Thermoplastics have become attractive alternatives to glass/quartz for microfluidics, but the realization of thermoplastic nanofluidic devices has been slow in spite of the rather simple fabrication techniques that can be used to produce these devices. This slow transition has in part been attributed to insufficient understanding of surface charge effects on the transport properties of single molecules through thermoplastic nanochannels. We report the surface modification of thermoplastic nanochannels and an assessment of the associated surface charge density, zeta potential and electroosmotic flow (EOF). Mixed-scale fluidic networks were fabricated in poly(methylmethacrylate), PMMA. Oxygen plasma was used to generate surface-confined carboxylic acids with devices assembled using low temperature fusion bonding. Amination of the carboxylated surfaces using ethylenediamine (EDA) was accomplished via EDC coupling. XPS and ATR-FTIR revealed the presence of carboxyl and amine groups on the appropriately prepared surfaces. A modified conductance equation for nanochannels was developed to determine their surface conductance and was found to be in good agreement with our experimental results. The measured surface charge density and zeta potential of these devices were lower than glass nanofluidic devices and dependent on the surface modification adopted, as well as the size of the channel. This property, coupled to an apparent increase in fluid viscosity due to nanoconfinement, contributed to the suppression of the EOF in PMMA nanofluidic devices by an order of magnitude compared to the micro-scale devices. Carboxylated PMMA nanochannels were efficient for the transport and elongation of λ-DNA while these same DNA molecules were unable to translocate through aminated nanochannels.

DNA methylation, which requires the universal methyl donor Sadenosyl-L-methionine (SAM), plays a pivotal role in eukaryotic gene regulation and when dysregulated, can result in severe alterations in cellular function. An emerging approach to further understand DNA methylation utilizes azide-and alkynefunctionalized N-mustard SAM analogues as biochemical tools to probe sites of DNA methylation. While the successful utility of these substituted analogues has been demonstrated with prokaryotic DNA methyltransferases, their utility with physio-logically-relevant eukaryotic DNA methyltransferase 1 (DNMT1) is examined for the first time here. A fluorescence-based magnetic bead assay was validated in initial experiments to measure the extent of DNA modification by the N-mustard analogues using Spiroplasma methylase, M.SssI, a prokaryotic model of DNMT1. Subsequent analysis with DNMT1 revealed limited utility of the analogues, as added azide-and alkynefunctionality appears to directly impact binding to DNMT1.[a] Dr.

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