title: Poly(methyl methacrylate) Surface Modification for Surfactant-Free Real-Time Toxicity Assay on Droplet Microfluidic Platform.
abstract: Microfluidic droplet reactors have many potential uses, from analytical to synthesis. Stable operation requires preferential wetting of the channel surface by the continuous phase which is often not fulfilled by materials commonly used for lab-on-chip devices. Here we show that a silica nanoparticle (SiNP) layer coated onto a Poly(methyl methacrylate) (PMMA) and other thermoplastics surface enhances its wetting properties by creating nanoroughness, and allows simple grafting of hydrocarbon chains through silane chemistry. Using the unusual stability of silica sols at their isoelectric point, a dense SiNP layer is adsorbed onto PMMA and renders the surface superhydrophilic. Subsequently, a self-assembled dodecyltrichlorosilane (DTS) monolayer yields a superhydrophobic surface that allows the repeatable generation of aqueous droplets in a hexadecane continuous phase without surfactant addition. A SiNP-DTS modified chip has been used to monitor bacterial viability with a resazurin assay. The whole process involving sequential reagents injection, and multiplexed droplet fluorescence intensity monitoring is carried out on chip. Metabolic inhibition of the anaerobe Enterococcus faecalis by 30 mg L-1of NiCl2was detected in 5 min.
authors.affiliation: School of Materials Science & Engineering, College of Engineering, Nanyang Technological University , 50 Nanyang Avenue, Singapore 639798, Singapore.|Advanced Environmental Biotechnology Centre, Nanyang Environment & Water Research Institute, Nanyang Technological University , 637141, Singapore.
authors.forename: Raphael
authors.identifier: http://orcid.org/0000-0002-7437-3198
authors.initials: R
authors.lastname: Ortiz
authors.affiliation: Advanced Environmental Biotechnology Centre, Nanyang Environment & Water Research Institute, Nanyang Technological University , 637141, Singapore.
authors.forename: Jian Lin
authors.initials: JL
authors.lastname: Chen
authors.affiliation: Advanced Environmental Biotechnology Centre, Nanyang Environment & Water Research Institute, Nanyang Technological University , 637141, Singapore.|Chemical Engineering Department, Imperial College London , London SW7 2AZ, United Kingdom.
authors.forename: David C
authors.identifier: http://orcid.org/0000-0002-6255-1153
authors.initials: DC
authors.lastname: Stuckey
authors.affiliation: School of Materials Science & Engineering, College of Engineering, Nanyang Technological University , 50 Nanyang Avenue, Singapore 639798, Singapore.
authors.forename: Terry W J
authors.identifier: http://orcid.org/0000-0001-8596-9619
authors.initials: TWJ
authors.lastname: Steele
keywords: PMMA; anaerobic toxicity; microfluidic; resazurin; silica nanoparticles; superhydrophobic