[Validation study on a multi-residue method for determination of pesticide residues in agricultural products by new automatic pretreatment equipment (FASRAC) and GC-MS/MS].

A validation study was performed on a multiresidue method for determination of pesticide residues in agricultural products according to the method validation guideline of the Ministry of Health, Labour and Welfare of Japan. FASRAC (Food Automatic Analytical Systems for Residual Agricultural Chemicals) automatically performs extraction of pesticide residues from agricultural products with acetonitrile, filtration, constant volume, mixing with the use of air, mixing acetonitrile with buffer solvent, separation, and dehydration with sodium sulfate. The extract was purified with a GC/NH2 column. For wheat flour and soybeans, a purification step with a C18 column was added before a GC/NH2 column. After removal of the solvent, the extract was resolved in n-hexane/acetone solvent for GC-MS/MS analysis. In the case of manual analysis, pesticide residues were analyzed according to official multiresidue methods and purification steps were the same as in FASRAC. Recovery tests were performed with wheat flour, soybeans, spinach and apples, by addition of 302 pesticides at the concentrations 0.01 mg/kg. The results indicate that automatic extraction using FASRAC is superior to manual analysis in trueness, repeatability and within-run reproducibility. Specially, automatic extraction using FASRAC is superior to manual analysis in trueness because it is optimized in various respects, for example reextraction at salting-out.

Precisely programmed and robust 2D streptavidin nanoarrays by using periodical nanometer-scale wells embedded in DNA origami assembly.

A new punched DNA origami assembly with periodic nanometer-scale wells has been successfully designed and constructed. Through the attachment of two biotins at the two edges of each well, just one streptavidin (SA) tetramer (d = 5 nm) was size-selectively captured in each 6.8 x 12 x 2.0 nm well; this allowed formation of a 28 nm-period SA nanoarray of individual molecules. The position of SA capture can be fully controlled by placement of biotins in the nanoarray well. Moreover, construction of a 2D nanoarray of individual SA tetramers through selective positioning of SA tetramers in any desired wells in a complex of such punched origami motifs is also possible. The stability of the SA captured by this fixation strategy (DNA wells and two biotin linkers) was directly compared on the same molecule with the stability of SA captured with other possible strategies that do not employ wells or two linkers. In this way, the robustness of this means of fixation was clearly established.