Neutralizer assay improves biological sensing
DNA probes designed to detect specific biomolecules coat the tips of gold electrodes, like these ones embedded in a silicon chip. A new assay developed at the University of Toronto pairs each DNA probe with a neutralizer made of peptide nucleic acid (PNA). The technique increases the sensitivity of the probes, and allows for a single chip that can detect hundreds of analytes at once, from adenosine triphosphate (ATP) to cocaine.
By Tyler Irving
Posted September 2012
Imagine a portable electronic device that could analyse blood for up to 180 different components at once: sequences of DNA and RNA, proteins and even small molecules like adenosine triphosphate (ATP). It sounds like science fiction, but a discovery at the University of Toronto is bringing such a device closer to reality.
Electrostatic sensor systems use probes composed of short DNA sequences attached to an electrode. Since DNA is negatively charged, binding of the probe with a complementary strand results in a higher magnitude of charge. This change triggers the reduction of reporter ions electrostatically associated with the DNA strands, creating an electric current that can be measured. However, there are drawbacks. “Traditional assays can only detect molecules with significant negative charges like DNA and RNA,” says Jagotamoy Das, who works under the supervision of Shana Kelley in the Department of Pharmaceutical Sciences at U of T. Additionally, because the change in charge is often small compared with the background, such sensors are not sensitive enough to detect analytes at low — but still physiologically relevant — concentrations. The new assay developed by Das and his colleagues relies on a neutralizer made of peptide nucleic acid (PNA). The charge of this synthetic DNA analogue can be tuned by adding cationic amino acids to the end, while its affinity for the DNA probe can be controlled by introducing mismatches to its sequence. A properly designed PNA sequence will neutralize the probe but will be dislodged when the molecule of interest binds to the probe instead. This results in a bigger charge difference than with DNA alone and allows for the detection of neutral molecules, even at low concentrations.
In a paper published in Nature Chemistry, the team shows that the new system works effectively with probes designed for DNA, RNA, ATP and even cocaine. Best of all, the electrodes can be miniaturized and embedded on chips, allowing for fast and portable systems capable of detecting hundreds of analytes simultaneously. A spin-off company founded by Kelley, Xagenic Inc., is working toward developing commercial systems. The technology could have applications in medicine, forensics and many other fields.
Photo Credit: Alya Bhimji
Write to the editor at email@example.com