Issue 1, 2011

Polymeradsorption onto a micro-sphere from optical tweezers electrophoresis

Abstract

We explore the design and operation of an optical-tweezers electrophoresis apparatus to resolve polymer adsorption dynamics onto a single micro-sphere in a micro-fluidic environment. Our model system represents a broader class of micro-fluidic electrophoresis experiments for biosensing and fundamental colloid and surface science diagnostics. We track the adsorption of 100 kDa poly(ethylene oxide) homopolymer onto a colloidal silica sphere that is optically trapped in a crossed parallel-plate micro-channel. The adsorption dynamics are probed on the ∼1 μm particle length scale with ∼1 s temporal resolution. Because the particle electrophoretic mobility and channel electro-osmotic flow are exquisitely sensitive to the polymer layer hydrodynamic thickness, particle dynamics can be complicated by polymer adsorption onto the micro-channel walls. Nevertheless, using experiments and a theoretical model of electro-osmotic flow in channels with non-uniform wall ζ-potentials, we show that such influences can be mitigated by adopting a symmetrical flow configuration. The equilibrium hydrodynamic layer thickness of 100 kDa poly(ethylene oxide) on colloidal silica is ∼10 nm at polymer concentrations ≳10 ppm (weight percent), with the dynamics reflecting polymer solution concentration, flow rate, and polydispersity.

Graphical abstract: Polymer adsorption onto a micro-sphere from optical tweezers electrophoresis

Article information

Article type
Paper
Submitted
22 Apr 2010
Accepted
20 Aug 2010
First published
18 Oct 2010

Lab Chip, 2011,11, 152-162

Polymer adsorption onto a micro-sphere from optical tweezers electrophoresis

J. A. van Heiningen and R. J. Hill, Lab Chip, 2011, 11, 152 DOI: 10.1039/C005217P

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