Non-Radioactive Tracer Alternative

A tracer is an isotope which can be monitored as it moves through the pathways of a living system or organism. For decades scientists have worked to increase the sensitivity of non-radioactive isotopes, which are now able to compete with radioactive tracers in the medical community, as well as other fields of biology.

Radioactive Tracers

• The advantage of using radioactive tracers initially was their relative high sensitivity, They are typically detectable at much lower concentrations than non-radioactive isotopes. However, there are potential problems in dealing with radioactive isotopes. For example, they are a potential health hazard, they require special handling, and the disposal of radioactive waste increasingly difficult and expensive.

How They Work

• According to the molecular biologists at Molecular Station, non-radioactive tracers use the multiple effect of an enzyme to compete with the sensitivity of radioactive tracers. If the enzyme is coupled with a probe that detects the targeted molecules, it will produce many molecules of the product, amplifying the signal.

  If the product of the enzyme is chemiluminescent, or light-emitting, the method is especially efficient. There, the molecule emits many photons, which further amplifies the signal. The light can be detected by autoradiography with x-ray film, or by a phosphorimager.

  Using enzyme substrates that change color is an alternative to chemiluminescence.
  These chromogenic substrates produce colored bands corresponding to the location of the enzyme, therefore to the location of the molecule targeted for detection.  The intensity of the color is directly related to the amount of the molecule of interest.

Uses

• The Department of Pediatrics in Toronto, Canada's Hospital for Sick Children has developed a simple non-radioisotopic method for rapidly identifying carriers of the Tays-Sachs Disease, a disease caused by genetic mutation. The mutations were traced through the polymerase enzyme in the DNA and coupled with a probe, which reacted with a phosphatase conjugate, producing a colorimetric demonstration. The simplicity and the avoidance of radioisotopes made this method potentially very useful.

  Scientists at the Department of Neurology at the University of Rochester School of Medicine and Dentistry in New York have developed a stable non-radioisotopic method to measure Immunoglobulin G secretion into plasma.

  Since 2004 a non-radioactive screen has been used to detect antimalarial compounds in Panama, The assay is based on fluorochrome binding to parasite double-stranded DNA. Developing countries may have more to gain by the use of non-radioactive tracers where access to and disposal of radioisotopes is more difficult and expensive.