DNA polymerases are known to recognize preferably d-nucleotides over l-nucleotides during DNA synthesis. Here, we report that several general DNA polymerases catalyze polymerization reactions of nucleotides directed by the DNA template containing an l-thymidine (l-T). The results display that the 5′–3′ primer extension of natural nucleotides get to the end at chiral modification site with Taq and Phanta Max DNA polymerases, but the primer extension proceeds to the end of the template catalyzed by Deep Vent (exo–), Vent (exo–), and Therminator DNA polymerases. Furthermore, templating l-nucleoside displays a lag in the deoxyribonucleotide triphosphate (dNTP) incorporation rates relative to natural template by kinetics analysis, and polymerase chain reactions were inhibited with the DNA template containing two or three consecutive l-Ts. Most interestingly, no single base mutation or mismatch mixture corresponding to the location of l-T in the template was found, which is physiologically significant because they provide a theoretical basis on the involvement of DNA polymerase in the effective repair of l-T that may lead to cytotoxicity.

The authors describe a colorimetric assay for the determination of As(III) in aqueous solution using citrate capped gold nanoparticles (AuNPs) which, in the presence of As(III), undergo aggregation due to the interaction of citrate ion with As(III). This results in an easily detectable color change from wine-red to blue. The ratio of the absorbances at 661 and 519 nm is linearly related to the As(III) concentration in the 4 to 100 ppb range, with a detection limit as low as 1.8 ppb (at 3σ) which is below the guideline value of 10 ppb. The method is rather simple in that it does not require the surface of the AuNPs to be modified. It was successfully applied to the determination of As(III) in spiked drinking water where it gave adequate recoveries.

In this paper, enantioselectivities of D-amino acid oxidase (DAAO) in ten ionic liquids were investigated in detail. Among the ionic liquids studied, 3-methylimidazolium formate ([MIM][COO]) was able to trigger enzyme activation with L-Ala as substrate. The enzyme activity of DAAO reached a maximum of 4.26 U mg−1 min−1 in the presence of 40% [MIM][COO], while no activity toward L-Ala was observed when DAAO was incubated with other ILs. Moreover, DAAO activities towards other L-amino acids such as L-Pro and L-Arg were also improved in [MIM][COO], which indicated that the enzymatic enantioselectivity of amino acids was lowered. This was further confirmed by capillary electrophoresis, circular dichrosim and fluorescence analysis. Molecular optimization supported that the protein–ionic liquid interactions modulated the structure of the enzyme, especially in [MIM][COO], leading to relaxation in the enantioselectivity of DAAO. This observation and exploration might open a new window for modulation enantioselectivity resolution in ionic liquids.

The prevalently used immunoassays for fast screening of aftatoxins (AFs) usually cannot meet the requirement for simultaneous determination of total AFs (aflatoxin B1 + aflatoxin B2 + aflatoxin G1 + aflatoxin G2) due to the deficiency of highly group-specific antibodies. This paper describes a two-step chromogenic reaction based method to quantitatively detect total AFs in rice using colorimetric measurement without antibody. In the method, colorless AFs transform into green-colored indophenol products through the reaction with sodium hydroxide and 2,6-dibromoquinone-4-chloroimide (DBQC) successively, allowing selectively determining total AFs up to 3.9 μg/kg over other competitive mycotoxins under optimal conditions by a UV–vis spectrophotometer. In addition, the colorimetric measurement results of the rice samples agree well with that of a standard HPLC method, demonstrating the good reliability and applicability of the method. Uniquely, the method has potential for on-site detection of total AFs in rice when using a nylon membrane-based device.

Introduction of 4,4′-bis(hydroxymethyl)-azobenzene (azo) to dumbbell hairpin oligonucleotides at the loop position was able to reversibly control the stability of the whole hairpin structure via UV or visible light irradiation. Here, we designed and synthesized a series of azobenzene linked dumbbell antisense oligodeoxynucleotides (asODNs) containing two terminal hairpins that are composed of an asODN and a short inhibitory sense strand. Thermal melting studies of these azobenzene linked dumbbell asODNs indicated that efficient trans to cis photoisomerization of azobenzene moieties induced large difference in thermal stability (ΔTm = 12.1–21.3 °C). In addition, photomodulation of their RNA binding abilities and RNA digestion by RNase H was investigated. The trans-azobenzene linked asODNs with the optimized base pairs between asODN strands and inhibitory sense strands could only bind few percentage of the target RNA, while it was able to recover their binding to the target RNA and degrade it by RNase H after light irradiation. Upon optimization, it is promising to use these azobenzene linked asODNs for reversible spatial and temporal regulation of antisense activities based on both steric binding and RNA digestion by RNase H.

The residual glyphosate (GLYP) in the environment is harmful to human health. Monitoring GLYP and its major metabolite aminomethylphosphonic acid (AMPA) in a complicated matrix is an important analytical task. Based on the affinity of phosphate groups to metal ions, iron oxide nanoparticles immobilized with Ti4+ using polydopamine (PDA) as bridging molecules (Fe3O4@PDA-Ti4+ NPs) were employed to develop a magnetic solid phase extraction (mSPE) method for GLYP and AMPA by electrostatic interaction. After extraction with Fe3O4@PDA-Ti4+ NPs and elution for 5 min, the purified and enriched analytes were derivatized, prior to CE with diode array UV detection. Relying on the coupled mSPE-CE method, the detection limits were 0.4 ng mL−1 for GLYP and AMPA. The present method was employed to monitor GLYP and AMPA in a Roundup® sample and river water sample, revealing its good possibilities for applicability. Herein, by virtue of the immobilized metal affinity extraction (IMAE), the coupled mSPE-CE method would be effective, easy to operate and applicable for analyzing herbicides in environmental samples.

A colorimetric detection method for melamine based on 1,4-dithiothreitol (DTT) functionalized gold nanoparticles (DTT–AuNPs) is reported. Hydrogen-bonding interaction between DTT and melamine resulted in the aggregation of AuNPs, which consequently resulted in a color change of the AuNPs from wine red to blue and a red-shift of the surface plasmon resonance (SPR) peak of the DTT–AuNPs. The concentration of melamine could be determined by the naked eye or using a UV-vis spectrometer. FT-IR and TEM were used to investigate the modification of DTT–AuNPs. The results showed that the absorption ratio (A680/A520) was linear with the logarithm of melamine concentration in the range of 8.0 × 10−8 M to 6.0 × 10−7 M and 6.0 × 10−7 M to 1.5 × 10−6 M with linear coefficients of 0.993 and 0.999, respectively. The detection limit (S/N = 3) of the proposed method was 2.4 × 10−8 M, which is considerably lower than the safety limit. Coexisting substances did not affect the determination of melamine. Furthermore, the proposed method was applied for the detection of trace amounts of melamine in real milk samples with recoveries of 96–103%.

A new method has been proposed to realize the visual detection of d-amino acids (DAAs) via the anti-aggregation of 4-mercaptobenzoic acid modified gold nanoparticles (AuNPs) in the presence of d-amino acid oxidase (DAAO). The negatively charged AuNPs were prepared using sodium citrate as a reducer and stabilizer. The presence of 4-mercaptobenzoic acid (4-MBA) and Cu2+ induces the aggregation of AuNPs, resulting in a color change from ruby red to royal purple. However, DAAO could oxidize DAAs to generate H2O2. In the presence of H2O2, the mercapto (SH) group in 4-mercaptobenzoic acid can be oxidized to form a disulfide (SS) bond. Based on these facts, the pre-incubation of DAAs and 4-mercaptobenzoic acid with DAAO would significantly reduce the concentration of free 4-mercaptobenzoic acid molecules, thus the aggregation of AuNPs was interrupted since due to the lack of inducer. As the concentration of DAAs increases, the color of the AuNPs solution would progress from royal purple to ruby red. Consequently, DAAs could be monitored by the colorimetric response of AuNPs using a UV–vis spectrophotometer or even naked eyes. This DAAO mediated visual detection method could determine d-alanine (d-Ala) as a representative DAA with concentrations ranging from 1.5 × 10−7 mol L−1 to 3.0 × 10−5 mol L−1, and the detection limit was as low as 7.5 × 10−8 mol L−1. The proposed method is convenient, low-cost and free of complex equipment, making it feasible to analyze the concentration of d-Ala in real samples of β-amyloid peptide (Aβ1–42).Colorimetric detection of d-amino acids was realized through anti-aggregation of gold nanoparticles.

The polymerase chain reaction (PCR) has become an indispensable technique in molecular biology, however, it suffers from low efficiency and specificity problems. Developing suitable additives to effectively avoid nonspecific PCR reactions and explore the mechanism for PCR enhancing is a significant challenge. In this paper, we report three different modified gold nanoparticles (AuNPs) with different surface charge polarities and poly (diallyl dimethylammonium) chloride (PDDA) for use as novel PCR enhancers to improve the efficiency and specificity. These AuNPs included the positively charged PDDA protected AuNPs (PDDA-AuNPs), the neutral PDDA-AuNPs modified with excess chloride ion (PDDA.C-AuNPs), and the negatively charged sodium citrate (Na3Ct) protected AuNPs (Na3Ct-AuNPs). Our data clearly suggests that the positively charged PDDA-AuNPs with an optimum concentration as low as 1.54 pM could significantly enhance the specificity and efficiency of PCR, however, the optimum concentration of the negatively charged Na3Ct-AuNPs (2.02 nM) was more than 3 orders of magnitude higher than that of positively charged PDDA-AuNPs. The PCR specificity and efficiency are also improved by the neutral PDDA.C-AuNPs with an optimum concentration, much more than that of the PDDA-AuNPs. This suggests that there should be an electrostatic interaction between the positively charged PDDA-AuNPs and the negatively charged PCR components, and the surface charge polarities of PDDA-AuNPs may play an important role in improving the PCR specificity and efficiency.

A highly sensitive and selective method was presented for colorimetric determination of melamine using gold nanoparticles (AuNPs). AuNPs were synthesized using ellagic acid (EA) as reducer in distilled water at room temperature without adding nanoparticle seeds and stabilizing agent. Melamine could interact with EA through a strong hydrogen-bonding interaction leading to weakening of the EA reducing ability, thus the formation of AuNPs was interrupted and the color of the solution changed from red to pale yellow. The concentration of melamine could be quantified visually or using a UV-vis spectrometer in the wide range from 1.6 × 10−8 M to 1.6 × 10−4 M with a correlation coefficient of 0.9961. The detection limit (3σ) was as low as 1.6 × 10−9 M. This sensor was simple, inexpensive and highly sensitive and could be successfully utilized to detect melamine in pretreated liquid milk products with high recoveries from 93% to 106%. Besides, it exhibited excellent selectivity against other interferences.

The residual glyphosate (GLYP) in the environment is harmful to human health. Monitoring GLYP and its major metabolite aminomethylphosphonic acid (AMPA) in a complicated matrix is an important analytical task. Based on the affinity of phosphate groups to metal ions, iron oxide nanoparticles immobilized with Ti4+ using polydopamine (PDA) as bridging molecules (Fe3O4@PDA-Ti4+ NPs) were employed to develop a magnetic solid phase extraction (mSPE) method for GLYP and AMPA by electrostatic interaction. After extraction with Fe3O4@PDA-Ti4+ NPs and elution for 5 min, the purified and enriched analytes were derivatized, prior to CE with diode array UV detection. Relying on the coupled mSPE-CE method, the detection limits were 0.4 ng mL−1 for GLYP and AMPA. The present method was employed to monitor GLYP and AMPA in a Roundup® sample and river water sample, revealing its good possibilities for applicability. Herein, by virtue of the immobilized metal affinity extraction (IMAE), the coupled mSPE-CE method would be effective, easy to operate and applicable for analyzing herbicides in environmental samples.

A highly sensitive and selective method was presented for colorimetric determination of melamine using gold nanoparticles (AuNPs). AuNPs were synthesized using ellagic acid (EA) as reducer in distilled water at room temperature without adding nanoparticle seeds and stabilizing agent. Melamine could interact with EA through a strong hydrogen-bonding interaction leading to weakening of the EA reducing ability, thus the formation of AuNPs was interrupted and the color of the solution changed from red to pale yellow. The concentration of melamine could be quantified visually or using a UV-vis spectrometer in the wide range from 1.6 × 10−8 M to 1.6 × 10−4 M with a correlation coefficient of 0.9961. The detection limit (3σ) was as low as 1.6 × 10−9 M. This sensor was simple, inexpensive and highly sensitive and could be successfully utilized to detect melamine in pretreated liquid milk products with high recoveries from 93% to 106%. Besides, it exhibited excellent selectivity against other interferences.