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In this work, a sandwich-type electrochemical biosensing platform is developed based on carbon sphere-MoS2 (CS-MoS2) and target recycling amplification of catalyzed hairpin assembly (CHA) strategy for ultrasensitive determination of microRNA (miRNA). The CS-MoS2 is prepared and used as sensing substrate, which shows high specific surface area, enhanced stability and good dispersibility. The capture probe is first modified on Au nanoparticles/CS-MoS2 modified glassy carbon electrode through Au-S band, and hairpin DNA1 (H1) then reacts with it and unfolds its loop domain by hybridizing with target miRNA-21. The opened H1 subsequently assembles with biotin labeled hairpin DNA 2 (H2) to displace the target. The liberated miRNA-21 is free and backs to the original solution to proceed next circulation, resulting in the generation of large amounts of H1–H2 duplex. Massive signal indicators horseradish peroxidase are then immobilized on electrode, and catalyze hydrogenperoxide + hydroquinone (H2O2 + HQ) system to produce a strong electrochemical response. The proposed assay benefits from advantages of sandwich-type structure, favorable electrochemical properties of CS-MoS2 and CHA target recycling amplification strategy. Therefore, it exhibits a wide linear relation between 1 × 10−16 and 1 × 10−10 M with a low detection limit of 1.6 × 10−17 M for miRNA-21 detection.

A novel competitive aptasensor for thrombin detection is developed by using a tetrahedral DNA (T-DNA) probe and hybridization chain reaction (HCR) signal amplification. Sulfur and nitrogen co-doped reduced graphene oxide (SN-rGO) is firstly prepared by a simple reflux method and used for supporting substrate of biosensor. Then, T-DNA probe is modified on the electrode by Au-S bond and a competition is happened between target thrombin and the complementary DNA (cDNA) of aptamer. The aptamer binding to thrombin forms an aptamer-target conjugate and make the cDNA remained, and subsequently hybridizes with the vertical domain of T-DNA. Finally, the cDNAs trigger HCR, which results in a great current response by the catalysis of horseradish peroxidase to the hydrogen peroxide + hydroquinone system. For thrombin detection, the proposed biosensor shows a wide linearity range of 10-13-10-8M and a low detection limit of 11.6fM (S/N = 3), which is hopeful to apply in biotechnology and clinical diagnosis.

MicroRNAs (MiRNAs) play multiple crucial regulating roles in cell which can regulate one third of protein-coding genes. MiRNAs participate in the developmental and physiological processes of human body, while their aberrant adjustment will be more likely to trigger diseases such as cancers, kidney disease, central nervous system diseases, cardiovascular diseases, diabetes, viral infections and so on. What's worse, for the detection of miRNAs, their small size, high sequence similarity, low abundance and difficult extraction from cells impose great challenges in the analysis. Hence, it's necessary to fabricate accurate and sensitive biosensing platform for miRNAs detection. Up to now, researchers have developed many signal-amplification strategies for miRNAs detection, including hybridization chain reaction, nuclease amplification, rolling circle amplification, catalyzed hairpin assembly amplification and nanomaterials based amplification. These methods are typical, feasible and frequently used. In this review, we retrospect recent advances in signal amplification strategies for detecting miRNAs and point out the pros and cons of them. Furthermore, further prospects and promising developments of the signal-amplification strategies for detecting miRNAs are proposed.

In this work, a sensitive, universal and reusable electrochemical biosensor based on stannic oxide nanocorals-graphene hybrids (SnO2 NCs-Gr) is developed for target DNA detection by using two kinds of DNA enzymes for signal amplification through an autonomous cascade DNA duplication strategy. A hairpin probe is designed composing of a projecting part at the 3'-end as identification sequence for target, a recognition site for nicking endonuclease, and an 18-carbon shim to stop polymerization process. The designed DNA duplication-incision-replacement process is handled by KF polymerase and endonuclease, then combining with gold nanoparticles as signal carrier for further signal amplification. In the detection system, the electrochemical-chemical-chemical procedure, which uses ferrocene methanol, tris(2-carboxyethyl)phosphine and l-ascorbic acid 2-phosphate as oxidoreduction neurogen, deoxidizer and zymolyte, separately, is applied to amplify detection signal. Benefiting from the multiple signal amplification mechanism, the proposed sensor reveals a good linear connection between the peak current and logarithm of analyte concentration in range of 0.0001-1 × 10-11molL-1 with a detection limit of 1.25 × 10-17molL-1 (S/N=3). This assay also opens one promising strategy for ultrasensitive determination of other biological molecules for bioanalysis and biomedicine diagnostics.

Sensitive detection of ochratoxin A (OTA) plays an important role in the field of food safety control. In this study, we are reporting for the first time an electrochemical biosensor which employs the integration of MoSe 2 nanoflowers, Au nanoparticles (AuNPs), aptamer and the guanine-rich complementary DNA sequence for the sensitive detection of OTA. MoSe 2 nanoflowers are prepared by a simple hydrothermal method and used as a promising sensing platform based on its large surface area. The methylene blue is used as a tracer and a guanine-rich complementary DNA sequence is designed to bind with the unbound OTA aptamer for signal amplification. The aptamer is immobilized on the AuNPs/MoSe 2 modified electrode surface through Au–S interaction. Since OTA can competitively bind with the aptamer due to their high affinity, the presence of OTA will induce the decrease of guanine-rich DNA on the electrode surface, in turn reduces the signal of methylene blue which can specifically adsorb to the guanine units of DNA. The proposed assay shows a good linear relationship within the range of 0.0001–1 nM with a detection limit of 0.08 pM for OTA. The developed biosensor has been applied to determine OTA concentration in wine samples.

Use of transgenic crops, including those expressing the insecticidal Cry protein from Bt, is increasing at a rapid rate in worldwide. Field and laboratory studies of transgenic Bt crops have been carried out to detect the persistence and activity of the Cry protein in soil and its effect on soil microorganisms to assess their risks to environment. However, there were few studies that evaluate the seasonal effects of Bt rice on rhizosphere soil microbial communities compared to those of insecticides commonly applied in paddy soil for the control of lepidopteran insects. In this study, seasonal effects of transgenic rice expressing the Cry1Ab insecticidal protein active against lepidoperan pests and the insecticide triazophos [3-(o,o-diethyl)-1-phenyl thiophosphoryl-1,2,4-triazol] on soil enzyme activities and microbial communities were compared under field conditions. During a 2-year field study, rhizosphere soil samples of transgenic-Bt rice (Bt), non-Bt parental rice (Ck) and non-Bt parental rice with triazophos (Ckp) applied were taken at four stages in the rice developmental cycle: seedling, booting, heading and maturing. Microbial processes were investigated by measuring different biochemical activities including those involved in C and P cycling. Denaturing gradient gel electrophoresis (DGGE) and terminal-restriction fragment length polymorphism (T-RFLP) analyses were used to compare rhizosphere microbial compositions. Some occasional and inconsistent effects of the application of triazophos on the bacterial composition in the rhizosphere soil of rice plant were found at the booting and heading stages as compared with that of transgenic-Bt rice. There were no statistically significant differences (P>0.05) in phosphatase activity, dehydrogenase activity, respiration, methanogenesis or fungal community composition in rhizosphere soil between Bt, Ck and Ckp over the rice cropping cycle. However, seasonal variations in the selected enzyme activities and microbial community composition in the rhizosphere soil of Bt, Ck and Ckp were clearly detected. These results suggested that the changes in rhizophere soil microbial community composition associated with the crop growth stage overweighed the application of triazophos and the cry1Ab gene transformation. KMD1 (Bt) rice expressing the cry1Ab gene had no measurable adverse effect on the key microbial processes or microbial community composition in rhizophere soil over 2 years of rice cropping.

The potential influences of cadmium (Cd) on the biochemical processes of the soil nitrogen (N) cycle, along with the dynamics of ammonification, nitrification, and denitrification processes in the rhizosphere and non-rhizosphere (bulk soil), respectively, were investigated in a Cd-stressed system during an entire soybean growing season. In terms of Cd pollution at the seedling stage, the ammonifying bacteria proved to be the most sensitive microorganisms, whereas the effects of Cd on denitrification were not obvious. Following the growth of soybeans, the influences of Cd on ammonification in the bulk soil were: toxic impacts at the seedling stage, stimulatory effects during the early flowering stage, and adaptation to the pollutant during the podding and ripening stages. Although nitrification and denitrification in the bulk soil decreased throughout the entire growth cycle, positive adaptation to Cd stress was observed during the ripening stage. Moreover, during the ripening stage, denitrification in the bulk soil under high Cd treatment (20 mg kg −1 ) was even higher than that in the control, indicating a probable change in the ecology of the denitrifying microbes in the Cd-stressed system. Changes in the activity of microbes in the rhizosphere following plant growth were similar to those in the non-rhizosphere in Cd treatments; however, the tendency of change in the rhizosphere seemed to be more moderate. This suggested that there was some mitigation of Cd stress in the rhizosphere.

To study Pseudomonas putida CZ1, having high tolerance to copper and zinc on the removal of toxic metals from aqueous solutions, the biosorption of Cu(II) and Zn(II) by living and nonliving P. putida CZ1 were studied as functions of reaction time, initial pH of the solution and metal concentration. It was found that the optimum pH for Zn(II) removal by living and nonliving cells was 5.0, while it was 5.0 and 4.5, respectively, for Cu(II) removal. At the optimal conditions, metal ion biosorption was increased as the initial metal concentration increased. The adsorption data with respect to both metals provide an excellent fit to the Langmuir isotherm. The binding capacity of living cells is significantly higher than that of nonliving cells at tested conditions. It demonstrated that about 40-50% of the metals were actively taken up by P. putida CZ1, with the remainder being passively bound to the bacterium. Moreover, desorption efficiency of Cu(II) and Zn(II) by living cells was 72.5 and 45.6% under 0.1M HCl and it was 95.3 and 83.8% by nonliving cells, respectively. It may be due to Cu(II) and Zn(II) uptake by the living cells enhanced by intracellular accumulation.

The role of rhizosphere bacteria in facilitating the solubility of copper (Cu) in contaminated soil and Cu accumulation in plant were studied. The bacteria strains were isolated from the rhizosphere of Elsholtzia splendens, a Cu accumulator growing on Tonglu Mountain copper mines. After the sandy soils containing 237 mg kg−1 were incubated with the bacteria strains, it was indicated that rhizosphere microbes played an important role in influencing the availability of water-soluble Cu in soils. Soils had greater concentrations of water-extractable Cu compared with axenic soils inoculated with different bacterial strains. Further evidence for bacterial facilitation of increased solubility of Cu in the soil was obtained using the antibiotic ampicillin (0.1 mg g−1). There were 36% decreases in Cu concentration in the presence of bacterial strain MS12 and ampicillin together compared with bacterial inoculation alone. Different bacterial strains had different abilities on soil water-soluble Cu. To achieve the highest rates of plant Cu accumulation, it was necessary for bacteria to be present in the rhizosphere of E. splendens. Inoculated plants supplied with 20 μmol L−1 CuSO4 had significantly greater concentrations of Cu in shoots and roots than uninoculated plants and bacterial strain MS2 was the most effective strain in promoting plant Cu uptake. There were 2.2-fold and 2.5-fold increases in Cu accumulation in the shoots and roots of plants inoculated with strain MS2 compared to axenic controls. Furthermore, when ampicillin and the bacterial strains were added together to the nutrient solution, the Cu concentrations in roots and shoots of ampicillin-treated plants were lower than those in inoculated plants. When ampicillin was added to the nutrient solution, Cu accumulation was inhibited by about 24–44% in shoots and 20–44% in roots. The above results provided a new insight into the phytoremediation of Cu-contaminated soil. Keywords: Phytoremediation, Soil bacteria, Copper, Mobilization

Biological removal of ammonia was investigated using two types of packing materials, compost and sludge in laboratory-scale biofilters (8 l reactor volume). The aim of this study is to investigate the potential of unit systems packed with these supports in terms of ammonia emissions treatment. Experimental tests and measurements included analysis of removal efficiency, metabolic products, and results of long-term operation. The inlet concentration of ammonia applied was 20–200 mg m−3. The ammonia loading rates of 24.9–566 g NH3 m−3 d−1 to compost biofilter (BF3) and 24.9–472 g NH3 m−3 d−1 to sludge biofilter (BF4) were applied for 210 days, respectively. Removal efficiencies of the compost and sludge biofilters were in the range of 97–99% and 95–99%, respectively when the inlet concentration of ammonia was below 110 mg m−3, and the maximum elimination capacities were 288 and 243 g NH3 m−3 d−1, respectively. However, removal efficiency and elimination capacity of both biofilters significantly decreased as the inlet concentration increased to above 110 mg m−3. By using kinetic analysis, the maximum removal rate of ammonia, Vm, and the saturation constant, Ks, were determined for both packing materials and the value of Vm for compost was found to be larger. Periodic analysis of the biofilter packing materials showed the accumulation of the nitrification product NO3- in the operation. During the experiment, the pressure drops measured were very low. The use of both packing materials requires neither nutritive aqueous solution nor buffer solution.

Geogenic, as well as anthropogenic heavy metals from distant sources, gradually increase the level of toxic metals in natural environments and these will be increasingly taken up by plants and transferred further up the food chain. To control any detrimental environmental impacts of soil contaminants, it is desirable to investigate the solubility and mobility of soil chemical contaminants under land-based agricultural systems. In this paper, a greenhouse experiment was conducted to assess the effects of rhizospheric dynamics on the bioavailability of lead. Rice (Oryza sativa L.) and Ultisol were used as the test materials. The results showed NH4OAc extractable Pb in rice rhizosphere was much higher than in bulk soil, which meant that the activation processes in the rhizosphere was significant and the amount of bioavailable Pb increased. The distribution of extractable Pb at a distance of 0–10 mm from the root compartment, however, varied and had a little depletion compared to that in the rhizosphere. The significant difference of Pb forms between the rhizosphere and bulk soil further demonstrated the root-induced changes of lead bioavailability in the rhizosphere might also be related to the various levels of Pb treatment and the simultaneity of Cd. It was observed the accumulation of soluble plus exchangeable Pb (SE-Pb) in the 500 mg kg−1 Pb treatment, and relatively stronger fixation of Pb to oxides in the 250 mg kg−1 Pb treatment. The activation of SE-Pb in rice rhizosphere was weaker in the 5 mg kg−1 Cd treatment and stronger in the 10 mg kg−1 Cd treatment than that in the treatment without Cd. The activation of lead in the rhizosphere of Oryza sativa L., suggested a potential risk of heavy metal accumulation and phytotoxicity in plants and soil ecosystem.

Tissue concentrations of some mineral elements appeared to be influenced by plant Fe status. The influence of Fe deficiency on Cu uptake and accumulation in Commelina communis , and the relationship between Cu uptake and root Fe(III) chelate reductase (FCR) activity were investigated in this study. The results showed that Cu accumulation in C. communis was increased with the drop of Fe concentration in nutrient solution. Cu uptake in C. communis was significantly enhanced by Fe deficiency. Cu uptake in Fe-deficient plants were still higher than that of Fe-sufficient plants when P-type ATPase inhibitor Na 3 VO 4 was added in the solution, which demonstrated that Fe deficiency induced stimulation of the plasma membrane H + -ATPase did not play a role in the enhanced Cu uptake. Fe and Cu deficiency could induced root Fe(III) chelate reductase activity in C. communis . Both Fe(III) chelate reductase activity aud Cu concentration in roots inhibited distinctly by cycloheximide, a kind of protein synthesis inhibitor. In the time course of Fe deficiency, there simultaneously appeared Cu concentration and FCR activity peaks in roots at day 9. All above evidences demonstrated Cu uptake aud accumulation in C. communis were probably related to the root FCR activity.