Target-switched artificial biochemical circuit for a versatile and sensitive colorimetric detection platform.

The presence of the target causes the structural switch of a metastable hairpin template probe (MH) for triggering a self-primed artificial biochemical circuit to produce numerous DNAzyme replicates, which in turn results in substantial signal amplification for highly sensitive colorimetric determination of nucleic acids.

Target-induced activation of DNAzyme for sensitive detection of bleomycin by using a simple MOF-modified electrode.

In this work, a sensitive electrochemical method for bleomycin (BLM) determination was reported on the basis of BLM-mediated activation of Zn2+-dependent DNAzyme and the adsorption of signal probes by a metal-organic framework (MOF) modified electrode. Two hairpin DNAs were employed in this protocol, one (HP1) for BLM recognition and one (HP2) for amplified signal output. The presence of BLM and Fe2+ caused the formation of BLM-Fe (II) complex to cleave HP1, releasing DNAzyme fragments, which could further hybridize with substrate HP2 to form a partial double-stranded DNA duplex and enable the activation of Zn2+-dependent DNAzyme with the coexistence of Zn2+. The Zn2+-dependent DNAzyme catalyzed the cyclic cleavage of magnetic beads (MB)-immobilized HP2 to release massive DNA fragments with a Fc-labeled- terminal, which could be used for BLM quantification through electrochemical measurement after their adsorption on a MOF modified electrode. Attributing to the high catalytic efficiency of DNAzyme and excellent electrochemical performance of MOF modified electrode, our method revealed an impressive limit of detection as low as 4 pM BLM with a linear range of 5-2000 pM. Besides, the easy synthesis of MOF without further modification and the easy way of adsorption for signal achievement facilitated the operation process. In virtue of the high sensitivity, selectivity and the simple-to-implement features, this method is believed to hold a great promising application for BLM determination in biomedical and clinical study.

Sensitive detection of streptomycin in milk using a hybrid signal enhancement strategy of MOF-based bio-bar code and target recycling.

A MOF-based bio-bar code material was synthesized and firstly applied to develop an electrochemical streptomycin (STR) aptasensor. By using MOF-based bio-bar code and enzyme-assisted target recycling for dual-signal amplification, highly sensitive detection of STR was achieved. The sensing surface was simply fabricated by immobilizing a mixed monolayer of thiolated cDNA/aptamer duplexes (dsDNA) and 6-mercapto-1-hexanol (MCH) on the gold nanoparticle modified screen printed carbon electrode (Au/SPCE). The presence of target STR caused highly efficient removal of the aptamers from dsDNA assisted by Exo I enzyme. Then MOF-based bio-bar codes were backfilled to achieve the adsorption of electroactive Ru(NH3)63+ (RuHex) on electrode surface. The electrochemical signal of the surface-confined RuHex was used for quantitation. The analytical performance for STR was satisfactory with a wide linear range of 0.005-150 ng mL-1, a low detection limit of 2.6 pg mL-1 and a good selectivity towards other three antibiotics. Moreover, the application of this aptasensor for determination of STR in real milk samples was also realized. With these merits, this dual-signal amplification assay might provide one of the effective ways for food safety monitoring.

A dual-response biosensor for electrochemical and glucometer detection of DNA methyltransferase activity based on functionalized metal-organic framework amplification.

DNA methylation is catalyzed by DNA methyltransferase (MTase) and concerned with many biological processes including pathogenesis of various human diseases. The monitoring of MTase activity is thus of great significance in disease diagnosis and drug screening. Herein, we developed a facile way to synthesize biocompatible invertase enzyme modified metal-organic framework (Invertase/MOF) materials, and explored its application in constructing a dual-response Dam MTase sensor for the first time. By using them as signal probes, in which high density of metal sites could be electrochemically detected and invertase could hydrolyze sucrose into glucose for generation of glucometer signal output, dual-response for accurate detection of Dam MTase was realized. In the presence of Dam MTase, the methylation of hairpin probe 1 (HP1) occurred and thus caused the cleavage of HP1 assisted by a restriction endonuclease (DpnI) to produce the binding sequences. The binding sequences then hybridized with the electrode-assembled HP2 to expose their sticky termini which sequentially hybridized with the Invertase/MOFs-tethered capture probes. Finally, the electrodes were incubated with a sucrose solution, followed by the separate electrochemical and glucometer detection. The present assay brought good performance which could detect Dam MTase activity as low as 0.001 U mL-1 with wide linear range and good selectivity against other cytosine MTase (M.SssI MTase). Moreover, it also owns ability to be potentially applied for the inhibitors screening by utilization of 5-fluorouracil as an inhibitor model. The results imply that our proposed method provides a convenient platform for early cancer diagnosis and therapeutic applications.

Commercial glucometer as signal transducer for simple evaluation of DNA methyltransferase activity and inhibitors screening.

DNA methyltransferase (MTase) plays an important role in many biological processes and has been recognized as a predictive cancer biomarker far before other signs of malignancy and a therapeutic target in cancer treatment. Thus simple and sensitive determination of DNA MTase activity is urgently required. The commercially available glucometer is considered as the most successful point-of-care (POC) sensor up to date, and researchers extend its application in monitoring different types of targets rather than only glucose. Here, we developed a simple strategy for the sensitive detection of the DNA MTase (using M.SssI as an example) activity by using a glucometer as the signal transducer. A S1/S2 hybrid probe was designed including a specific recognition sequence for both DNA MTase and restriction endonuclease, and a complementary sequence for biotin-S3. Firstly, the S1/S2 hybrid probe was self-assembled on the gold electrode and methylated by M.SssI MTase to form the methylated dsDNA. Then, HpaII endonuclease specifically cleaved the residue of the unmethylated dsDNA. Subsequently, biotin-S3 hybridized with the overhang sequence of the methylated dsDNA. Finally, the biotin tag was successively combined with streptavidin (STV) and biotin-invertase. The invertase efficiently catalyzed the hydrolysis of sucrose to generate abundant glucose, which led to an amplified response of glucometer. This strategy could detect DNA MTase activity as low as 0.3 U mL-1 with good selectivity against other two cytosine MTases (HaeIII MTase and AluI MTase), and be successfully applied for screening the DNA MTase inhibitors (5-azacytidine and 5-aza-2'-deoxycytidine), implying our proposed method holds great promising application in early cancer diagnosis and therapeutics.

The intrinsic cause of color fading in sliced cooked cured beef during chilled storage.

The relationship between color change and other physical and chemical characteristics of sliced cooked cured beef (SCCB) during chilled storage were investigated using principal components analysis (PCA) to determine the color fading causes. Samples were prepared and stored at 8°C for up to 35 days in a vacuum package to simulate a supermarket storage environment; related indicators were measured periodically every week. The results showed that the first PC explained 59.82% of the total variation, and the second explained 22.28%. PC1 was a concentrated reflection of color changes of SCCB during storage and PC2 was an environment factor causing the change of color. The change in apparent redness is mainly caused by redox reaction of the nitroso hemochromogen (NH) (eigenvectors of a*, C and NH in PC1 were all the maximum value of 0.28); a* was correlated with NH (0.96), free sulfhydryls (0.98), carbonyl derivatives (-0.95) formed during protein oxidation, and malondialdehyde (-0.98) and dienes (-0.92) formed by lipid oxidation. Color fading was significantly correlated with oxidizing and reducing power, existing forms of nitrogen and with the pH of the meat matrix. Changes in the internal environment of the sample initially influenced L* and b* values, and subsequently a*.

Enhancement effect of sodium dodecyl benzene sulfonate (SDBS) and its application into voltammetric determination of telmisartan.

A sensitive and rapid electrochemical method was developed for the determination of telmisartan based on the enhancement effect of sodium dodecyl benzene sulfonate (SDBS). In 0.1 mol L(-1) HClO(4) and in the presence of 7.5x10(-5)mol L(-1) SDBS, a well-defined and sensitive oxidation peak was observed for telmisartan at the acetylene black (AB) paste electrode. However, the oxidation peak is poor-shaped and the peak current is very low in the absence of SDBS, suggesting that SDBS shows obvious enhancement effect for the determination of telmisartan. After all the experimental parameters were optimized, a sensitive and simple electrochemical method was developed for determining telmisartan. The oxidation peak current is proportional to the concentration of telmisartan over the range from 2.5x10(-7) to 2.0x10(-5)mol L(-1). The detection limit is 7.5x10(-8)mol L(-1) after 2 min of accumulation. This new voltammetric method was successfully used to detect telmisartan in drugs.

Anodic stripping voltammetric determination of mercury using multi-walled carbon nanotubes film coated glassy carbon electrode.

An electrochemical method for the determination of trace levels of mercury based on a multi-walled carbon nanotubes (MWNT) film coated glassy carbon electrode (GCE) is described. In 0.1 mol L(-1) HCl solution containing 0.02 mol L(-1) KI, Hg(2+) was firstly preconcentrated at the MWNT film and then reduced at -0.60 V. During the anodic potential sweep, reduced mercury was oxidized, and then a sensitive and well-defined stripping peak at about -0.20 V appeared. Under identical conditions, a MWNT film coated GCE greatly enhances the stripping peak current of mercury in contrast to a bare GCE. Low concentrations of I(-) remarkably improve the determining sensitivity, since this increases the accumulation efficiency of Hg(2+) at the MWNT film coated GCE. The stripping peak current is proportional to the concentration of Hg(2+) over the range 8 x 10(-10)-5 x 10(-7) mol L(-1). The lowest detectable concentration of Hg(2+) is 2 x 10(-10) mol L(-1) at 5 min accumulation. The relative standard deviation (RSD) at 1 x 10(-8) mol L(-1) Hg(2+) was about 6% ( n=10). By using this proposed method, Hg(2+) in some water samples was determined, and the results were compared with those obtained by atomic absorption spectrometry (AAS). The two results are similar, suggesting that the MWNT-film coated GCE has great potential in practical analysis.