Colorimetric detection of penicillin G in milk using antibody-functionalized dendritic platinum nanoparticles

A facile colorimetric method for detecting residual penicillin G in milk using amine-immobilized glass vials and dendritic platinum nanoparticles has been developed. Two distinct methods, liquid-phase and vapor-phase deposition, were used to treat a glass vial with 3-aminopropyl triethoxysilane (APTES) to produce amine groups on the internal surface of the vial. A milk solution spiked with penicillin G was introduced into the glass vial and any compounds in the milk containing carboxylic acid groups (including penicillin G) were allowed to bind to the glass surface through the formation of amide bonds. However, subsequently-added antibody-functionalized dendritic platinum nanoparticles were found to bind only to the penicillin G, which provides the specificity of the proposed assay. Addition of 3,3′,5,5′-tetramethylbenzidine (TMB) solution to the glass vial induced color changes owing to the platinum-nanoparticle-mediated oxidation of TMB. The color change could be identified with the naked eye and the limit of detection was found to be 1 ng/mL. The observed color change in the glass vial treated with APTES in the vapor phase was higher than that in the liquid phase, which was attributed to the presence of a higher density of accessible amine groups.