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Dual Path Platform Technology: A Basis for Next-Generation Rapid Diagnostic Testing

Thu, 09/02/2010 - 7:08am
Lawrence A. Seibert

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A patented technology known as Dual Path Platform (DPP), intended for point-of-care immunoassays, offers a number of advantages over the widely used lateral flow technology. A DPP assay device has already been developed for HIV, as have prototypes for other conditions that range from hepatitis C to influenza. 

 

Chembio
Patented Dual Path Platform (DPP) Technology: Chembio has developed a new and innovative chromatographic immunoassay technology for rapid, point-of-care diagnostic testing of a wide variety of analytes.  This technology offers significant advantages over Lateral Flow (LF) technology.

The success as well as specific limitations of existing rapid screening assays has inspired the innovation of a patented, next-generation testing approach known as Dual Path Platform (DPP) technology. The original focus for DPP is rapid HIV testing, although it can be adapted to test for numerous infectious diseases. These tests are intended to significantly shorten the time to diagnosis and to lessen the costs of testing.

DPP technology was patented by Chembio Diagnostics Inc. in 2007. DPP enables development of POC assays that offer unique features and capabilities such as multiplexing. It also enables better control of challenging sample types, such as oral fluid. Tests created to date on DPP include an oral fluid HIV 1/2 test, a five-band POC confirmatory test for HIV 1/2, and a combination screening and confirmation test for syphilis. Prototypes of an oral fluid test for hepatitis C and various strains of influenza have also been created.

The traditional screening tests for antibodies to HIV include the enzyme immunoassay (EIA or ELISA), as well as Western Blots and PCR-based assays. The EIA test requires two visits to a clinic or medical facility: one to receive pretest counseling and to have blood drawn for HIV testing, and the second to receive test results and additional counseling (and, if needed, referrals). In contrast, rapid tests such as those made possible by DPP produce results within 20 minutes and permit testing, counseling and referrals to be secured in one visit. Rapid tests are cheaper for testing agencies to perform since fewer outreach visits are needed to deliver results. Also, studies reveal that rapid tests are as sensitive and specific as conventional immunoassays. In addition, the tests can be safely stored at room temperature for up to two years before use, making them ideal for the OTC market as viable at-home HIV tests.

DPP technology has several advantages over the commonly used lateral flow (LF) technology conventionally used in home pregnancy tests. First, DPP offers significantly greater analytical and clinical sensitivity. DPP HIV rapid test results show significantly better sensitivity ranging from 10 to 50 times that of LF. Independent migration paths for the sample and conjugate account for this increased sensitivity is coupled with a more effective method of binding the analyte to the binding site in the test zone prior to the reaction of the conjugated marker with the test zone complex.

Second, the speed and sensitivity of DPP assays are greater, due to improved membrane clearance resulting from better uniformity and consistency of conjugate particles that can migrate without the sample particles. In particular, DPP is able to effectively resolve common aggregation issues presented in LF assays with large particle analytes (e.g., bacteria). In DPP, the bacterial samples (after filtering) are applied directly to the test site and immobilized while the marker conjugate is free to migrate without the sample to the test zone. This approach allows DPP assays to be extremely sensitive and specific.

DPP allows an enhanced multiplex capability with independent and simultaneous delivery of samples. The technology offers multiple analyte results with a heightened level of sensitivity without compromising specificity due to cross-reactivity as is common in LF methods. Analytes are able to migrate independently without the conjugate and reach the test zone independently. They are therefore able to bind equally so that an equal level of sensitivity is maintained across all different analytes.

DPP is able to run tests on various kinds of body fluids, including blood, serum, oral fluids, sputum, urine, or feces, while maintaining a high level of sensitivity and the ability to test for the presence of any ligand.

The DPP HIV 1/2 Screen Assay is a single-use immunochromatographic, rapid screening test using immobilized antigens to detect antibodies to Human Immunodeficiency Virus types 1 and 2 in oral fluid, fingerstick whole blood, venous whole blood, serum, or plasma samples. This Assay uses a unique combination of a specific antibody binding protein, which is conjugated to colloidal gold dye particles, and HIV 1/2 antigens, which are bound to the membrane solid phase. The sample is applied to the device’s SAMPLE + BUFFER well. After sample and buffer have migrated onto the test strip, additional buffer is added to the BUFFER well. The buffer releases the conjugate to the antigens. In a reactive sample, the conjugate is captured in the TEST area, producing a pink/purple line. In the absence of HIV antibodies, there is no pink/purple line. In all cases, sample and conjugate have each also migrated further along the strip to create a pink/purple line in the CONTROL area containing immunoglobulin G antigens. This procedural control serves to show that sample and reagents have been properly applied and have migrated through the device. A pink/purple line should always appear in the CONTROL area, whether or not a line shows in the TEST area.

There are two possible interpretations of results. One pink/purple line in the CONTROL area, with no line in the TEST area, indicates a nonreactive result; at 10 minutes from the addition of the second buffer, this indicates that there are no detectable HIV antibodies in the sample. However, two pink/purple lines, one in the TEST area and one in the CONTROL area, indicate a reactive result. The line in the TEST area may differ from the one in the CONTROL area. Intensities of the TEST and CONTROL lines may vary. A test result with visible lines in both the TEST and CONTROL areas is considered reactive and means that HIV-1 and/or HIV-2 antibodies have been detected—a preliminary positive for HIV-1 and/or HIV-2 antibodies.

Given the demand for heightened sensitivity, use of different bodily fluid sample types, and the attraction of testing for multiple analytes in one point-of-care device, DPP may lead to a new generation of testing options.

For additional information on the products and technologies discussed in this article, see Chembio Diagnostic Systems.

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