Investigation of Functional Electrospun Bionanofibers in Microfluidic Channels

In this study, we investigated the incorporation of poly(vinyl alcohol) (PVA) nanofibers within poly(methyl methacrylate) (PMMA) microchannels in order to allow for sample preparation and concentration within microfluidic detection systems. Nanofibers were electrospun onto gold microelectrodes and integrated into polymer microfluidic systems using ultraviolet (UV)-assisted thermal bonding. We determined that nanofibers spun across microchannels maintain their morphology during fluid flow at linear velocities of 3.4 and 13.6 mm/s. In addition, we showed the ability of positively charged nanofibers to serve as bioseparators for negatively charged nanovesicles using hexadimethrine bromide (polybrene) modified PVA fibers. Summary of Research: Sample purification and concentration are essential to the success of miniaturized detection assays that use small feature sizes and sample volumes in the nL­μL range [1]. Lab­on­a­chip devices aim to incorporate sample preparation and analyte detection within the same device, however this has proven difficult for many detection systems [2]. We aim to address this need for sample preparation within microfluidic systems by incorporating functionalized electrospun nanofibers within polymer microchannels. Gold microelectrodes were fabricated on PMMA using standard microfabrication tech­ niques. A 10 nm layer of chrome and a 200 nm layer of gold were evaporated onto the PMMA using a CHA evaporator. After evaporation, the PMMA was coated with positive photoresist (Shipley 1813) at 3000 rpm for 30 seconds. The PMMA was then exposed for 11 seconds using an ABM contact aligner and developed for one minute in MF 321. The PMMA was then etched for one minute in gold etchant and 15 seconds in chrome etchant. We studied the effects of electrode spacing and width on nanofiber orientation using a basic five fingered electrode design with a large square electrode pad. Electrodes were fabricated with various gap sizes (0.1 mm to 10 mm), square sizes (50 μm to 500 μm), and electrode widths (1 mm to 2.5 mm). We determined that electrodes with a gap of 5 mm and width of 1 mm produced well aligned nanofiber mats between the electrode fingers (Figure 1). The PMMA microchannels were formed using hot embossing with a copper template [3]. The copper masters were fabricated using negative photoresist (SU­ 8) photolitography and copper electroplating to produce raised copper channels on the copper plate. The microchannels were embossed onto PMMA using a Carver Laboratory Hot Press. Completed microfluidic devices were fabricated by bonding a piece of PMMA containing channels and a piece of PMMA patterned with a microelectrode and nanofibers using UV­assisted thermal bonding. Nanofibers spun across microfluidic channels were subjected to fluid flow and analyzed to confirm that the fibers were not damaged during fluid flow. DI water was injected into the microchannels at 3.4 and Figure 1: Five fingered electrode design with 5 mm spacing.