The concept of a microfluidic biosensing device based on reflective interferometric spectroscopy (RIfS) is presented in
this article. The key element of the sensor is a highly ordered nanoporous structure of anodic aluminium oxide (AAO)
integrated into a microfluidic chip combined with an optical fiber spectrophotometer. AAO was prepared by
electrochemical anodization of aluminium using 0.3 M oxalic acid. The structural and geometrical features of the AAO
porous structures were controlled to provide optimal RIfS sensing characteristics and there sensing capabilities were
explored using two different strategies; i) detection based on the response generated by pefusion of analyte ions inside
the pores and ii) detection based on specific adsorption of analyte molecules on surface of AAO pores. The second
strategy is based on chemical modification of the AAO surface to target molecules based on specific surface binding
reactions. In this work two cases are presented, including the binding of small thiol molecules on gold-modified AAO
(Au-AAO) and binding of larger targets such as circulating tumour cells (CTC) on antibody-modified AAO. Our
preliminary results show an excellent capability of our system in the detection of different analytes using both strategies,
and confirm good potential for the development and application of interferometric label-free biosensing devices in a
wide range of biomedical applications.
Dielectrophoresis, the induced motion of polarisable particles in non-homogenous electric field, has been proven
as a versatile mechanism to transport, immobilise, sort and characterise micro/nano scale particle in microfluidic
platforms. The performance of dielectrophoretic (DEP) systems depend on two parameters: the configuration of
microelectrodes designed to produce the DEP force and the operating strategies devised to employ this force in
such processes. This work summarises the unique features of curved microelectrodes for the DEP manipulation
of target particles in microfluidic systems. The curved microelectrodes demonstrate exceptional capabilities
including (i) creating strong electric fields over a large portion of their structure, (ii) minimising electro-thermal
vortices and undesired disturbances at their tips, (iii) covering the entire width of the microchannel influencing
all passing particles, and (iv) providing a large trapping area at their entrance region, as evidenced by extensive
numerical and experimental analyses. These microelectrodes have been successfully applied for a variety of
engineering and biomedical applications including (i) sorting and trapping model polystyrene particles based on
their dimensions, (ii) patterning carbon nanotubes to trap low-conductive particles, (iii) sorting live and dead
cells based on their dielectric properties, (iv) real-time analysis of drug-induced cell death, and (v) interfacing
tumour cells with environmental scanning electron microscopy to study their morphological properties. The
DEP systems based on curved microelectrodes have a great potential to be integrated with the future lab-on-achip
systems.
Presented is the dielectrophoresis of multiwalled carbon nanotubes on piezoelectric substrates patterned with gold inter
digitated electrodes. An alternating current oscillating at frequencies of 1 kHz and 150 kHz at a peak-to-peak (p-p)
voltage of 1V to 10V was applied to the electrodes, aligning carbon nanotubes suspended in droplets of isopropyl alcohol
(IPA). The carbon nanotubes were suspended in a dielectric medium (IPA) at a concentration of approx 0.1 mg/mL and
stabilized with sodium citrate (0.02 mg/ml). Sonicated for two hours and spun down in a centrifuge for 30 minutes at
4500 rpm. The carbon nanotubes used in the DEP experimentation were multiwalled carbon nanotubes with aspect ratios
of approx 100:1.
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