DNA Aptamer Sensors: Glucose Meters modified to measure many different analytes

Researchers from the U. Illinois have devised a way to use inexpensive personal glucose meters (PGMs) to detect and measure a wide variety of substances in solution, including cocaine, biomolecules like adenosine and interferon, and metal ions like uranium (1, 2). Chemist Yi Lu of the University of Illinois, Urbana-Champaign, and postdoc Yu Xiang used functional DNA, or aptamers, to recognize molecules of interest. Aptamers are similar to antibodies in that they have strong affinity for paticular molecules based on charge and shape. Instead of protein-based antibodies, aptamers are short (20–80mer) DNA sequences that bind a target molecule with high affinity and specificity.

Aptamers are generated by a process that combines combinatorial chemistry with in vitro evolution, known as SELEX (Systematic Evolution of Ligands by EXponential enrichment) (3-5). Following the incubation of a protein with a library of random DNA sequences, typically 10e14 molecules, target-DNA complexes are isolated. The DNA is amplified and the process is repeated until the sample is enriched with sequences that display high affinity for the molecule of interest.

Figure 1. Repurposed Personal glucose meters can measure invertase-catalyzed glucose production to quantify a target substance (6).

This novel sensor is based on the target-induced release of invertase from a functional DNA-invertase conjugate. The released invertase converts sucrose into glucose, which is detectable using the meter. The approach should be easily applicable to the detection of many other targets through the use of suitable functional-DNA partners.

Coupled with the glucose meter detection, the DNA aptamer segments are coupled to the enzyme invertase and immobilized on magnetic particles. Functionally, the user would add a sample of blood, serum or water to the functional DNA sensor to test for drugs, disease markers, contaminants or other molecules. When the target molecule binds to the functional DNA molecule, the covalently attached invertase is released into solution. The invertase then catalyzes the conversion of sucrose into glucose. After removing the magnetic particle by a magnet, the glucose level of the sample rises in proportion to the amount of invertase released, so the user then can employ a glucose meter to quantify the target molecule in the original sample (2).

Next, the researchers plan to further simplify their method, which now requires users to first apply the sample to the functional DNA sensor and then to the glucose meter. They are working on integrating the procedures into one step to make it even simpler.

References
1. Yu Xiang, Yi Lu. Using personal glucose meters and functional DNA sensors to quantify a variety of analytical targets. Nature Chemistry, 2011; DOI: 10.1038/nchem.1092
2. http://news.illinois.edu/news/11/0725glucose_meter_YiLu.html
3. Tuerk, C. & Gold, L. (1990) Science 249, 505-510
4. Musheev, M.U., Krylov, S.N., Selection of aptamers by systematic evolution of ligands by exponential enrichment: Addressing the polymerase chain issue. Analytica Chimica Acta. (2006); 564: 91-96.
5. Murphy M.B., Fuller, S.T., Richardson, P.M., Doyle, S.A. An improved method for the in vitro evolution of aptamers and applications in protein detection and purification. Nucleic Acids Res. (2003); 31(18): e110.
6. Chemical & Engineering News (ISSN 0009-2347) July, 2011 89 (30) p. 9

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