For effective treatment of the disease, early diagnosis and understanding its pathophysiology is very important. Which of the following molecular diagnostic techniques is very useful for early detection?

Early detection of disease relies on techniques that can identify specific biomarkers—such as proteins, nucleic acids, or antibodies—at very low concentrations before clinical symptoms become apparent.

1. ELISA (Enzyme‑Linked Immunosorbent Assay)

ELISA is a highly sensitive immunoassay that detects the presence of antigens or antibodies in a sample. The steps are:

• Coat a micro‑plate well with a capture antibody that specifically binds the target antigen.
• Add the patient sample; if the antigen is present, it binds to the capture antibody.
• Introduce a detection antibody linked to an enzyme (e.g., horseradish peroxidase).
• Add a substrate that the enzyme converts into a colored product.
• Measure the color intensity with a spectrophotometer; the signal is proportional to the amount of antigen.

Because ELISA can detect picogram‑level concentrations of proteins or antibodies, it is ideal for identifying infections or immune responses very early in the disease course.

2. Southern Blotting

Southern blotting is a DNA‑based technique that detects specific nucleic‑acid sequences within a complex mixture. The procedure includes:

• Isolate genomic DNA from the patient sample.
• Digest the DNA with restriction enzymes to produce fragments.
• Separate the fragments by agarose‑gel electrophoresis.
• Transfer (blot) the resolved DNA onto a nylon membrane.
• Hybridize the membrane with a labeled DNA probe that is complementary to the target sequence.
• Visualize the probe‑DNA hybrids using autoradiography or chemiluminescence.

Southern blotting can reveal the presence of pathogen DNA, viral integration, or specific genetic mutations at very low copy numbers, making it a powerful tool for early molecular diagnosis.

Both ELISA and Southern blotting provide the sensitivity and specificity required to detect disease markers well before overt clinical signs appear, which is why they are considered very useful for early detection.