## 3 Results
### The Influence of Non-Conductive Materials on Charge Generation in Water Flow
#### 3.2.1 The Influence of Polypropylene Tube on Charge Generation in the Flow-based System
As seen from these data, the increase in the value of charge accumulated in the cell in 7 min in the presence of the water-filled polypropylene tube, was 33%. The charge on a water-filled polypropylene tube was measured. The measured charge of a water-filled polypropylene tube was \(-6\) nC. Figure 7: The effect of the presence of an empty polypropylene tube on the charge generation in water. Averaged \(\Delta q(t)\) dependencies obtained upon pumping of water through the injector. Experimental conditions: (**1**) without polypropylene; (**2**) with polypropylene tube; (**3**) polypropylene tube filled with water. The distance between the injector nozzle and the polypropylene tube is \(l\) = 10 mm. T = 35 \({}^{\circ}\)C. The data of one and the same experimental series obtained using one and the same tube-pipe-tip set (see the Materials and Methods section) are presented. _Polyppropylene Tube Filled with Protein Solution or Ethyl Alcohol_  
In the presence of a polypropylene tube filled with protein solution or ethyl alcohol and placed at a distance \(l=1\) cm from the injector nozzle, the obtained results were similar to those obtained for a water-filled tube. The data obtained are listed in Table 1 (see Discussion section). The measured value of charge of a polypropylene tube filled with protein solution and ethyl alcohol were \(-6\) nC and \(-5\) nC, respectively. The Influence of a Highly Dilute Protein on the Stimulation of Charge Generation in Flow-Based Biosensors  
Several sets of experiments were carried out. In these experiments, we have found that, along with linear ones, linear-stepwise \(\Delta q\)_(t)_ dependencies can also be observed both in the absence and in the presence of protein. In Figures 9 and 10, characteristic \(\Delta q\)_(t)_ dependencies for both these variants--linear-stepwise and linear dependencies--are presented. For the first variant, characteristic linear-stepwise dependencies are presented in Figure 9.  
Figure 9 (with an inset) displays typical time dependencies of charge accumulation in the measuring cell obtained upon flow of water in the presence of BSA protein at \(10^{-15}\) M concentration (at which highly sensitive biosensors operate) and in the absence of the protein. The data presented in the inset indicate that linear-stepwise dependencies are observed. Such a stepwise change (by 1 nC, i.e., a \(\sim\)30% increase) is observed, particularly, on one of the curves (obtained in the absence of the protein) at the time point \(t=2.5\) min. In the presence of the protein, such stepwise changes are observed on all curves (for instance, at \(t=3.5\) min). That is, the stepwise changes are observed both in the absence and in the presence of protein. The main graph in Figure 9 demonstrates that, after averaging, an increasing time dependence of charge accumulation was observed. Figure 8: The effect of the presence of a water-filled polypropylene tube on the charge generation in water. Averaged \(\Delta q\)_(t)_ dependencies obtained upon pumping of water through the injector. Experimental conditions: (**1**) without the water-filled polypropylene tube; (**2**) with the water-filled polypropylene tube. T = 35 \({}^{\circ}\)C. The distance between the injector nozzle and the polypropylene tube is \(l=10\) mm. The data of one and the same experimental series obtained using one and the same tube-pipe-tip set (see the Materials and Methods section) are presented. Figure 10: The effect of the presence of BSA protein on the charge generation in water. Averaged \(\Delta q(t)\) dependencies obtained upon flow of water through the injector nozzle in the absence and in the presence of \(10^{-15}\) M BSA. Main graph presents averaged \(\Delta q(t)\) dependencies obtained in experiments without BSA (**1**) and with BSA (**2**). Inset displays typical \(\Delta q(t)\) dependencies obtained in a series of experiments upon pumping of water through the injector. Experimental conditions: (**1**) without BSA (”water”); (**2**) with BSA (”BSA”).