Which technique is not used in the diagnosis of AIDS infection?

Options

A. ELISA
B. PCR
C. Western blot
D. Southern blot

Answer

To determine which technique is not used in the diagnosis of AIDS infection, we can analyze each option provided:

1. **ELISA (Enzyme-Linked Immunosorbent Assay)**:
- This technique is widely used for the detection of antibodies against HIV in the blood. It is based on the principle of antigen-antibody interaction. Therefore, ELISA is indeed used in the diagnosis of AIDS.

2. **PCR (Polymerase Chain Reaction)**:
- PCR is a highly sensitive technique that can amplify small amounts of DNA, making it possible to detect the presence of HIV DNA in a sample. This method is routinely used in the diagnosis of AIDS. Hence, PCR is also used in the diagnosis of AIDS.

3. **Western Blot**:
- The Western blot technique is used to identify specific proteins in a sample. It is often used as a confirmatory test for HIV infection after an initial positive ELISA test. Thus, Western blot is used in the diagnosis of AIDS.

4. **Southern Blot**:
- Southern blotting is a technique used to detect specific DNA sequences in DNA samples. However, HIV is an RNA virus, and Southern blot is not suitable for detecting RNA. Therefore, Southern blot is not used in the diagnosis of AIDS.

Based on the analysis of the techniques:
- The technique that is not used in the diagnosis of AIDS infection is **Southern blot**.

### Step-by-Step Solution:
1. Identify the techniques listed for diagnosing AIDS.
2. Analyze each technique:
- ELISA: Used for detecting antibodies.
- PCR: Used for amplifying and detecting HIV DNA.
- Western Blot: Used for confirming HIV infection by detecting proteins.
- Southern Blot: Used for detecting DNA, not suitable for RNA viruses like HIV.
3. Conclude which technique is not applicable for AIDS diagnosis.