Poly-methionine/graphitic carbon nitride modified screen-printed electrodes: A metal-free, bio-interface for tryptophan sensing

Tryptophan (TRP) is an essential amino acid needed for the growth and proper functioning of the human body. A balanced intake of TRP-rich food products is essential to meet the daily requirements. As both low and high levels of TRP are associated with clinical disorders, an optimum amount of TRP intake is critical. Hence, developing a method to efficiently detect TRP in food and nutritional supplements is essential. Accordingly, this study reports the electrochemical detection of TRP using poly-methionine/graphitic carbon nitride modified screen-printed electrode (gCN.Meth|SPE). To our knowledge, this study is the first attempt to decipher the electrodeposition of gCN.Meth on a conducting substrate through a systematic analysis of the electro-functionalized gCN.Meth surface using XRD, FT-IR, HR-SEM, EDX, and AFM. The synergistic benefits of both the gCN and conducting poly(methionine) resulted in augmented electrochemical performance exhibiting a pronounced TRP oxidation peak in both cyclic voltammetry (CV) and square wave voltammetry (SWV). The improved electrochemical response can be ascribed to the specific interactions between the TRP and gCN through pi- pi interactions and hydrogen bonding and electrostatic interaction between TRP and methionine. This facilitated interaction resulted in the electro-catalytic oxidation of TRP with a negative potential shift of 0.126 V and a 16.6-fold increase in the current response compared to unmodified SPE. The gCN.Meth|SPE exhibited a 25.12 times higher sensitivity compared to bare SPE, with a linear response in the concentration ranges of 1.0-300.0 mu M and a low detection limit of 29.9 nM. The interference study further indicated that gCN.Meth-modified SPEs is highly effective for the precise and reliable detection of tryptophan in real samples.