F. De Bisschop

Electronic Gating for Particle/Cell Counting and Sizing, DSP-operated

A hardware and software solution is proposed for the development of a DSP-operated cell/particle counting and sizing system. LabVIEW, which is a graphical programming language, was adopted as the DSP programming platform. Special attention was paid to data reduction, noise elimination, baseline restoration, and pulsewidth discrimination. Global accuracy is verified based on externally generated test signals and using particle size standards. The hardware and software, with minor modifications, are also suitable as a detection system for cell/particle chromatography and flow cytometry.

Electronic gate detection for cell or particle counting and sizing in liquids: front-end characteristics, flow-dependent gate impedance, and its remediation

The detection sensitivity and the sizing resolution of electronic gating are inherently limited by fluctuating gate impedance and flow-induced noise. Instabilities of this type, as shown, are due to varying flow patterns of the carrier liquid beyond the gate. Their effects, although largely hidden in dc-operated gating, cause broadening and shift of cell/particle-size distributions under measurement. RF-operated gating, more specifically the demodulation operation, is much more hindered. For an investigation of these effects, a physical model is proposed along with a procedure for the identification of the system parameters. A detector of dedicated concept is used for evaluating the model, and, more specifically, for investigating the impact of configurational and hydrodynamic parameters. Experiments prove that the origin of flow-dependent gate impedance is to be located inside a zone of only a few-micrometer extent at the gate outlet. This is confirmed by the calculated electric field patterns. On such grounds, electrode configurations are proposed that minimize the current density in the zone of hydrodynamic instability and, hence, the flow-induced noise. The same configurations also minimize the impedance of the gate as signal source, facilitating broadband operation, and multifrequency cell impedance measurements

Low-frequency electronic gate detection for the counting and sizing of cells, bacteria, and colloidal particles in liquids

Low frequency electronic gating is proposed for the detection and sizing of cells, bacteria and colloidal particles in liquids. LF gating avoids the disturbing effects of electrolysis inherent to DC-operated systems and the poor sensitivity of HF gating. The technique is intended for continuous operation online, in chromatography-like experiments.

Improved electronic gate technique, for particle counting and sizing in liquids

Particle counting and measurements of particle size distributions in liquids can be based on pulse height analysis of signals obtained from a changing gate impedance, upon particle transition. Signal-to-noise ratio is markedly improved, making use of a four-electrode detector. An instrumentation amplifier with a high-pass filter is used as a preamplifier. Cylindrical electrodes and a coaxial aperture location result in a decreased detector capacitance, lowering the signal detection level and contributing to improved pulse shape. Volume sampling is flexible and accurate, making use of a stepping motor acutated digital sampling system. A newly developed baseline restorer, combined with a log-antilog amplifier circuit, allows for linearisation of the pulse height/particle size relationship.

Instrumental method for quantitative evaluation of cell/particle adhesion based on transport measurements in capillary flow. Part II: Experimental feasibility study

The method proposed in part I is applied in experiments with capillaries of various lengths and wall coatings, and at various flow rates of the carrier liquid. Latex particles of known density and size distribution are used as a reference material. The Segre-Silberberg effect is shown to be fully established at any capillary length of more than a few decimetres. The transport retardation of the latex particles observed at specific flow rates of the carrier liquid, is governed by the chemical nature of the capillary wall coating. Cumulative plots of the cell/particle elution offer a highly reproducible measure of adherence. Tests with increasing particle numbers show the saturation of the exposed surface area. The technique is sensitive, fast, reliable and fully automated.

Electronic Gate Detection for the Counting and Sizing of Cells or Colloidal Particles in Liquids: Front-End Characteristics, Specific Problems and their Remediation. Part 2: Experimental

Occurring jet flow and turbulence in the output compartment of gate detectors constitute presumed causes of fluctuating gate impedance and of dominant noise. Experiments with a dedicated detector, to some extent, confirm that presumption but also show a noticeable impact of configurational and hydrodynamic parameters

Electronic Gate Detection for the Counting and Sizing of Cells or Colloidal Particles in Liquids: Front-end Characteristics, Specific Problems and their Remediation. Part 1: Physical Model and Equivalent Circuits.

DC, RF and LF operated gating for cell/particle counting and sizing in liquids are hindered by unstable gate impedance. Most problematic appear transients and fluctuations due to varying flow patterns of the carrier liquid. Their effects, largely hidden in DC-operated gating, cause broadening and shift of cell/particle size distributions. RF/LF-operated gating, more specifically the demodulation of the AM-encoded gate signal, is much more disturbed. For a systematic study of these effects, an equivalent circuit is presented along with a procedure to determine the system parameters

Instrumental method for quantitative evaluation of cell or particle adhesion, based on transport measurements in capillary flow

An instrumental method is proposed for the quantitative evaluation of cell/particle adhesion at solid/liquid interfaces. As a measure of adhesion, the retardation of convective transport in capillary flow tubes is determined. The flow tubes, for such purposes, have been internally coated with the substance under investigation. AC-operated electronic gating is applied, preferentially, for the determination of the elution rate. This technique, to some extent, is similar to that of high-pressure liquid chromatography (HPLC). However, the transport mechanism is different as in this case, where transport mainly takes place about halfway between the capillary axis and the wall (Segre-Silberberg effect). At specific flow rates of the carrier liquid, cells/particles repeatedly contact the wall, only to be released again as a consequence of increasing lift and drag. This phenomenon depends on the chemical nature of the capillary wall coating and causes measurable retardation of transport. A transport model is proposed that predicts flow conditions under which transport retardation and adhesive interaction are to be expected. Experiments prove that the Segre-Silberberg effect, i.e., the occurrence of a preferential pathway of transport, is fully established already at capillary lengths of a few decimeters, and that the occurring retardation of transport, if any, is governed by the chemical nature of the capillary wall coatings. The area enclosed between the cumulative elution curves of sample and reference materials offers a reproducible measure of adhesion. The technique is fast, sensitive, and reliable.

Instrumental method for quantitative evaluation of cell/particle adhesion based on transport measurements in capillary flow. Part I: The measuring system

An instrumental method is proposed for quantitative evaluation of cell/particle adhesion at solid/liquid interfaces. The retardation of convective cell/particle transport is measured in capillary flow tubes (columns), that have been internally coated with the substance under investigation. Ac-operated electronic gating is used for the determination of the elution rate. The technique is similar to that of HPLC (high pressure liquid chromatography). Cell/particle transport however, on column, is totally different from that of solutes: transport mainly takes place at a radial distance about halfway the axis and the wall (Segre-Silberberg effect). At specific flow rates of the carrier, cells/particles contact the wall and may be released again as a consequence of increasing lift and drag. The resulting transport retardation depends on the chemical nature of the capillary wall coatings.