Portable Diagnostic Technique Detects Specific Proteins in Blood

Aptamers are custom-made and commercially available short strands of nucleic acid.

Aptamers resemble antibodies found in the body because they connect to one type of molecule only. Specific aptamers can be used to search for target compounds ranging from small molecules–such as drugs and dyes–to complex biological molecules such as enzymes, peptides, and proteins.

However, aptamers have advantages over antibodies in clinical testing. They are able to tolerate a wide range of pH (acid and base environments) and salt concentrations. They have high heat stability, are easily synthesized, and cost efficient. Aptamer sensors are also capable of being reversibly denatured, meaning they can easily release their target molecules, which makes them perfect receptors for biosensing applications.

To demonstrate the applicability of the system, the scientists chose thrombin and thrombin-binding aptamers. Thrombin is a naturally occurring protein in humans that plays a role in clotting. The aptamers were attached to a sensor surface, in this case a glass slide coated with a nanoscale layer of gold. As the blood sample was applied to the testing surface, the aptamer and their corresponding proteins latched together.

A real-time optical sensing technique known as Surface Plasmon Resonance (SPR) was then used to determine if the couples pairing was successful. If the protein is present and has bound to the aptamer, conditions for which resonance will occur at the gold layer will change. This resonance change is detected through a simple reflectance technique that is coupled to a linear detector.

“The advantage of this surface plasmon sensor,” said Brent D. Cameron from the department of bioengineering at the University of Toledo, “is that it enabled us to demonstrate low sample consumption, high sensitivity, and fast response time.” The direct detection of blood proteins in this manner can benefit a number of scientific and clinical applications, such as monitoring diabetes, drug research, environmental monitoring, and cancer diagnosis.

The new technique was described in the September 1, 2011, issue of the Optical Society’s (OSA) open-access journal, Biomedical Optics Express.

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