Current diagnostic techniques for the detection of protein-type disease markers require expensive facilities and specialized laboratory personnel. Therefore, new approaches that allow for quick, easy and straightforward detection are being developed. The main goal of this research line is to develop a point-of-care biosensor that allows protein detection within less than 15 minutes in physiological –and pathophysiological concentration ranges (10 – 100 nM) in complex matrices such as blood serum. The proof of principle protein used for this research is C-Reactive Protein (CRP). CRP is an indicator for chronicle inflammations and cardiovascular diseases, and plays a major role in diagnosing of general healthcare.
The central part of the protein sensor is a molecular receptor layer based on immunoglobulins (IgG), which are naturally occurring antibodies for proteins. These receptors are immobilized on boron-doped nanocrystalline diamond electrodes, which serve as a transducer and the readout is based on Electrochemical Impedance Spectroscopy (EIS). EIS allows for label-free, fast, and reliable data acquisition and can be easily integrated in compact, user friendly devices. The molecular recognition of CRP by the receptor layer alters the physical properties of the system and results in an increase of the impedance, which can be understood in terms of a decreasing surface capacity. Real time sensitivity experiments in buffer solutions showed a clear discrimination between 1 µM, 100 nM, and 10 nM of CRP within 10 minutes. Selectivity tests with the serum protein plasminogen turned out to be negative. First measurements on human blood serum indicate that the detection limit is sufficiently low to distinguish between samples from healthy test persons and intentionally CRP-spiked serum.