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Enzyme-like metal–organic frameworks are currently one type of star material in the fields of artificial enzymes and analytical sensing. However, there has been little progress in making use of MOF structures based on a catalytically active metal center. Herein, transition metal coordination frameworks (Cu–HMT and Ni–HMT) are used as artificial nanozymes for the visual detection of a Parkinson's disease biomarker (dopamine, DA) through peroxidase-like catalytic activity. We prepared hexamine and transition metal coordination frameworks (Cu–HMT and Ni–HMT) through a trouble-free green synthetic route and characterized them in detail. Comparative studies of peroxidase mimic activity were conducted in the presence of the as-prepared Cu–HMT and Ni–HMT. Impressively, Cu–HMT possesses formidable peroxidase mimic activity, which allows UV-vis spectra and naked-eye detection of DA. Furthermore, Ni–HMT has its own limitations, including lower water stability and poorer activity compared to Cu–HMT. However, the peroxidase-like activity of Cu–HMT was strongly inhibited in the presence of DA. Notably, the proposed sensing system was proven to show an enhanced inhibition effect, including visual detection, high selectivity, specificity and low detection limits of 0.7 and 4.2 mM for H2O2 and DA, respectively. Based on this phenomenon, the as-synthesized Cu–HMT could be used as a kind of nanozyme to enhance the performance of colorimetric sensors.

In this paper, we propose a fluorescent biosensor for the sequential detection of Pb2+ ions and the cancer drug epirubicin (Epn) using the interactions between label-free guanine-rich ssDNA (LFGr-ssDNA), acridine orange (AO), and a metal–phenolic nanomaterial (i.e., nano-monoclinic copper–tannic acid (NMc-CuTA)). An exploration of the sensing mechanism shows that LFGr-ssDNA and AO strongly adsorb on NMc-CuTA through π–π stacking and electrostatic interactions, and this results in the fluorescence quenching of AO. In order to sense the target Pb2+, initially, LFGr-ssDNA specifically binds with Pb2+ ions to form a G4 complex (G–Pb2+–G base pair), which was released from the surface of NMc-CuTA with strong AO fluorescence enhancement (Turn-ON). The subsequent addition of a biothiol, like cysteine (Cys), to the G4 complex decreases the fluorescence, as the Pb2+ ions released from the G4 complex have a higher interaction affinity with the sulfur atoms of Cys; this further induces the unwinding of the G4 complex to form LFGr-ssDNA. Finally, Epn was added to this, which intercalates with LFGr-ssDNA to form a G4 complex via G–Epn–G, resulting in fluorescence recovery (Turn-ON). Accordingly, the Turn-ON fluorescent probe had subsequent limits of detection of 1.5 and 5.6 nM for Pb2+ and Epn, respectively. Hence, the reported NMc-CuTA-based sensing platform has potential applications for the detection of Pb2+ and Epn in real samples with good sensitivity and selectivity.

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.

In this work, hybrid magnetic core-shell fibrous silica (Py-CoFe2O4/SiO2/KCC-1) as a fluorescence sensor has been developed for the sensitive and selective detection of Hg (II) ion. The pyrene-base...

A novel colorimetric sensing platform using the peroxidase mimicking activity of ternary MoS2-loaded ZnO–g-C3N4 nanocomposites (ZnO–g-C3N4/MoS2) has been developed for the determination of Hg(II) ions over co-existing metal ions. The nanocomposite was prepared using an exfoliation process, and the product was further characterized using SEM, TEM, XRD and FTIR analysis. The ZnO–g-C3N4/MoS2 possesses excellent intrinsic catalytic activity to induce the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) in aqueous solution in the presence of H2O2 to generate deep blue coloured cation radicals (TMB+) which can be viewed with the naked eye and produce absorbance at a wavelength of 652 nm. The addition of a well known bioradical scavenger, glutathione (GSH), to the solution hinders the generation of cation radicals and turns the solution colourless. The introduction of Hg(II) to this solution brings the blue colour back into it, due to the strong affinity of the thiol in the GSH. Based on this mechanism, we have developed a simple and rapid colorimetric sensor for the highly sensitive and selective detection of Hg(II) ions in aqueous solution with a low detection limit of 1.9 nM. Furthermore, the prepared colorimetric sensor was effectively applied for the quantification analysis of real water samples.

In this study, we report the dual detection of kanamycin (KMY) and oxytetracycline (OTC) using metal polydopamine frameworks (MPDA) for the first time. This sensing system employed metal polydopamine frameworks (MPDA), which acted as a fluorescence quencher in the interaction between MPDA and dye-labeled DNA molecules; the metal polydopamine frameworks exhibited an excellent fluorescence quenching behaviour and good analytical response towards the detection of the biomolecules KMY and OTC. The accumulated kanamycin and oxytetracycline in the sensing system were recovered, and changes in their fluorescence intensity were monitored at 525 and 583 nm. Under the optimal conditions, the proposed sensing system remarkably achieved highly sensitive and selective detection of KMY and OTC with the limit of detection of 304 pM and 481 pM, respectively. In addition, the selectivity of the developed sensor was explored in the presence of competitive biomolecules. Moreover, this sensing system demonstrated great potential and versatility for the rapid detection of molecules. In addition, this biosensor was successfully evaluated for the dual detection of KMY and OTC in different real samples.

An extremely sensitive colorimetric sensor has been developed for selective determination of Hg2+ in aqueous solution based on magnetic nanocomposite (Fe3O4@ZIF-67), which results in an effective intrinsic peroxidase mimicking activities and makes the composites oxidize the 3, 3′, 5, 5′- tetramethyl benzidine (TMB) in the presence of hydrogen peroxide (H2O2) to produce a blue coloured solution. Significantly, the oxidation of TMB was retarded or prevented in the presence of antiradical biomolecules Glutathione (GSH) because of its strong cation restoration property. When Hg2+ is added, the strong affinity of mercury ions with thiol groups of GSH provokes the oxidation of the substrates, which helps the solution turn into blue colour. The absorbance intensity was proportional to the concentration of Hg2+ in the wide range of 0–30 nM and detection limit was successfully as low as 0.36 nM. The resultant nanocomposite based peroxidase mimicking activity applied as a versatile platform in the colorimetric detection of Hg2+ was established the other co-existing metal ions in aqueous solutions. Finally the sensor was applied to detect Hg2+ in real water sample with satisfactory recovery results. Interestingly, the proposed colorimetric sensing platform held great potential in the application of mercury contamination in industrial sewage.

A novel significant colorimetric sensor has been developed for the selective detection of Hg(II) ions based on Fe3O4@ZnO nanocomposite as peroxidase mimics. We have successfully synthesized nanocomposite by solvothermal method and it is characterized by analytical technique using scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, and vibrating sample magnetometry. This nanocomposite exhibits a peroxidase mimetic activity that could efficiently catalyze the oxidation of tetramethylbenzidine (TMB) in the presence of H2O2 to form blue colored cation radical. In addition, the biomolecule of Cysteine (Cys) easily hinder the cation radical formation and turns back TMB molecules into colourless. Whereas the Hg(II) ion, having strong affinity to thiol group easily binds with Cys. As a result of it, the blue colour of the solution is recovered in presence of Fe3O4@ZnO nanocomposite. Based on this mechanism, we have developed a simple and rapid colorimetric detection of Hg2+ ions, which is found to be 23 nM. Furthermore, the colorimetric sensor has been applied to detect Hg2+in real water samples and find convenient potential applications in the biological and environmental field.

We describe a highly sensitive fluorescence biosensor incorporating polydopamine nanotubes (PDNTs) based on the mechanism of exonuclease III (Exo III) assisted signal amplification for the determination of Hg2+ in aqueous solution. Fluorescent probes of FAM labeled ssDNA (FAM-ssDNA) adsorbed on the PDNTs act as an efficient quencher. In the presence of Hg2+, the FAM-ssDNA can bind to Hg2+ to form double stranded DNA (dsDNA) via the formation of T-Hg2+-T base pairs. Then, the dsDNA was removed from the surface of the PDNTs to restore the fluorescence. The release of the dsDNA was triggered by Exo III digestion. At the same time, the liberated Hg2+ mediates a new cycle of digestion. This assay is ultrasensitive for the selective recognition of Hg2+, and a detection limit as low as 10 pM was achieved. In addition, the fluorescent biosensing system also displays remarkable specificity to Hg2+ in the presence of other possible competing ions. This approach was applied to the determination of Hg2+ in real water samples with good recovery and high efficiency for practical analysis.

In this paper, we present a novel colorimetric sensor for the detection of arsenate in aqueous solution. Magnetic nanoparticles (Fe3O4 NPs) prepared by a hydrothermal process were characterized by SEM, XRD, FT-IR, and VSM analysis. The Fenton-like catalytic reaction of Fe3O4 NPs promoted the oxidation of methylene blue indicator (MB) in the presence of H2O2 which resulted in the diminishing of the dark blue colour of the solution, due to generation of ·OH radicals in the solution. This can be viewed by the naked eye and monitored by UV-Vis spectroscopy at 664 nm. Upon addition of arsenate to this system the blue colour regenerated in solution due to the agglomeration of As(V) on Fe3O4 which may block the active sites of the Fe3O4 NPs and decrease their intrinsic catalytic activity. Under optimal conditions, the proposed colorimetric sensor exhibited rapid and selective detection of As(V) in aqueous solution with a detection limit of 0.358 nM with a linear relationship with R2 = 0.997. To the best of our knowledge, this is the first report where arsenates can be detected colorimetrically by this sensing system (Fe3O4/MB/H2O2). The designed colorimetric strategy may provide a promising alternative method for detection of arsenates in real water samples.

A self-assembled discrete Pd3L′3L3 type circular helicate of hitherto unknown architecture is disclosed in this work where L′ stands for 1,10-phenanthroline (phen) and L for a triazole appended bidentate nonchelating ligand, i.e., 1,4-bis((1H-1,2,3-triazol-1-yl)methyl)benzene. The coordination environment of palladium(II) in any given PdN4 coordination planes of the helicate is described by one phen moiety and two triazole moieties belonging to different ligand strands. All the three bound phen moieties are uniquely turned inside and lodged in the internal cavity of the molecule; hence the term “intro-vertere circular helicate” is introduced. One of the PdN4 square planes is sandwiched between the other two via phen-inspired intramolecular π-stacking making a cylindrical stacking arrangement. A racemic pair designated as MPP and PMM isomers, where M and P stand for the handedness of the ligand L, is observed in the crystal structure. In the crystal packing, the trinuclear intro-vertere circular helicate m...

Maize is the third most important cereal crop next to rice and wheat in the world as well as in India. Maize has the higher yield potential and responds greatly to applied fertilizers especially in the irrigated conditions in Tamil Nadu. Phosphorus and sulphur are the major yield limiting factors after nitrogen in the study area (Sivagangai district of Tamil Nadu) and proper management of nutrients is essential to realize the maximum potential of the crop and to get higher economic benefit. This study aimed at investigating the releasing pattern of P and S from the experimental soil at different incubation period. The experiment was laid out in Completely Randomized Design replicated thrice. The soil samples were collected from the experimental plots and used for incubation studies. There were five levels of P and five levels of S analysed in 15, 30, 45 and 60 days of incubation period. The results found that with progress of time (15 to 60 days of incubation), increasing levels of P and sulphur and their interaction significantly increased the phosphorous release from the soil. Similarly, sulphur availability was also influenced by S levels and P levels, with maximum release of S from 15 days to 30 days. Key words: Maize, phosphorus, sulphur, releasing pattern, incubation periods.

Herein, a novel hybrid magnetic core–shell fibrous silica nanocomposite (RhB–Fe3O4/MnO2/SiO2/KCC-1) probe-based chemosensor was designed and its behaviour towards Cu(II) metal ion was investigated using a fluorescence spectrometer. The organic receptor rhodamine B (RhB) fluorophore derivative was covalently grafted onto the surface of the magnetic core–shell fibrous silica nanocomposite. This sensing probe achieved the selectivity towards Cu(II) in an aqueous solution, and other competing metal ions basically induced no spectral change. Thus, this sensing probe can work as a Cu(II) selective fluorescent sensor. The synthesized material was characterized using transmission electron microscopy (TEM), scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), surface analysis (with BET), Fourier transform infrared spectroscopy (FT-IR), X-ray diffractometry, and thermogravimetric analysis (TGA). The rhodamine B derivative has a unique signalling probe that exhibits a turn-on fluorescence enhancement upon the recognition of Cu(II) ion with an excitation at 569 nm. The linearity of the Stern–Volmer plot (R2 = 0.9882) and the detection limit of 12.3 × 10−8 M were achieved. Finally, the sensor was tested to detect Cu(II) ion in different real water samples.

Maize has the highest potential yield and responds greatly to applied fertilizers especially in the irrigated conditions in Tamil Nadu. Phosphorus and sulphur are the major yield limiting factor after nitrogen in the study area- Sivagangai district of Tamil Nadu. Therefore, this study was initiated with the aim of increasing the yield of hybrid maize by optimizing the phosphorus and sulphur fertilizers in the farmer's field. The experiment was laid out in a Factorial Randomized Block Design replicated thrice with five levels of phosphorus viz., 0, 50, 75, 100, 125 kg P 2 O 5 per ha and five levels of sulphur viz., 0, 20, 40, 60, 80 kg S per ha. The results revealed that plant height, dry matter production, cob length, cob girth, the number of grains per cob and hundred grain weight were significantly increased with increased dose of P and S, and significantly higher at 125 kg P 2 O 5 per ha and 80 kg S per ha. Similarly, the maize grain yield was higher at 125 kg P 2 O 5 per ha (5964 kg per ha) and 80 kg S per ha (5035 kg per ha). Interaction of phosphorus and sulphur was additive with respect to growth and yield of maize.

Biodiesel is produced from edible/non-edible plants oil. However, alkaline transesterification of these oils makes the process challenging due to the presence of large amount of free fatty acids (FFA), which forms soap on reaction with alkali. Hence, it is necessary to reduce FFA present so that alkaline catalyzed transesterification can be carried out. In this work, biodiesel fuel was produced using diphenylamine functionalized magnetic mesoporous silica SBA-15 as catalyst for the esterification of free fatty acid (FFA) present in neem oil (NO) and its effect on esterification reaction was studied. Optimum catalyzed esterification was achieved using 1 g diphenylamine functionalized magnetic mesoporous silica SBA-15 as a solid base catalyst with a methanol to oil ratio of 9:1, at 60°C and reaction time of 1.25 h. During this process, FFA was converted into fatty acid methyl esters. The acid value of NO oil was reduced to 7.34 mg KOH/g from 52.45 mg KOH/g, accounting for 86% conversion efficiency. Consequently, this pretreatment reduces the overall complexity of the process and reduces the cost of producing biodiesel fuel. Pretreated NO was converted to biodiesel by a process of alkaline catalyzed transesterification using 1% KOH in methanol. Key words: Biodiesel, esterification, transesterification, free fatty acid, neem oil.

We report a simple new approach on green synthesized carbon dots@graphitic-carbon nitride (CDs@g-C3N4) nanocomposite to explore the potential application of "Turn-On" fluorescent sensor for signaling the detection of multiple heavy metal ions. As prepared fluorescent CDs exhibits a high dispersibility and g-C3N4 nanosheets show a good exfoliation to strongly hold the CDs over its surface to constitute a label-free sensor. Initially, the fluorescence intensity of CDs was quenched via excited state non-radiative energy transfer process from CDs to g-C3N4 sheets. However, on hosting of metal ions into CDs@g-C3N4 nanocomposite it forms a strong surface complex with g-C3N4 nanosheets, which may encourage the recovery of CDs. More interestingly, the sensing performance was investigated at different pH to understand the switching in surface charge of g-C3N4 nanosheets, which has significantly improved the sensitivity for detection of Cr (VI), Cu (II) and Pb (II) ions with a LOD of 0.54 nM, 0.18 nM and 0.2 nM respectively. Moreover, this proposed sensor was expected to be prompt, convenient, low cost, an eco-friendly and sensitive platform for the detecting of heavy metal ions in practical samples with satisfying results.

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.

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 (Pb

A label -free DNAzyme amplified biosensor is found to be highly selective and sensitive towards fluorescent detection of Pb2+ ions in aqueous media. The DNAzyme complex has designed by the hybridization of the enzyme and substrate strand. In the presence of Pb2+, the DNAzyme activated and cleaved the substrate strand of RNA site (rA) into two oligonucleotide fragments. Further, the free fragment was hybridized with a complementary strand on the surface of MBs. After magnetic separation, SYBER Green I was added and readily intercalate with the dsDNA to gives a bright fluorescence signal with intensity directly proportional to the concentration of Pb2+ions. A detection limit of 5 nM in Pb2+ the detection range 0 to 500 nM was obtained. This label- free fluorescent biosensor has been successfully applied to the determination of environmental water samples. Then results open up the possibility for real-time quantitative detection of Pb2+ with convenient potential applications in the biological and environmental field. Graphical Abstract.

A field experiment was conducted on vertisolsat Natural Resources Protection and Development Society Research Station, Namakkal during Rabi season of 2012-13 and 2013-14 to study the effect of organic manure sand rock phosphate on growth and yield of Bengal gram (Cicer arietinum L.) in vertisols of Tamil Nadu. Significantly higher grain yield was recorded with rock phosphate application @ 200 kg/ha (2140 kg/ha) over 50 kg and 100 kg of rock phosphate per hectare except rock phosphate @ 150 kg /ha (2069kg/ha). Interaction effect of compost 5 t along with rock phosphate 200 kg/ha recorded significantly higher grain yield 2130 kg/ha) and haulm yield (3300kg/ha) over other treatment combinations except either for organic manures FYM 5 to rcompost 5 t along with 150 to 200 kg rock phosphate per ha. Significantly higher B:C ratio (3.32)was recorded with rock phosphate @ 200 kg / ha over other lower levels. Similarly, combination of compost @ 5 t/ ha with 150 kg rock phosphate resulted in higher B:C ratio (3.37).

Diabetes mellitus (DM) is a global health problem and the incidence of DM is increasing at alarming rate all over the world. Many Indian medicinal plants have been reported to possess potential anti diabetic activity and could play important role in the management diabetes. The present study aimed to evaluate anti diabetic activities of ethylacetate extract of Azima tetracantha Lam leaf in streptozotocin-induced diabetic rats. Diabetes was induced in male wistar rats by single intraperitoneal injection of streptozotocin (50 mg/kg b.wt.). The diabetic rats were administered orally with Azima tetracantha Lam leaf ethyl acetate extract at two different doses (150 and 250 mg/kg b.wt./day) for 18 days. At dose levels of 150 and 250 mg/kg, glucose levels were decreased by 24.8% and 29.9% at the 6th hour, respectively. Anti diabetic effect of the extract was slightly decreased at the 8th hour, but remained statistically significant. An overall reduction of 26% was observed on the 18th day by 50mg/kg administration (p

Ni(II) ions removal using maghemite nanoparticle on bentonite-clay was investigated. Adsorbent was synthesized using the sol-gel method characterized by the surface area Brunauer, Emmett, and Teller (BET), scanning electron microscopy and energy dispersive X-Ray spectrometer, transmission electron microscopy, FTIR spectroscopy, and zero-point-charge. Experiments were done as a function of solute concentration and temperature. Various kinetic models were evaluated and effective diffusion coefficient, activation energy, and entropy of activation were determined. The adsorption isotherm data were fitted to the Langmuir and Freundlich equations, and the Langmuir adsorption capacity was found to be 114.9 mg/g. These results showed that the adsorbent is an attractive option for Ni(II) removal.

Fractional factorial design is used to identify the significant variables that have large effects on the COD reduction and decolorization of methylene blue dye aqueous solution, through adsorption process. Four factors (pH, adsorbent dosage, temperature, and contact time) were screened by using the 24 fractional factorial designs. The results showed that all the main factors have first-order interaction effects and second-order interaction effect, which were significantly affecting decolorization and COD reduction. Results obtained indicated that fractional factorial design can be used as a method to screen a large number of factors and to reduce the number of experimental runs.