Hybrid Optoelectrochemical Sensor for Superselective Detection of 2,4,6-Trinitrotoluene Based on Electrochemical Reduced Meisenheimer Complex.

2,4,6-Trinitrotoluene (TNT) is known as one of the most used explosives, and its detection is significant in public security, human health, and environmental protection. The fabrication of absorbance based optical sensors for TNT is a serious challenge due to poor selectivity and sensitivity. We reported the design and fabrication of a superselective hybrid optoelectrochemical sensor based on the electrochemical reduction of Meisenheimer complex in a deep eutectic solvent (DES) modified with n-butylamine (nBA) for determination of TNT. The hybrid optoelectrochemical sensor (HOPES) that placed in DES modified with nBA and also an optical sensor (OPS) were fabricated. The electrochemical reduction of Meisenheimer complex occurred at HOPES when the potential was applied and consequently the sensing performance (sensitivity and selectivity) was dramatically enhanced compared to OPS. The both OPS and HOPES responded linearly to TNT with detection limits of 310 and 8 nmol L-1 , respectively. The selectivity observed for the HOPES toward TNT compared to the other interferences was enhanced by a factor of 103 -104 , thus we can use the term "superselectivity" for HOPES. The mechanism of HOPES response was proved by optoelectrochemical and electrochemical impedance spectroscopy (EIS) techniques. The field emission scanning electron microscope (FESEM) was employed for the characterization of electrodeposited Meisenheimer layer. Finally, we presented a proposed model for the sensing mechanism of OPS and HOPES based on TNT complexation in the absence and presence of electric potential, respectively.