Highly sensitive exonuclease III-assisted fluorometric determination of silver(I) based on graphene oxide and self-hybridization of cytosine-rich ss-DNA

A Novel Cu2+ Quantitative Detection Nucleic Acid Biosensors Based on DNAzyme and “Blocker” Beacon

In this paper, a “turn-off” biosensor for detecting copper (II) ions based on Cu2+-dependent DNAzyme and a “blocker” beacon were developed. Upon the copper ion being added, the Cu2+-dependent DNAzyme substrate strand was irreversibly cleaved, thereby blocking the occurrence of the ligation reaction and PCR, which inhibited the G-rich sequence from forming the G-quadruplex structure, efficiently reducing the detection signal. This method had the characteristics of strong specificity and high sensitivity compared with the existing method due to the application of ligation-dependent probe signal recognition and amplification procedures. Under the optimized conditions, this method proved to be highly sensitive. The signal decreased as the concentration of copper ions increased, exhibiting a linear calibration from 0.03125 μM to 0.5 μM and a limit of detection of 18.25 nM. Subsequently, the selectivity of this biosensor was verified to be excellent by testing different relevant metal ions. Furthermore, this detection system of copper (II) ions was successfully applied to monitor Cu2+ contained in actual water samples, which demonstrated the feasibility of the biosensor.

Dual-emissive ratiometric fluorescent nanosensor based on multi-nanomaterials for Ag+ determination in lake water

In this study, a sensitive ratiometric fluorescent nanosensor was constructed using a facile one-pot method by encapsulating carbon dots (CDs) and cadmium telluride quantum dots (CdTe QDs) into the pore cavities of a metal-organic framework (ZIF-8). In this nanosensor (CD/CdTe QD@ZIF-8), the fluorescence attributed to CdTe QDs was quenched by silver ions (Ag⁺), and the fluorescence intensity of CDs did not change. The introduction of ZIF-8 into the system can not only adsorb Ag⁺ but also easily separate CDs and CdTe QDs from the matrix. The developed CD/CdTe QD@ZIF-8 composite used as a ratiometric fluorescent probe exhibited high sensitivity and selectivity towards Ag⁺. The working linear range was 0.1-20 μM with a limit of detection (LOD) of 1.49 nM. Finally, the proposed nanosensor was applied to determine Ag⁺ in lake water with satisfactory results.

Unexpected cytosine-AuCl4- interaction under electrospray ionization mass spectrometry conditions-Formation of cytosine-Au(I) complexes

The interaction of cytosine with AuCl₄^-, under electrospray ionization mass spectrometric conditions, is discussed. On the basis of respective full scan mass spectra and product ion spectra, obtained in positive and negative ion mode, it has been deduced that cytosine is very prone to form Au(I)-containing complexes. The complexes may be formed in the gas phase by decomposition of Au(III)-containing complexes and also in the electrospray ionization source as a result of the occurrence of redox process. It has also been found that the interaction of cytosine with Au⁺ is stronger than that with Cu⁺ or Ag⁺, although taking into account the electrostatic attraction, it is not expected.

Metal-Polydopamine Framework as an Effective Fluorescent Quencher for Highly Sensitive Detection of Hg(II) and Ag(I) Ions through Exonuclease III Activity

In this paper, we propose a metal-polydopamine (MPDA) framework with a specific molecular probe which appears to be the most promising approach to a strong fluorescence quencher. The MPDA framework quenching ability toward various organic fluorophore such as aminoethylcoumarin acetate, 6-carboxyfluorescein (FAM), carboxyteramethylrhodamine, and Cy5 are used to establish a fluorescent biosensor that can selectively recognize Hg²⁺ and Ag⁺ ions. The fluorescent quenching efficiency was sufficient to achieve more than 96%. The MPDA framework also exhibits different affinities with ssDNA and dsDNA. In addition, the FAM-labeled ssDNA was adsorbed onto the MPDA framework, based on their interaction with the complex formed between MPDA frameworks/ssDNA taken as a sensing platform. By taking advantage of this sensor, highly sensitive and selective determination of Hg²⁺ and Ag⁺ ions is achieved through exonuclease III signal amplification activity. The detection limits of Hg²⁺ and Ag⁺ achieved to be 1.3 and 34 pM, respectively, were compared to co-existing metal ions and graphene oxide-based sensors. Furthermore, the potential applications of this study establish the highly sensitive fluorescence detection targets in environmental and biological fields.

Ultrasensitive colorimetric determination of silver(I) based on the peroxidase mimicking activity of a hybrid material composed of graphitic carbon nitride and platinum nanoparticles

A hybrid material composed of graphitic carbon nitride (g-C₃N₄) and platinum nanoparticles (PtNPs) with peroxidase mimicking activity was used to design a rapid, sensitive and low-cost colorimetric method for the determination of Ag(I). The g-C₃N₄-PtNPs hybrid was synthesized by reduction of chloroplatinic acid using sodium borohydride under ultrasonication and in the presence of g-C₃N₄. The hybrid can catalyze the oxidation 3,3',5,5'-tetramethylbenzidine (TMB) to produce a blue-colored product with an absorption maximum at 652 nm. On addition of Ag(I) and in the presence of citric acid, it will be reduced to form Ag(0) under the catalytic action of PtNPs. Ag(0) is then adsorbed on the surface of the g-C₃N₄-PtNPs. This results in the inhibition of the enzyme mimetic activity of the hybrid. Hence, less blue product will be formed from TMB. Under optimum conditions, Ag(I) can be quantified in the 0.05-5.0 nM concentration range with a 22 pM detection limit. This assay is rapid and reliable and was applied to the determination of Ag(I) in spiked real water samples. Graphical abstract A hybrid nanomaterial consisting of graphitic carbon nitride and platinum nanoparticles (g-C₃N₄-PtNPs) can catalyze the oxidation of tetramethylbenzidine (TMB) to produce a blue-colored product (TMBox). The enzyme mimetic activity of the hybrid is inhibited by Ag⁺, thereby decreasing the generation of blue product from TMB.

Lateral flow test for visual detection of silver (I) based on cytosine-Ag(I)-cytosine interaction in C-rich oligonucleotides

The authors describe an oligonucleotide-based lateral flow test for visual detection of Ag(I). The assay is based on cytosine-Ag(I)-cytosine [C-Ag(I)-C] coordination chemistry to capture gold nanoparticle (AuNP) tags in the test zone. A thiolated C-rich oligonucleotide probe was immobilized on the AuNPs via gold-thiol chemistry, and a biotinylated C-rich oligonucleotide probe was immobilized on the test zone. The AuNPs labelled with C-rich oligonucleotides are captured by Ag(I) ions in the test zone through the C-Ag(I)-C coordination. The resulting accumulation of AuNPs produces a readily visible red band in the test zone. Under optimized conditions, the test is capable of visually detecting 1.0 ppb of Ag(I) which is 50 times lower than the maximum allowable concentration as defined by the US Environmental Protection Agency for drinking water. Hence, the test is inexpensive and highly sensitive. It was applied to the detection of Ag(I) in spiked samples of tap water and river water. In our perception, the test is a particularly valuable tool in limited resource settings.

Polyoxy-Derivatized Perylenediimide as Selective Fluorescent Ag (I) Chemosensor

Recent investigations indicated that same concentrations of the ionic silver have harmful effects on aquatic life, bacteria and human cells. Herein we report chemosensory properties of N,N ^' -Bis(4-{2-[2-(2-methoxyethoxy)ethoxy] eth- oxy}phenyl) -3,4:9,10-perylene tetracarboxydiimide (PERKAT) towards ionic silver. The dye doped sensing agents were prepared utilizing ethyl cellulose (EC) and poly (methylmethacrylate) (PMMA) and then forwarded to electrospinning to prepare sensing fibers or mats. The PERKAT exhibited bright emission in embedded forms in EC or in the solvents of N,N-Dimethylformamide (DMF), Dichloromethane (DCM), Tetrahydrofurane (THF) and in the mixture of DCM/ethanol. The PERKAT exhibited selective and linear response for ionic silver in the concentration range of 10^-10 - 10^-5 M Ag (I) at pH 5.5. Detection limits were found to be 2.6 × 10^-10 and 4.3 × 10^-11 M, in solution phase studies and PERKAT doped sensing films, respectively. Cross sensitivity of the PERKAT towards pH and some metal ions was also studied. There were no response for the Li⁺, Na⁺, K⁺, Ca²⁺, Ba²⁺, Mg²⁺, NH₄⁺, Ni²⁺, Co²⁺, Cu²⁺,Pb²⁺, Al³⁺, Cr³⁺,Mn²⁺, Sn²⁺, Hg⁺, Hg²⁺, Fe²⁺ and Fe³⁺ in buffered solutions. To the best of our knowledge, this is the first study investigating silver sensing abilities of the PERKAT.