Here, a new polymeric microfluidic platform using off-stoichiometric thiol-ene (OSTE) polymers was developed. Thiolene polymers were chosen as they afford rapid UV curing, low volume shrinkage and optical transparency for use in microfluidic devices. Three different off-stoichiometric thiol-ene polymers with 30% excess allyl, 50% excess thiol and a 90% excess thiol (OSTE Allyl-30, OSTE-50 and OSTE-90, respectively) were fabricated. Attenuated reflectance Fourier transform infrared (ATR-FTIR) spectroscopy and solid-state cross polarisation-magic angle spinning (CP-MAS) nuclear magnetic resonance (NMR) spectroscopy confirmed which functional groups (thiol or allyl) were present in excess in the OSTE polymers. The polymers were shown to have a more hydrophilic surface (water contact angle of 65°± 3) compared to polydimethylsiloxane (water contact angle of 105° ± 5). Testing of the mechanical properties showed the glass transition temperatures to be 15.09 °C, 43.15 °C and, 57.48 °C for OSTE-90, OSTE Allyl-30 and, OSTE-50, respectively. The storage modulus was shown to be less than 10 MPa for the OSTE-90 polymer and approximately 1750 MPa for the OSTE Allyl-30 and OSTE-50 polymers. The polymers were then utilised to fabricate microfluidic devices via soft lithography practices and devices sealed using a one-step UV lamination “click” reaction technique. Finally, gold nanoparticles were used to form gold films on the OSTE-90 and OSTE-50 polymers as potential electrodes. Atomic force microscopy and sheet resistances were used to characterise the films.
Harmful algal bloom (HAB) events have been on the rise in the last few decades with some of the causative microalgae exhibiting toxic properties. Therefore, detection is essential in order to prevent mortality of aquatic life and poisoning events from consumption of these biotoxins. Here, oligonucleotide modified glass and poly(dimethylsiloxane) (PDMS) surfaces have been developed for the detection of the HAB causing microalgae, Alexandrium catenella, in a model system. Our preliminary studies show that the glass surface offers superior stability and analytical response when compared to those prepared from PDMS.
Capacitively coupled contactless conductivity detection (C4D) and its integration with Lab-on-a-Chip (LOC) systems has been well studied. However, most reported methods require multi-step electrode patterning/fabrication processes which
in turn leads to difficulty in consistently aligning detection electrodes. These limitations have the potential to
compromise analytical performance of the electrodes and increase the time and cost of device production. We have
previously demonstrated a simplified approach for C4D electrode integration with poly(dimethylsiloxane) electrophoresis LOC devices by utilizing ‘injected’ gallium electrodes.1 The developed fabrication process is fast, highly reproducible, and eliminates difficulties with electrode alignment. Using this approach C4D can be readily achieved in any microchip by simply adding extra ‘electrode’ channels to the microchip design. This design flexibility allows for straightforward optimization of electrode parameters. Here, we present the optimization of physical electrode parameters including orientation, length and distance from separation channel. The suitability of the optimized system for on-chip C4D detection was demonstrated through the excellent intra- and inter-day repeatability (< 4 %RSD) of electrophoretically
separated lithium, sodium and potassium ions.
Poly(dimethylsiloxane) (PDMS) is an elastomeric material used for microfluidic devices and is especially suited to
medical and forensic applications. This is due to its relatively low cost, ease of fabrication, excellent optical transmission
characteristics and its ability to support electroosmotic flow, required during electrophoretic separations. These aspects
combined with its large range of surface modification chemistries, make PDMS an attractive substrate in microfluidic
devices for, in particular, DNA separation. Here, we report the successful wet chemical surface modification of PDMS
microchannels using a simple three step method to produce an isothiocyanate-terminated surface. Initially, PDMS was
oxygen plasma treated to produce a silanol-terminated surface, this was then reacted with 3-aminopropyltriethoxysilane
with subsequent reaction of the now amine-terminated surface with p-phenylenediisothiocyanate. Water contact angle
measurements both before and after modification showed a reduction in hydrophobicity from 101o for native PDMS to
94o for the isothiocyante-terminated PDMS. The isothiocyanate-terminated surface was then coupled with an amineterminated
single-stranded DNA (ssDNA) oligonucleotide capture probe via a thiourea linkage. Confirmation of capture
probe attachment was observed using fluorescent microscopy after hybridization of the capture probes with fluorescently
labeled complimentary ssDNA oligonucleotides.
Here, we report on a novel method of incorporating carbon nanotubes into a polymer matrix by using
carbon nanotubes as a chain transfer agent (CTA) in Reversible Addition-Fragmentation chain Transfer
(RAFT) polymerisations. The dithioester RAFT agents were covalently linked to multi-walled carbon
nanotubes (MWCNTs) via a method, which involved the reaction of acyl halide MWCNTs with a
magnesium chloride dithiopropanoate salt. Polystyrene (PSt) was subsequently grafted from the
MWCNT surface via the core-first technique, which implies an outward growth of polymer chains
from the core, using the R-group approach. The structure and morphology of the hybrid nanomaterials
were investigated using FTIR, NMR, thrmogravimetric analysis (TGA) and atomic force microscopy
(AFM) techniques. The results showed that the MWCNT chain transfer agent could be successfully
used to mediate the growth of polystyrene polymer from the MWCNT surface via the living radical
polymerisation approach.
Poly(dimethylsiloxane) (PDMS) is a popular material for microfluidic devices due to its relatively low cost, ease of
fabrication, oxygen permeability and optical transmission characteristics. However, its highly hydrophobic surface is still
the main factor limiting its wide application, in particular as a material for biointerfaces. A simple and rapid method to
form a relatively stable hydrophilised PDMS surface is reported in this paper. The PDMS surface was treated with pure
undecylenic acid (UDA) for 10 min, 1 h and 1 day at 80 °C in a sealed container. The effects of the surface modification
were investigated using water contact angle (WCA) measurements, Fourier transform infrared spectroscopy in attenuated
total reflection mode (FTIR-ATR), and streaming zeta-potential analysis. The water contact angle of 1 day UDAmodified
PDMS was found to decrease from that of native PDMS (110 °) to 75 °, demonstrating an increase in
wettability of the surface. A distinctive peak at 1715 cm-1 in the FTIR-ATR spectra after UDA treatment was
representative of carboxylation of the PDMS surface. The measured zeta-potential (ζ) at pH 4 changed from -27 mV for
pure PDMS to -19 mV after UDA treatment. In order to confirm carboxylation of the surface visually, Lucifer Yellow
CH fluorescence dye was reacted via a condensation reaction to the 1 day UDA modified PDMS surface. Fluorescent
microscopy showed Lucifer Yellow CH fluorescence on the carboxylated surface, but not on the pure PDMS surface.
Stability experiments were also performed showing that 1 day modified UDA samples were stable in both MilliQ water
at 50 °C for 17 h, and in a desiccator at room temperature for 19.5 h.
Vertically aligning carbon nanotubes (VACNTs) onto 2D porous materials is advantageous for many conceivable
electronic applications but also for investigating the unique water transport properties of CNTs and the molecular
separation of molecules during fluid transport through their inner shell. Here we report a wet chemical technique to
produce vertically-aligned single walled CNT arrays on porous silicon (pSi). The nanotubes were first acid treated to
produce carboxylic acid functionalities on the single-walled CNT. The carboxy-functional nanotubes were then
covalently immobilised on a pSi surface that had been either ozone treated or silanated with aminopropyl triethoxysilane
(APTES). The VACNT surfaces were analysed with atomic force microscopy (AFM), confocal Raman spectral imaging
and Fourier transform infrared (FTIR) spectroscopy. Dense arrays of VACNTs were observed with the obtained CNT
orientation and surface coverage depending upon attachment method and attachment reaction time.
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