Enzyme-free dual-amplification assay for colorimetric detection of tetracycline based on Mg2+-dependent DNAzyme assisted catalytic hairpin assembly.

Detection of ultralow concentration of tetracycline (TC) plays a key role in food safety and human health. Herein, we fabricated an enzyme-free dual-amplification assay for sensitive detection of TC in milk. The sensing system ingeniously combined Mg2+-dependent DNAzyme (MNAzyme) cleavage and catalytic hairpin assembly (CHA). Through the binding of TC and specific aptamer (Apt), DNA1 was released from the Apt-DNA1 complex. Then the separated DNA1 would hybridize with DNA2 to activate the catalytic activity of MNAzyme, which subsequently cleaved the substrate H0 and generated a new unit to trigger the following CHA reaction between H1 and H2, thereby releasing the G-rich sequence of H1 to induce the formation of G-quadruplex-hemin DNAzyme as a colorimetric signal readout. Under optimal conditions, the absorption intensity exhibited a significant linear correlation with the logarithm of the target TC concentration over a range of 4 orders of magnitude dynamic range from 1 pM to 10 nM. The limit of detection was calculated to be 0.89 pM and the method showed high selectivity for TC. More impressively, the proposed method was employed for TC determination in the milk sample.

Study of silver aerosol source term at different specific internal energy input from HE detonation devices.

Radioactive aerosols harmful to humans are often produced in nuclear accidents, and their source term characteristics (total volume and particle size distribution) and dispersion patterns have important implications for accident response and hazard assessment. However, experimental studies of radioactive aerosols cannot be directly conducted in open space due to the hazardous nature of radioactive aerosols. In this study, silver was used instead of plutonium to study the aerosol source term under different specific internal energy inputs (SIEI) to simulate a low order explosion in an accident. Results show that aerosol release fraction (ARF) and respirable release fraction (RRF) of silver increase linearly with SIEI first, then varies in a range of 8% ~ 19%, with a turning point at SIEI of 1.4 MJ/kg. Analysis suggests an increase of difference between ARF and RRF with respect to SIEI. The size distribution of silver aerosol around 10 µm is influenced by SIEI significantly, which could be possibly attributed to the interactions between silver aerosol and ambient aerosol (solid HE products or rust). Comparison between the source term of silver and plutonium suggests that silver is a good surrogate of plutonium in studying aerosol for SIEI of MJ/kg level.

Distribution, pollution, and human health risks of persistent and potentially toxic elements in the sediments around Hainan Island, China.

Human activities have changed the global concentration of potentially toxic elements (PTEs) and significantly altered the marine ecosystem. Little is known about the concentrations of these PTEs around Hainan Island in China, or their distribution and human health risks. Understanding the variability of PTEs in marine sediments and how they accumulate is important not only for biodiversity and ecological conservation, but also for management of aquatic natural resources and human health risk assessments. This study showed that the concentrations of six PTEs (Cd, Cu, Zn, As, Pb, and Hg), sampled in nine different cities, were linked to human activities. In order to understand the ecological risks associated with PTE pollution, we calculated the contamination factor (CF), enrichment factor (EF), pollution load index (PLI), and geo-accumulation index (Igeo) of each element in each city. These indicators suggest that the pollution of Cd and Zn in the sediments of these cities is higher than that of the other PTEs. We also carried out a human health risk assessment which demonstrated the carcinogenic effects of Zn on children and adults in ChengMai, while Pb showed non-carcinogenic effects at all the studied sites, suggesting that Zn pollution in the sediments of ChengMai may pose human health risks. We would therefore advise that follow-up studies endeavor to monitor the levels of PTEs in the flora and fauna of these cities.