Motile bacteria respond to changing chemical environment by moving towards or away from a particular location. Bacterial migration under chemical gradient is one of the most studied areas in biomedical field. In this work we looked into how bacterial cells respond to sudden change in the microfluidic chemical environment. E.coli DH5α cells were subjected to an attractant gradient (0.1 mM sorbitol - attractant to E.coli cells) and after 120 min the same cells were exposed to an inhibitor (0.1 mM NiSO₄) gradient in the same microfluidic device. Our studies revealed that when the E.coli DH5α cells were exposed to 0.1 mM sorbitol, they showed faster chemotaxis towards the attractant (0.1 mM sorbitol) and achieved steady state by 60 min. When we replaced 0.1 mM sorbitol with 0.1 mM NiSO₄ in the device we found that that the E.coli DH5α cells started responding to change in chemical environment within 10 min and achieved steady state at the end of 60 min. This shows that the bacterial cells respond to change in local chemical environment is within few minutes.