Phytolith assaying using a micron-scale electrokinetic sorting ring

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ORIGINAL PAPER

Phytolith assaying using a micron-scale electrokinetic sorting ring Kevin G. Stanley & Elizabeth Cornelia Robertson & Rene d’Entremont & Ted Hubbard & Marek Kujath

Received: 11 March 2010 / Accepted: 22 June 2011 / Published online: 15 July 2011 # Springer-Verlag 2011

Abstract A particularly useful indicator of past vegetation are phytoliths, glassy products of plant metabolism which have distinctive size and morphology based on the plant taxa which produced them; however, their analysis is a time-consuming task. Building on investigations into mobilizing and sorting of synthetic polystyrene microspheres using a closed loop rectangular microelectromechanical systems (MEMS) electrokinetic array, we investigate these devices’ utility for sorting natural microparticles. Using phytolith samples extracted from archaeological sediment, we show that closed loop MEMS can separate the glassy bodies from both mineral contaminants and each other. Also, small differences in polarization between the phytoliths cause lateral segregation between particles of different sizes and shapes. This process facilitates manual analysis by providing a motive force to the phytoliths that translates and rotates them, showing different configurations as they are propelled by the MEMS array. The organization of the phytoliths into streams also opens the door to automated analysis using image processing. Phytolith assaying is therefore feasible using a MEMS K. G. Stanley Department of Computer Science, University of Saskatchewan, Room 176 Thorvaldson Building, 110 Science Place, Saskatoon, SK S7N 5C9, Canada E. C. Robertson (*) Department of Archaeology and Anthropology, University of Saskatchewan, Room 123 Archaeology Building, 55 Campus Drive, Saskatoon, SK S7N 5B1, Canada e-mail: [email protected] R. d’Entremont : T. Hubbard : M. Kujath Department of Mechanical Engineering, Dalhousie University, 1360 Barrington Street, Halifax, NS B3J 1Z1, Canada

electrokinetic ring and merits additional research to explore the potential of this innovative approach. Keywords Phytolith analysis . Paleoenvironmental reconstruction . Microelectromechanical systems . Electrokinetic microsorting . Computer vision

Introduction Phytoliths are microscopic opal silica particles that are formed by plant metabolism and vary in size and morphology based on the plant taxa which produced them. They are useful indicators of past vegetation distributions because they often survive in archaeological contexts where organic plant remains, such as pollen, are not preserved (Piperno 1985: 255, 1988: 46; Rovner 1983: 235). However, their analysis requires microscopic examination of phytolith assemblages, which can be a time-intensive task. This paper will investigate the use of electrokinetic micro-flow techniques and computer vision to facilitate the process of analyzing phytolith assemblages. Electrokinetic flow of microparticles suspended in fluid can be generated with miniaturized interdigitated electrode structures fabricated using microelectromechanica