An analytical pesticide assay of O-ethyl-O-4-(nitrophenyl)phenyl phosphonothioate (EPN) was carried out using the following: a carbon nanotube paste electrode, a mercury-immobilized carbon nanotube paste electrode, a glassy carbon electrode, a metal–gold electrode, and a DNA-immobilized carbon nanotube paste electrode (DPE), which is two-fold more sensitive than other sensors. The DPE was optimized using cyclic and square wave stripping voltammetry. Linear working ranges approached 5–55 mg L^–1 EPN and the nano-range of 10–210 ng L^–1 in a 0.1 mol L^–1 NH₄H₂PO₄ electrolyte solution, with a speedy analytical time of 30-s stripping. The detection limit was 2.57 ng L^–1 (7.94 × 10^–12 mol L^–1), and the precision was 0.102% relative standard deviation (n = 15) at the 10.0 mg L^–1 EPN spike. This indicates that the method is more sensitive than common voltammetric methods. This method was applied to fruit samples using patch- and needle-type electrodes, specifically on the skin tissues of an orange and an apple. Moreover, the implanted electrode was interfaced with a fish brain cell at the electrochemical workstation. Results showed that the aforementioned method can be used to conduct a pesticide assay in neuro-treated and non-treated cell systems.