A selective oligonucleotide-based luminescent switch-on probe for the detection of nanomolar mercury(II) ion in aqueous solution

Zinc(ii), copper(ii) and cadmium(ii) complexes as fluorescent chemosensors for cations

The fluorescence chemosensing behavior of Zn(ii), Cu(ii), and Cd(ii) based complexes toward cations has been described. Cation detection via conventional mechanisms, metal-metal exchange and chemodosimetric approaches along with the importance of metal ions and the scope, significance, and challenges with regard to the detection of cations by metal complex based probes will be discussed in detail. The fundamentals of photophysical behavior and mechanisms involved in the fluorescence detection of analytes will also be described. This article provides a detailed overview of Zn(ii), Cu(ii), and Cd(ii) based complexes as fluorescent probes for cations, together with essential discussions pertaining to detection mechanisms.

Recent developments of nanoenzyme-based colorimetric sensors for heavy metal detection and the interaction mechanism

This work highlights the application and interaction mechanism of metal nanoparticles, metal oxides, metal sulfides, graphene-based nanomaterials and G-quadruplex, etc. in nanoenzyme-based colorimetric sensors.

Adsorption Behavior of Polycyclic Aromatic Hydrocarbons on Zn-Based Coordination Cluster Zn5: Competition, Synergy, and Mechanism

In this work, adsorption behaviors of pyrene (PYR), fluoranthene (FLT), phenanthrene (PHE), and fluorene (FLU) on the coordination cluster [Zn₅(H₂Lⁿ)₆](NO₃)₄]·8H₂O·2CH₃OH (Zn₅) were studied. The adsorption mechanism and spectrum analyses revealed that the synergistic effect of hydrophobic interaction, π-π stacking, and N-H···π interaction played a crucial role during the adsorption process. The maximum adsorption capacities of PYR, FLT, PHE, and FLU were 406.4, 399.7, 153.7, and 114.3 mg g^-1, respectively, resulting from the Langmuir isotherm model. Quick removal of PYR and FLT was found in kinetic experiments with the adsorption equilibrium being reached within 1 min. Competitive adsorption indicated that the adsorption sites for PYR, FLT, PHE, and FLU on Zn₅ were identical, and synergistic effects also existed in the adsorption process. Therefore, Zn₅ has the potential to be used as an adsorbent in the field of wastewater treatment.

Synthesis and Enzymatic Incorporation of a Responsive Ribonucleoside Probe That Enables Quantitative Detection of Metallo-Base Pairs

Synthesis of a highly responsive fluorescent ribonucleoside analogue based on a 5-methoxybenzofuran uracil core, enzymatic incorporation of its triphosphate substrate into RNA transcripts, and its utility in the specific detection and estimation of Hg²⁺-ion-mediated metallo-base pair formation in DNA–RNA and RNA–RNA duplexes are described.

Dinuclear HgII tetracarbene complex-triggered aggregation-induced emission for rapid and selective sensing of Hg2+ and organomercury species

Mercury-mediated chelate ring formation and subsequent aggregation gives strong fluorescence for rapid and selective sensing of Hg²⁺ and organomercury.

Rapid, reliable and highly selective detection of mercury species, including Hg²⁺ ions and organomercury, is of significant importance for environmental protection and human health. Herein, a new fluorescent dye 1,1,2,2-tetrakis[4-(3-methyl-1H-benzimidazol-1-yl)phenyl ethylene tetraiodide (Tmbipe) with aggregation-induced emission (AIE) potential was prepared and characterized. The presence of four positively charged methylated benzimidazole groups endows Tmbipe with excellent water solubility and almost undetectable background fluorescence. However, it can coordinate with two Hg²⁺ ions or two organomercury molecules (e.g. methylmercury and phenylmercury) to form a planar dinuclear Hg^II tetracarbene complex, which can then self-aggregate to turn on AIE fluorescence. Such a fluorescence turn-on process can be completed in 3 min. In addition, synergic rigidification of the tetraphenylethylene-bridged Tmbipe molecule by mercury-mediated chelate ring formation and subsequent aggregation results in obviously higher fluorescence enhancement than that given by the single aggregation-induced one. Low background, high fluorescence enhancement and rapid response time make Tmbipe a good fluorescent probe for reliable, sensitive and highly selective quantitation of both inorganic and organic mercury species. This probe was also demonstrated to work well for identification of mercury species accumulation in living cells.

Temperature dependence of photophysical properties of a dinuclear C^N-cyclometalated Pt(ii) complex with an intimate Pt–Pt contact. Zero-field splitting and sub-state decay rates of the lowest triplet

A dinuclear Pt(ii) complexes exhibits an unusually large zero field splitting in its metal–metal-to-ligand charge transfer triplet excited state.

A novel cyclometalated Ir(iii) complex based luminescence intensity and lifetime sensor for Cu2+

A novel green luminescent complex [Ir(dfppy)₂(bpy-BiDPA)]PF₆ was prepared for the reversible detection of Cu²⁺.

A label-free G-quadruplex-based mercury detection assay employing the exonuclease III-mediated cleavage of T-Hg2+-T mismatched DNA

We report herein the use of an exonuclease III and G-quadruplex probe to construct a G-quadruplex-based luminescence detection platform for Hg2+. Unlike common DNA-based Hg2+ detection methods, when using the dsDNA probe to monitor the hairpin formation, the intercalation of the dsDNA probe may be influenced by the distortion of dsDNA. This 'mix-and-detect' methodology utilized the G-quadruplex probe as the signal transducer and is simple, rapid, convenient to use and can detect down to 20 nM of Hg2+.

On the use of metal purine derivatives (M=Ir, Rh) for the selective labeling of nucleosides and nucleotides

The reactions of neutral or cationic IrIII and RhIII derivatives of phenyl purine nucleobases with unsymmetrical alkynes produce new metallacycles in a predictable manner, which allows for the incorporation of either photoactive (anthracene or pyrene) or electroactive (ferrocene) labels in the nucleotide or nucleoside moiety. The reported methodology (metalation of the purine derivative and subsequent marker insertion) could be used for the postfunctionalization and unambiguous labeling of oligonucleotides.

A review of biosensing techniques for detection of trace carcinogen contamination in food products

Carcinogen contaminations in the food chain, for example heavy metal ions, pesticides, acrylamide, and mycotoxins, have caused serious health problems. A major objective of food-safety research is the identification and prevention of exposure to these carcinogens, because of their impossible-to-reverse tumorigenic effects. However, carcinogen detection is difficult because of their trace-level presence in food. Thus, reliable and accurate separation and determination methods are essential to protect food safety and human health. This paper summarizes the state of the art in separation and determination methods for analyzing carcinogen contamination, especially the advances in biosensing methods. Furthermore, the application of promising technology including nanomaterials, imprinted polymers, and microdevices is detailed. Challenges and perspectives are also discussed.

G-quadruplex-based logic gates for HgII and AgI ions employing a luminescent iridium(iii) complex and extension of metal-mediated base pairs by polymerase

We report herein the synthesis of a series of cyclometallated iridium(iii) complexes as luminescent G-quadruplex-selective probes to construct AND, OR and INHIBIT logic gates for the detection of Hg^II and Ag^I ions.

Turning an aptamer into a light-switch probe with a single bioconjugation

We describe a method for transforming a structure-switching aptamer into a luminescent light-switch probe via a single conjugation. The methodology is demonstrated using a known aptamer for Hg²⁺ as a case study. This approach utilizes a lanthanide-based metallointercalator, Eu-DOTA-Phen, whose luminescence is quenched almost entirely and selectively by purines, but not at all by pyrimidines. This complex, therefore, does not luminesce while intercalated in dsDNA, but it is bright red when conjugated to a ssDNA that is terminated by several pyrimidines. In its design, the light-switch probe incorporates a structure-switching aptamer partially hybridized to its complementary strand. The lanthanide complex is conjugated to either strand via a stable amide bond. Binding of the analyte by the structure-switching aptamer releases the complementary strand. This release precludes intercalation of the intercalator in dsDNA, which switches on its luminescence. The resulting probe turns on 21-fold upon binding to its analyte. Moreover, the structure switching aptamer is highly selective, and the long luminescence lifetime of the probe readily enables time-gating experiments for removal of the background autofluorescence of the sample.

A colorimetric and luminescent dual-modal assay for Cu(II) ion detection using an iridium(III) complex

A novel iridium(III) complex-based chemosensor bearing the 5,6-bis(salicylideneimino)-1,10-phenanthroline ligand receptor was developed, which exhibited a highly sensitive and selective color change from colorless to yellow and a visible turn-off luminescence response upon the addition of Cu(II) ions. The interactions of this iridium(III) complex with Cu2+ ions and thirteen other cations have been investigated by UV-Vis absorption titration, emission titration, and 1H NMR titration.

Cyclometallated ruthenium complex-modified upconversion nanophosphors for selective detection of Hg2+ ions in water

Upconversion detection nanocomposites were assembled for the selective luminescent detection of mercury ions in water. A hydrophobic cyclometallated ruthenium complex [Ru(II)(bpy)2(thpy)]PF6 (abbreviated as Ru1; bpy = 2,2'-bipyridine and thpy = 2-(2-thienyl)pyridine) is employed as a chemodosimeter to assemble on amphiphilic polymer-coating upconversion nanophosphors (UCNPs) based on the hydrophobic-hydrophobic interaction. Upon addition of Hg(2+), the nanocomposite not only exhibits a remarkable color change from deep-red to yellow, but also an enhanced upconversion luminescence (UCL) emission by hindering the luminescent resonance energy transfer (LRET) process from the upconversion emission of UCNPs to Ru1. Using the ratiometric UCL emission as a detection signal, the detection limit of Hg(2+) for this nanoprobe in aqueous solution is 8.2 ppb, which is much lower than that (329 ppb) determined by UV/Vis technology. Such an Hg(2+)-tunable LRET process provides a general strategy for fabricating a water-soluble upconversion-based nanoprobe for some special analyte.

A G-quadruplex-based platform for the detection of Hg2+ ions using a luminescent iridium(iii) complex

We report herein the synthesis of a series of cyclometalated iridium(iii) complexes as luminescent G-quadruplex-selective probes, which were used to construct an oligonucleotide-based platform for the dual detection and removal of Hg²⁺ ions.

Design of two and three input molecular logic gates using non-Watson–Crick base pairing-based molecular beacons

A single, resettable, and sensitive molecular beacon has been developed to operate two-input, three-input, and set–reset logic gates.

A label-free luminescent switch-on assay for ATP using a G-quadruplex-selective iridium(III) complex

We report herein the G-quadruplex-selective property of a luminescent cyclometallated iridium(III) complex for the detection of adenosine-5'-triphosphate (ATP) in aqueous solution. The ATP-binding aptamer was employed as the ATP recognition unit, while the iridium(III) complex was used to monitor the formation of the G-quadruplex structure induced by ATP. The sensitivity and fold enhancement of the assay were higher than those of the previously reported assay using the organic dye crystal violet as a fluorescent probe. This label-free luminescent switch-on assay exhibits high sensitivity and selectivity towards ATP with a limit of detection of 2.5 µM.

Label-free luminescent oligonucleotide-based probes

Breakthrough advances in chemistry and biology over the last two decades have vastly expanded the repertoire of nucleic acid structure and function with potential application in multiple areas of science and technology, including sensing and analytical applications. DNA oligonucleotides represent popular tools for the development of sensing platforms due to their low cost, rich structural polymorphism, and their ability to bind to cognate ligands with sensitivity and specificity rivaling those for protein enzymes and antibodies. In this review, we give an overview of the "label-free" approach that has been a particular focus of our group and others for the construction of luminescent DNA-based sensing platforms. The label-free strategy aims to overcome some of the drawbacks associated with the use of covalently-labeled oligonucleotides prevalent in electrochemical and optical platforms. Label-free DNA-based probes harness the selective interaction between luminescent dyes and functional oligonucleotides that exhibit a "structure-switching" response upon binding to analytes. Based on the numerous examples of label-free luminescent DNA-based probes reported recently, we envisage that this field would continue to thrive and mature in the years to come.

A label-free G-quadruplex-based luminescent switch-on assay for the selective detection of histidine

A label-free G-quadruplex-based luminescent switch-on assay has been developed for the selective detection of micromolar histidine in aqueous solution. In this study, an iridium(III) complex was employed as a G-quadruplex-specific luminescent probe while a guanine-rich oligonucleotide (Pu27, 5'-TG4AG3TG4AG3TG4A2G2-3')/cupric ion (Cu(2+)) ensemble was employed as a recognition unit for histidine. The initial luminescence of the iridium(III) complex in the presence of G-quadruplex DNA is effectively quenched by Cu(2+) ions due to the Cu(2+)-mediated unfolding of the G-quadruplex motif. The addition of histidine sequesters Cu(2+) ions from the ensemble, thereby restoring the luminescence of the system. The assay could detect down to 1 μM of histidine in aqueous media, and also exhibited good selectivity for histidine over other amino acids with the use of the cysteine, masking agent N-ethylmaleimide. Furthermore, the application of the assay for the detection of histidine in diluted urine samples was demonstrated.

A parallel G-quadruplex-selective luminescent probe for the detection of nanomolar calcium(II) ion

A parallel G-quadruplex-selective iridium(III) complex has been synthesized and employed as a luminescent probe in a label-free G-quadruplex-based detection assay for Ca(2+) ions in aqueous solution. In this assay, a guanine-rich oligonucleotide (G4, 5'-G4T4G4-3') initially exists in an antiparallel G-quadruplex conformation, resulting in a low luminescence signal. Upon incubation with Ca(2+) ions, the antiparallel G-quadruplex is induced into a parallel G-quadruplex conformation, which greatly enhances the luminescence emission of the iridium(III) probe. This method was highly sensitive for Ca(2+) ions with a limit of detection in the nanomolar range, and was selective for Ca(2+) over other metal ions.

Preferences of rhodamine coupled (aminoalkyl)-piperazine probes towards Hg(II) ion and their FRET mediated signaling

The metal ion induced absorption and emission signaling pattern of rhodamine coupled bis-(aminopropyl)-piperazine (1-3) and (aminoethyl)-piperazine (4) based probes evaluated in MeCN as well as in an MeCN-H2O binary mixture medium revealed that these probes exhibit optical signaling perturbations to a varying extent in MeCN, however, their complexation induced signaling could be tuned selectively towards Hg(II) in the presence of an aqueous component in the solvent medium where competitive interactions such as metal-probe interactions and hydration of metal ions play the determining factor to induce aqueous promoted Hg(II) selectivity. Attachment of another fluorophore (anthracene and nitrobenzofurazan moieties in 2 and 3 respectively) at the other end of the rhodamine coupled bis-(aminopropyl)-piperazine receptor enabled these probes to facilitate a complexation induced fluorescence resonance energy transfer (FRET) from the excited fluorophore to the ring-opened rhodamine along with contributions through operative PET inhibition and rhodamine delactonization processes. The enhancement in absorption transition of these probes at ~557 nm upon selective Hg(II)-complexation and consequent colourless to pink colour change in the solution imply a chromogenic signaling pattern whereas simultaneous fluorescence amplification and/or FRET initiation lead to fluorogenic signaling to facilitate detection at lower concentration. The Hg(II)-selective photo-physical spectral modulation in the presence of other competitive metal ions, and their reversible dual channel signaling pattern under the action of counter anions or chelating agents such as EDTA or ethylenediamine establish the potential of these probes for highly selective, sensitive and reversible 'OFF-ON-OFF' detection of Hg(II). The complexation induced optical signaling pattern of probes with a propyl-linker in their receptor (1-3) in comparison with that of 4 consisting of an ethyl-spacer indicate that signaling probe design with a substituted 'aminoalkyl-lactonized-rhodamine' subunit preferentially exhibit Hg(II) selective and sensitive dual mode signaling in an organic-aqueous mixture medium irrespective of carbon-length of the flexible alkyl spacer.

Formation of a thymine-Hg(II)-thymine metal-mediated DNA base pair: proposal and theoretical calculation of the reaction pathway

A reaction mechanism that describes the substitution of two imino protons in a thymine:thymine (T:T) mismatched DNA base pair with a Hg(II) ion, which results in the formation of a (T)N3-Hg(II)-N3(T) metal-mediated base pair was proposed and calculated. The mechanism assumes two key steps: The formation of the first Hg(II)-N3(T) bond is triggered by deprotonation of the imino N3 atom in thymine with a hydroxo ligand on the Hg(II) ion. The formation of the second Hg(II)-N3(T) bond proceeds through water-assisted tautomerization of the remaining, metal-nonbonded thymine base or through thymine deprotonation with a hydroxo ligand of the Hg(II) ion already coordinated to the thymine base. The thermodynamic parameters ΔGR =-9.5 kcal mol(-1), ΔHR =-4.7 kcal mol(-1), and ΔSR =16.0 cal mol(-1)  K(-1) calculated with the ONIOM (B3LYP:BP86) method for the reaction agreed well with the isothermal titration calorimetric (ITC) measurements by Torigoe et al. [H. Torigoe, A. Ono, T. Kozasa, Chem. Eur. J. 2010, 16, 13218-13225]. The peculiar positive reaction entropy measured previously was due to both dehydration of the metal and the change in chemical bonding. The mercury reactant in the theoretical model contained one hydroxo ligand in accord with the experimental pKa  value of 3.6 known for an aqua ligand of a Hg(II) center. The chemical modification of T:T mismatched to the T-Hg(II)-T metal-mediated base pair was modeled for the middle base pair within a trinucleotide B-DNA duplex, which ensured complete dehydration of the Hg(II) ion during the reaction.

A highly sensitive G-quadruplex-based luminescent switch-on probe for the detection of polymerase 3'-5' proofreading activity

We report herein a luminescent switch-on label-free G-quadruplex-based assay for the rapid and sensitive detection of polymerase proofreading activity using a novel iridium(III) complex as a G-quadruplex-selective probe. The interaction of the iridium(III) complex with the G-quadruplex motif facilitates the highly sensitive switch-on detection of polymerase proofreading activity. Using T4 DNA polymerase (T4 pol) as a model enzyme, the assay achieved high sensitivity and selectivity for T4 pol over other tested enzymes.

Aptamer functionalized gold nanoparticles based fluorescent probe for the detection of mercury (II) ion in aqueous solution

A method is proposed for the detection of Hg(2+) using Hg(2+) specific DNA (MSD) functionalized gold nanoparticles (AuNPs) based on the formation of T-Hg(2+)-T complex and the excellent quenching fluorescence property of AuNPs. The MSD is rich in thymine (T) and readily forms T-Hg(2+)-T configuration in the presence of Hg(2+). The MSD which is labeled with a fluorescein (FAM) at the 3'-end and a thiol at the 5'-end is bounded to the AuNPs through Au-S covalent bonds to form the probes (AuNPs-MSD). Hg(2+) detection can be easily realized by monitoring the change of fluorescence signal of AuNPs-MSD probes. Hg(2+) can be detected in a range of 0.02-1.0 µM with a detection limit of 16 nM. Besides, the assay shows excellent selectivity for Hg(2+) over other metal cations such as Fe(3+), Ca(2+), Mg(2+), Mn(2+), Cr(3+), Ni(2+), Cu(2+), Co(2+) and Pb(2+). The major advantages of this Hg(2+) assay are its water-solubility, simplicity, low cost and high sensitivity. Moreover, this method provides a potentially useful method for the Hg(2+) detection in aqueous solution.

A highly selective and non-reaction based chemosensor for the detection of Hg2+ ions using a luminescent iridium(III) complex

We report herein a novel luminescent iridium(III) complex with two hydrophobic carbon chains as a non-reaction based chemosensor for the detection of Hg(2+) ions in aqueous solution (<0.002% of organic solvent attributed to the probe solution). Upon the addition of Hg(2+) ions, the emission intensity of the complex was significantly enhanced and this change could be monitored by the naked eye under UV irradiation. The iridium(III) complex shows high specificity for Hg(2+) ions over eighteen other cations. The system is capable of detecting micromolar levels of Hg(2+) ions, which is within the range of many chemical systems.

Label-free sensing of pH and silver nanoparticles using an "OR" logic gate

Many natural phenomena are associated with the presence of two or more separate variables. We report here an "OR" DNA logic gate based on a luminescent platinum(II) switch-on probe for silver nanoparticles and pH, both of which may be considered putative indicators of pollution. The modulation of metal complex/double-stranded DNA complex phosphorescence by Ag(+) and H(+) was used to construct a simple, rapid and label-free method for the label-free detection of pH and nanomolar Ag(+) ions and nanoparticles in aqueous solutions with high selectivity.

A label-free G-quadruplex-based switch-on fluorescence assay for the selective detection of ATP

A G-quadruplex-based, label-free, switch-on fluorescence detection method has been developed for the selective detection of ATP in aqueous solution using crystal violet as a G-quadruplex-selective probe. The assay is highly simple and rapid, and does not require the use of fluorescent labeling.

Oligonucleotide-functionalized silver nanoparticle extraction and laser-induced fluorescence for ultrasensitive detection of mercury(II) ion

This study describes the development of a simple, sensitive, and selective detection system for Hg(2+) ion by combining nanoparticle extraction, fluorescent dye labeling, and flow injection analysis (FIA) detection. Repeats of 33 thymine nucleotides-functionalized silver nanoparticles (T(33)-AgNPs) specifically capture Hg(2+) from aqueous solution through the coordination between T(33) and Hg(2+). Meanwhile, Hg(2+) ion drives a T(33) conformational change from a random coil to a folded structure. The T(33)-Hg(2+)complexes adsorbed on the NP surface were collected from the initial sample by centrifugation, and they were then detached from the NP surface by addition of H(2)O(2). The T(33)-Hg(2+) complexes preferentially bind to SYBR Green I (SG), enhancing the SG fluorescence. By contrast, SG fluoresces only weakly in the presence of T(33) alone. The extraction efficiency of Hg(2+) was highly dependent on polythymine length, the concentration of T(33)-AgNPs, and the incubaton time of T(33)-AgNPs with Hg(2+). Under optimal extraction and labeling conditions, FIA detection showed the limit of detection (at a signal-to-noise ratio of three) for Hg(2+)of 3 pM. The selectivity of our analytical system is more than 1000-fold for Hg(2+) over any metal ions. We validated the applicability of this system for the determination of Hg(2+) concentrations in tap water.

Oligonucleotide-based label-free Hg2+ assay with a monomer-excimer fluorescence switch

A novel fluorescent Hg(2+) sensor was developed based on the T-Hg(2+)-T structure and a thioflavine T monomer-excimer fluorescent switch. Under optimum conditions, the selectivity is remarkably high, and Hg(2+) can be quantified over the dynamic range of 0.1 to 1.2 μM, with a limit of detection (LOD) of ~20 nM and a linear correlation coefficient of 0.995.

Vanillin-coumarin hybrid molecule as an efficient fluorescent probe for trace level determination of Hg(II) and its application in cell imaging

An efficient Hg(2+) selective fluorescent probe (vanillin azo coumarin, VAC) was synthesized by blending vanillin with coumarin. VAC and its Hg(2+) complex were well characterized by different spectroscopic techniques like (1)H NMR, QTOF-MS ES(+), FTIR and elemental analysis as well. VAC could detect up to 1.25 μM Hg(2+) in aqueous methanol solution through fluorescence enhancement. The method was linear up to 16 μM of Hg(2+). Negative interferences from Cu(2+), Ni(2+), Fe(3+), and Zn(2+) were eliminated using EDTA as a masking agent. VAC showed a strong binding to Hg(2+) ion as evident from its binding constant value (2.2×10(5)), estimated using Benesi-Hildebrand equation. Mercuration assisted restricted rotation of the vanillin moiety and inhibited photoinduced electron transfer from the O, N-donor sites to the coumarin unit are responsible for the enhancement of fluorescence upon mercuration of VAC. VAC was used for imaging the accumulation of Hg(2+) ions in Candida albicans cells.

Thermoresponsive core cross-linked micelles for selective ratiometric fluorescent detection of Hg2+ ions

We report on the fabrication of core cross-linked (CCL) micelles possessing thermoresponsive cores and their application as sensitive and selective ratiometric Hg(2+) probes with thermo-tunable detection efficiency. Well-defined double hydrophilic block copolymer (DHBC) bearing naphthalimide-based Hg(2+)-reactive moieties (NUMA, 4), PEO-b-P(NIPAM-co-NAS-co-NUMA), was synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization, where PEO, NIPAM, and NAS represent poly(ethylene oxide), N-isopropylacrylamide, and N-acryloxysuccinimide. At 25 °C, PEO-b-P(NIPAM-co-NAS-co-NUMA) unimers in aqueous solution can act as ratiometric Hg(2+) probes with a detection limit of ∼10.1 nM. After core cross-linking of the micellar nanoparticles formed at elevated temperatures, structurally stable CCL micelles with well-solvated PEO coronas and thermoresponsive cores embedded with Hg(2+)-reactive NUMA moieties were obtained. Upon Hg(2+) addition, the aqueous dispersion of CCL micelles exhibit a colorimetric transition from yellowish to colorless and a fluorometric emission transition from green to bright blue. Moreover, Hg(2+) detection limits of CCL micelles were considerably enhanced to 3.0 and 1.8 nM at 25 and 40 °C, when the thermoresponsive cores are at their swollen and collapsed state, respectively. The high selectivity of CCL micelles to Hg(2+) over other common cations was also demonstrated. Furthermore, in vitro studies revealed that CCL micelles can effectively enter into living cells and sensitively respond to the presence of Hg(2+) ions via the change of fluorescence emission color. This work represents the first example of DHBC-based CCL micelle acting as highly selective and sensitive ratiometric metal ion probes. The structural stability, water dispersibility, biocompatibility, and most importantly the thermo-tunable detection sensitivity of this novel type of CCL micelle-based sensing systems augur well for their future applications as multifunctional nanocarriers for drug delivery, sensing, imaging, and diagnosis.

A highly selective, label-free, homogenous luminescent switch-on probe for the detection of nanomolar transcription factor NF-kappaB

Transcription factors are involved in a number of important cellular processes. The transcription factor NF-κB has been linked with a number of cancers, autoimmune and inflammatory diseases. As a result, monitoring transcription factors potentially represents a means for the early detection and prevention of diseases. Most methods for transcription factor detection tend to be tedious and laborious and involve complicated sample preparation, and are not practical for routine detection. We describe herein the first label-free luminescence switch-on detection method for transcription factor activity using Exonuclease III and a luminescent ruthenium complex, [Ru(phen)₂(dppz)]²⁺. As a proof of concept for this novel assay, we have designed a double-stranded DNA sequence bearing two NF-κB binding sites. The results show that the luminescence response was proportional to the concentration of the NF-κB subunit p50 present in the sample within a wide concentration range, with a nanomolar detection limit. In the presence of a known NF-κB inhibitor, oridonin, a reduction in the luminescence response of the ruthenium complex was observed. The reduced luminescence response of the ruthenium complex in the presence of small molecule inhibitors allows the assay to be applied to the high-throughput screening of chemical libraries to identify new antagonists of transcription factor DNA binding activity. This will allow the rapid and low cost identification and development of novel scaffolds for the treatment of diseases caused by the deregulation of transcription factor activity.

Oligonucleotide-based luminescent detection of metal ions

Metal ions are prevalent in biological systems and are critically involved in essential life processes. However, excess concentrations of metals can pose a serious danger to living organisms. Oligonucleotides represent a versatile sensing platform for the detection of various molecular entities including metal ions. This review summarizes the recent advances in the development of oligonucleotide-based luminescent detection methods for metal ions.