In this report 5,10,15,20-tetrakis(4-methoxyphenyl)porphyrin (H2TMPP) has been used as electrode material for an easy and direct detection of NO in cancer cells using different electrochemical techniques. Cyclic voltammograms of H2TMPP-modified GCE in aqueous electrolyte showed oxidation peaks at 0.5 and 0.73 V and reduction peak at 0.64 V and a small peak at 0.4 V which are attributed to the redox processes of the system. The anodic and cathodic peak currents were proportional to the square root of the scan rate indicating a diffusion controlled mechanism. The H2TMPP-modified GC electrode exhibits a good stability after several circles. The fabricated electrode system was used to probe the concentration change of NO in HeLa cells using chronoamperometry. The NO sensor registered an amperometric current sensitivity of 0.0138 nA/μL with a linear correlation coefficient of 0.99571 in the presence of extracellular NO released upon activation of HeLa cells. Via confocal laser scanning microscopy, it has been demonstrated that H2TMPP could be used as a fluorescent indicator for cell imaging.