Bimodal Electrochemical and Photoelectrochemical Detection of Enantiomeric Tryptophan through MWCNT/Oligo-Thiophene Modified Electrodes

The discrimination between enantiomers—molecules that are non-superimposable mirror images—represents a major challenge in electroanalytical chemistry [1]. Different strategies have been proposed for chiral electrochemical sensing, including the incorporation of chiral ionophores into ion-selective membranes, the use of molecularly imprinted polymers (MIPs) capable of selective enantiomer recognition, and the exploitation of chirality generated during the electrochemical deposition of conducting polymers. Among the most effective approaches is the use of “inherently chiral” molecules, whose chirality is directly embedded in their electronic structure, enabling them to act simultaneously as electrode modifiers and chiral selectors. In this context, the oligo-2,2′-bis(2,2′-bithiophen-5-yl)-3,3′-bi-1-benzothiophene monomer (BT2T4) is one of the most extensively investigated systems. Previous studies demonstrated that oligo-thiophene films electrogenerated on electrode surfaces can selectively discriminate chiral analytes, producing marked differences in peak potentials due to diastereomeric interactions occurring at the inherently chiral interface during electron transfer [2]. Moreover, these oligomers display semiconducting and photoactive properties, generating photocurrents under suitable irradiation conditions. Herein, we present for the first time the fabrication of a hybrid carbon screen-printed electrode (C-SPE) modified with a drop-cast layer of multi-walled carbon nanotubes (MWCNTs) and subsequently coated with a conducting photoactive oligo-thiophene film obtained by anodic electropolymerization in ionic liquids. The resulting platform was characterized and investigated for the detection of Tryptophan (Trp). The combination of the excellent conductivity and fast electron-transfer kinetics of MWCNTs with the chiral and photoresponsive behavior of the oligo-thiophene layer enabled the development of a bimodal sensing platform operating in both electrochemical (EC) and photoelectrochemical (PEC) modes. The integration of multiple transduction mechanisms improves analytical reliability and selectivity by providing complementary sensing information [3], ultimately enhancing Trp detection performance. References [1] S. Arnaboldi, Current Opinion in Electrochemistry, 2018, 8, 60. [2] M. Donnici, Molecules, 2020, 25. [3] W. Aidli, Current Opinion in Electrochemistry, 2025, 50, 101655.