In this paper we describe the spatial surface chemical modification of bonded microchannels through the integration of
microplasmas into a microfluidic chip (MMC). The composite MMC comprises an array of precisely aligned electrodes
surrounding the gas/fluid microchannel. Pairs of electrodes are used to locally ignite microplasmas inside the
microchannel. Microplasmas, comprising geometrically confined microscopic electrically-driven gas discharges, are
used to spatially functionalise the walls of the microchannels with proteins and enzymes down to scale lengths of 300
μm inside 50 μm-wide microchannels. Microchannels in poly(dimethylsiloxane) (PDMS) or glass were used in this
study. Protein specifically adsorbed on to the regions inside the PDMS microchannel that were directly exposed to the
microplasma. Glass microchannels required pre-functionalisation to enable the spatial patterning of protein. Firstly, the
microchannel wall was functionalised with a protein adhesion layer, 3-aminopropyl-triethoxysilane (APTES), and
secondly, a protein blocking agent (bovine serum albumin, BSA) was adsorbed onto APTES. The functionalised
microchannel wall was then treated with an array of spatially localised microplasmas that reduced the blocking
capability of the BSA in the region that had been exposed to the plasma. This enabled the functionalisation of the
microchannel with an array of spatially separated protein. As an alternative we demonstrated the feasibility of depositing
functional thin films inside the MMC by spatially plasma depositing acrylic acid and 1,7-octadiene within the
microchannel. This new MMC technology enables the surface chemistry of microchannels to be engineered with
precision, which is expected to broaden the scope of lab-on-a-chip type applications.
This paper presents a method for chemical and biomolecule patterning on planar (2D) surfaces using atmospheric
pressure microplasmas. Spatially controlled surface modification is important for the development of emerging
technologies such as microfluidic lab-on-a-chip devices, biosensors and other diagnostics tools. A non-fouling layer of
poly(N-isopropylacrylamide) aldehyde (pNIPAM-ald) polymer, grafted onto heptylamine plasma polymer (HApp)
modified silicon substrates, was used to achieve this goal. The non-fouling behaviour of the pNIPAM-ald coating was
investigated at a temperature below its lower critical solution temperature (LCST) using human serum albumin (HSA).
XPS and ToF-SIMS were used to characterise the plasma polymer coating and its subsequent modification with
pNIPAM-ald before and after HSA adsorption. A 7 x 7 microcavity plasma array device (each cavity had a 250 Νm
diameter and was separated by 500 μm) was used for microplasma patterning. In a non-contact mode, helium
microplasma treatment of the pNIPAM-ald coating was carried out for 60 s. The polymer coating was removed from
regions directly exposed to microplasma cavities, as shown by ToF-SIMS. Microplasma treated regions were able to
support the adsorption of fluorescently-labelled streptavidin whereas the rest of the coating was still non-fouling. This
approach therefore resulted in spatially separated areas of immobilised protein.
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