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How large a hormone can be measured by microencapsulated antibody?
1Department of Clinical Biochemistry, Royal Infirmary, Glasgow.
The Journal of Endocrinology
|October 1, 1987
Summary
This study determined the molecular weight cut-off for semipermeable microcapsules used in immunoassays. Molecules under 6000 molecular weight and within a 1.8-3.5 nm diameter range can be measured, enhancing assay specificity.
Area of Science:
- Biomaterials Science
- Analytical Chemistry
- Immunotechnology
Background:
- Immunoassay sensitivity is limited by the molecular size exclusion of semipermeable microcapsules.
- Antibody encapsulation within microcapsules restricts measurable analyte size based on membrane pore dimensions.
Purpose of the Study:
- To determine the approximate molecular weight cut-off (MWCO) of semipermeable microcapsules used in immunoassays.
- To establish the size limitations for analytes measurable with antibody-encapsulated microcapsules.
Main Methods:
- Assessing microcapsule membrane permeability using labelled hormones of varying molecular weights.
- Measuring the ability of labelled hormones to enter and bind to microencapsulated antibodies.
Main Results:
- Hormones < 4000 MW (e.g., angiotensin II, thyroxine) permeated freely.
- Hormones > 10,000 MW (e.g., parathyroid hormone, human GH) could not permeate.
- Insulin (6000 MW, ~3.5 nm diameter) showed restricted entry, while a 4000 MW fragment (~1.8 nm) bound readily, indicating a pore diameter between 1.8 and 3.5 nm.
Conclusions:
- The microcapsule system is suitable for measuring compounds with molecular weights below 6000 and diameters between 1.8 and 3.5 nm.
- This size-exclusion property can improve immunoassay specificity by excluding larger cross-reactive molecules.