-yl)-1H-imidazo[4,5-f][1,10]phenanthroline) and its interaction with N-acetyl-2-aminofluorene-dG (AAF-dG). The sequences used in this work are NarI sequence (-CG₁G₂CG₃CX-) in which Gs are modified with AAF and X is either C or T. Luminescence studies reveal that the Ir(III) complexes bind to AAF-dG adduct with high specificity toward G₁ and G₃ compared to G₂ and unmodified control. The selectivity also depends on the next flanking base as cytosine favors G₃^AAF, while thymine favors G₁^AAF in complex 1 and vice versa for complex 2. The quenching studies confirm that Ir(III) complexes bind with AAF-dG sequences through the minor groove. The outcome of this work reveals that the switch-on effect by the complexes can be utilized for determining the conformational heterogeneity of the adduct and also for similar covalent-DNA adducts.

Green Layer-by-Layer Assembly of Porphyrin/G-Quadruplex-Based Near-Infrared Nanocomposite Photosensitizer with High Biocompatibility and Bioavailability

A simple and green layer-by-layer assembly strategy is developed for the preparation of a highly bioavailable nanocomposite photosensitizer by assembling near-infrared (NIR) light-sensitive porphyrin/G-quadruplex complexes on the surface of a highly biocompatible nanoparticle that is prepared via Zn²⁺-assisted coordination self-assembly of an amphiphilic amino acid. After being efficiently delivered to the target site and internalized into tumor cells via enhanced permeability and retention effect and interactions between aptamers and tumor markers, the as-prepared nanoassembly can be directly used as an NIR light-responsive photosensitizer for tumor photodynamic therapy (PDT) since the porphyrin/G-quadruplex complexes are exposed on the nanoassembly surface and kept in an active state. It can also disassemble under the synergistic stimuli of an acidic pH environment and overexpressed glutathione, leasing more efficient porphyrin/G-quadruplex composite photosensitizers while reducing the interference caused by glutathione-dependent ¹O₂ consumption. Since the nanoassembly can work no matter if it is disassembled or not, the compulsory requirement for in vivo photosensitizer release is eliminated, thus resulting in the great improvement of the bioavailability of the photosensitizer. The PDT applications of the nanoassembly were well demonstrated in both in vitro cell and in vivo animal experiments.

Isothermal cross-boosting extension–nicking reaction mediated exponential signal amplification for ultrasensitive detection of polynucleotide kinase

A novel nucleic acid-based isothermal signal amplification strategy, named cross-boosting extension–nicking reaction (CBENR) is developed and successfully used for rapid and ultrasensitive detection of polynucleotide kinase (PNK) activity.

Nucleic Acid Aptamer: A Novel Potential Diagnostic and Therapeutic Tool for Leukemia

Leukemia immunotherapy has been dominant via using synthetic antibodies to target cluster of differentiation (CD) molecules, nevertheless inevitable cytotoxicity and immunogenicity would limit its development. Recently, increasing reports have focused on nucleic acid aptamers, a class of high-affinity nucleic acid ligands. Aptamers purportedly serve as “chemical antibodies”, have negligible cytotoxicity and low immunogenicity, and would be widely applied for the therapy and diagnosis of various diseases, especially leukemia. In the preclinical applications, nucleic acid aptamers have displayed the augmented specificity and selectivity via recognizing targets on leukemia cells based on unique three-dimensional conformations. As small molecules with nucleic acid characteristics, aptamers need to be chemically modified to resist nuclease degradation, renal clearance and improve binding affinities. Moreover, aptamers can be linked with neoteric detection techniques to enhance sensitivity and selectivity of diagnosis and therapy. In this review, we summarized aptamers’ preparation, chemical modification and conjugation, and discussed the application of aptamers in diagnosis and treatment of leukemia through highly specifically recognizing target molecules. Significantly, the application prospect of aptamers in fusion genes would be introduced.

Dual mode of binding of anti cancer drug epirubicin to G-quadruplex [d-(TTAGGGT)]4 containing human telomeric DNA sequence induces thermal stabilization

Epirubicin exerts its anti cancer action by blocking DNA/RNA synthesis and inhibition of topoisomerase-II enzyme. Recent reports on its influence on telomere maintenance, suggest interaction with G-quadruplex DNA leading to multiple strategies of action. The binding of epirubicin with parallel stranded inter molecular G-quadruplex DNA [d-(TTAGGGT)]₄ comprising human telomeric DNA sequence TTAGGG was investigated by absorption, fluorescence, circular dichroism and nuclear magnetic resonance spectroscopy. The epirubicin binds as monomer to G-quadruplex DNA with affinity, K_b1 = 3.8 × 10⁶ M^-1 and K_b2 = 2.7 × 10⁶ M^-1, at two independent sites externally. The specific interactions induce thermal stabilization of DNA by 13.2-26.3 °C, which is likely to come in the way of telomere association with telomerase enzyme and contribute to epirubicin-induced apoptosis in cancer cell lines. The findings pave the way for drug designing in view of the possibility of altering substituent groups on anthracyclines to enhance efficacy using alternate mechanism of its interaction with G4 DNA, causing interference in telomere maintenance pathway by inducing telomere dysfunction.

Preparation and Characterization of Four Major Novel Degradation Products of Pralatrexate Injection and Validation of HPLC-UV Method

Background:

Four major degradation products (1-4) of pralatrexate injection were formed under hydrolytic and light stress conditions. The impurities 1 and 2 were the potential photo degradation products and the impurities 3 and 4 were the potential hydrolytic degradation products.

Objective:

To prepare and characterize the novel degradation impurities 1, 2, 3 and 4 of pralatrexate injection using NMR, HR MS and IR techniques; and to develop and validate stability indicating analytical reverse phase HPLC-UV method for quantitative simultaneous determination of potential degradation impurities, related substances of pralatrexate and pralatrexate active in pralatrexate liquid formulation.

Methods:

Gradient HPLC-UV method was developed for the quantification of degradation impurities, related substances and pralatrexate in pralatrexate injection. The separation was achieved on C18 column (250 mm X 4.6 mm, 5µm) using a mobile phase composed of sodium dihydrogen phosphate monohydrate in water (pH 3.0; 0.01M) and methanol. The components were monitored by the UVvisible detector at 242 nm with a flow rate of 1.0 mL/min.

Results:

The method validation parameters such as accuracy, selectivity, linearity, LOD, LOQ, precision, ruggedness and robustness were demonstrated successfully for pralatrexate and its degradation impurities. The stability-indicating capability of the developed HPLC method was demonstrated by adequate separation of all potential pralatrexate related substances from pralatrexate stressed drug product samples.

Conclusion:

The developed stability indicating HPLC method was found to be suitable for the simultaneous quantitative determination of potential degradation impurities and related substances of pralatrexate and pralatrexate active in pralatrexate liquid formulation.

Targeting G-Rich DNA Structures with Photoreactive Bis-Cyclometallated Iridium(III) Complexes

The synthesis and characterisation of three novel iridium(III) bis-cyclometallated complexes is reported. Their photophysics have been fully characterised by classical methods and revealed charge-transfer (CT) and ligand-centred (LC) transitions. Their ability to selectively interact with G-quadruplex telomeric DNA over duplex DNA has been studied by circular dichroism (CD), bio-layer interferometry (BLI) and surface plasmon resonance (SPR) analyses. Interestingly, one of the complexes was able to promote photoinduced electron transfer (PET) with the guanine DNA base, which in turn led to oxidative damage (such as the formation of 8-oxoguanine) to the telomeric sequence. To the best of our knowledge, this is the first study of highly photo-oxidising bis-cyclometallated iridium(III) complexes with G-quadruplex telomeric DNA.

Non-Invasive Extraction of Gabapentin for Therapeutic Drug Monitoring by Reverse Iontophoresis: Effect of pH, Ionic Strength, and Polyethylene Glycol 400 in the Receiving Medium

Background:

Monitoring of plasma concentrations is a necessity for narrow therapeutic index potent drugs. Development of non-invasive methods can save the patients from the trauma of needles and hence is considered as a research priority.

Introduction:

Gabapentin, an anti-epileptic drug requires therapeutic monitoring because of its narrow therapeutic index. The objective of the study was to develop a suitable method for the non-invasive extraction of gabapentin for the same.

Methods:

Transdermal reverse iontophoresis was performed using pig ear skin as a barrier membrane. Three compartment iontophoretic cells were used for the extraction study. Extractions were carried out under low intensity electric field (current intensity- 0.5 mA/cm2, electrical field approximately 5 V). The donor compartment was charged with aqueous gabapentin (10 µg/ml in phosphate buffer of pH 7.4). For studying the effect of receiving vehicle (pH, ionic strength, and enhancer) on the extraction efficiency of gabapentin, the two receiver chambers were charged with media having varying concentration of these factors. Drug content was determined by HPLC.

Results:

Compared to other pHs, cumulative extraction of gabapentin at pH 5 was significantly higher at both anode and cathode (p<0.001). At low ionic strength, extraction of gabapentin increased linearly with the increase in concentration of ions up to a certain value but at very high ionic strength the pattern reversed. Similar results were obtained with enhancer (polyethylene glycol 400). Extraction increased with increase in polyethylene glycol 400 up to 3% and then decreased.

Conclusion:

Extraction flux can be optimized by manipulation of the receiver media.

G-Quadruplex-Based Fluorescent Turn-On Ligands and Aptamers: From Development to Applications

Guanine (G)-quadruplexes (G4s) are unique nucleic acid structures that are formed by stacked G-tetrads in G-rich DNA or RNA sequences. G4s have been reported to play significant roles in various cellular events in both macro- and micro-organisms. The identification and characterization of G4s can help to understand their different biological roles and potential applications in diagnosis and therapy. In addition to biophysical and biochemical methods to interrogate G4 formation, G4 fluorescent turn-on ligands can be used to target and visualize G4 formation both in vitro and in cells. Here, we review several representative classes of G4 fluorescent turn-on ligands in terms of their interaction mechanism and application perspectives. Interestingly, G4 structures are commonly identified in DNA and RNA aptamers against targets that include proteins and small molecules, which can be utilized as G4 tools for diverse applications. We therefore also summarize the recent development of G4-containing aptamers and highlight their applications in biosensing, bioimaging, and therapy. Moreover, we discuss the current challenges and future perspectives of G4 fluorescent turn-on ligands and G4-containing aptamers.

An iridium(III) complex/G-quadruplex ensemble for detection of ochratoxin A based on long-lifetime luminescent

A G-quadruplex-based platform has been developed for the time-resolved monitoring of ochratoxin A (OTA). The simple platform displays good sensitivity for OTA with a detection limit of 40 nM via steady-state emission spectroscopy. Notably, the platform showed a detection limit of 10.8 nM via time-resolved emission spectroscopy (TRES), which is about 4 times more sensitive than steady-state mode. Moreover, the probe showed excellent selectivity for OTA over other mycotoxins. Furthermore, OTA was successfully detected in actual herbal plant extracts samples. Our platform is the first to detect OTA using TRES to distinguish between the target signals versus the auto-fluorescence of real samples. This platform shows improved detection speed, accuracy and sensitivity with simple operation, low cost, and no requirement for complicated pre-processing.

A reaction-based luminescent switch-on sensor for the detection of OH- ions in simulated wastewater

A series of luminescent iridium(iii) complexes were synthesized and evaluated for their ability to interact with hydroxide ions in semi-aqueous media at ambient temperature. Upon the addition of OH^-, a nucleophilic aromatic substitution reaction takes place at the bromine groups of the N^N ligand of complex 1, resulting in the generation of a yellow-green luminescence. Complex 1 showed a 35-fold enhanced emission at pH 14 when compared to neutral pH, and the detection limit for OH^- ions was 4.96 μM. Complex 1 exhibited high sensitivity and selectivity, long-lived luminescence and impressive stability. Additionally, we have demonstrated the practical application of complex 1 to detect OH^- ions in simulated wastewater.

Phenanthroline polyazamacrocycles as G-quadruplex DNA binders

Several phenanthroline polyazamacrocycles are proposed as ligands for c-MYC and telomeric G-quadruplex structures.

Specific Light-Up System for Protein and Metabolite Targets Triggered by Initiation Complex Formation

Gene regulation systems are mimicked by simple quantitative detection of non-nucleic acid molecular targets such as protein and metabolite. Here, we describe a one-tube, one-step real-time quantitative detection methodology for isothermal signal amplification of those targets. Using this system, real-time quantitative detection of thrombin and streptomycin, which were used as examples for protein and metabolite targets, was successfully demonstrated with detection limits of at most 50 pM and 75 nM, respectively. Notably, the dynamic range of target concentrations could be obtained for over four orders of magnitude. Thus, our method is expected to serve as a point-of-care or on-site test for medical diagnosis and food and environmental hygiene.

Construction of a Nano Biosensor for Cyanide Anion Detection and Its Application in Environmental and Biological Systems

We have developed a Ag@Au core-shell nanoparticle (NP)/iridium(III) complex-based sensing platform for the sensitive luminescence "turn-on" sensing of cyanide ions, an acutely toxic pollutant. The assay is based on the quenching effect of Ag@Au NPs on the emission of complex 1, but luminescence is restored after the addition of cyanide anions due to their ability to dissolve the Au shell. Our sensing platform exhibited a high sensitivity toward cyanide anions with a detection limit of 0.036 μM, and also showed high selectivity for cyanide over 10-fold excess amounts of other anions. The sensing platform was also successfully applied to monitor cyanide anions in drinking water and in living cells.

Luminescent turn-on detection of Hg(II) via the quenching of an iridium(III) complex by Hg(II)-mediated silver nanoparticles

A novel luminescent turn-on detection method for Hg(II) was developed. The method was based on the silver nanoparticle (AgNP)-mediated quenching of Ir(III) complex 1. The addition of Hg(II) ions causes the luminescence of complex 1 to be recovered due to the oxidation of AgNPs by Hg(II) ions to form Ag(I) and Ag/Hg amalgam. The luminescence intensity of 1 increased in accord with an increased Hg(II) concentration ranging from 0 nM to 180 nM, with the detection limit of 5 nM. This approach offers an innovative method for the quantification of Hg(II).

Label-free and rapid detection of ATP based on structure switching of aptamers

In this work, an aptamer-based fluorescent strategy for label-free detection of ATP was developed by using Thioflavin T (ThT) as a fluorescence indicator, which can specifically bind with G-quadruplex DNAs to generate enhanced fluorescence intensity. In the absence of ATP, the folded structure of ATP aptamer allows the intercalation of ThT to produce strong fluorescence signal. However, upon ATP binding to the aptamer where ThT intercalated, the conformational change or distortion of the aptamer is large enough to cause much less intercalation of ThT and consequently drastic suppression of the fluorescence intensity. As such, the concentration of ATP could be identified very easily by observing fluorescence changes of this sensing system. This label-free assay could be accomplished very easily and quickly with a "mix-and-detect" detection method and exhibits high sensitivity to ATP with a detection limit of 33 nM in a wide range of 0.1-1000 μM. Furthermore, this proposed method is capable of detecting ATP in human serum and cell extracts. This method offers several advantages such as simplicity, rapidity, low cost, good stability and excellent selectivity, which make it hold great potential for the detection of ATP in bioanalytical and biological studies.

The application of a G-quadruplex based assay with an iridium(iii) complex to arsenic ion detection and its utilization in a microfluidic chip

In this work, the iridium(iii) complex 1 was synthesized and employed in constructing an assay which is based on a G-quadruplex for detecting arsenic ions in aqueous solution.

Near-infrared emitting iridium(iii) complexes for mitochondrial imaging in living cells

Two NIR-emitting cationic iridium(iii) complexes with phenylbenzo[g]quinoline ligands were found to selectively accumulate in mitochondria, superior photostability, low cytotoxicity. Thus they were demonstrated to have good potential as NIR-emitting mitochondrial imaging agents.

A long-lived iridium(iii) chemosensor for the real-time detection of GHB

In this work, a long-lived iridium(iii) chemosensor 1 has been synthesized for the detection of GHB. The luminescence signal of iridium(iii) complex 1 could also be distinguished from strongly fluorescent media using time-resolved emission spectroscopy.