Optimizing particle collection for enhanced surface-based biosensors

Abstract

T here exists a number of applications where a method of rapid detection of particlulate biomatter on the micron-and submicron scale, such as cells, bacteria, proteins, and viruses, is of great importance. Such applications include the development of point-of-care diagnostic devices for the detection of rare cells, the testing of water quality for the detection of microorganisms , and the monitoring of the environment for the detection of bioweapons such as anthrax. In order to detect such particles, a highly sensitive biosensor must be employed. Many biosensors technologies involve the detection of particles adsorbed on a surface. These methods, including examples such as evanescent light scattering and surface plasmon resonance [1], [2], require that the particle to be detected be captured onto the surface of the sensor for detection. However, the effectiveness of such detection methods can be limited when used to detect colloidal bioparticles, since low particle concentrations and dominance of effects such as buoyancy or Brownian motion can limit the contact between sensor surface and particle. Dielectrophoresis is the motion of particles caused by induced polarization effects in inhomogeneous electric fields [3]-[5]. Depending on the electrical properties of the medium and the particle, it can be attractive or repulsive, which we term positive and negative dielectrophoresis respectively. In the case of positive dielectrophoresis, the particle moves toward the greater field inhomogeneity, and in negative dielec-trophoresis it moves away from the field inhomogeneity. Since electrodes induce the electric field, the field inhomo-geneity is greatest at the edges of the electrodes; therefore, the particles move either toward or away from the electrodes. Used for a range of biomedical settings including the manipulation of bacteria (e.g., [6]-[8]), viruses (e.g., [9]-[11]), and cells such as cancers and algae (e.g., [12]-[15]), the technique has been used in conjunction with methods such as bulk light scattering [16] and evanescent light scattering [17] to detect the motion of particles. However, conventional dielec-trophoretic methods also present limitations. Where the particles are attracted to the surface on which microelectrodes have been patterned, the collection generally occurs along the edge of the electrodes; many sensing devices require collection to take place primarily on top of the electrode (metal) surface (e.g., [1]). Secondly, since field inhomogeneity reduces rapidly with distance from the electrode edge, the trapping of small particles (e.g., bacteria and viruses) has in the past only taken place using electrodes with very fine structures (sometimes of the order of a few µm) and very constrained volumes in which the particles can be detected (of the order of a few nanoliters). In addition to dielectrophoretic forces, another form of behavior is observed in particle solutions when exposed to lower-frequency nonuniform fields. This phenomenon occurs due to a combination of dielectrophoresis and ac-...

Clarification of Colloidal Particles in Lake and River Water Using AC Electrokinetic

“…This suggested that the electric field acts directly on the particles hence DEP were occurred. This has confirmed the previous works done by Mohtar [3], Hoettges [5] and Hubner [6]. This has also means that the manipulation of colloids is selective according to the electrical potential supplied.…”

“…al. [5]. Zipper geometry is selected because the geometry will have electric potentials of opposing polarity applied allowing focusing of particles across a large area toward a central spot.…”

“…The electrodes were micro fabricated on Indium Tin Oxide (ITO) coated glass slide using laser etching technique. In previous works the micro fabrication were done using lithography techniques [3][4] [5] The laser etching techniques is easy to use and applicable practically to the whole classes of materials, such as silicon, germanium, glass, oxides, nitrides, salts, alloys, binary and ternary compounds and alloys and metals. The laser etching is done using Resonetics RapidX250-L Series as shown in Fig.…”

Review Article—Dielectrophoresis: Status of the theory, technology, and applications

“…Anomalous frequency effects, not explainable by DEP forces alone, were also observed by Voldman et al 67 for particles held in traps, and this was also attributed to electrohydrodynamic flow. Hoettges et al 82 later designed a DEP particle trap to exploit such fluid flow effects in a so-called "zipper" electrode design. A DEP device architecture that offers interesting possibilities for particle transport without the use of fluid flow is the ratchet geometry described by Gonzalez and Remcho.…”

“…For example, they have been developed as single-cell trapping devices for fluids having conductivities ͑1.25 S/m͒ typical of physiological fluids and culture growth conditions. 86 A zipper electrode design has been described by Hoettges et al 82 in the form of an array of interlocking, approximately circular electrode pads. As already mentioned, this design exploits field-induced electrohydrodynamic fluid flow to direct particles toward the electrode pads, and then DEP forces to trap them.…”