# Modeling of Integrated Nanoneedle-Microfluidic System for Single Cell Temperature Measurement
## 3 Results and Discussion  
The analysis covered the design, characterizations, intracellular temperature detection and nanoneedle-microfluidic channel integration. Figure 8 illustrates the simulation results of the first stage of the designing process, covering mainly the nanoneedle design. The gap was the first factor considered in the analysis, as it is evident in Figure 8a,b. The current density shown by the color bar did not flow to the tip of nanoneedle (where the detection would happen after penetration) when the gap was only at the electrodes. As the gap increased towards the tip, the current density distribution was more noticeable within the nanoneedle. Figure 6: Backward velocity resulting from the electrode height. Figure 7: **(a)** Flow rate optimization simulation setup; **(b)** Height manipulation for simulation of flow rate optimization. However, the current density did not achieve uniformity, which would affect the accuracy of the measurement. This was solved by manipulating the cross-sectional area shape from being circular to a square (Figure 8c,d). The final selected design (Figure 8e) had an even current density distribution throughout the sensor, a gap of 10.8 \(\upmu\)m and a square cross-sectional area. After the cross-sectional area shape was decided, the size was analyzed by viewing the effect of the penetration of different nanoneedle sizes (90, 160, 250, 360, 490 nm\({}^{2}\)) into a yeast cell (Figure 9a-e). As can be seen, all the nanoneedle sizes could penetrate the cell with the same applied force without causing any immediate bursting. However, the damage (scale of 0 in blue color and 1 in red color) of the inner part of the cell wall (marked in red circles) increased as the cross-sectional area of the nanoneedle increased. This can be explained by the increased pressure on the cell when a larger surface is pressing against it. From the Figure 9a, the damage caused by the 90 nm\({}^{2}\) cross-sectional area was the most reasonable as it did not cause any tearing of the inner cell wall. Thus, the final design was chosen with a gap of 10.8 \(\upmu\)m and a 90 nm\({}^{2}\) square shaped cross-sectional area. Figure 8: Diagram showing the results of the nanoneedle design highlighting the shape and the gap studied. (**a,b**) The current distribution with the sensor due to the gap effect manipulation; (**c,d**) The cross-sectional shape effect on the current distribution; (**e**) The current density distribution due to a gap of 10.8 \(\upmu\)m and a square cross-sectional area. Figure 9: The penetration effect of the different nanoneedle sizes (cross-sectional areas) of (**a**) 90 nm\({}^{2}\); (**b**) 160 nm\({}^{2}\); (**c**) 250 nm\({}^{2}\); (**d**) 360 nm\({}^{2}\); and (**e**) 490 nm\({}^{2}\) on the single cell. The red circles shows the damage of the inner part of the cell wall. The second stage of the designing was the characterization of the nanoneedle. Thermal/electric characterization was performed in order to characterize the nanoneedle response to temperature and validate whether it follows the concept of the resistance temperature detectors that the design was based on. Figure 10a,b present the simulation results of the current density of the nanoneedle defined at 293.15 K (room temperature) and 333.15 K. It was observed from the results that the intensity of current density decreased as the temperature increased. The behavior was the same as the resistance temperature detector's (RTD) response to temperature, which confirms the concept. Mechanical characterization of the nanoneedle was done to characterize the needle performance under the effect of external forces. When an external force was applied, pressure was clearly observed at the nanoneedle tip, which indicated the location prone to damage (Figure 11a). Furthermore, displacement of the nanoneedle tip study was done to determine the effects of the forces applied on the nanoneedle, which will cause it to start to bend (Figure 11b).