4-Channel Bioassay Operational Details

Performance Overview

CBRN International's biosensor systems are based on monolayer receptor-ligand reactions taking place on the surface of injection molded polystyrene waveguides. All fluidic and optoelectronic steps associated with the assay are performed automatically. The baseline protocol used to Equivalent to standard ELISA fluoroimmunoassay. In a typical waveguide-based sandwich immunoassay, the cylindrical waveguide has a monolayer of capture antibody immobilized on its surface as shown in Figure 1. Such factory-coated waveguides will maintain activity for a period of months if stabilized and not subjected to high temperatures.

Optical and biochemical processes associated with a waveguide bioassay
Figure 1: Optical and biochemical processes associated with a waveguide bioassay.

At the time of use, the waveguide is first incubated with the fluid sample for three to five minutes. After a wash step, the waveguide is incubated with fluorophore-labeled antibody for three to five minutes to form an antibody/antigen/labeled-antibody sandwich. These molecular sandwiches generate an optical signal when excitation light is injected into the waveguide. The excitation light creates an electromagnetic 'skin effect' in adjacent fluid and it is this so-called evanescent wave electric field that excites bound reporter molecules to fluoresce. As a final step, individual molecular signals are collectively coupled into the waveguide and monitored with a sensitive photodetector that looks down the waveguide axis.

A major problem with evanescent-excited fluoroimmunoassays has been low excitation efficiency. Light injected into a waveguide is most effective at exciting surface-bound fluorophores if the light's propagation angle is near the condition of total internal reflection (TIR) at the waveguide surface. Research International has discovered and patented a novel aspheric dielectric structure that injects light into the waveguide in such a way that evanescent electric field intensities are at near-theoretical limits. This structure, the waveguide and a signal collection lens are molded as one component, providing a highly efficient, low cost, and compact optical sensor element.


Four of the waveguide sensors are mounted in a disposable plastic coupon (see Figure 2), allowing four different pathogens to be detected in a sample; or multiple channels may target the same pathogen to improve statistical certainty. An elastomer needle septum connects RAPTOR™ fluidics with fluid distribution channels molded into the coupon's body. In addition to providing controlled flow over the optical detectors, an assay recipe identification system is incorporated that automatically reads a coupon bar code when the coupon is mounted into the RAPTOR™ instrument. This bar code identifies the type of assay to be run by the instrument and allows very sophisticated assays to be performed by unskilled persons. A computer embedded within the RAPTOR™ performs and controls all steps in the assay procedure.

RAPTOR bioassay coupon
Figure 2: RAPTOR™ bioassay coupon.

Assay Procedure/Specifications

To begin an assay, a coupon is inserted into a docking bay in the instrument's top surface. RAPTOR and coupon optics and fluidics are automatically connected when the compartment's door is closed. The user performs an assay by turning the instrument on and pressing the Run button. During the assay, a timer in the LCD display window provides time remaining until completion. On completion, assay results for the four channels are displayed.

Behind the scenes, an onboard computer reads the recipe code on the coupon, primes the coupon for flow and controls fluidics and optoelectronic steps during the assay. All fluids needed to perform an assay, with the exception of sample, are contained in the unit. Buffer and reagent are contained in flexible on-board pressurized bags, and waste in a third unpressurized bag. The reagent bag is housed in a phase-change module that keeps the reagent at a temperature of 30°C or less, preventing deterioration of any thermally sensitive reagents.

The instrument package provides a backlit six-key keypad and a four-line LCD readout. The unit can talk, control, or be controlled by other instrumentation via an RS-232 channel or RF links accessed through a connector in the instrument's battery compartment. A second connector that can supply DC power to and digitally control ancillary electronics is also provided. The unit incorporates a one-megabyte nonvolatile flash memory that can store a large number of assay protocols as well as a step-by-step log of each assay performed. An on-board BA-5590/U battery provides power for 9 to 24 hours of continuous operation depending on the backlighting intensity selected. With the battery installed, overall unit weight is about 14.2 lbs (6.45 kg), and the unit's size is 11.0" W x 7.95" H x 7.29" D.

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