Metal‐Ion‐Triggered Exonuclease III Activity for the Construction of DNA Colorimetric Logic Gates

The logic system is obtained by using a series of double‐stranded (ds) DNA templates with mismatched base pairs (T–T or C–C) and ion‐modulated exonuclease III (Exo III) activity, in which the Exo III cofactors, Hg²⁺ and Ag⁺ ions, are used as inputs for the activation of the respective scission of Exo III based on the formation of T–Hg²⁺–T or C–Ag⁺–C base pairs. Additionally, two kinds of signal probes are utilized to transduce the logic operations. One is the two split G‐rich DNA strands that are used to design the OR, AND, INHIBIT, and XOR gates, whereas the other is the self‐assembled split G‐quadruplex structure to construct NOR, NAND, IMPLICATION, and XNOR operations based on DNA hybridization and strand displacement. In the presence of hemin, the split G‐quadruplex biocatalyzes the formation of a colored product, which is an output signal for the different logic gates. Thus, we have constructed a complete set of colorimetric DNA logic gates based on the Exo III and split G‐quadruplex for the first time. In addition, we are able to effortlessly recognize the logic output signals by the naked eye and their simplicity and cost‐effective design is the most apparent feature for the logic gates developed in this work.     

Electrochemiluminescence Immunosensor Based on Functionalized Graphene/Fe3O4‐Au Magnetic Capture Probes for Ultrasensitive Detection of Tetrodotoxin

An ultrasensitive electrochemiluminescence (ECL) immunosensor for the detection of tetrodotoxin (TTX) is proposed, which are composed of the branched poly‐(ethylenimine) (BPEI) functionalized graphene (BGNs)/Fe₃O₄‐Au magnetic capture probes and luminol‐capped gold nanocomposites (luminol‐AuNPs) as the signal tag. Herein, a typical sandwich immunecomplex was constructed on the glassy carbon electrode. The BGNs/Fe₃O₄‐Au hybrids could efficiently conjugate primary antibody via the Au−S chemical bonds or Au−N chemical bonds and rapidly separate under external magnetic field. The introduction of BPEI to GO could enhance the luminol‐ECL intensity. Meanwhile, the multifunctional nanocomposites have been proved with good water‐solubility, excellent electron transfer, outstanding stability, etc. The luminescent luminol‐AuNPs, a high efficient electrochemiluminescence marker, can be assembled on the second antibody, which can produce the ECL signal to achieve the determination of TTX. This proposed ECL immunosensor with a linear range from 0.01–100 ng/mL can be applied in the detection of TTX in real samples with satisfactory results.     

Dual Amplified Electrochemical Immunosensor for Hepatitis B Virus Surface Antigen Detection Using Hemin/G‐Quadruplex Immobilized onto Fe3O4‐AuNPs or (Hemin‐Amino‐rGO‐Au) Nanohybrid

A sensitive electrochemical immunosensor for Hepatitis B virus surface antigen (HBsAg) detection was fabricated based on hemin/G‐quadruplex interlaced onto Fe₃O₄‐AuNPs or hemin ‐amino‐reduced graphene oxide nanocomposite (H‐amino‐rGO‐Au). G‐quadruplex DNAzyme, which is composed of hemin and guanine‐rich nucleic acid, is an effective signal amplified tool for its outstanding peroxidase activity and Fe₃O₄‐AuNPs or (H‐amino‐rGO‐Au) nanocomposites with quasi‐enzyme activity provide appropriate support for the immobilization of hemin/G‐quadruplex. The target protein was sandwiched between the primary antibody immobilized on the GO and secondary antibody immobilized on the Fe₃O₄‐AuNPs or (H‐amino‐rGO‐Au) nanocomposites and glutaraldehyde was used as linking agent for the immobilization of primary antibody on the surface of GO. Both Fe₃O₄‐AuNPs and H‐amino‐rGO‐Au nanocomposite and also hemin/G‐quadruplex can cooperate the electrocatalytic reduction of H₂O₂ in the presence of methylene blue as mediator. The proposed immunosensor has a wide linear dynamic range of 0.1 pg/ml to 300 pg/ml with a detection limit of 60 fg/ml when Fe₃O₄‐AuNPs was used for immobilization of hemin/G‐quadruplex, while the dynamic range and DL were 0. 1–1000 pg/mL and 10 fg/mL, respectively in the presence of H‐amino‐rGO‐ Au nanocomposite as platform for immobilizing of hemin/G‐quadruplex. The proposed immunosensor was also used for analysis of HBsAg in spiked human serum samples with satisfactory results.     

Structurally Precise Silver Sulfide Nanoclusters Protected by Rhodium(III) Octahedra with Aminothiolates

A 60‐nuclear silver sulfide nanocluster with a highly positive charge ( 1 ) has been synthesized by mixing an octahedral Rh^III complex with 2‐aminoethanethiolate ligands, silver(I) nitrate, and d ‐penicillamine in water under mild conditions. The spherical surface of 1 is protected by the chiral octahedral Rh^III complex, with cleavage of the C?S bond of the d ‐penicillamine supplying the sulfide ions. Although 1 does not contain d ‐penicillamine, it is optically active because of the enantiomeric excess of the Rh^III molecules induced by chiral transfer from d ‐penicillamine. 1 can accommodate/release external Ag⁺ ions and replace inner Ag⁺ ions by Cu⁺ ions. The study demonstrates that a thiolato metal complex and sulfur‐containing amino acid can be used as cluster‐surface‐protecting and sulfide‐supplying regents, respectively, for creating chiral, water‐soluble, structurally precise silver sulfide nanoclusters, the properties of which are tunable through the addition/removal/exchange of Ag⁺ ions.     

DNA Triplexes‐Guided Assembly of G‐Quadruplexes for Constructing Label‐free Fluorescent Logic Gates

Assembly of G‐quadruplexes guided by DNA triplexes in a controlled manner is achieved for the first time. The folding of triplex sequences in acidic conditions brings two separated guanine‐rich sequences together and subsequently a G‐quadruplex structure is formed in the presence of K⁺. Based on this novel platform, label‐free fluorescent logic gates, such as AND, INHIBIT, and NOR, are constructed with ions as input and the fluorescence of a G‐quadruplex‐specific fluorescent probe NMM as output.     

Ultrasensitive determination of DNA sequences by flow injection chemiluminescence using silver ions as labels

We presented a new strategy for ultrasensitive detection of DNA sequences based on the novel detection probe which was labeled with Ag⁺ using metallothionein (MT) as a bridge. The assay relied on a sandwich-type DNA hybridization in which the DNA targets were first hybridized to the captured oligonucleotide probes immobilized on Fe₃O₄@Au composite magnetic nanoparticles (MNPs), and then the Ag⁺-modified detection probes were used to monitor the presence of the specific DNA targets. After being anchored on the hybrids, Ag⁺ was released down through acidic treatment and sensitively determined by a coupling flow injection–chemiluminescent reaction system (Ag⁺–Mn²⁺–K₂S₂O₈–H₃PO₄–luminol) (FI–CL). The experiment results showed that the CL intensities increased linearly with the concentrations of DNA targets in the range from 10 to 500 pmol L⁻¹ with a detection limit of 3.3 pmol L⁻¹. The high sensitivity in this work may be ascribed to the high molar ratio of Ag⁺–MT, the sensitive determination of Ag⁺ by the coupling FI–CL reaction system and the perfect magnetic separation based on Fe₃O₄@Au composite MNPs. Moreover, the proposed strategy exhibited excellent selectivity against the mismatched DNA sequences and could be applied to real samples analysis.     

Highly Sensitive INHIBIT and XOR Logic Gates Based on ICT and ACQ Emission Switching of a Porphyrin Derivative

Fluorescence‐switch‐based logic devices are very sensitive compared with most of the reported devices based on UV/Vis absorption systems. Herein, we demonstrate that a simple molecule, 5,10,15,20‐tetra‐(4‐aminophenyl)porphyrin (TAPP), shows protonation‐induced multiple emission switches through intramolecular charge transfer and/or aggregation‐caused quenching. Highly sensitive INHIBIT and XOR logic gates can be achieved by combining the intermolecular assembly with the intramolecular photoswitching of diprotonated TAPP (TAPPH₂²⁺). In addition, molecular simulations have been performed by DFT for a better understanding of the emission‐switching processes.     

Molecular Logic Gates and Switches Based on 1,3,4‐Oxadiazoles Triggered by Metal Ions

Organic molecular devices for information processing applications are highly useful building blocks for constructing molecular‐level machines. The development of “intelligent” molecules capable of performing logic operations would enable molecular‐level devices and machines to be created. We designed a series of 2,5‐diaryl‐1,3,4‐oxadiazoles bearing a 2‐(para‐substituted)phenyl and a 5‐(o‐pyridyl) group (substituent X=NMe₂, OEt, Me, H, and Cl; 1 a – e ) that form a bidentate chelating environment for metal ions. These compounds showed fluorescence response profiles varying in both emission intensity and wavelength toward the tested metal ions Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Hg²⁺, and Pb²⁺ and the responses were dependent on the substituent X, with those of 1 d being the most substantial. The 1,3,4‐oxadiazole O or N atom and pyridine N atom were identified as metal‐chelating sites. The fluorescence responses of 1 d upon metal chelation were employed for developing truth tables for OR, NOR, INHIBIT, and EnNOR logic gates as well as “ON‐OFF‐ON” and “OFF‐ON‐OFF” fluorescent switches in a single 1,3,4‐oxadiazole molecular system.     

Fourier transform infrared spectroscopy study of the effect of pH on anion and cation adsorption onto poly(acrylo‐amidino diethylenediamine)

The role of hydrogen bonding in the chemistry of transition‐metal complexes remains a topic of intense scientific and technological interest. Poly(acrylo‐amidino diethylenediamine) was synthesized to study the effects of hydrogen bonding on complexes at different pHs. The polymer was synthesized through the coupling of diethylene triamine with polyacrylonitrile fiber in the presence of AlCl₃ · 6H₂O addition. The adsorption capacity of this polymer was 11.4 mequiv/g. The ions used for the adsorption test were CrO, PO, Cu²⁺, Ni²⁺, Fe²⁺, and Ag⁺. All experiments were confirmed with Fourier transform infrared. In the study of anion adsorption, at low pHs, only ionic bonds existed, whereas at high pHs, no bonds existed. However, in the middle pH region, both ionic bonds and hydrogen bonds formed between poly(acrylo‐amidino diethylenediamine) and the chromate ion or phosphate ion. When poly(acrylo‐amidino diethylenediamine) and metal ions (Cu²⁺, Ni²⁺, Fe²⁺, and Ag⁺) formed complexes, a hydrogen‐bonding effect was not observed with Fourier transform infrared. The quantity of metal ions adsorbed onto poly(acrylo‐amidino diethylenediamine) followed the order Ag⁺ > Cu²⁺ > Fe²⁺ > Ni²⁺. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2010–2018, 2004     

Orthogonal Dual‐Triggered Shape‐Memory DNA‐Based Hydrogels

DNA‐based shape‐memory hydrogels revealing switchable shape recovery in the presence of two orthogonal triggers are described. In one system, a shaped DNA/acrylamide hydrogel is stabilized by duplex nucleic acids and pH‐responsive cytosine‐rich, i‐motif, bridges. Separation of the i‐motif bridges at pH 7.4 transforms the hydrogel into a quasi‐liquid, shapeless state, that includes the duplex bridges as permanent shape‐memory elements. Subjecting the quasi‐liquid state to pH 5.0 or Ag⁺ ions recovers the hydrogel shape, due to the stabilization of the hydrogel by i‐motif or C‐Ag⁺‐C bridged i‐motif. The cysteamine‐induced transformation of the duplex/C‐Ag⁺‐C bridged i‐motif hydrogel into a quasi‐liquid shapeless state results in the recovery of the shaped hydrogel in the presence of H⁺ or Ag⁺ ions as triggers. In a second system, a shaped DNA/acrylamide hydrogel is generated by DNA duplexes and bridging Pb²⁺ or Sr²⁺ ions‐stabilized G‐quadruplex subunits. Subjecting the shaped hydrogel to the DOTA or KP ligands eliminates the Pb²⁺ or Sr²⁺ ions from the respective hydrogels, leading to shapeless, memory‐containing, quasi‐liquid states that restore the original shapes with Pb²⁺ or Sr²⁺ ions.     

A H+/Ag+ Dual‐Target Responsive Label‐Free Light‐Up Probe Based on a DNA Triplex

We developed a dual‐target responsive sensor for label‐free light‐up fluorescent detection of protons (H⁺) and silver ions (Ag⁺) using an “OR′′ logic gate. Berberine, a cost‐effective and non‐toxic indicator, partially intercalates the formed triplex DNA in the presence of H⁺ or Ag⁺, generating enhanced fluorescence. The designed Ag⁺ probe has high selectivity and desirable sensitivity, which is necessary for practical use. The robust ”OR“ logic gate is capable of a rapid and reversible response to the H⁺ and/or Ag⁺ inputs.     

Formation of Silver Nanoparticles by Electron Transfer in Peptides and c-Cytochromes

The reduction of Ag⁺ ions to Ag⁰ atoms is a highly endergonic reaction step, only the aggregation to Ag_n clusters leads to an exergonic process. These elementary chemical reactions play a decisive role if Ag nanoparticles (AgNPs) are generated by electron transfer (ET) reactions to Ag⁺ ions. We studied the formation of AgNPs in peptides by photoinduced ET, and in c-cytochromes by ET from their Fe²⁺/hemes. Our earlier photoinduced experiments in peptides had demonstrated that histidine prevents AgNP formation. We have now observed that AgNPs can be easily synthesized with less-efficient Ag⁺-binding amino acids, and the rate increases in the order lysine<asparagine<aspartate<serine. The ability of Fe²⁺/hemes of c-cytochromes to reduce Ag⁺ to AgNPs was studied in an enzymatic experiment and with living bacteria Geobacter sulfurreducens (Gs).     

A Colorimetric and Fluorimetric Chemodosimeter for Copper Ion Based on the Conversion of Dihydropyrazine to Pyrazine

In this research, we successfully synthesized and fully characterized the new compound 5,8,13,16,21,24‐hex‐(triisopropylsilyl)ethynyl)‐6,23‐dihydro‐6,7,14,15,22,23‐hexaza‐trianthrylene ( HHATA , brown color in a mixed solvent of CH₂Cl₂/CH₃CN 1:1, v/v, weakly blue fluorescent), which can be easily oxidized to 5,8,13,16,21,24‐hex‐(triisopropylsilyl)ethynyl)‐6,7,14,15,22,23‐hexazatrianthrylene ( HATA ) (yellow color in CH₂Cl₂/CH₃CN 1:1, v/v), red fluorescent) by Cu²⁺ ions. This reaction only proceeds efficiently in the presence of Cu²⁺ ions when compared with other common metal ions such as Fe³⁺, Co²⁺, Mn²⁺, Hg²⁺, Ni²⁺, Pb²⁺, Ag⁺, Mg²⁺, Ca²⁺, K⁺, Na⁺, and Li⁺. Our result suggests that this reaction can be developed as an effective method for the detection of Cu²⁺ ions.     

A Highly Copper‐Selective Ratiometric Fluorescent Sensor Based on BODIPY

A new ratiometric fluorescent sensor ( 1 ) for Cu²⁺ based on 4,4‐difluoro‐4‐bora‐3a,4a‐diaza‐s‐indacene (BODIPY) with di(2‐picolyl)amine (DPA) as ion recognition subunit has been synthesized and investigated in this work. The binding abilities of 1 towards different metal ions such as alkali and alkaline earth metal ions (Na⁺, K⁺, Mg²⁺, Ca²⁺) and other metal ions ( Ba²⁺, Zn²⁺, Cd²⁺, Fe²⁺, Fe³⁺, Pb²⁺, Ni²⁺, Co²⁺, Hg²⁺, Ag⁺) have been examined by UV‐vis and fluorescence spectroscopies. 1 displays high selectivity for Cu²⁺ among all test metal ions and a ～10‐fold fluorescence enhancement in I₅₈₂/I₅₅₈ upon excitation at visible excitation wavelength. The binding mode of 1 and Cu²⁺ is a 1:1 stoichiometry determined via studies of Job plot, the nonlinear fitting of the fluorometric titration and ESI mass.     

A Bis‐Oxime Derivative of Diaza‐18‐Crown‐6 as an Ionophore for Silver Ion

A new pendant‐arm derivative of diaza‐18‐crown‐6, containing two oxime donor groups, has been synthesized and incorporated into a polyvinyl chloride (PVC) membrane ion‐selective electrode. The electrode shows selectivity for Ag⁺ ion, with a near Nernstian response. Pb²⁺, Cu²⁺, Hg²⁺, and Tl⁺ are major interfering ions, with Cd²⁺ having minor interference. The electrode shows no potentiometric response for the ions Mg²⁺, Al³⁺, K⁺, Ca²⁺, Ni²⁺, Fe³⁺, and La³⁺, and is responsive to H⁺ at pH<6.     

A New Fluorescent Chemosensor for Metal Ions Based upon 1,8‐Naphthalimide and 8‐Hydroxyquinoline

A new fluorescent chemosensor based upon 1,8‐naphthalimide and 8‐hydroxyquinoline was synthesized, and its fluorescent properties in the presence of different metal cations (Hg²⁺, Ag⁺, Zn²⁺, Fe²⁺, Cd²⁺, Pb²⁺, Ca²⁺, Cu²⁺, Mg²⁺, and Ba²⁺) were investigated. It displayed fluorescence quenching with some heavy and transition metal (HTM) ions, and the quenching strongly depended on the nature of HTM ions.     

A Novel Polymeric Chemosensor: Dual Colorimetric Detection of Metal Ions Through Click Synthesis

A highly colored polystyrene derivative bearing side chain chromophores composed of dialkylanilino donor and cyano‐based acceptor groups, prepared by atom‐economic click postfunctionalization, displays the dual colorimetric detection behavior of several metal ions based on the specific interactions with different nitrogen atoms. Hard to borderline metal ions, such as Fe³⁺, Fe²⁺, and Sn²⁺, are always recognized by the dialkylanilino nitrogen atom, resulting in a decrease in the charge‐transfer (CT) band intensity of the donor–acceptor chromophores. On the other hand, the recognition site of a soft metal ion of Ag⁺ is the cyano nitrogen atom due to the readily formed multivalent coordination, which produces a bathochromic shift of the CT band.     

A Highly Selective and Sensitive Fluorescent Chemosensor for Detection of Al3+ in Totally Aqueous Media

A fluorescent chemosensor ( 1 ) based on 2‐hydroxy‐1‐naphthaldehyde Schiff‐base was developed for the detection of Al³⁺ in 100% aqueous solution. Upon addition of Al³⁺, a significant fluorescence enhancement was observed, which was not affected by other metal ions including Na⁺, K⁺, Ca²⁺, Mg²⁺, Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺, Cr³⁺, Ag⁺, Pb²⁺, Zn²⁺, Cd²⁺, Hg²⁺, Fe²⁺ and Fe³⁺ under weak acid conditions. Moreover, the specific response to Al³⁺ was visible under natural light. The binding mode between 1 and Al³⁺ was clarified by ESI‐MS and ¹H NMR.     

Aptamer‐based detection and quantitative analysis of human immunoglobulin E in capillary electrophoresis with chemiluminescence detection

A novel aptamer‐based CE with chemiluminescence (CL) assay was developed for highly sensitive detection of human immunoglobulin E (IgE). The IgE aptamer was conjugated with gold nanoparticles (AuNPs) to form AuNPs‐aptamer that could specifically recognize the IgE to produce an AuNPs‐aptamer‐IgE complex. The mixture of the AuNPs‐aptamer‐IgE complex and the unbounded AuNPs‐aptamer could be effectively separated by CE and sensitively detected with luminol‐H₂O₂ CL system. By taking the advantage of the excellent catalytic behavior of AuNPs on luminol‐H₂O₂ CL system, the ultrasensitive detection of IgE was achieved. The detection limit of IgE is 7.6 fM (S/N = 3) with a linear range from 0.025 to 250 pM. Successful detection of IgE in human serum samples was demonstrated and the recoveries of 94.9–103.2% were obtained. The excellent assay features of the developed approach are its specificity, sensitivity, adaptability, and very small sample consumption. Our design provides a methodology model for determination of rare proteins in biological samples.     

Efficient ensemble and IDA system based on the metal binding motif for highly sensitive and selective detection and determination of carbonate and citrate ions

Herein, we have reported a novel naked eye detection method which is based on the analyte competing for a metal reporter with a chromogenic indicator. This assay is based on the highly specific interaction between the anions and the metal ions and murexide (Mure) probe in a competition assay format. The resulting high sensitivity and selectivity for citrate and carbonate were achieved by changing the metal ions. The indicator is set free due to its displacement from the Mure/Cu²⁺ complex by citrate (Cit³ˉ) and the change in absorbance may be due to the further complexation of carbonate (CO₃²ˉ) with the additional coordination sites present in the zinc atom of Mure/Zn²⁺ complex. The dye-based ensemble systems are expected to be a potential and practical way for the detection of nanomolar concentrations of analytes in 100% aqueous solutions. The chemosensor enabled sensitive and selective detection of Cit³ˉ and CO₃²ˉ with detection limits of 19.1 and 9.4 nmol L^?1, respectively. These systems are simple in design, fast in operation and are more promising than previous methods. This novel method eliminated the need for separation processes, chemical modifications, organic cosolvents, and sophisticated instrumentations. Chiefly, the protocol offers high selectivity for the determination of Cit³ˉ and CO₃²ˉ among anions found in human urine samples in the presence of some biological species, including K⁺, Mg²⁺, Fe³⁺, Ca²⁺, Zn²⁺, Na⁺, glucose, urea, uric acid and ascorbic acid. Further, NAND and INHIBIT molecular logic gates were obtained using chemical inputs and UV–Vis absorbance signal as the output.