Biomolecular Measurement on a Chip

Introduction

Label-free biomolecular measurement techniques, such as surface plasmon resonance imaging (iSPR), are emerging as important complementary methods to conventional bioassays, which typically use a fluorophore label, because real-time binding kinetics information can be determined [1]. Recent advances in iSPR are becoming increasingly important to label-free microarray-based assay applications, where multiple biomolecular interactions can be measured simultaneously, between 500 to 1000 on modern iSPR systems. However, conventional iSPR microarray assay approaches rely on protein printing techniques for immobilization of the ligand to the gold imaging surface [2]. The combination of microfluidics with iSPR allows the in-situ immobilization of ligands and subsequent analyte transport for the biomolecular interaction assay [3].

Ongoing work

An integrated microfluidics and iSPR platform, where ligand immobilization and subsequent sample solutions are precisely positioned with an electroosmotically driven address-flow guiding technique is underway in our lab. This approach does not require complicated microfluidic channel arrangements or pressure driven transport, which requires external pumps and valves. Address-flow sample guiding is a valve-less electroosmotically driven technique used for controlling the sample stream in a microfluidic chip [4]. The microfluidic chip arrangement (figure 1) uses the center inlet for sample introduction and upper and lower inlets for guiding. Electrical voltages V_u and V_l control the y-direction position of the sample. Voltage V_c is used to transport the sample in the x-direction. The biomolecular interactions between the sample and ligand are measured at each gold island using surface plasmon resonance. The address-flow chip consists of two layers, a bottom glass layer with 24 gold islands, and a poly(dimethylsiloxane) (PDMS) top layer consisting of the microchannels, inlets, outlet and interaction chamber.

Figure1: (a) Microfabricated chip (b) iSPR gold imaging array with location (row, column) (c) iSPR chip interface module and (d) the iSPR system used for biomolecular imaging

Project description

The goal of this project is to design a chip for multiple, at least 36, biomolecular interactions measured (iSPR) in parallel using an all-electrical sample flow system. The present approach uses high electrical voltage to induce electro-osmtic flow that delivers the sample to the gold surfaces for SPR imaging. The combination of the high voltage and conductive sample leads to two problems: i. the thin adhesion layer under the gold layer is electrochemically removed resulting in the gold layer detaching from the glass substrate, and ii) bubble formation on the gold surface due to electrolysis. To overcome these problems, the microfluidic chip is to be designed such that the gold and adhesion layers are not affected and proper channel design to limit the voltage drop across each of the gold islands, and electrolysis. Additionally, the effect of applied electric voltage on the biomolecular interaction is to be investigated and compared to the conventional approach, which uses pressure driven flow. This project will provide the following training:

- Design and fabrication of the microfluidic transport systems

- Cleanroom experience in metal deposition, photolithography and etching

- Design and testing of electro-osmotic pumping system

- Measurement and analysis of the biomolecular interactions and binding kinetics

- An opportunitiy to work in an exciting and emerging group and field of research

References

1.	T.A. Morton, D.G. Myszka, Methods Enzymol., 295, 268 (1998).

2.	A. Lokate, B. Beusink, G. Besselink, G. Pruijn, R.B.M. Schasfoort, J. Am. Chem. Soc., 129, 14013 (2007).

3.	H.J. Lee, D. Nedelkov, R.M. Corn, Anal. Chem., 78, 6504 (2006).

4.	G.A.J. Besselink, P. Vulto, R.G.H. Lammertink, S. Schlautmann, A. van den Berg, W. Olthuis, G.H.M. Engbers, R.B.M. Schasfoort, Electrophoresis, 25, 3705 (2004).

Contact information:

Ganeshram Krishnamoorthy/Edwin T. Carlen

Bios – Lab on a Chip Group

MESA+ Institute for Nanotechnology

University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands

Email: g.krishnamoorthy@utwente.nl

Phone: 0031-053-489-2724