Wenxin Zhu

Facile colorimetric method for simple and rapid detection of endotoxin based on counterion-mediated gold nanorods aggregation

Existence of endotoxin in food and injection products indicates bacterial contaminations and therefore poses threat to human health. Herein, a simple and rapid colorimetric method for the effective detection of endotoxin in food and injections based on counterion-mediated gold nanorods aggregation is first proposed. By taking advantage of the color change of unmodified gold nanorods resulted from endotoxin mediated gold nanorods aggregation, endotoxin could be detected in the concentration range of 0.01-0.6 μM. Further, we studied the performance of gold nanorods with different aspect ratios (2.7 and 3.3) in determination of endotoxin and found that gold nanorods with higher aspect ratio (AR) showed superiority in the sensing sensitivity of endotoxin. A good specificity for endotoxin, a detection limit of 0.0084 μM and recoveries ranging from 84% to 109% in spiked food and injection samples are obtained with the colorimetric method. Results demonstrate that the present method provides a novel and effective approach for on-site screening of endotoxin in common products, which is beneficial for monitoring and reducing the risk of bacterial contaminations in food and injections production.

DNA-mediated gold nanoparticle signal transducers for combinatorial logic operations and heavy metal ions sensing

Herein, the structure of two DNA strands which are complementary except fourteen T-T and C-C mismatches was programmed for the design of the combinatorial logic operation by utilizing the different protective capacities of single chain DNA, part-hybridized DNA and completed-hybridized DNA on unmodified gold nanoparticles. In the presence of either Hg(2+) or Ag(+), the T-Hg(2+)-T or C-Ag(+)-C coordination chemistry could lead to the formation of part-hybridized DNA which keeps gold nanoparticles from clumping after the addition of 40 μL 0.2M NaClO4 solution, but the protection would be screened by 120 μL 0.2M NaClO4 solution. While the coexistence of Hg(2+), Ag(+) caused the formation of completed-hybridized DNA and the protection for gold nanoparticles lost in either 40 μL or 120 μL NaClO4 solutions. Benefiting from sharing of the same inputs of Hg(2+) and Ag(+), OR and AND logic gates were easily integrated into a simple colorimetric combinatorial logic operation in one system, which make it possible to execute logic gates in parallel to mimic arithmetic calculations on a binary digit. Furthermore, two other logic gates including INHIBIT1 and INHIBIT2 were realized to integrated with OR logic gate both for simultaneous qualitative discrimination and quantitative determination of Hg(2+) and Ag(+). Results indicate that the developed logic system based on the different protective capacities of DNA structure on gold nanoparticles provides a new pathway for the design of the combinatorial logic operation in one system and presents a useful strategy for development of advanced sensors, which may have potential applications in multiplex chemical analysis and molecular-scale computer design.

Au Promoted Nickel–Iron Layered Double Hydroxide Nanoarrays: A Modular Catalyst Enabling High-Performance Oxygen Evolution

Oxygen evolution reaction (OER) plays a key role in various energy conversion and storage technologies, such as water electrolysis, regenerative fuel cells, and rechargeable metal-air batteries. However, the slow kinetics of OER limit the performance and commercialization of such devices. Herein, we report on NiFe LDH@Au hybrid nanoarrays on Ni foam for much enhanced OER. By hybridization of electronegative Au and NiFe LDH with intrinsic remarkable OER catalytic activity, this modular electrode could drive an overall ultrahigh-performance and robust OER in base with the demand of overpotentials of only 221, 235, and 270 mV to afford 50, 100, and 500 mA cm-2, respectively. Also, it exhibits superior catalytic activity and durability toward OER in 30 wt % KOH.

Dual role of hydrogen peroxide on the oxidase-like activity of nanoceria and its application for colorimetric hydrogen peroxide and glucose sensing

Nanoceria (cerium oxide nanoparticles) exhibits excellent catalytic activity towards chromogenic substrate 3,3,5,5-tetramethylbenzidine (TMB) in the presence of hydrogen peroxide (H2O2), which has been reported. However, the understanding of the interaction between H2O2 and nanoceria is far from comprehensive. Herein, we further studied the interaction between H2O2 and dextran-coated nanoceria and found that H2O2 plays a dual role in nanocerias oxidase activity both as an inhibitor and a promoter, depending on its concentration. At millimolar levels, H2O2 can promote nanocerias oxidase activity; however, micromolar concentrations of H2O2 can inhibit its catalytic activity. In addition, this inhibiting effect is linearly dependent on the concentration of H2O2. Based on these findings, a simple, rapid and highly sensitive colorimetric method was established for the determination of H2O2 with a limit of detection (LOD) of 2.5 μM (3σ/slope) and a linear range from 4−40 μM. When coupled with glucose oxidase, glucose can be detected down to 2 μM in the linear range of 4−40 μM. Furthermore, this method was successfully applied in the determination of glucose in mouse serum samples. With the new understanding of the interaction between H2O2 and nanoceria, applications of nanoceria-based sensors in engineering, biotechnology and environmental chemistry can be further exploited.

In-Situ Fixation of All-Inorganic Mo–Fe–S Clusters for the Highly Selective Removal of Lead(II)

The selective adsorption by suitable substrate materials is considered one of the most economical methods. In this work, an all-inorganic bimetallic Mo-Fe-S cluster is facilely achieved through in situ chemical fixation of tetrathiomolybdate (TTM) on Fe3O4 nanoparticles (NPs) at room temperature (donated as FeMoS NPs). The bimetallic building blocks on the obtained FeMoS NPs possess a monovacancy species of sulfur, endowing FeMoS NPs with a selectivity order of Zn2+, Mn2+, Ni2+ < Cd2+ ≪ Cu2+ < Pb2+ for metal-ion adsorption, a novel application for the Mo-Fe-S clusters. Particularly, with the highest selectivity for Pb2+ (Kd ≈ 107), which is about 3 × 103-1 × 106 times higher than those for other ions and has exceeded that of a series of outstanding sorbents reported for Pb2+, FeMoS NPs can efficiently reduce the concentration of Pb2+ from ∼10 ppm to an extremely low level of ∼1 ppb. This facile and rational fabrication of the Mo-Fe-S cluster with Fe3O4 represents a feasible approach to cheaply develop novel and efficient materials for the selective removal of lead(II).

Highly Sensitive and Selective Determination of Tertiary Butylhydroquinone in Edible Oils by Competitive Reaction Induced “On–Off–On” Fluorescent Switch

As one of most common synthetic phenolic antioxidants, tertiary butylhydroquinone (TBHQ) has received increasing attention due to the potential risk for liver damage and carcinogenesis. Herein, a simple and rapid fluorescent switchable methodology was developed for highly selective and sensitive determination of TBHQ by utilizing the competitive interaction between the photoinduced electron transfer (PET) effect of carbon dots (CDs)/Fe(III) ions and the complexation reaction of TBHQ/Fe(III) ions. This novel fluorescent switchable sensing platform allows determining TBHQ in a wider range from 0.5 to 80 μg mL(-1) with a low detection limit of 0.01 μg mL(-1). Furthermore, high specificity and good accuracy with recoveries ranging from 94.29 to 105.82% in spiked edible oil samples are obtained with the present method, confirming its applicability for the trace detection of TBHQ in a complex food matrix. Thus, the present method provides a novel and effective fluorescent approach for rapid and specific screening of TBHQ in common products, which is beneficial for monitoring and reducing the risk of TBHQ overuse during food storage.

A hybrid monolithic column based on layered double hydroxide-alginate hydrogel for selective solid phase extraction of lead ions in food and water samples

In order to develop an accurate and precise determination method based on solid phase extraction of Pb(II) in food and water samples, a hybrid monolithic column based on layered double hydroxides (LDHs) nanosheets-alginate hydrogel has been synthesized. Combining the advantages of porous 3D framework of hydrogel with selective adsorption of LDHs toward Pb(II), the hydrogel-based hybrid monolithic column shows enhanced enrichment selectivity and efficiency for target ions. Effects of hydrogel composition, pH, concentration and type of eluent, sample volume, and interfering ions on the recoveries of the analytes were also investigated. Under the optimal experiment conditions of method, the limit of detection, preconcentration factor and precision as RSD% are found to be 0.39 μg L-1, 53.7 and 2.65%, respectively. Trace Pb(II) can be quantitatively preconcentrated at pH 6.0 with recoveries >97%. Finally, the method was successfully verified by analyzing spiked Pb2+ in water and drinking samples.

Changes of dehydrin profiles induced by drought in winter wheat at different developmental stages

Two cultivars of winter wheat (Triticum aestivum L.) differing in their drought tolerance (KTC86211 and ND7532) were subjected to a progressive soil water stress and recovery at four developmental stages. Dehydrins with molecular masses of 45 and 37 kDa were constitutively accumulated during all stages in both genotypes. The 28 kDa dehydrin accumulated exclusively at seedling stage in both genotypes. The 49 and 40 kDa dehydrins accumulated at both tillering and jointing stages but showed a genotype-specific pattern. The content of most dehydrins increased with decreased soil moisture and then decreased during recovery. These results suggest that accumulation pattern of dehydrins during water stress was related to the genotype and developmental stage.

Facile and sensitive electrochemical detection of methyl parathion based on a sensing platform constructed by the direct growth of carbon nanotubes on carbon paper

This work developed an economic, convenient, sensitive and practical methyl parathion sensor using an easy-to-fabricate, reusable, inexpensive carbon nanotube/carbon paper composite as the working electrode. Carbon nanotubes form a network structure and provide large surface area, which can enhance the electron transfer capability of the carbon paper electrode. As an electrochemical sensing platform, the constructed carbon nanotube/carbon paper sensor allows sensitive determination of methyl parathion in the range of 10 ng mL−1 to 1000 ng mL−1 with a low detection limit of 3.9 ng mL−1. Importantly, the present study demonstrated the high sensitivity, satisfactory stability and good anti-interference capabilities of this new electrode platform for methyl parathion detection. Furthermore, the present method was successfully applied to determine methyl parathion in kiwi samples with satisfactory precision (3.74–5.05%) of relative standard deviation (RSD) and acceptable recoveries (99.67–108%), which demonstrated the applicability of the carbon nanotube/carbon paper composite sensor. Such a facile approach for the detection of OPs may provide some guidance for designing nanomaterial-based sensors.

“Pulling” π-conjugated polyene biomolecules into water: enhancement of light-thermal stability and bioactivity by a facile graphene oxide-based phase-transfer approach

This work demonstrated that graphene oxide (GO) could not only be exploited as a nanovector to efficiently transfer π-conjugated polyene biomolecules from the organic phase to the aqueous phase, but also could enhance light-thermal stability and bioactivity of the transferred π-conjugated polyene biomolecules.