Capillary Fill Research Articles

The fluorescent capillary fill device

The fluorescent capillary fill device (FCFD) is an indirect optical immunosensor which consists of two sheets of glass held apart by a gap of capillary dimensions. Within the device are all the reagents needed to complete the assay, at least one of which is fluorescently labelled. Once the sample has entered the device, an immune complex, including an amount of the fluorophore label, rapidly forms on one of the surface of the device. Exploitation of the evanescent optical properties of the glass sheet used to fabricate the device enables the fluorophore bound immunologically to be discriminated from that which remains free (unbound) within the device. This allows the assay to be performed without the need for a wash and/or separation step. Both competitive and immunometric assays can be performed within the FCFD and the device will operate with a variety of untreated sample types (e.g., whole blood, serum, plasma, urine, saliva). A major technical challenge facing the development of immunosensors, the need to incorporate a reference/calibration system into the sensor, has been tackled and a reference system incorporated into the FCFD. The FCFD requires only simple instrumentation to interrogate bound fluorescence and, as its fabrication is based upon that of liquid-crystal displays, there is the possibility of developing a high-volume low-cost manufacturing process for its production. These factors, along with the ease of use of the device and the ability to incorporate a referencing system into it, result in the FCFD being an ideal immunosensor for decentralized testing.

The calibration of an optical immunosensor — the FCFD

The calibration of immunosensors is a major technical challenge to be overcome before such devices achieve commercial acceptance. This paper reports a method for calibrating one optical immunosensor, the fluorescence capillary fill device (FCFD), which functions by exploitation of the physical structure of the device, precomplexing reagents within the device and appropriate signal processing. This enables a calibration system to function in the sample of interest and in the presence of the analyte under assay.

Disposable Capillary Fill Device for the Colorimetric Determination of p-Aminophenol as Indophenol Blue

Abstract The construction of a disposable capillary fill device, by which p-aminophenol in the range 10-40 μg ml−1 can be determined by a visual comparison method, is described. The inside face of one glass plate of which the device is constructed is coated with a reagent layer produced by brushing on to it a soluble starch solution containing sodium hydroxide, potassium dihydrogen phosphate, and phenol, which is subsequently dried. When a sample solution containing p-aminophenol is taken up into the device by capillary action, the reagent layer dissolves and indophenol is formed by oxidation of the p-aminophenol with phenol in the alkaline conditions by dissolved oxygen in the sample solution. The p-aminophenol concentration of sample solutions is determined by visual inspection compared with the known colour produced by a series of standards.

An electrochemical capillary fill device for the analysis of glucose incorporating glucose oxidase and ruthenium (III) hexamine as mediator

AbstractThis article describes a coulometric measurement device for glucose based on thin‐layer bulk electrolysis. The analysis is carried out in a specially constructed cell, the electrochemical capillary fill device, which has a total volume of less than 20μl. Once the sample enters the cell by capillary action, the freeze‐dried assay components (glucose oxidase, ruthenium (III) hexamine, buffer salts, etc.) become solubilized and quickly disperse throughout the volume of the cell. After a period of one min, the time taken for the enzyme catalyzed oxidation of glucose to gluconic acid to reach completion, a potential step is applied and the current transient, resulting from the oxidation of reduced mediator at the working electrode, integrated over a period of 60 s. From the resultant charge value, the concentration of glucose in the sample can be unambiguously determined. The response of the sensor is both linear and accurate over the range 2–30 mM, which covers the normally accepted range for blood glucose levels in diabetic patients. The second order rate constant for the reaction between reduced glucose oxidase and ruthenium (III) hexamine was evaluated by conducting a numerically based analysis that was designed to separate the diffusional and catatytic components of current transients.

Optical immunosensing systems — meeting the market needs

Optical immunosensors and sensing systems are biosensors which produce a quantitative measure of the amount of antibody, antigen or hapten present in a complex sample such as serum or whole blood. The market needs for such devices and their associated instrumentation are reviewed. A brief history of the development of optical immunosensors is presented and the performance of the most well-developed optical immunosensors for meeting these market needs is reviewed. One device, the fluorescent capillary fill device (FCFD) is reviewed in detail with respect to it fulfilling the market needs for an optical immunosensor. Areas for the future development of such sensing systems are also discussed.

An assay for human chorionic gonadotrophin using the capillary fill immunosensor

Recently there has been much research effort directed towards the development of immunosensors. Optical technologies are currently proving very attractive for the construction of such sensors. The fluorescence capillary fill device (FCFD) has been designed to fulfil these needs. The development of an assay for human chorionic gonadotrophin (hCG) in the FCFD for a variety of body fluids (whole blood, serum, urine and saliva) demonstrates the versatility and assay performance of the device.