Microchip Coulter particle counter

Abstract

SUMMARYThis paper presents a micro device employing the Coulter principle for counting and sizing of living cells and particles in liquid suspension. The microchip Coulter Particle Counter (pCPC) has been employed into a planar silicon structure covered with glass, which enables detailed observation during operation possible. By sheathing of a non-conductive liquid on either side of an electrolyte, it is possible to optimize the sensitivity to a specific cell-size dynamically. A method for measuring the relative flow-rates between liquid phases with different conductivity is presented. The method utilizes the laminar flow and short contact time of liquids in microchannels. As a result, the width of the liquids can be controlled without knowing the actual flow rates. The pCPC have been fabricated by standard microfabrication techniques, including NE, wet silicon etching, metalization and anodic bonding. The manufacturing is compatible with the fabrication of many different devices such as particle sorters and mixers.

Integrated Coulter counter based on 2-dimensional liquid aperture control

“…Another limitation of the classical Coulter counter is that frequently it is necessary to physically exchange the apertures in between runs, since the operative size range is 3-40% of the diameter of the Coulter aperture [8]. In [9], it was proposed for the first time to make a one-dimensional adaptive aperture, using a laminated flow profile that consisted of a combination of organic and in-organic liquids. A drawback of this approach is that the interface between the liquids can be unstable due to surface tension forces between the liquids.…”

A fast passive and planar liquid sample micromixer

“…Manz et al presented a continuous flow mixer based on separating liquid in narrower channels and reunifying them allowing faster molecular diffusion. 7 Other passive lamination based mixers where fluid is split in a parallel or serial manner have also been demonstrated by Wurmus et al, 8 Branebjerg et al, 9 Larsen et al, 10 and Jensen et al 11 Yet others have created plumes to increase the surface area for mixing. 12 Active mixers include a simple channel system where side channels introduce pressure perturbations or time-dependent dielectrophoresis forces to induce chaotic advection.…”

Low cost micro-Coulter counter with hydrodynamic focusing

“…One particularly important application is the development of cell counters, which can be used as a stand alone device for counting, and sizing, or in more complex Particle counting can be based on two detection methods. Optical methods extract information from light dispersed by particles and from specific fluorescent excitation (Schrum et al 1999;McClain et al 2001;Fu et al 2004), whereas electrical methods (referred to as Coulter counters) extract information from the modulation of the electrical resistance in an orifice due to the passage of the particle (Larsen et al 1997;Koch et al 1999;Ayliffe et al 1999;Saleh and Sohn 2001;. Optical methods have the advantage of being able to incorporate fluorescent markers that are widely used in biology, but at the price of increased integration complexity.…”

“…Electrical methods, on the other hand, present advantages from the point of view of integration, particularly after the demonstration of entirely electrical-based micro-flow cytometers and sorters utilizing electrical impedance methods (Cheung et Micro-Coulter counters, i.e. micro-dimensioned particle counters based on electrical detection methods, have been fabricated using a variety of materials -e. g. silicon (Schrum et al 1999;McClain et al 2001;Fu et al 2004;Larsen et al 1997;Koch et al 1999), glass (Ayliffe et al 1999), glass-polyimide (Cheung et al 2005;Holmes et al 2005;Morgan et al 2005;Gawad et al 2001), polymer , and quartz (Saleh and Sohn 2001)-and with different particle alignment methods -geometric (Saleh and Sohn 2001;, hydrodynamic (Larsen et al 1997) and electrokinetic (Schrum et al 1999;McClain et al 2001;Fu et al 2004;Holmes et al 2005;Morgan et al 2005;Cheung et al 2005). Particles with diameters from several micrometers down to tens of nanometers (Saleh and Sohn 2001; have been examined with detection ratios varying from a few counts per second, if electrophoretic forces are utilized for particle manipulation (Saleh and Sohn 2001), to hundreds of counts per second, if pressure forces are utilized (Morgan et al 2005;Gawad et al 2001).…”

“…The use of hydrodynamic focusing together with electrical detection (to our knowledge only previously reported in Larsen et al 1997) makes the device highly versatile, allowing the possibility of examining particles with a broad range of sizes in a single device. Fabrication of the channel structure of the device in a polymer (Poly-dimethylsiloxane (PDMS)) using a rapid prototyping technology (Qin et al 1996;McDonald et al 2000) offers low fabrication costs compared to equivalent devices based on micromachined silicon (Schrum et al 1999;McClain et al 2001;Fu et al 2004;Larsen et al 1997;Koch et al 1999) or microfabricated glass/pyrex (Cheung et al 2005;Holmes et al 2005). …”