Density functional theory-assisted electrochemical sensing of caffeic acid using an iron(ii) complex of diethyl thiophene-2,5-dicarboxylate-modified carbon paste electrode

Abstract

In this work, density functional theory calculations along with the electrochemical technique were employed to design and evaluate an efficient sensing platform for detecting caffeic acid (CA). The role of electronic interactions was examined with an iron complex of diethyl thiophene-2,5-dicarboxylate-modified carbon paste electrode (Fe-TDC/MCPE). DFT calculations revealed that Fe-TDC/MCPE possesses a remarkable adsorption energy of 87.86 kcal mol⁻¹ on the carbon surface to enable efficient charge transfer processes with a maximum at Fe metal sites. On the other hand, CA had weak electronic interactions and adsorption on pristine surfaces, which were determined to be 18.31 kcal mol⁻¹. However, the Fe-TDC/MCPE sensing interface enhanced the adsorption energy of 24.27 kcal mol⁻¹ due to strong polarisation and Fe–O coordination bonds. The theoretical results were validated experimentally using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Fe-TDC/MCPE demonstrated substantially higher electrochemical response compared to the bare carbon paste electrode. The sensitivity of the sensor with the use of a diffusion-controlled mechanism had an LOD of 0.12 µM and a linear detection range of 30–120 µM. In addition to this, the developed sensor interface showed excellent stability and repeatability; therefore, CA in coffee decoction could be detected easily. This work demonstrates the value of DFT-guided electrode design for improving electroanalytical performance.