Generation and accumulation of charge in a flow system for detecting protein markers of diseases

Abstract

Water is the main component of the human body, which determines hemodynamics. Electrokinetic properties of moving water provide generation of a charge. This work focuses on time dependence of charge generation and accumulation in water passing through a flow-based system. It was shown that under certain conditions, the time dependence of charge accumulation was nonlinear; the recorded value changed in a stepwise manner (effect of electrodynamic barrier for the charge run-off, EBCRO). Emergence of these stepwise changes depends on the distance between the tip of the input pipe and the ground electrode inserted in this pipe. This effect was observed at a distance of l~10 cm and more. The discovered effect should be taken into account in developing flow-based, highly sensitive analytic systems, such as nanowire, atomic-force microscope (AFM) based, and other systems designed to improve early detection of pathological processes. Aim: To monitor electric charge generation and accumulation in moving water as a main component of the body and a vehicle of solutions used in analytical systems. Methods: The process of charge generation and accumulation was studied in water during its motion in a flow system. In the experiments, the flow-based part of an AFM-based fishing system was used since this system provides a high concentration sensitivity in detecting protein markers of diseases. Electric charge values were measured using an electrometer incorporated in the flow system that feeds samples into the AFM-fishing system. The major elements of the sample feeding system included a peristaltic pump, a pipe for sample delivery from a tapered tip, and a measuring cell connected to an electrometer developed at the Institute of Biomedical Chemistry. During the measurements, deionized water was continuously pumped into the cell. The flow rate (~15 mL/s) was selected so that drops form on the tip nozzle (inner diameter, 0.4 mm) of the inlet pipe. To maintain a constant potential in the stock solution, a ground electrode was inserted into the inlet pipe. The distance between the electrode inside the pipe and the tip varied and was 5, 10, or 15 cm. Experiments were conducted at t = 35°C and 49% humidity. Results. In the fishing system, after the deionized water has passed through the feeding pipe of this system through the tip, an electric charge is generated and recorded when the water enters the measuring cell. According to results of measurements charge accumulation is observed. At a constant rate of water supply, accumulation of the charge in the measuring cell can be either linear or stepwise. Emergence of this effect depends on the distance between the tip and the ground electrode in the input pipe: the effect was detected at a distance of l~10 cm and more. The discovered stepwise dependence was named the effect of electrodynamic barrier for the charge run-off (EBCRO). Conclusion. In the process of water motion during its continuous pumping through the flow-based system, a charge accumulates in the measuring cell; this charge is delivered with the water from the tip of the feeding pipe. A linear-stepwise dependence of charge accumulation in the cell (EBCRO effect) is determined. Magnitude of the stepwise change in this charge (approximately several nC) depends on the distance between the tip and the ground electrode inserted into the inlet pipe. This effect should be taken into account in both basic research focusing on physicochemical properties of water and applied research focusing on development of the models describing hemodynamics in the body. In addition, the obtained results might be used in developing highly sensitive diagnostic systems, such as nanowire, AFM-based, and other fishing systems to enhance early detection of pathological process.