[Pollution Characteristics of Microplastics in Migratory Bird Habitats Located Within Poyang Lake Wetlands].

Microplastic pollution (plastics with particle sizes<5 mm) has become a serious problem. In this study, we sampled the surface water, sediment, and bird excrement from the shore, center of the lake, and active areas for birds in Baisha Lake, which is key habitat for migratory birds in the Poyang Lake wetlands. The microplastics were separated by flotation separation, and then, we analyzed the pollution characteristics of this area. The main results were as follows. ① There were significant differences in the abundance of microplastics in water and sediment at different sampling points in the study area. The average abundance of microplastics in water and sediment were 263.28 per·m-3 and 215.9 per·kg-1, respectively. The average abundance of microplastics in migratory bird feces was 4.93 per·g-1. ② There were four kinds of microplastics in the surface water in terms of the different morphologies of particles, namely, pellets, films, fragments, and fibers, among which pellets were the major type. The main colors of microplastics were red, yellow, green, blue, purple, black, and transparent. The rank in terms of the size of microplastics was follows: < 1 mm > 1-2 mm > 2-3 mm > 3-5 mm, and the abundance decreased with the increase of particle size. ③ There were also four kinds of microplastics with different morphologies in the sediment, namely, pellets, films, fragments, and fibers. The main colors of these microplastics were red, yellow, blue, purple, black, and transparent. Microplastic sizes on the shore of the lake and bird habitat were mainly < 1 mm, and 1-2 mm particles were mainly detected in the center of the lake. ④ There were four types of microplastics in the excrement of migratory birds, namely, pellets, films, fragments, and fibers. The colors of these microplastics were red, yellow, green, purple, and transparent, and the particle size was mainly < 1 mm. ⑤ There was no consistency in the types of microplastics in the water body, sediment, and bird droppings. However, the size distribution for water and bird excrement was consistent. The results indicate that Poyang Lake bird habitat is polluted by microplastics, and the birds are inevitably exposed to microplastics. This study warns that microplastics will be an emerging threat to migratory birds.

A sensitive and label-free impedimetric biosensor based on an adjunct probe.

A highly sensitive and label-free impedimetric biosensor is achieved based on an adjunct probe attached nearby the capture probe. In this work, the adjunct probe was co-assembled on the surface of gold electrode with the capture probe hybridized with the reporter probe, and then 6-mercapto-1-hexanol was employed to block the nonspecific binding sites. When target DNA was added, the adjunct probe functioned as a fixer to immobilize the element of reporter probe displaced by the target DNA sequences and made the reporter probe approach the electrode surface, leading to effective inhibition of charge transfer. The increase in charge transfer resistance is related to the quantity of the target DNA in a wide range. The linear range for target DNA with specific sequences was from 0.1 nM to 0.5 µM with a good linearity (R=0.9988) and a low detection limit of 6.3 pM. This impedimetric biosensor has the advantages of simplicity, sensitivity, good selectivity, and large dynamic range.

Electrochemical strategy for sensing DNA methylation and DNA methyltransferase activity.

The present work demonstrates a novel signal-off electrochemical method for the determination of DNA methylation and the assay of methyltransferase activity using the electroactive complex [Ru(NH3)6](3+) (RuHex) as a signal transducer. The assay exploits the electrostatic interactions between RuHex and DNA strands. Thiolated single strand DNA1 was firstly self-assembled on a gold electrode via Au-S bonding, followed by hybridization with single strand DNA2 to form double strand DNA containing specific recognition sequence of DNA adenine methylation MTase and methylation-responsive restriction endonuclease Dpn I. The double strand DNA may adsorb lots of electrochemical species ([Ru(NH3)6](3+)) via the electrostatic interaction, thus resulting in a high electrochemical signal. In the presence of DNA adenine methylation methyltransferase and S-adenosyl-l-methionine, the formed double strand DNA was methylated by DNA adenine methylation methyltransferase, then the double strand DNA can be cleaved by methylation-responsive restriction endonuclease Dpn I, leading to the dissociation of a large amount of signaling probes from the electrode. As a result, the adsorption amount of RuHex reduced, resulting in a decrease in electrochemical signal. Thus, a sensitive electrochemical method for detection of DNA methylation is proposed. The proposed method yielded a linear response to concentration of Dam MTase ranging from 0.25 to 10UmL(-1) with a detection limit of 0.18UmL(-1) (S/N=3), which might promise this method as a good candidate for monitoring DNA methylation in the future.

A simple and label-free electrochemical biosensor for DNA detection based on the super-sandwich assay.

The focus of this work was on designing a label-free DNA biosensor based on a super-sandwich assay using the electrochemical impedance spectroscopy technique. For this purpose, we designed a signal-up configuration whose linker probes could hybridize with two regions of the target DNA. In this configuration, the presented target DNA would effectively decrease the electron transfer, which would improve the sensitivity of the sensor. Ultimately, we employed gel electrophoresis to further confirm the formation of the proposed super-sandwich structure.