A Novel Polydopamine Grafted 3D MOF Nanocubes Mediated GR-5/GC DNAzyme Complex with Enhanced Fluorescence Emission Response toward Spontaneous Detection of Pb(II) and Ag(I) Ions.

In this work, we have proposed a novel DNAzyme/MnCoPBAs-PDANCs complex-based fluorescence biosensor for subsequent detection of Pb2+ and Ag+ ions. The GR-5/GC-rich DNAzymes are strongly anchored or quenched on the surface of polydopamine hybridized 3D metal-organic framework MnCoPBAs-PDANCs by π-π stacking interaction. Addition of Pb2+ ions has exhibited a catalytic inner cleavage of DNAzyme complex and disturbs to release shorter GC-rich sequence over the surface of MnCoPBAs-PDANCs complexes. Later on, addition of intercalating dye ThT interacts with free GC-rich substrate strand to form a G-quadruplex-ThT structure and thereby effectively enhanced the fluorescence intensity ("turn-on"). Interestingly, subsequent addition of Ag+ ions has an uncoiled GQ-ThT structure to provide a robust double-stranded DNA featuring C-Ag+-C, which diminishes ("turn-off") the fluorescence intensity. This improved hybrid sensor exhibited a linear response in a concentration range of 3-9 nM for Pb2+, while 4-20 nM for Ag+ ions with a lower detection limit of 1.6 and 4.2 nM, respectively. Further, the method was successfully implemented for the analysis of Pb2+ and Ag+ ions in real water samples with a good regaining and high efficacy for practical analysis.

A magnetic nanoscale metal-organic framework (MNMOF) as a viable fluorescence quencher material for ssDNA and for the detection of mercury ions via a novel quenching-quenching mechanism.

A novel fluorescent biosensor has been designed and synthesized comprising a magnetic nanoscale metal-organic framework (MNMOF) functionalized with fluorescein amidite (FAM)-labeled ssDNA. It exhibits good sensitivity and selectivity for Hg(ii) cations over other co-existing metal ions. MNMOF was fabricated by a one-pot synthetic method and it was successfully characterized with various techniques such as UV-visible spectroscopy, fluorescence spectroscopy, Fourier-transform infrared (FT-IR) spectrometry, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The FAM-labeled ssDNA was adsorbed onto the surface of MNMOF through π-π stacking and electrostatic interactions, which resulted in the partial quenching of its fluorescence intensity (65%). Upon the subsequent addition of Hg(ii) ions, the fluorescence intensity was further quenched at 52%, due to the re-adsorption of dsDNA onto the surface of MNMOF. Thus, the FAM-labeled ssDNA showed a drastic decrease in fluorescence intensity with Hg(ii). This quenching-quenching mechanism led to a linear response in the fluorescence intensity to Hg(ii) concentration (R 2 = 0.934) with a low detection limit of 8 nM. The specific merits of MNMOF make it an ideal platform for mercury sensor applications.

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.

Fluorometric determination of lead(II) and mercury(II) based on their interaction with a complex formed between graphene oxide and a DNAzyme.

The authors have designed a DNAzyme where graphene oxide (GO) interacts with the ssDNA stem loop region. The DNAzyme strand and substrate strand are hybridized and bind to the surface of GO which act as a signal reporter, while GO act as a strong quencher. The presence of Pb(II) ion disturbs the GO-DNAzyme complex and causes internal cleavage of the DNAzyme complex. On addition of Thioflavin T (ThT) as a quadruplex inducer, fluorescence intensity (best measured at excitation/emission peaks of 425/490 nm) is strongly enhanced. Subsequent addition of Hg(II) to ThT/G-quadruplex complex decreases fluorescence because the G-quadruplex is unwinding to form a T-Hg(II)-T dsDNA system. Therefore, the change in fluorescence intensity of ThT is directly correlated to the concentration of Pb(II) and Hg(II). As a result, the assay is highly selective and sensitive. The limits of detection are 96 pM for Pb(II) and 356 pM for Hg(II). Moreover, the method was applied to the detection of the two ions in spiked real samples and gave satisfactory results. Graphical abstract A label free sensitive and selective "on-off" fluorescent assay for detection of Pb(II) and Hg(II) based on graphene oxide -DNAzyme complex with fluorogenic dye thioflavin T. The limits of detection are 96 pM (Pb2+) and 356 pM (Hg2+).

Synthesis and anti-microbial screening of some Schiff bases of 3-amino-6,8-dibromo-2-phenylquinazolin-4(3H)-ones.

In the present study, a series of novel Schiff bases were synthesized by condensation of 3-amino-6,8-dibromo-2-phenylquinazolin-4(3H)-ones with different aromatic aldehydes via cyclized intermediate 6,8-dibromo-2-phenyl benzoxazin-4-one. The chemical structures were confirmed by means of IR, (1)H NMR, (13)C NMR, Mass spectral and Elemental analysis. These compounds were screened for anti-bacterial (Staphylococcus aureus ATCC-9144, Staphylococcus epidermidis ATCC-155, Micrococcus luteus ATCC-4698, Bacillus cereus ATCC-11778, Escherichia coli ATCC-25922, Pseudomonas aeruginosa ATCC-2853, and Klebsiella pneumoniae ATCC-11298) and anti-fungal (Aspergillus niger ATCC-9029 and Aspergillus fumigatus ATCC-46645) activities by paper disc diffusion technique. The minimum inhibitory concentrations (MICs) of the compounds were also determined by agar streak dilution method. Among the synthesized compounds 3-(3,4,5-trimethoxybenzylideneamino)-6,8-dibromo-2-phenylquinazolin-4(3H)-one 10 was found to be the most potent anti-microbial activity with MICs of 18.9, 19.1, 18.8, 21.7, 18.2, 19.3, 16.7, 8.6 and 10.1 microg/ml against above mentioned respective strains. Compounds were found to exhibit more anti-fungal than anti-bacterial activity.

Synthesis of Schiff bases of 4-(4-aminophenyl)-morpholine as potential antimicrobial agents.

In the present study, a novel series of Schiff bases of 4-(4-aminophenyl)-morpholine were synthesised and characterised by IR, 1H-NMR, 13C-NMR, Mass spectral and elemental analysis. The compounds were screened for antibacterial (Staphylococcus aureus (ATCC 9144), Staphylococcus epidermidis (ATCC 155), Bacillus cereus (ATCC 11778), Micrococcus luteus (ATCC 4678), and Escherichia coli (ATCC 25922)) and antifungal (Candida albicans (ATCC 2091) and Aspergillus niger (ATCC 9029)) activities. The minimum inhibitory concentrations of the compounds were also ascertained by agar streak dilution method. 4-(4-(4-Hydroxy-benzylidene-imino)phenyl)-morpholine (7) was found to be the most potent antimicrobial activity with MIC of 25, 19, 21, 16, 29, 20 and 40 microg/ml against S. aureus, S. epidermidis, B. cereus, M. luteus, E. coli, C. albicans and A. niger, respectively. All the other compounds exhibited moderate activity against the bacterial and fungal organisms tested.