Responses of nickel bioavailability and toxicity of Prorocentrum Donghaienses to dissolved organic matter (DOM) fractions incubated in urea.

Urea, nickel (Ni) and dissolved organic matter (DOM) from land varied with different sources have a great impact on the offshore ecosystem. The heterogeneity of Ni bioavailability and toxicity of Prorocentrum donghaiense influenced by DOM fractions incubated in urea was investigated in this study. On the occasion, chlorophyll (Chl a) concentration, growth rate, and photosynthesis parameters were monitored to track changes occurring in the test organism. Chl a concentration and photosynthesis parameters in the treatment of hydrophilic DOM (HPI) with Ni-free was significantly higher than that in the control treatment, and similar data were shown in the treatment of hydrophobic DOM（HPO）with the low Ni environment (0.17µmol L-1). However, the opposite phenomena were observed in the treatments of HPO with the higher Ni environment (over 170µmol L-1). Moreover, the EC50 of Ni for P.donghaiense incubated in HPO was relatively lower than that in HPI and control treatment, which implied that HPO elevated the toxicity of Ni. Therefore, the varied DOM compositions because of different origins, as a chelating agent and potential nutrient source in coastal waters, shows the significantly different bioavailability and toxicity of Ni with the increasing inputs of urea, which in turn influences the dynamics of phytoplankton.

Ultrasensitive supersandwich-type biosensor for enzyme-free amplified microRNA detection based on N-doped graphene/Au nanoparticles and hemin/G-quadruplexes.

A simple, enzyme-free supersandwich-type biosensor is fabricated for the ultrasensitive detection of microRNAs (miRNAs) using N-doped graphene/Au nanoparticles (NG-AuNPs) and hemin/G-quadruplexes. In the proposed strategy, AuNPs are deposited on the surface of a MoSe2 modified electrode to immobilize the thiol-modified hairpin probe through the strong Au-S bond. When the target miRNA is added, capture DNA hybridizes with it and unfolds its stem-and-loop structure. The NG-AuNP hybrids are the main amplification element and are modified by hybridization with assistance DNA and the terminus of capture DNA, resulting in the formation of the supersandwich structure. The assistance DNA is embedded into the hemin/G-quadruplex complexes in the presence of hemin and K+ to provide an exceptional current signal for the detection of miRNAs. Under the optimized experimental conditions, a detection limit of 0.17 fM is obtained with a linear range of 10 fM-1 nM. In addition, the present biosensor shows outstanding selectivity towards mismatched miRNAs. This biosensor platform successfully realized the combination of the signal amplification technique with the supersandwich structure, providing a promising approach for the detection of miRNA-21 in practical applications.