A novel metal-organic framework of Co-hemin for portable and visual colorimetric detection of 2,4-dichlorophenoxyacetic acid.

On-site quantitative analysis of 2,4-dichlorophenoxyacetic acid (2,4-D) is of significant importance for addressing increasing concerns about public health and environmental quality. Here, a novel metal-organic framework (MOF) of Co-hemin is synthesized and first used for on-site colorimetric monitoring of 2,4-D. 2,4-D as an inhibitor of alkaline phosphatase could specifically suppress the production of ascorbic acid, which restrained in situ etching of Co-hemin and further triggered the colorimetric response. In the colorimetric assay, Co-hemin displayed good oxidase-like activity without addition of H2O2, which could avoid the shortcomings of H2O2 such as toxicity and instability. The Co-hemin biosensor exhibited a relatively low detection limit of 33 ng mL-1 for 2,4-D by the UV method. Moreover, a smartphone based RGB analysis system for the sensitive detection of 2,4-D was developed, and exhibited a good linear relationship between the RGB model parameter and the concentration of 2,4-D. The operability and accuracy of the Co-hemin biosensor were confirmed by the quantitative determination of 2,4-D in real samples, such as serum and tap water. Also, the Co-hemin based colorimetric biosensor showed good selectivity and specificity. Moreover, the developed assays displayed good application in constructing complex logic gates. This work not only provided a portable and visual platform for on-site monitoring of 2,4-D, but also expanded application prospects in the field of complex biological analysis.

L-Cysteine modified gold nanoparticles for tube-based fluorometric determination of mercury(II) ions.

A fluorescent probe is described for detection of mercury(II) ion by using L-cysteine-modified gold nanoparticles (Cys-AuNP). These were fabricated by a tube-based redox reaction where Cys acts as both the reducing reagent and capping ligand. The Cys-AuNP display red fluorescence, with excitation/emission peaks at 373/625 nm. Owing to the high-affinity of the Hg(II)-Au(I) interaction and the Hg(II)/carboxy or amino group interaction, the presence of Hg(II) cause selective quenching the fluorescence, while other metal ions do not give such an effect. Based on these findings, a method was designed for the determination of Hg(II) that has attractive figures of merit. These include a low limit of detection (1.3 nM), a wide detection range (from 2 nM to 30µM), and excellent specificity. The method was applied to Hg(II) screening in (spiked) tap and river water, and it gave satisfactory results. Graphical abstract Schematic representation of the application of L-cysteine modified gold nanoparticles (Cys-AuNP) for qualitative and quantitative detection of mercury(II) ions. Based on the interaction between Cys-AuNP and mercury(II) ion to quench the red fluorescence of Cys-AuNP, the target mercury(II) can in turn be determined by a fluorometric method.

Mercaptosuccinic acid-coated NIR-emitting gold nanoparticles for the sensitive and selective detection of Hg2.

A sensitive fluorescent detection platform for Hg2+ was constructed based on mercaptosuccinic acid (MSA) coated near-infrared (NIR)-emitting gold nanoparticles (AuNPs). The thiolated mercaptosuccinic acid was employed as both reducing agent and surface coating ligand in a one-step synthesis of NIR-emitting AuNPs (MSA-AuNPs), which exhibited stable fluorescence with the maximum wavelength at 800nm and a wide range of excitation (220-650nm) with the maxima at 413nm. The MSA coated NIR-emitting AuNPs showed a rapid fluorescence quenching toward Hg2+ over other metal ions with a limit of detection (LOD, 3δ) as low as 4.8nM. The sensing mechanism investigation revealed that the AuNPs formed aggregation due to the "recognition" of Hg2+ from the MSA, and the resultant strong coupling interaction between Hg2+ and Au (I) to further quench the fluorescence of the AuNPs, which synergistically resulted in a highly sensitive and selective fluorescence response toward Hg2+. This proposed strategy was also demonstrated the possibility to be used for Hg2+ detection in water samples.

Coordination-induced decomposition of luminescent gold nanoparticles: sensitive detection of H2O2 and glucose.

The surface inert of luminescent gold nanoparticles (AuNPs) toward biomolecules set a challenge to further exploit their bioanalytical applications using the direct luminescence response. Herein, we report a novel approach to induce significant luminescence quenching of the AuNPs upon the interaction with a metal coordination ligand tris(2-carboxyethyl)phosphine (TCEP), providing a strategy for the detection of H2O2 with a limit of detection (LOD) of 14 nM through the reaction between H2O2 and TCEP to protect the luminescence quenching of the AuNPs. Furthermore, this strategy is also extended for sensitive and selective detection of glucose with a LOD of 1.1 µM based on monitoring the production of H2O2 catalyzed from the oxidation of glucose. The highly extendable feature of this strategy can have great potential in the sensitive detection of other biomolecules. Graphical Abstract A facile and extendable strategy has been developed for the sensitive detection of H2O2 and glucose based on the interaction between luminescent gold nanoparticles and TCEP, a metal coordination ligand.

Preparation of Pb(II) Ion Imprinted Polymer and Its Application as the Interface of an Electrochemical Sensor for Trace Lead Determination.

An ion imprinted polymer (IIP) was synthesized by using Pb(II) as a template, methacrylic acid as a monomer, 8-hydoxyquinoline as a ligand, ethylene glycol dimethacrylate (EGDMA) as a crosslinker, and azobisisobutyronitrile as initiator. It can be applied to prepare lead ion selective voltammetric sensor for Pb(II) adsorption and trace detection. The Pb(II)-IIP was characterized by FTIR spectra and SEM image. Under optimized conditions of polymerization, the Pb(II)-IIP showed good adsorption behavior toward Pb(II), with a magnitude of three times higher than that of the non imprinted polymer (NIP). Also, it exhibited a favorable selectivity for Pb(II), compared with other heavy metal ions of Hg(II), Cd(II), Cu(II), and a negligible adsorption to the other cations. The synthesized IIP was used to determine trace levels of Pb(II) in food and water samples, with a calibration linear range over Pb(II) concentrations of 0.05 - 60 µM and a limit of detection at 0.01 µM.

Study on the interaction between quinine sulfate and DNA by multiple spectral methods and their analytical applications.

The interaction of quinine sulfate (QS) and DNA has been investigated by spectra methods including fluorescence spectroscopy and resonance light scattering (RLS) technique in aqueous solutions. The QS showed an obvious decrease of fluorescence intensity upon the addition of trace amounts of DNA, and the quenching mechanism was suggested to be static quenching according to the Stern-Volmer equation. Under the acidic condition of pH 2.5, the quenched fluorescence intensity of the QS-DNA system was linearly dependent on the concentration of ctDNA ranging from 0.02 to 2.5 mg/L. The interaction between QS and DNA as well as the detection of DNA was further confirmed by RLS technique, and the results showed that enhanced RLS intensity was linearly related to the concentration of ctDNA from 0.01 to 3.5 mg/L. Therefore, two spectral methods for the detection of ctDNA have been established with the use of a QS small molecular probe.

[Synthesis and spectral properties of L-amino acid tailed porphyrin and their zinc(II) complexes].

Three new L-amino acid tailed porphyrins and their zinc(II) complexes were synthesized by L-amino acid and 5-[o-(bromnoethoxyl)phenyl]-10,15,20-triphenyl prophyrin. FABMS, UV-Vis, IR, elemental analysis and chemical analysis were used to determine the structures of these porphyrins and their zinc complexes. The FTIR spectra (4000-400 cm(-1)) of L-amino acid tailed porphyrin and its zinc(II) complexes were measured and investigated. The major bands have been empirically assigned in comparison with L- amino acid tailed porphyrin and its zinc(II) complexes.