How pregnancy test kits work (PART I) (FL-Immuno/73)

Summary

This video lecture explores how home pregnancy test strips work, particularly focusing on the detection of the hormone HCG (human chorionic gonadotropin) in urine. The test strips use monoclonal and polyclonal antibodies to bind to HCG molecules, with an enzyme-linked indicator that causes color change in the test zones. The lecture explains the components of the pregnancy test strip, including reaction, test, and control zones, and how they function in detecting HCG. Understanding the biochemical elements in these strips allows us to better grasp how pregnancy tests confirm the presence of pregnancy.

Takeaways

• 😀 Sandwich ELISA technique involves detecting target antigens between two antibodies: the capture antibody and the detection antibody.
• 😀 Home pregnancy test kits use sandwich ELISA, where the target antigen is HCG (Human Chorionic Gonadotropin) present in urine.
• 😀 Pregnancy test strips have two zones: the test zone (T) and the control zone (C), where specific reactions occur to give a result.
• 😀 A positive pregnancy test occurs when both the test zone (T) and the control zone (C) show a color change.
• 😀 A negative pregnancy test occurs when only the control zone (C) shows a color change.
• 😀 The main substance detected by pregnancy test strips is the hormone HCG, produced by the developing placenta after fertilization.
• 😀 HCG is a heterodimer composed of alpha and beta subunits, with the beta subunit being key for detection in immunoassays.
• 😀 Pregnancy test strips contain monoclonal and polyclonal antibodies to detect HCG molecules in urine.
• 😀 The test strip has three functional zones: the reaction zone (R), test zone (T), and control zone (C), each with different roles.
• 😀 In the reaction zone, monoclonal anti-HCG antibodies are present, which are conjugated with an enzyme for color development when HCG is present.
• 😀 The test zone has polyclonal anti-HCG antibodies and inactive dye molecules, which, upon activation, result in a color reaction indicating the presence of HCG.
• 😀 The control zone contains anti-mouse antibodies, which bind to the mouse antibodies from the reaction zone to ensure proper test function.

Q & A

What is Sandwich ELISA, and how is it relevant to pregnancy test kits?

Sandwich ELISA is an immunoassay where the target antigen is sandwiched between two antibodies: the capture antibody and the detection antibody. This method is used in pregnancy test kits to detect the hormone HCG in urine samples.

What are the key zones in a pregnancy test strip, and what do they signify?

A pregnancy test strip has three key zones: the Reaction zone (R), the Test zone (T), and the Control zone (C). The reaction zone contains enzyme-conjugated anti-HCG antibodies, the test zone contains polyclonal anti-HCG antibodies and inactive dye molecules, and the control zone contains anti-mouse antibodies and inactive dye molecules.

What is the role of HCG in pregnancy tests?

HCG (Human Chorionic Gonadotropin) is a hormone produced by the developing placenta after fertilization. It is the key target antigen detected by pregnancy test strips to confirm pregnancy.

What biochemical components are present in pregnancy test strips?

Pregnancy test strips contain monoclonal and polyclonal antibodies that recognize and bind to HCG, as well as inactive dye molecules. These components work together to produce a color change, indicating the test result.

How are the antibodies in the reaction zone of a pregnancy test strip designed?

The antibodies in the reaction zone are monoclonal, meaning they are specific to a single epitope on the HCG molecule. These antibodies are produced in mice and are covalently attached to an enzyme for color development.

What is the significance of the polyclonal antibodies in the test zone?

The polyclonal antibodies in the test zone are designed to recognize and bind to different epitopes on the HCG molecule. These antibodies are produced in mice and are distinct from the monoclonal antibodies in the reaction zone.

How do the inactive dye molecules function in the test strip?

The inactive dye molecules in the test and control zones act as substrates for the enzyme present in the reaction zone. When the enzyme interacts with the dye, it results in a color change that indicates a positive or negative test.

What is the role of the anti-mouse antibodies in the control zone?

The anti-mouse antibodies in the control zone bind to the monoclonal antibodies from the reaction zone. These antibodies are produced in goats and help confirm the test's validity by ensuring the test strip is functioning properly.

What happens if both the test line and the control line are colored in a pregnancy test?

If both the test line (T) and the control line (C) become colored, the pregnancy test result is positive, indicating the presence of HCG in the urine sample.

What would the result indicate if only the control line is colored in a pregnancy test?

If only the control line (C) becomes colored, the pregnancy test result is negative, indicating that HCG is not present in the urine sample.