Interfacial superassembly of flower-like NiMn-LDH@poly-l-lysine composites for selective electrochemical sensing of tryptophan

Development of sensitive, selective, and facile electrochemical analytical approaches to monitor tryptophan in different samples is of high significance. For such approaches, efficient electrodes play the key role. Herein, a NiMn-layered double hydroxide (LDH)@poly-l-lysine (PLL) composite has been prepared through in-situ electro-polymerization and further utilized to monitor tryptophan in medicament and biological systems. The as-synthesized NiMn-LDH@PLL composite is highly stable and features a flower-like morphology. It is found that the electron transfer rate of NiMn-LDH@PLL is greatly improved due to the introduction of PLL. The existing Lewis acid—base interaction between LDH and PLL contributes to the increase of unsaturated metal sites and endows this heterojunction composite with high electrocatalytic activity. Especially, the NiMn-LDH (2:1)@PLL composite displays much improved electrochemical response toward tryptophan sensing. This is due to reasonable balance between the outstanding electrocatalytic ability of nickel and the conductivity improvement caused by manganese species. On the other hand, the coordination promotion between NiMn-LDH and PLL is also conducive to improve the sensitivity of electrochemical response. The fabricated sensor exhibits wide linear response in the concentration ranges of 0.1–40 μM and 40–130 μM for tryptophan detection, along with a low detection limit of 52.7 nM. It further displays a high anti-interference ability for tryptophan monitoring even in the presence of other coexistent amino acids and small-sized biological molecules. This study provides a new way to employ LDHs as brilliant sensing platform to ensemble electrochemical sensors for the monitoring of biomolecules.