Electronic DNA Detection via Magnetic Particles Preconcentration
There are growing demands for point-of-care diagnostics, the rapid detection of biowarfare agents under realistic civil defense conditions and for field deployable methods for environmental monitoring. Thus motivated, we have recently demonstrated an electronic DNA sensing platform (E-DNA) with outstanding performance compared to most optical DNA sensors. This approach is not only sensitive, specific, and operationally convenient, but also fully electronic, reusable, and functional in various contaminant-rich samples. Nevertheless, the approach exhibits two drawbacks as currently implemented. First, while the sensitivity of the E-DNA sensor is near state-of-the-art, it remains a few orders of magnitude lower than required for direct (i.e., no polymerase-chain reaction (PCR)-based amplification) DNA or RNA detection. Second, the E-DNA sensor cannot be employed directly in whole blood, owing to the undesirable reactions betwesen the redox labels (e.g. methylene blue, ferrocene) and the iron center of hemoglobin, a major component of whole blood. While alternative redox labels can be used, most known electrochemically active labels within the restricted potential range of interest (i.e., a potential range in which the thiolated self-assembled monolayer is stable) are reactive to hemoglobin and other iron contaminants. To overcome these limitations, we are using a hybrid sensing approach that combines the current E-DNA sensor with magnetic nanoparticles (MP)-assisted DNA extraction and preconcentration (MP/E-DNA).
The Figure shows the processes involved in a typical MP/E-DNA assay:
Schematic of MP/E-DNA sensor. Step:
1: Target DNA extraction and preconcentration;
2: Magnetic separation;
3: Removal of interfering species;
4: Target DNA release;
5: Transfer of recovered target DNA for E-DNA detection;
6: DNA hybridization and quantification which is obtained by monitoring changes in electron transfer efficiency between the electrode and a redox label attached to the distal end of the bound sensor strand. The distance between the label and electrode changes upon hybridization.