DNAzyme-embedded hyperbranched DNA dendrimers as signal amplifiers for colorimetric determination of nucleic acids

A DNAzyme-embedded hyperbranched DNA dendrimer is used as a colorimetric signal amplifier in an ultrasensitive detection scheme for nucleic acids. The hyperbranched DNA dendrimers were constructed by single-step autonomous self-assembly of three structure-free DNA monomers. A cascade of self-assembly reactions between the first and second strands leads to the formation of linear DNA concatemers containing overhang flank fragments. The third strand, which bears a peroxidase-mimicking DNAzyme domain, serves as a bridge to trigger self-assembly between the first and second strands across the side chain direction. This results in a chain branching growth of the DNAzyme-embedded DNA dendrimer. This signal amplifier was incorporated into the streptavidin-biotin detection system which comprises an adaptor oligonucleotide and a biotinylated capture probe. The resulting platform is capable of detecting a nucleic acid target with an LOD as low as 0.8 fM. Such sensitivity is comparable if not superior to most of the reported enzyme-free (and even enzyme-assisted) signal amplification strategies. The DNA dendrimer based method is expected to provide a universal platform for extraordinary signal enhancement in detecting other nucleic acid biomarkers by altering the respective sequences of adaptor and capture probe.

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Graphical abstract Schematic of an assembly of a DNAzyme-embedded hyperbranched DNA dendrimer which operates as a signal amplifier for nucleic acids detection. The nanostructure is constructed by autonomous self-assembly of three DNA monomers. Colored letters represent each domain, and complementary domains are marked by asterisk. Domain d represents the DNAzyme sequence.

     

Novel Cesium Membrane Sensor Based on a Cavitand

A PVC‐based membrane sensor was prepared for Cs⁺ ions, which was based on 7,11,15,28‐tetraiodo‐1,21,23,25‐tetramethyl‐2,20:3,19‐dimethano‐1H,21H,23H,25H‐bis[1,3]dioxocino[5,4‐i:5′,4′i′] benzo[1,2‐d:5,4‐d′]‐bis[1,3]benzodioxocin stereoisomer (cavitand). The proposed membrane electrode exhibits a linear dynamic range of 1.0 × 10^?;1–1.0 × 10^?;5M, with a Nernstian slope of 59.1 ± 0.3 mV per decade, and a detection limit of 5.0 × 10^?;6 M. It has a very fast response time of <10 s and can be used for at least eight weeks without any considerable divergence in its potentials. The best sensor performance was obtained with a membrane containing 30% PVC, 62% dibutylphthalate (DBP), 6% cavitand, and 2% potassium tetrakis(p‐chlorophenyl) borate (KTpClPB). The sensor could be used in a pH range of 4.3–9.5.     

Sulfate-selective PVC membrane electrode based on a strontium Schiff's base complex

A strontium Schiff's base complex (SS) can be used as a suitable ionophore to prepare a sulfate-selective PVC-based membrane electrode. The use of oleic acid (OA) and hexadecyltrimethylammonium bromide (HTAB), as additives, and nitrobenzen (NB), dibutyl phthalate (DBP) and benzyl acetate (BA) as solvent mediators, were investigated. The best performance was observed with a membrane composition PVC: NB: SS: HTAB of 30%: 62%: 5%: 3% ratio. The resulting sensor works well over a wide concentration range (1.0 x 10(-2)-1.0 x 10(-6) M) with a Nernstian slope of -29.2 mV per decade of sulfate activity over a pH range 4.0-7.0. The limit of detection of the electrode is 5 x 10(-7) M. The proposed sensor shows excellent discriminating ability toward SO4(2-) ions with regard to many anions. It has a fast response time of about 15 s. The membrane electrode was used to the determination of zinc in zinc sulfate tablets. The sensor was also used as an indicator electrode in the potentiometric titration of SO4(2-) against barium ion.     

Synthesis of a charge-transfer complex of (1,3-diphenyldihydro-1H-imidazole)-4,5-dione dioxide with iodide and its application to the development of a highly selective and sensitive triiodide PVC-membrane electrode

In this paper, a novel membrane triiodide sensor based on a charge-transfer complex of (1,3-diphenyldihydro-1H-imidazole)-4,5-dionedioxime with iodine (CTCI) as a membrane carrier is introduced. The best performance was obtained with a membrane containing 30% polyvinylchloride (PVC), 63% dibutylphthalate (DBP), 5% CTCI, and 2% hexadecyltrimethylammonium bromide (HTAB). The electrode shows a Nernstian behavior (slope of 58.2 ± 0.3) over a very wide triiodide ion concentration range (5.0 × 10⁻⁸−1.0 × 10⁻² M), and has a low detection limit (4.0 × 10⁻⁸ M). The potentiometric response of the sensor is independent of pH of the solution in the pH range 3.0–9.0. The proposed sensor has a very low response time (<12 s) and a good selectivity relative to a wide variety of common inorganic and organic anions, including iodide, bromide, chloride, nitrate, sulfate, thiocyanate, monohydrogen phosphate, and acetate. In fact, the selectivity behavior of the proposed triiodide ion-selective electrode shows great improvements compared to the previously reported electrodes for triiodide ion. The proposed membrane sensor can be used for at least 6 months without any divergence in its potentials. The electrode was successfully applied as an indicator electrode in the titration of triiodide with thiosulfate ion. The text was submitted by the authors in English.     

Novel Metronidazole Membrane Sensor Based on a 2,6‐(p‐N,N‐Dimethylaminophenyl)‐4‐Phenylthiopyrylium Perchlorate

A novel PVC‐based membrane sensor based on 2,6‐(p‐N,N‐dimethylaminophenyl)‐4‐phenylthiopyrylium perchlorate (DAPP) is described. The electrode exhibits a sub‐Nernstian response to 1‐(beta‐hydroxyethyl)‐2‐methyl‐5‐nitroimidazole (metronidazol) over a relatively wide concentration range (1.0 × 10^?1 to 1.0 × 10^?5 M) with a detection limit of 8.0 × 10^?6 M. The best performance was obtained with the membrane containing 30% poly (vinyl chloride), 50% dibutyl phthalate, 7% DAPP and 13% oleic acid. It has a fast response time (< 30 s) and can be used for at least four weeks without any major deviation. The proposed sensor revealed very good selectivity for metronidazole over a wide variety of common cations, anions and amino acids and could be used in the pH range of 6.0–7.5. It was successfully used for direct determination of metronidazole in an oral synthetic antiprotozoal as an antibacterial agent, in metronidazole tablets, and metronidazole injections and metronidazole gels.     

Fluoride determination in some mouth wash preparations by a novel La(III) graphite coated membrane sensor based on amitraz

Solution studies on the binding properties of N-2,4-dimethylphenyl-N′-ethylformamidine (amitraz) toward nine lanthanide ions including lanthanum, cerium, neodium, samarium, europium, gadolinium, terbium, dysprosium, ytterbium and some other transition and heavy metal ions such as copper, lead, cobalt, nickel ions, showed a selective 1:1 complexation between amitraz and lanthanum ions. Consequently, amitraz was applied as an ion carrier in construction of a novel poly(vinyl chloride) membrane sensor for La(III). The sensor has a linear dynamic range of 1.0 × 10⁻¹ to 1.0 × 10⁻⁷ M with a Nernstian slope of 19.8 ± 0.2 mV per decade and a detection limit of 8.0 × 10⁻⁸ M. The proposed sensor displays a fast response time (<8 s), and can be used for at least 2 months without any considerable divergences in the potentials. The La(III) membrane sensor revealed comparatively good selectivity with respect to most of cations including alkaline, alkaline earth, and some transition and heavy metal ions. It could be used in a pH range of 3.0-9.0. The proposed membrane electrode was used as an indicator electrode in the potentiometric titration of La(III) ions with an EDTA solution, and also in the determination of fluoride concentration in some mouth wash preparations.     

PVC‐Based on Thiopyrilium Derivatives Membrane Electrodes for Determination of Histamine

This study describes novel histamine‐selective electrodes, having their basis on thiopyrilium (TP) derivatives as suitable ionophores. The electrodes were prepared by incorporating the TP derivatives into plasticized poly(vinyl chloride) (PVC) membranes. These electrodes demonstrate high selectivity as far as the histamine response is considered, as compared with many common inorganic anions and other kinds of amino acids. The influence of membrane composition, pH and the effect of lipophilic cationic and anionic additives on the response characteristics of the electrode were investigated. The resulting sensor based on 2,6‐bis(4‐dimethyl amino phenyl)‐4‐phenyl thiopyrilium perchlorate (TP4) responds to histamine in a wide concentration range from 5.0 × 10^?6 to 1.0 × 10^?1 M with a slope of 54.8 ± 0.6 mV decade^?1 and detection limit of 3.0 μ mol L^?1 (～0.3 ppm). The electrode illustrates fast response time and good long‐term stability (more than 2 months). The ability to design histamine‐selective electrodes based on new thiopyrilium derivatives and both to alter selectivity and improve the response characteristics through structural changes to the charged ionophore, has been investigated. The prepared electrode was used for the determination of histamine in a synthetic human serum sample. Consequently, satisfactory recovery results were obtained over a wide concentration range of histamine.     

Host (nanocavity of zeolite Y)/guest (Co(II), Ni(II) and Cu(II) complexes of unsaturated 16-membered octaaza; 3,4,11,12-tetramethyl-1,2,5,6,9,10,13,14-octaazacyclohexadecane; Me4[16]aneN8 nanocomposite materials (HGNM): template synthesis, characterization and catalytic oxidation of benzyl alcohol

Nanocavity zeolite-Y (host) encapsulated Co(II), Ni(II) and Cu(II) complexes of unsaturated 16-membered octaaza; 3,4,11,12-tetramethyl-1,2,5,6,9,10,13,14-octaazacyclohexadecane ‘Me₄[16]aneN₈’; macrocycle (guest) were synthesized and characterized by chemical analyses, s.e.m., x.r.d., u.v.–vis., d.r.s., surface area, pore volume, conductometric, magnetic measurements and i.r. spectroscopy with a view to confirming the encapsulation of complexes and to arrive at the composition, structure and geometry of encapsulated complexes. The characterization data show the absence of extraneous complexes, retention of zeolite crystaline structure and encapsulation in the nanocavities. Host–Guest Nanocomposite Materials (HGNM) ‘[M(Me₄[16]aneN₈)]²⁺-NaY’ are catalytically very efficient as compared to other neat complexes for the partial oxidation of benzyl alcohol which is stable and becomes recycled without much deterioration.     

Application of Tetra Cyclohexyl Tin(IV) as an Anionic Carrier for the Construction of a New Salicylate Membrane Sensor

A new tin complex namely tetracyclohexyl tin(IV) (TCHT) was synthesized and used as the ion carrier for the construction of a highly selective salicylate sensor. This sensor shows a Nernstian response to salicylate ions over a very wide concentration (1.0 × 10^?7–1.0 × 10^?1 M) in a pH range of 5.5–10.5. The optimum selectivity and response could be obtained for a membrane incorporating 30% PVC, 61% BA, 3% of cationic additive (HTAB) and 6% of TCHT. The response time of the electrode is very short in the whole concentration range (15 s). The electrode also shows an excellent discriminating ability for salicylate ions with respect to the most common organic and inorganic anions including chloride, sulfate, nitrate, nitrite, cyanide, sulfite, iodide, thiocyanate, phosphate, acetate, oxalate, citrate, and tartarate ions. The detection limit of the proposed sensor is 8.0 × 10^?8 M. The electrode was successfully used for determining the concentration of salicylate ion in synthetic serums.     

Highly Selective PVC‐Based Membrane Electrode Based on 2,6‐Diphenylpyrylium Fluoroborate

A highly selective PVC‐membrane electrode based on 2,6‐diphenylpyrylium fluoroborate is presented. The electrode reveals a Nernstian potentiometric response for sulfate ion over a wide concentration range (5.0 × 10^?6‐1.0 × 10^?1 M). The electrode has a response time of about 10 s and can be used for at least 2 months without any divergence. The proposed sensor revealed very good selectivities for sulfate over a wide variety of common organic and inorganic anions and could be used over a wide pH range (2.5–9.5). The detection limit of the sensor is 3.0 × 10^?6 M. It was successfully applied to the direct determination of salbutamol, paramomycin tablets, and as an indicator electrode for potentiometric titration of sulfate ions with barium ions.