- Jafar Al-Hakkak
- Maan M. Alkaisi
- Mike Arnold
- Ali M. Azam
- Keith H.R. Baronian
- Olaf Bork
- Paula A. Brooksby
- Craig R. Bunt
- Tim David
- Alison J. Downard
- James Dunlop
- Pablo G. Etchegoin
- John J. Evans
- Alan Fernyhough
- Paul T. Gaynor
- Juliet A. Gerrard
- Patrick Gladding
- David P. L. Green
- Shaun C. Hendy
- Justin M. Hodgkiss
- Shazlina Johari
- Nigel G. Larsen
- Conrad D. Lendrum
- Duncan J. McGillivray
- Kathryn M. McGrath
- Susie J. Meade
- Peter Metcalf
- John S. Mitchell
- Lynn M. Murray
- Volker Nock
- Mike A. Packer
- Jasna Rakonjac
- Bern H. A. Rehm
- Eric C. Le Ru
- Mathieu M. Sellier
- Fahmi Samsuri
- John C. Sharpe
- Rahul K. Shastry
- Vikki L. Smithem
- Christian Soeller
- Mark P. Staiger
- Richard D. Tilley
- Jadranka Travas-Sejdic
- Nick Tucker
- Mark R. Waterland
- Geoff R. Willmott
- Donald Wlodkowic
- Tim B.F. Woodfield
- Bryon E. Wright
- Samuel S. C. Yu
- Bioimprint – Photo nanoimprint lithography of biological samples
- Characterisation of Endometrial Cancer Cells by Atomic Force Microscopy
- Force Pattern Characterization of C. elegans in Motion
- Self-propelling coalescing droplets
- Spatially Resolved Measurement of Dissolved Oxygen in Multistream Microﬂuidic Devices
- Electrical and Computer Engineering, UoC
- Department of Chemistry, UoC
- Centre for Bioengineering, UoC
- Centre for Bioengineering & Nanomedicine, UoO
- The Raman Laboratory, UoV
- Laboratory for Cell & Protein Regulation, UoO
- School of Chemical and Physical Sciences, UoV
- School of Chemical Sciences, UoA
- The Cawthron Biosecurity & Biotechnology Group
Spatially Resolved Measurement of Dissolved Oxygen in Multistream Microﬂuidic Devices
The characteristics of laminar flow, as observed in microfluidic devices, allow one to generate parallel multi-stream flows with stable inter-stream interfaces in a single microchannel. Material transport across these interfaces is by diffusion only and can be controlled using the flow speed of the individual streams. In cell biology, this phenomenon can be applied to produce controlled chemical microenvironments down to sub-cellular dimensions [1, 2], enabling one to study the biochemical and biophysical processes of cells. To this day the use of multiple parallel flow streams has been explored mostly for the partial treatment of individual and patterned cells with biochemical reagents [1-3]. In an extension of this concept, it has further been shown that the shape of the interface between the parallel flow streams can be selectively modified by modulating the driving pressures to produce arbitrary shaped chemical signal streams .
Beyond the use for the delivery of reagents or nanoparticles, multi-stream laminar flows also have the potential to be used to generate microenvironments with controlled oxygen concentrations inside a single channel. In cell-based applications in particular, the oxygen concentration of a sample stream itself represents a parameter with significant effect on cellular development and function. For example, the dissolved oxygen (DO) concentration has been found to be intimately linked to cell survival, metabolism and function [5,6]. The capability to expose regions of a cell-culture or individual cells and regions on the cell surface to controlled DO levels therefore has the potential to yield novel insights into cell biology. Furthermore, measuring and controlling the DO concentrations of sample streams will increase the relevance of existing small-molecule delivery applications, which previously have been performed mostly with media equilibrated under atmospheric oxygen conditions [1-4,7].
Achieving this requires a means of measuring spatially-distributed DO concentrations inside the particular microdevice. Thus, we have recently developed a robust deposition and patterning method for optical oxygen sensors based on Platinum(II) octaethylporphyrin ketone (PtOEPK) in polystyrene (PS) as microporous oxygen-permeable matrix . This material system has attracted considerable interest due to the long wavelength shift and long-term photo stability exhibited by the PtOEPK molecule . In addition, the homogeneous nature of spin-coated sensor films as obtained with our fabrication process allows one to visualize spatially-varying DO concentrations in-situ, such as generated by two independent flow streams .
The sensor concept is further extended by demonstrating the advanced capabilities of the integrated sensor system for spatially-resolved measurement of DO in two microfluidic devices related to the generation of localized microenvironments. The in-situ measurement of local oxygen concentration is demonstrated both in flow streams hydrodynamically focused to cellular dimensions, as well as multiple parallel streams with variable concentration levels. The former represents an important example of how the spatial resolution of applied stimuli, such as oxygen, can be improved towards cellular and sub-cellular dimensions. While this has previously been demonstrated as a means to improve the sample control for small molecular reagents , we showed for the first time how this principle can be extended to the delivery of biologically relevant oxygen.
The latter example demonstrates the use of the sensors to control oxygen in parallel molecule delivery cell-network assays for active exposure of cultures to locally different oxygen concentrations within a single device. In addition, the sensor can be used, similar to a T or H-filter [10,11], to measure the coefficient of diffusion of oxygen for the perfusion media in this specific configuration. The integrated sensor and devices provide novel tools for lab-on-a-chip based oxygen concentration dependent biological assays and cell biology experiments.
 S. Takayama, E. Ostuni, P. LeDuc, K. Naruse, D. E. Ingber, and G. M. Whitesides, “Selective chemical treatment of cellular microdomains using multiple laminar streams,” Chem. Biol., vol. 10, pp. 123–130, 2003.
 H. Kaji, M. Nishizawa, and T. Matsue, “Localized chemical stimulation to micropatterned cells using multiple laminar ﬂuid ﬂows,” Lab Chip, vol. 3, pp. 208–211, 2003.
 B. Kuczenski, W. C. Ruder, W. C. Messner, and P. R. LeDuc, “Probing cellular dynamics with a chemical signal generator,” in PLoS ONE, 2009, vol. 4, e4847.
 S. Roy, S. Khanna, A. A. Bickerstaff, S. V. Subramanian, M. Atalay, M. Bierl, S. Pendyala, D. Levy, N. Sharma, M. Venojarvi, A. Strauch, C. G. Orosz, and C. K. Sen, “Oxygen sensing by primary cardiac ﬁbroblasts: A key role of p21Waf1/Cip1/Sdi1,” Circ. Res., vol. 92, pp. 264–271, 2003.
 H. Zhang and G. Semenza, “The expanding universe of hypoxia,” J. Mol. Med., vol. 86, pp. 739–746, 2008.
 F. Wang, H. Wang, J. Wang, H.-Y. Wang, P. L. Rummel, S. V. Garimella, and C. Lu, “Microﬂuidic delivery of small molecules into mammalian cells based on hydrodynamic focusing,” Biotechnol. Bioeng., vol. 100, pp. 150–158, 2008.
 V. Nock, R. J. Blaikie, and T. David, “Patterning, integration and characterization of polymer optical oxygen sensors for microﬂuidic devices,” Lab Chip, vol. 8, pp. 1300–1307, 2008.
 D. B. Papkovsky, G. V. Ponomarev, W. Trettnak, and P. O’Leary, “Phosphorescent complexes of porphyrin ketones: Optical properties and application to oxygen sensing,” Anal. Chem., vol. 67, pp. 4112–4117, 1995.
 M. S. Munson, K. R. Hawkins, M. S. Hasenbank, and P. Yager, “Diffusion based analysis in a sheath ﬂow microchannel: The sheath ﬂow T-sensor,” Lab Chip, vol. 5, pp. 856–862, 2005.
 A. E. Kamholz, E. A. Schilling, and P. Yager, “Optical measurement of transverse molecular diffusion in a microchannel,” Biophys. J., vol. 80, pp. 1967–1972, 2001.
|V. Nock, M. M. Alkaisi, and R. J. Blaikie||Photolithographic patterning of polymer-encapsulated optical oxygen sensors||Microelectronic Engineering||87||814-816||2010||paper|
|V. Nock and R.J. Blaikie||Spatially-Resolved Measurement of Dissolved Oxygen in Multi-Stream Microfluidic Devices||IEEE Sensors Journal||10 (12)||1813-1819||2010||paper|
|V. Nock||Control and measurement of oxygen in microfluidic bioreactors.||PhD Thesis, University of Canterbury, New Zealand||1||1-243||2009||fulltext|
|V. Nock, R. J. Blaikie, and T. David||Oxygen Control For Bioreactors And In-vitro Cell Assays||AIP Proceedings||1151||67-70||2009||paper|
|V. Nock, R. J. Blaikie, and T. David||In-situ Optical Oxygen Sensing for Bio-artificial Liver Bioreactors||IFMBE Proceedings||23||778-781||2009||paper|
|V. Nock, R. J. Blaikie, and T. David||Patterning, integration and characterisation of polymer optical oxygen sensors for microfluidic devices||Lab on a Chip||8||1300-1307||2008||paper|
|V. Nock, R. J. Blaikie, and T. David||Micro-patterning of polymer-based optical oxygen sensors for lab-on-chip applications||Proceedings of SPIE||6799||10.1117/12.759023||2007||paper|
|V. Nock, R. J. Blaikie, and T. David||Microfluidics for bioartificial livers||NZ Medical Journal||120||2-3||2007||abstract|