Microfluidic Diamond Biosensor Using NV Centre Charge State Detection

In this work we develop DNA sensors that are based on charge switching in colour centres in diamond. The presented method allows the combination of luminescence sensor and electrochemical sensor working on the principle of electrochemical impedance spectroscopy (EIS). The sensor employs specifically designed diamond structures grown by the means of chemical Vapour deposition (CVD). This diamond structure consists of highly boron doped diamond electrode on which an intrinsic diamond layer is deposited. This intrinsic layer is about 15 nm thick and it contains NV colour centres. The device is then embedded in polydimethylsiloxane (PDMS) microfluidic flow cell and covered by a transparent indium tin oxide (ITO) coated electrode. The switching of the NV centre charge state as a response, on diamond surface termination, is crucial tool for the sensitive charged molecules sensing. First we demonstrated high sensitivity of the near surface NV centres on a diamond biosensor surface charge termination. The measured data are supported by band bending modelling. Negative O- terminated surface results in a preferable NV centre charge state of NV⁰ or NV⁻, whereas positive H^- terminated surface leads to mostly non-PL NV⁺ charge state. By this principle any charged molecule, such as polymer on DNA, can be detected by a customized surface functionalization. Functionality of the microfluidic diamond device is also verified by the EIS.