Enhanced label-free DNA hybridisation detection using Open Circuit Potential measurement with gold nanoparticles

Electronic detection of DNA hybridisation is a growing field, in particular on label-free electrochemical techniques. However different levels of success have been achieved. We here report a new simple and inexpensive method to detect DNA using direct Open Circuit Potential (OCP) measurements. Monitoring of OCP for detection of biomolecules has been used previously to detect proteins [1] but its application to DNA sensing is problematic due to charge screening by the electrolyte and counterion condensation effects, which significantly reduce the amount of measurable charge. We here report on an amplification method with positively charged nanoparticles on PNA-DNA systems.

By using an ultra low input bias current instrumentation amplifier circuit, the potential difference between an electrode and a reference electrode can be measured without applying current on the electrode. Thus a true OCP measurement can be achieved. We here used uncharged PNA probes immobilised onto a gold electrode and monitor the variations of OCP upon DNA hybridisation, followed by the addition of positively charged gold nanoparticles.

An optimized ratio of PNA and mercaptohexanol self-assembled monolayer was immobilized onto a gold electrode. Upon hybridisation of target DNA, a reduction on the OCP of the system is observed due to the negative charge of the DNA. The electrode is then exposed to positively charged gold nanoparticles, which electrostatically bind to the target DNA, making the surface positively charged. This change of charge on the surface made a significant amplification of the OCP signal towards more positive values. The sensor clearly distinguished the significant change between complementary target and control electrodes in a dual-channel measurement.

We demonstrated a promising cost effective biosensor with simple instrumentation and read out system. Multiplexing of the system can easily be achieved, providing a simple electronic DNA microarray platform.