title: A rapid and sensitive colorimetric assay method for Co2+ based on the modified Au nanoparticles (NPs): understanding the involved interactions from experiments and simulations.
abstract: We previously reported a colorimetric assay method for Co(2+) based on the thioglycolic acid (TGA) functionalized hexadecyl trimethyl ammonium bromide (CTAB) modified Au NPs. However, the detection limit of 3×10(-7) M was still higher than that of the sanitary standard for drinking water (6.8×10(-8) M). In addition, the interactions between the modifier and Au NPs, and between the modifier-Au NPs and Co(2+) remain to be clarified and confirmed. Thus, in the present study, the modified Au NPs solution was dialyzed and its detection limit was optimized to be 5×10(-10) M. The interactions between the modifier and Au NPs, and between the modifier-Au NPs and Co(2+) were investigated in both experimental characterizations and theoretical calculations, consistently confirming that the Au NPs were modified by the negatively charged anions of [SCH(2)CO(2)](2-) through Au-S bonds and Co(2+) was recognized by the modifier-Au NPs through Co-O chelate bonds. The results of X-ray photoelectron spectroscopy (XPS) suggest that there were no chemical bonds formed between CTAB and Co(2+). Moreover, the colorimetric assay of Co(2+) using the modified Au NPs has been proved to be a rapid, very sensitive and highly selective method. The validation of the method was carried out by analysis of a certified reference material, GSBZ 50030-94.
authors.affiliation: Ningbo Institute of Materials Technology & Engineering (NIMTE), Chinese Academy of Sciences (CAS), Ningbo 315201, China.
authors.forename: Yumin
authors.initials: Y
authors.lastname: Leng
authors.forename: Fuqiang
authors.initials: F
authors.lastname: Zhang
authors.forename: Yujie
authors.initials: Y
authors.lastname: Zhang
authors.forename: Xiaoqin
authors.initials: X
authors.lastname: Fu
authors.forename: Yanbo
authors.initials: Y
authors.lastname: Weng
authors.forename: Liang
authors.initials: L
authors.lastname: Chen
authors.forename: Aiguo
authors.initials: A
authors.lastname: Wu
mesh_terms: D000077286:Cetrimonium; D002593:Cetrimonium Compounds / Q000737:chemistry; D003035:Cobalt / Q000032:analysis* / Q000737:chemistry; D003124:Colorimetry / Q000379:methods*; D003956:Dialysis; D060766:Drinking Water / Q000737:chemistry*; D006046:Gold / Q000737:chemistry*; D006801:Humans; D057230:Limit of Detection; D053768:Metal Nanoparticles / Q000737:chemistry*; D056951:Photoelectron Spectroscopy; D012015:Reference Standards; D013864:Thioglycolates / Q000737:chemistry; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: D002593:Cetrimonium Compounds; D060766:Drinking Water; D013864:Thioglycolates; D014874:Water Pollutants, Chemical; D003035:Cobalt; D006046:Gold; C017487:2-mercaptoacetate; D000077286:Cetrimonium