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.
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