Home IVD ManufacturingQualitative Tests: Exploring Lateral Flow Assays and Their Applications

Qualitative Tests: Exploring Lateral Flow Assays and Their Applications

Collection of Estapor® Microspheres in red, blue, yellow, black, and white displayed on a mirrored surface, showcasing their vibrant colors for diagnostic manufacturing applications.

Section Overview

Understanding Qualitative Tests
Types of Qualitative Tests
Mechanism of Action
Positive and Negative Test Results
Industrial Applications of Qualitative Tests
Benefits of Qualitative Tests
Assay Types in Qualitative Testing
The Role of Dyed Estapor^® Microspheres
Custom Development of Dyed Microspheres

Understanding Qualitative Tests

In qualitative tests, results are simplified to a straightforward “yes or no,” visualized by colored capture lines. One of the earliest examples of this assay is the pregnancy test, a one-step lateral flow chromatographic immunoassay.

Types of Qualitative Tests

Several types of tests have been created, including:

Monotest Monochromatic - This test features the same color line for both the analyte and the control test.
Monotest Bichromatic - This format has two color lines—one for the analyte and one for the control test.
Multitest Monochromatic - Similar to the monotest monochromatic, but allows for multiple analytes with the same color line.
Multitest Polychromatic - This test displays several color lines, one for each analyte and one for the control test.

Mechanism of Action

This method employs a colored conjugate (mouse anti-hCG monoclonal antibody + colored Dyed Estapor^®Microspheres complex) pre-dried on the test strip.

Illustration of a monotest monochromatic lateral flow test setup, depicting the test sample on the left, the antibody and microsphere in the center for reaction, and the control line on the right, with the sample flowing from left to right.

Figure 1.Monotest monochromatic lateral flow test setup.

When a sufficient sample volume is added, the conjugate selectively reacts with hCG in the test samples, forming an antibody-antigen complex. The mixture then moves upward on the membrane by capillary action, producing a visible blue band.

Illustration of a positive result in a monotest monochromatic lateral flow test, showing the test sample on the left, the antibody and microsphere in the center reacting with the sample, and the control line on the right, with the sample flowing from left to right.

Figure 2.Positive monotest monochromatic lateral flow test result.

In the absence of hCG, there is no line in the test zone. The reaction mixture continues flowing through the absorbent device to the immobilized antibody placed in the control band region and a red band appears (control band), regardless of the presence of hCG.

Illustration of a negative result in a monotest monochromatic lateral flow test, showing the test sample on the left, the antibody and microsphere in the center not reacting with the sample, and the control line on the right, with the sample flowing from left to right.

Figure 3.Negative monotest monochromatic lateral flow test result.

Positive and Negative Test Results

Positive Test: A blue band appears in the test zone.
Negative Test: No line appears in the test zone, but a red band indicates the control.

Industrial Applications of Qualitative Tests

The development of simple and rapid detection tests using lateral flow technology fulfills the need for point-of-care (POC) testing across various fields:

Clinical and Veterinary Diagnostics

Applications include pregnancy tests, HIV tests, drug abuse detection, and infectious disease testing (e.g., Adenovirus, Helicobacter Pylori, Rotavirus).

Food Industry

Tests for pathogens such as Salmonella, E. Coli, and Listeria.

Environmental Testing

Detection of Legionella and Amibia.

Benefits of Qualitative Tests

Visualized Coloration: Easy interpretation of results.
Faster Time to Result: Quick turnaround for testing.
User-Friendly: Simple to administer and read.

Assay Types in Qualitative Testing

In qualitative tests, various assay types can be selected:

Monochromatic / Monoparametric Test
Bichromatic / Monoparametric Test
Multichromatic / Multiparametric Test
One example is the influenza virus test.

Illustration of a monochromatic monoparametric lateral flow test, displaying the test sample pad on the left, the Ag Capture line in red in the center, and the control line in blue on the right, with the sample flowing from left to right.

Figure 4.Monochromatic monoparametric lateral flow test setup.

Illustration of a bichromatic monoparametric lateral flow test, featuring the test sample pad on the left, the Ag Capture line in blue in the center, and the control line also in blue on the right, with the sample flowing from left to right.

Figure 5.Bichromatic monoparametric lateral flow test setup.

One example of a multichromatic/multiparametric test is the influenza virus test and is depicted in the illustration below. Multiplex tests allow for the simultaneous detection of multiple analytes within a single sample, enhancing efficiency and reducing the time needed for diagnosis. In the influenza virus test, this method utilizes different colored capture lines for each viral strain, enabling healthcare professionals to quickly identify the presence of multiple influenza viruses in one test, all while maintaining high sensitivity and specificity.

Illustration of a multichromatic multiparametric (multiplex) lateral flow test for influenza viruses, showing the test sample on the left, the Influenza A Capture line in blue and Influenza B Capture line in green in the center, and the control line in red on the right, with the sample flowing from left to right.

Figure 6.Influenza virus multiplex lateral flow test setup.

The Role of Dyed Estapor^® Microspheres

In lateral flow tests, we recommend using Dyed Estapor^® Microspheres or Estapor^® Color Intense Microspheres. The Dyed Estapor^® Microspheres are internally dyed for uniformity, ensuring maximum color brilliance and preventing dye leaching in water or aqueous buffers. Over 100 dyed microspheres are available in various colors, creating what is known as the Rainbow Effect.

The Estapor^® Color Intense Microspheres are specifically designed to boost the functionality of lateral flow tests, allowing for the simultaneous detection of multiple analytes on a single test strip. Each analyte is distinctly identifiable by microspheres colored in red, blue, or black, enhancing clarity and easing interpretation.

Custom Development of Dyed Microspheres

If standard dyed microspheres do not meet your needs, Estapor^® offers custom development for the diagnostics, biotech, and pharmaceutical industries. Our technical department can quickly produce custom microspheres tailored to your specific requirements. Contact your Estapor^® representative for more information.