Arsenic distribution in soils and rye plants of a cropland located in an abandoned mining area.

A mining impacted cropland was studied in order to assess its As pollution level and the derived environmental and health risks. Profile soil samples (0-50 cm) and rye plant samples were collected at different distances (0-150 m) from the near mine dump and analyzed for their As content and distribution. These cropland soils were sandy, acidic and poor in organic matter and Fe/Al oxides. The soil total As concentrations (38-177 mg kg(-1)) and, especially, the soil soluble As concentrations (0.48-4.1 mg kg(-1)) importantly exceeded their safe limits for agricultural use of soils. Moreover, the soil As contents more prone to be mobilized could rise up to 25-69% of total As levels as determined using (NH4)2SO4, NH4H2PO4 and (NH4)2C2O4·H2O as sequential extractants. Arsenic in rye plants was primarily distributed in roots (3.4-18.8 mg kg(-1)), with restricted translocation to shoots (TF=0.05-0.26) and grains (TF=<0.02-0.14). The mechanism for this excluder behavior should be likely related to arsenate reduction to arsenite in roots, followed by its complexation with thiols, as suggested by the high arsenite level in rye roots (up to 95% of the total As content) and the negative correlation between thiol concentrations in rye roots and As concentrations in rye shoots (|R|=0.770; p<0.01). Accordingly, in spite of the high mobile and mobilizable As contents in soils, As concentrations in rye above-ground tissues comply with the European regulation on undesirable substances in animal feed. Likewise, rye grain As concentrations were below its maximum tolerable concentration in cereals established by international legislation.

DNA single-base mismatch study with an electrochemical enzymatic genosensor.

A thorough selectivity study of DNA hybridization employing an electrochemical enzymatic genosensor is discussed here. After immobilizing on a gold film a 30-mer 3'-thiolated DNA strand, hybridization with a biotinylated complementary one takes place. Then, alkaline phosphatase is incorporated to the duplex through the interaction streptavidin-biotin. Enzymatic generation of indigo blue from 3-indoxyl phosphate and subsequent electrochemical detection was made. The influence of hybridization conditions was studied in order to better discern between fully complementary and mismatched strands. Detection of 3, 2 and 1 mismatch was possible. The type and location of the single-base mismatch, as well as the influence of the length of the strands was studied too. Mutations that suppose displacement of the reading frame were also considered. The effect of the concentration on the selectivity was tested, resulting a highly selective genosensor with an adequate sensitivity and stability.

Genosensor on gold films with enzymatic electrochemical detection of a SARS virus sequence.

A hybridisation-based genosensor was designed on a 100 nm sputtered gold film. This material worked as an immobilisation and transduction surface. A 30-mer sequence that encodes a short lysine-rich region, unique to SARS (severe acute respiratory syndrome) virus, was chosen as target. A complementary strand (probe), labelled with a thiol group at the 3'-end, was immobilised on the film. After blocking the surface, hybridisation with the biotin-conjugated SARS strand (at the 3'-end) took place. Interaction with alkaline phosphatase-labelled streptavidin permits amplified indirect electrochemical detection. The analytical signal is constituted by an electrochemical process of indigo carmine, the soluble product of the enzymatic hydrolysis of 3-indoxyl phosphate. The use of a sensitive electrochemical technique such as square wave voltammetry allowed a detection limit of 6 pM to be obtained for this DNA sequence, lower than any other found in the bibliography. The parameters affecting the methodology were studied, with special attention being placed on selectivity. Specificity was clearly enhanced when interaction time and stringency (in the form of formamide percentage) were increased. With 1h of strand interaction and employing 50% of formamide in the hybridisation buffer, a 3-base mismatch strand was perfectly distinguished from the complementary.