Question

Arrange the components of membrane-based rapid diagnostic test in the order of specimen flow
A. Soak pad
B. Test band
C. Control band
D. Sample pad
E. Conjugate pad
Choose the correct answer from the options given below :

• A. A, B, C, D, E
• B. D, B, A, C, E
• C. D, E, B, C, A
• D. A, B, D, C, E

Hint:

Remember the flow logic: Put the sample in (Sample pad), mix with detectors (Conjugate), read the result (Test), confirm it worked (Control), and soak up the trash (Soak pad).

Answer 1

The Correct Option is C

Step 1: Concept:
The question asks for the sequential arrangement of physical structural components in a standard Lateral Flow Immunoassay (LFIA) based on the direction the liquid specimen travels.

Step 2: Step-by-step Explanation:

• A Lateral Flow Immunoassay (like a rapid pregnancy or COVID-19 antigen test) relies entirely on the principle of capillary action to draw a liquid sample across a series of reactive zones.

• 1. Sample pad (D): This is the initial port of entry. The patient specimen (blood, urine, saliva) is dropped here. It acts as a sponge, filtering out large particulates and uniformly distributing the fluid to the next stage.

• 2. Conjugate pad (E): The liquid flows immediately into the conjugate pad, which contains freeze-dried, artificially labeled antibodies (often conjugated with colored gold nanoparticles). If the target antigen is present in the sample, it binds to these colored antibodies here to form a mobile complex.

• 3. Test band (B): The fluid then wicks across the nitrocellulose membrane, reaching the Test line first. This band contains immobilized capture antibodies. If the target antigen is present, the colored complex binds here, generating a visible colored line indicating a positive result.

• 4. Control band (C): The fluid continues past the test line to the Control line. This band contains secondary antibodies that bind to the unbound, excess labeled antibodies migrating from the conjugate pad. A visible line here proves the fluid successfully migrated across the entire membrane, confirming the test is functionally valid.

• 5. Soak pad Absorbent pad (A): Finally, the fluid reaches the absorbent pad at the very end. This acts as a reservoir to aggressively draw the remaining liquid forward, ensuring continuous unidirectional capillary flow and preventing backflow.

• Sequence of flow: D \(\rightarrow\) E \(\rightarrow\) B \(\rightarrow\) C \(\rightarrow\) A.

Step 3: Final Answer:
The correct order of specimen flow is strictly Option (C).