Microarrays are widely used for DNA sequencing since they are faster,simpler and cheaper than traditional methods. The readout schemes are typically optical and require sophisticated equipments and fluorescence-labeling molecules which make them expensive. Moreover, thermal cycling of PCR is required to amplify the DNA and reach the detection threshold. In this respect, electrical detection methods would be preferable, due to their predisposition to the miniaturization and compatibility with the microfabrication techniques.
Here, we demonstrate DNA sensors based on nanoelectrodes and able to detect also single hybridization events. Our electrical detection approach exploits a completely new interconnection technique which allows the cheap fabrication of large-scale arrays of nanojunctions by optical lithography of a quantum well (QW). The thickness of the QW and of the deposited metal layer control the gap size on a sub-nanometer level.
5’-SH-DNA capture probes are then immobilised on the electrodes and complementary DNA strands are conjugated to gold nanoparticles (AuNPs). After hybridization AuNPs self-assembles onto the nanoelectrodes acting as a bridge between the gap. As a consequence, hybridization events are detected as an increase in the current flowing in the nanojunction and we are able to identify also single events demonstrating the great sensitivity of our device that make unnecessary the use of PCR to amplify the DNA target. Our device joins a great sensitivity with an innovative and cheaper nanofabrication method, so it is a fundamental step towards a new generation of highly sensitive and robust low-cost nanosensors, which could be easily multiplexed at very high level. Thanks to the ability to identify single hybridization events, our approach offers also new possibilities in terms of fabrication of nanosized integrated systems and point-of-care analysis. Moreover, the proposed approach is very versatile and can be applied also to detect other biorecognition events involving different proteins, antibodies, ligands and receptors. For example, we also demonstrate as transport in proteins can be investigated at the single-molecule level using the same nanoelectrodes. |