Q. 34 Which one of the following is the most sensitive immunoassay?
(A) Immunoelectrophoresis
(B) Immunofluorescence
(C) Radial immunodiffusion
(D) Radioimmunoassay

Radioimmunoassay (RIA) is the most sensitive immunoassay among the given options. It detects antigens at picogram levels due to the high precision of radioactive signal measurement.​

Option Analysis

Immunoelectrophoresis (A)
Combines electrophoresis with immunodiffusion to separate and identify proteins, but requires microgram quantities (20-200 μg antibody/ml) and is less sensitive overall.​
It excels in qualitative analysis of complex mixtures yet lacks the detection limit for trace analytes.​

Immunofluorescence (B)
Uses fluorescent dyes for antigen visualization under microscopy, offering good sensitivity but typically outperformed by RIA in direct quantitative comparisons (e.g., 133-437-fold less sensitive for some antibodies).​
Direct or indirect formats provide visual detection, though signal quenching limits ultra-low detection.​

Radial immunodiffusion (C)
Antigen diffuses into antibody-containing gel, forming precipitin rings proportional to concentration, but sensitivity is low at 2-200 μg/ml.​
Quantitative for serum proteins like immunoglobulins, yet unsuitable for trace-level analytes.​

Radioimmunoassay (D)
Employs radiolabeled antigens in competitive binding; measures picograms via scintillation counting, making it the gold standard for sensitivity.​
Developed by Yalow and Berson, it revolutionized hormone detection like insulin.​

The most sensitive immunoassay technique, Radioimmunoassay (RIA), detects antigens at picogram levels, far surpassing alternatives in competitive exams like CSIR NET. This article breaks down immunoassay sensitivity across options, aiding life sciences students.​

Immunoassay Basics

Immunoassays leverage antigen-antibody specificity for detection. Sensitivity varies by label and format: radioactive (RIA) achieves pg/ml, while diffusion-based methods need μg/ml. RIA’s competitive binding with isotopes like I-125 yields unmatched precision.​

Detailed Comparison

RIA leads as the most sensitive immunoassay for trace analytes like hormones.​

CSIR NET Relevance

For Unit 13 (Methods in Biology), RIA’s picogram detection trumps diffusion techniques. Practice questions often test this hierarchy.​