Colorimetric detection of pathogenic bacteria using platinum-coated magnetic nanoparticle clusters and magnetophoretic chromatography Donghoon Kwon a , Sanghee Lee a , Myung Mo Ahn a , In Seok Kang a , Ki-Hwan Park b , Sangmin Jeon a, * a Department of Chemical Engineering, Pohang University of Science and Technology (POSTECH), Pohang, Republic of Korea b Department of Food Science and Technology, Chung-Ang University, Seoul, Republic of Korea H I G H L I G H T S G R A P H I C A L A B S T R A C T  Pt/MNCs and magnetophoretic chromatography were used to detect E. coli.  MNCs/E. coli were separated from free MNCs by magnetophoretic chromatography.  Color change by Pt enabled detection of 10 cfu/mL E. coli with the naked eye. A R T I C L E I N F O Article history: Received 12 December 2014 Received in revised form 17 April 2015 Accepted 22 April 2015 Available online 24 April 2015 Keywords: Magnetophoretic chromatography Pathogenic bacteria Platinum nanoparticles Colorimetric detection A B S T R A C T A colorimetric method that uses platinum-coated magnetic nanoparticle clusters (Pt/MNCs) and magnetophoretic chromatography is developed to detect pathogenic bacteria. Half-fragments of monoclonal Escherichia coli O157:H7 (EC) antibodies were functionalized to Pt/MNCs and used to capture E. coli bacteria in milk. After magnetic separation of free Pt/MNCs and Pt/MNC-EC complexes from the milk, a precision pipette was used to imbibe the E. coli-containing solution, then a viscous polyethylene glycol solution. Due to difference in viscosities, the solutions separate into two liquid layers inside the pipette tip. The Pt/MNC-EC complexes were separated from the free Pt/MNCs by applying an external magnetic field, then added to a tetramethylbenzidine (TMB) solution. Catalytic oxidation of TMB by Pt produced color changes of the solution, which enabled identification of the presence of 10 cfu mL 1 E. coli bacteria with the naked eye. The total assay time including separation, binding and detection was 30 min. ã 2015 Elsevier B.V. All rights reserved. 1. Introduction Prevention of food poisoning requires intense inspection of all food served in homes and restaurants. Considering the short time interval between meals, on-site inspection should be completed * Corresponding author. Tel.: +82 54 279 2392; fax: +82 54 279 5528. E-mail address: jeons@postech.ac.kr (S. Jeon). http://dx.doi.org/10.1016/j.aca.2015.04.044 0003-2670/ ã 2015 Elsevier B.V. All rights reserved. Analytica Chimica Acta 883 (2015) 61–66 Contents lists available at ScienceDirect Analytica Chimica Acta journa l home page : www.e lsevier.com/loca te/aca