To reduce the cost of patient care, a novel type of microprobe that measures the levels of drugs, hormones, or proteins in 1 drop sample of a biologic fluid has been designed. With this device physicians can diagnose various diseases, monitor progress of a therapy, and follow patient compliance with a drug regimen in their office without having to send out samples for analysis. This speeds diagnosis while reducing costs of medical care.
The microprobe on which the device is based is part of a circuit consisting of an anode, cathode, and device (ammeter) that measures the flow of electrons between the two (Fig. 2). The microprobe component of the device consists of a gold-coated wire (anode) coated with a hydrophobic layer that renders it non-conductive when placed in an aqueous sample. Antibodies containing a conductive channel penetrate the non-conductive surface and bind to the gold surface. Normally, electrons from the cathode flow through the solution and then the channel in the antibody to reach the anode, completing the circuit. When an antigen of interest is present in the sample, it binds to the surface of the antibody, blocks the conductive channel, and stops the flow of electrons between the cathode and anode. The reduction in current is proportional to the amount of material (antigen) present in the sample (Fig. 2). The probe can measure the amount of any material that an antibody can be raised against.
The antibodies containing the conductive channel that coat the probe and provide a path for electron flow are heavy-chain variable domains (VHH) described in last year’s competition that won mention as one of the top 100 entrants. These 110-amino acid VHH are chemically synthesized and contain special aromatic amino acids in the middle b-sheet of the antibody (D and F segments) that improve conductivity of electrons through the body of the protein. In addition, a special amino acid linked to the C-terminus of the antibody selectively joins the conducting antibody to the gold wire that serves as an anode.