L methionine

Nickel chloride hexahydrate (NiCl₂·6H₂O, ≥98.0%), ascorbic acid (AA, AR), and thiourea (CH₄N₂S, AR) were purchased from Shanghai Macklin Biochemical Co., Ltd., Shanghai, China. 3,3′,5,5′-tetramethylbenzidine (TMB, ≥98%) and p-benzoquinone (C₆H₄O₂, 99%) were purchased from Shanghai Aladdin Biochemical Technologh Co., Ltd., Shanghai, China. Sulfur sublimed (S, AR), sodium acetate trihydrate (CH₃COONa·3H₂O, AR), copper nitrate trihydrate (Cu(NO₃)₂·3H₂O, AR), ethanol (CH₃CH₂OH, AR), hydrogen peroxide (30 wt%, H₂O₂, AR), and glacial acetic acid (CH₃COOH, AR) were purchased from Chengdu Cologne Chemicals Co., Ltd., Chengdu, China. l-arginine, l-valine, l-methionine, l-histidine, l-glutamate, glycine, Dl-aspartic acid, l-threonine, l-cysteine and other amino acids were purchased from Sinopharm Chemical Reagents Co., Ltd. (BR), Shanghai, China. Gram-negative E. coli (ATCC25922) and Gram-positive S. aureus (ATCC29213) were obtained from Shanghai Jiachu Bioengineering Co., Ltd., Shanghai, China. Propidium iodide (PI) and SYTO 9 were obtained from Invitrogen Life Technology Co., Ltd., California, America. Ultra-pure water (18.2 M Ω cm) was used in all solutions and experiments. All chemicals were not further purified. Caution: These reagents are toxic, please use as required.