ABS

The Array Biosensor (ABS) consists of a patterned array of capture antibodies immobilized on the surface of a planar waveguide, and a sandwich immunoassay is conducted using fluorescent tracer antibodies. Upon excitation of the fluorescent label using a diode laser, a CCD camera detects the pattern of fluorescent antigen/antibody complexes on the waveguide surface. Image analysis software correlates the position of the fluorescent signals with the identity of the analyte. The ABS includes a flow cell mounted on the waveguide and a fluidics component milled in a plastic cube. The following sketches depict the sandwich immunoassay and the sensor layout.

A portable prototype unit is shown below.

The advantages of the ABS technology include:

• Simultaneous detection of as many analytes as have had capture reagents developed

• Not limited to antibodies as capture reagents

• Reusable sensor surface and tracer reagents. This eliminates the requirement for a particle detector as a trigger, making it more useful in urban environments.

• Little, if any, sample preparation

• Low sensitivity to interferents

• On-board controls for false positives and false negatives

• Potential for culture or PCR of captured pathogens after initial screening

• Useable with air samples, food, water, clinical fluids

Constellation is developing the ABS into a fully automated biodetection system, the Automated, Continuous Analysis – Array Bio-Sensor (ACA-ABS). This system can detect bacteria with genus and species specificity as well as detect and identify viruses and toxins. The photos below show the ACA-ABS with the covers on and off the case.

Current specifications and capabilities of the ACA-ABS are listed in Table I. Limits of detection are generally 0.5-10 ng/mL for proteins, 10⁷ pfu/ml for viruses and 10²-10⁵ cfu/mL for bacteria, depending on the antibody affinity. It is important to note that complex sample matrices, including clinical fluids and environmental contaminants, are easily processed and do not cause false positive or false negative responses. Additionally, assays can be developed for any analytes for which antibodies are available.

ACA-ABS assays have been developed for the following biological warfare (BW) agent simulants: B. globigii (Anthrax simulant), Erwinia Herbicola (bacteria simulant), MS2 (virus simulant), and ovalbumin (toxin simulant). Additionally, assays have been developed for the following BW agents: B. anthracis (Anthrax), Staphylococcal enterotoxin B, Botulinum toxin and Yersinia pestis. An additional assay is currently under development for Vaccinia (smallpox simulant). Additional assays can be developed as necessary.

Teaming with business partners led to the development of the Automated Bioaerosol Collection and Detection System an automated, continuously operating system for the collection, detection, alerting and data logging of events involving the detection of BW agents. The unit was field tested during the Technical Readiness Evaluation (TRE-02) conducted at Dugway Proving Ground (DPG) from September 22, 2003 through October 3, 2003. During this test, the system was one of approximately ten systems that were challenged with disseminations of B. globigii, Erwinia herbicola, and MS2. A photograph of the system at the test site is shown below. Further field testing is planned to occur at DPG during TRE-04 in June 2004.

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