Protein Arrays

At Biosite, the integration of several core scientific and engineering disciplines has yielded products that are deceptively simple. What looks like a small plastic chip is actually a highly engineered device incorporating microcapillary fluidics, signaling chemistry and other biological systems to replicate those processes performed by laboratory technicians using large analyzers.

In 1999, Biosite commercialized its first protein array, the Triage^® Cardiac Panel, an aid in the diagnosis of acute myocardial infarction, commonly known as heart attack. The array simultaneously and quantitatively assays three different proteins in a whole-blood sample within 15 minutes.

Biosite expects to maintain its leadership in the field of protein arrays by:

• Leveraging its Triage platform technology across new applications
• Providing high quality antibody reagents for other platforms
• Collaborating with content providers and protein array end-users to validate multiple genomics/proteomics targets and identify promising candidates.

How the Array Functions

Biosite’s protein array is comprised of two components: the protein array device, and the Triage Meters.

1. When a sample of blood is added to the protein array, a fibrous filter contained within the array separates red blood cells from plasma.
2. The plasma then exits the filter and flows into a region of higher capillarity called the Sample Reaction Barrier.
3. The plasma then enters a Reaction Chamber of lower capillarity, which contains reagents in a dry form. The plasma reconstitutes the reagents to form a reaction mixture. The reagents include antibodies bound to fluorescence energy transfer particles (FETL).
4. A time gate delays the flow of plasma out of the Reaction Chamber to define an incubation time. This time gate is composed of hydrophobic surfaces that prevent fluid flow. These surfaces are converted into hydrophilic surfaces by the proteins in the sample, allowing the reaction mixture to flow into a Diagnostic Lane.
5. The Diagnostic Lane is a capillary channel containing discrete zones of immobilized antibodies to the analytes. Any analytes bound to FETL from the reaction mixture will bind to the immobilized antibodies as the reaction mixture moves through the Diagnostic Lane. Excess plasma from the blood filter washes unbound FETL from the Diagnostic Lane.
6. The fluorescence at each discrete zone is measured by a handheld fluorometer called the Triage Meters. When inserted into the Triage Meters, the protein array device is scanned by a laser diode. The FETL fluorescence emission is detected by a photodiode in a high gain circuit. The fluorescence intensity is integrated over each discrete zone to give a quantitative measurement of the analyte concentrations.

Biosite’s Proprietary Protein Array Technology

Biosite’s protein array technology is geared toward fast and accurate simultaneous determination of protein levels in whole-blood (or any other sample matrix). Biosite’s unique combination of technologies has resulted in one of the most sensitive array platforms on the market. The core proprietary technologies employed are the following:

Microcapillary Fluidics

Biosite developed proprietary technology to design, develop and manufacture protein arrays containing microcapillaries to control the flow of fluids in immunoassay processes. The protein array format uses several different microcapillary designs to control the contact of sample with reagents and to control the flow of fluid throughout the protein array. When a sample is added to the protein array, a filter contained within the array separates blood cells from plasma, which capillary forces then direct into a chamber that contains dried immunoassay reagents. After an incubation time that is determined by another microcapillary element of the array, the volume of sample that contacted the reagents flows down a capillary path that brings it into contact with an antibody array. Biosite also developed the engineering capability to design unique microcapillary structures in plastic parts and to fabricate them in commercial scale quantities using injection molding processes.

High Sensitive Fluorescence Energy Transfer Dyes

Immunoassays require the attachment of a detectable label to an antibody or target analyte. Although fluorescence is a powerful label for use in immunoassays, its potential has been limited by the lack of available dyes that are stable and have no sample interference, and by the requirement of a complex instrument for detection. We have invented our own proprietary dyes, which satisfy three criteria: (1) they are excited at near infrared wavelengths, and therefore are usable with complex biological samples such as serum, plasma, and whole blood; (2) they are stable for the dating period of the product; (3) they show no overlap between emission and excitation, so that detection can be performed with inexpensive solid state components.

Antibody Development

Biosite’s internal antibody development capabilities allow rapid identification and development of antibodies with optimal specificity, affinity, and stability characteristics. Several key features of our Omniclonal^® technology make it particularly suitable for building protein arrays. Omniclonal antibodies’ high-affinity and lack of cross-reacitivity are essential elements to eliminate the high false-positive rate typical of highly multiplexed immunoassays. The Omniclonal library can be quickly re-selected when new analytes are added to the array. Tailored protein arrays with novel content can be easily built due to the fast turnaround and high throughput capabilities of the Omniclonal technology.

• Multiple proteins simultaneously measured
• Quantitative reading over wide range
• Easy calibration
• One–step operation from whole blood (or any other fluid)
• Sensitive (sub-pM detection)