title: A hybrid dielectrophoretic system for trapping of microorganisms from water.
abstract: Assessment of the microbial safety of water resources is among the most critical issues in global water safety. As the current detection methods have limitations such as high cost and long process time, new detection techniques have transpired among which microfluidics is the most attractive alternative. Here, we show a novel hybrid dielectrophoretic (DEP) system to separate and detect two common waterborne pathogens, Escherichia coli (E. coli), a bacterium, and Cryptosporidium parvum (C. parvum), a protozoan parasite, from water. The hybrid DEP system integrates a chemical surface coating with a microfluidic device containing inter-digitated microelectrodes to impart positive dielectrophoresis for enhanced trapping of the cells. Trimethoxy(3,3,3-trifluoropropyl) silane, (3-aminopropyl)triethoxysilane, and polydiallyl dimethyl ammonium chloride (p-DADMAC) were used as surface coatings. Static cell adhesion tests showed that among these coatings, the p-DADMAC-coated glass surface provided the most effective cell adhesion for both the pathogens. This was attributed to the positively charged p-DADMAC-coated surface interacting electrostatically with the negatively charged cells suspended in water leading to increased cell trapping efficiency. The trapping efficiency of E. coli and C. parvum increased from 29.0% and 61.3% in an uncoated DEP system to 51.9% and 82.2% in the hybrid DEP system, respectively. The hybrid system improved the cell trapping by encouraging the formation of cell pearl-chaining. The increment in trapping efficiency in the hybrid DEP system was achieved at an optimal frequency of 1 MHz and voltage of 2.5 Vpp for C. parvum and 2 Vpp for E. coli, the latter is lower than 2.5 Vpp and 7 Vpp, respectively, utilized for obtaining similar efficiency in an uncoated DEP system.
authors.forename: Narjes
authors.initials: N
authors.lastname: Allahrabbi
authors.affiliation: Department of Chemical and Biomolecular Engineering, National University of Singapore , 10 Kent Ridge Crescent, Singapore 119260, Republic of Singapore.
authors.forename: Yi Shi Michelle
authors.initials: YS
authors.lastname: Chia
authors.affiliation: Institute of Materials Research and Engineering , ASTAR (Agency for Science, Technology and Research), 3 Research Link, Singapore 117602, Republic of Singapore.
authors.forename: Mohammad S M
authors.initials: MS
authors.lastname: Saifullah
authors.affiliation: Department of Mechanical Engineering, National University of Singapore , 9 Engineering Drive 1, Singapore 117576, Republic of Singapore.
authors.forename: Kian-Meng
authors.initials: KM
authors.lastname: Lim
authors.affiliation: Department of Chemical and Biomolecular Engineering, National University of Singapore , 10 Kent Ridge Crescent, Singapore 119260, Republic of Singapore.
authors.forename: Lin Yue Lanry
authors.initials: LY
authors.lastname: Yung