Responses of soil microbial biomass nitrogen to organic fertilizer with different degrees of maturity and regu-lation to soil mineral nitrogen.

By combining the composting process with soil culture experiment, we conducted an experiment with four treatments, including conventional chemical fertilizer (CK), chemical fertilizer + compost maturity reaching 50% germination index (GI, the same below) organic fertilizer (CO1), chemical fertilizer + compost maturity reaching 80% GI organic fertilizer (CO2), chemical fertilizer + compost maturity reaching 100% GI organic ferti-lizer (CO3). We measured soil microbial biomass nitrogen (MBN), mineral nitrogen (NH4+-N, NO3--N), net nitrification rate, microbial biomass carbon (MBC), dissolved organic carbon (DOC), soil urease and soil protease, aiming to reveal the regulatory effect of soil MBN on mineral nitrogen. The results showed that organic fertilizer application significantly increased MBN and NH4+-N concentrations by 50.1%-62.4% and 109.9%-147.1%, reduced NO3--N concentration and net nitrification rate by 23.3%-46.8%, and 26.2%-51.5%, and enhanced MBC, DOC, urease and protease activities by 33.8%-69.6%, 7.4%-20.8%, 11.2%-69.0% and 9.4%-25.1%, respectively. The change ranges of CO2 and CO3 were significantly higher than CO1. Redundancy analysis (RDA) and structural equation model (SEM) results showed that the application of organic fertilizer with higher degree of maturity (GI≥80%) positively regulated soil MBC, MBN, NH4+-N, and the activities of urease and protease, but had a negative effect on soil net nitrification rate. The combined application of chemical fertilizers and high decomposed organic fertilizers could significantly increase soil MBN and NH4+-N contents, as well as soil urease and protease activities, but reduce soil net nitrification rate. To efficiently utilize organic solid wastes, it is recommended to use chemical fertilizer in combination of organic fertilizers with 80% decomposing degree in practical production to reduce the cost in both economy and time.

A reagentless electrochemiluminescent immunosensor for apurinic/apyrimidinic endonuclease 1 detection based on the new Ru(bpy)3(2+)/bi-arginine system.

Apurinic/apyrimidinic endonuclease 1 (APE-1), a kind of multifunctional protein widely-distributed in the body, plays an essential role in the DNA base excision repair and serves as multiple possible roles in the response of human cancer to radiotherapy and chemotherapy. In this work, an ultrasensitive solid-state electrochemiluminescence (ECL) immunosensor is designed to determine APE-1 based on the new Ru(bpy)3(2+)/bi-arginine system. The bi-arginine (bi-Arg) is decorated on the Au nanoparticles functionalized magnetic Fe3O4/reduced graphene oxide (bi-Arg/Au@Fe3O4-rGO) according to the self-assembling and covalent cross-linking interaction to obtain the functionalized nanocomposite of bi-Arg/Au@Fe3O4-rGO. Herein, the bi-Arg/Au@Fe3O4-rGO plays not only an amplification label to enhance the ECL signal of Ru(bpy)3(2+) due to the coreactant of bi-Arg but also an ideal nanocarrier to load numerous secondary antibody. Based on sandwich-type immunoassay format, this proposed method offers a linear range of 1.0fgmL(-1)-5.0pgmL(-1) and an estimated detection limit of 0.3fgmL(-1) for the APE-1. Moreover, the reagentless ECL immunosensor also exhibits high sensitivity, excellent selectivity and good stability, which has greatly potential development and application in clinical diagnostics, immunology and biomedical research.