Porous Transducers and Hybrid Recognition for Bulky Nitrosamine Impurities: Toward 3D–MXene–Aptamer Detection of Tricyclic NDSRIs

Pharmaceutical quality control faces an emerging problem with Tricyclic nitrosamine drug substance-related impurities (NDSRIs), for example, N-nitroso clozapine. The impurities preserve the compl ete structure of their parent active pharmaceutical ingredients, which consist of bulky lipophilic molecules with restricted conformational flexibility. The retention of bulky lipophilic structures from the parent active pharmaceutical ingredients in these impurities results in their complete overlap with other substances, which causes matrix ion suppression and weak ionization and unstable mass-spectrometric responses. The LC–MS/MS method functions as the official standard but its workflow requires excessive solvent use and produces complicated equipment systems, which prevent its use for routine ultra-trace monitoring. This narrative review analyzes hybrid electrochemical sensing technology to determine if it can solve the current problem by using tricyclic NDSRIs steric complexity as a functional benefit for detection purposes. The research combines data from nitrosamine detection with studies on porous 3D-printed electrodes, MXene electrochemistry, molecularly imprinted polymers, aptamer engineering and the computational systematic evolution of ligands by exponential enrichment (SELEX), molecularly imprinted polymer (MIP) and signal-off aptasensing. This review presents that planar electrodes create an unfavorable structure for bulky tricyclic analytes because they lead to surface obstruction and increased resistance during charge transfer. This review demonstrates that gyroid and TPMS-type porous scaffolds with a Ti3C2Tx MXene coating offer superior internal surface area, enhanced diffusion channels and accelerated electron movement. The dual MIP–aptamer system enables selective recognition by using MIP to perform shape-based target capture and specimen protection and aptamer to recognize specific molecular targets. The design process for aptamers includes E/Z nitrosamine isomer modeling, docking and molecular dynamics, and AI-based sequence selection methods, which form the core approach to targeting N-nitroso clozapine (N-CZN)-like proteins. This research outlines a new technique, which uses steric hindrance to block redox-probe entry, thus generating an electrical signal through current reduction. This review presents a fundamental operational model which supports the development of eco-friendly portable electrochemical devices to detect tricyclic NDSRIs with maximum sensitivity.