We propose a label-free biosensor concept based on the charge state manipulation of nitrogen-vacancy (NV) quantum color centers in diamond, combined with an electrochemical microfluidic flow cell sensor, constructed on boron-doped diamond. This device can be set at a defined electrochemical potential, locking onto the particular chemical reaction, whilst the NV center provides the sensing function. The NV charge state occupation is initially prepared by applying a bias voltage on a gate electrode and then subsequently altered by exposure to detected charged molecules. We demonstrate the functionality of the device by performing label-free optical detection of DNA molecules. In this experiment, a monolayer of strongly cationic charged polymer polyethylenimine is used to shift the charge state of near surface NV centers from negatively charged NV- to neutral NV0 or dark positively charged NV+. Immobilization of negatively charged DNA molecules on the surface of the sensor restores the NV centers charge state back to the negatively charged NV-, which is detected using confocal photoluminescence microscopy. Biochemical reactions in the microfluidic channel are characterized by electrochemical impedance spectroscopy. The use of the developed electrochemical device can also be extended to nuclear magnetic resonance spin sensing.

Department of Biomedical Technology Faculty of Biomedical Engineering Czech Technical University Prague Sítna sq 3105 27201 Kladno Czech Republic

FZU Institute of Physics of the Czech Academy of Sciences Na Slovance 2 182 21 Prague 8 Czech Republic

IMOMEC division of MEC Wetenschapspark 1 B 3590 Diepenbeek Belgium

Institute for Materials Research Material Physics Division University of Hasselt Wetenschapspark 1 B 3590 Diepenbeek Belgium

Institute of Organic Chemistry and Biochemistry of the Czech Academy of Sciences 166 10 Prague Czechia

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Room-temperature control and electrical readout of individual nitrogen-vacancy nuclear spins