Abstract: The present invention provides an aspartase mutant, a recombinant expression vector and recombinant bacterium containing the aspartase mutant, and the use thereof, and belongs to the technical field of genetic engineering. The amino acid sequence of the aspartase mutant is as set forth in SEQ ID NO: 1. In the aspartase mutant of the present invention, on the basis of wild type aspartase (with an amino acid sequence as set out in SEQ ID NO: 3), glutamic acid at position 427 is mutated into glutamine. In the present invention, by mutating the amino acid residue at position 427 into glutamine, the polar environment near an active site is changed, and thus ammonia supply during substrate reaction is further facilitated, thereby improving an enzyme activity, enhancing the ability of the enzyme in synthesizing a ?-amino acid, and providing a practical and effective strategy for industrial production of the ?-amino acid.

Abstract: A method for preparing nanoparticles includes preparing a mixture containing an organic solvent, surfactant and water; adding a first quantity of a first silica precursor and ammonia to the mixture; adding a second quantity of the first silica precursor and a second silica precursor to the mixture; adding acetone to the mixture; removing silica nanoparticles from the mixture; and drying the silica nanoparticles.

Abstract: A nanoaggregate composition and method for making nanoaggregate compositions constructed with one, two, and three nanoparticle building blocks includes coating the building blocks with a concentration of polyvinylpyrrolidone (PVP) molecules based on a known relationship between the concentration and an extent of aggregation of the building blocks, and producing nanoaggregates from the building blocks comprising a mixture of single-core nanoaggregates, double-core nanoaggregates, and triple-core nanoaggregates as a function of the extent of aggregation.