Rapid Quantitative Detection of Melatonin By Electrochemical Sensor Based on Carbon Nanofibers with Embedding FeCo Alloy Nanoparticles
Authors: Duan Dingding , Ding Yaping , Li Li , Ma Guohong 
Published: May 2020

Introduction
Melatonin (MT), as an efferent hormonal signal of the circadian clock, is an indoleamine neuroendocrine hormone synthesized and secreted principally by the pineal gland at night under normal environmental conditions [1]. Melatonin exerts various physiological functions by binding to melatonin receptors, including regulating day and night rhythms, inhibiting tumor development, and regulating immunity [2].
In present work, we prepared an electrochemical sensor that can quickly detect melatonin and further studied the its electrooxidation behavior and reaction mechanism. This sensor is based on carbon nanofibers with FeCo bimetallic alloy dispersed and embedded in (FeCo@CNFs) by electrospinning and a thermal treatment process. Through the analysis and comparison of various characterization methods, it can be proved that the combination of bimetal and CNF can improve the electrochemical properties of the composites. We also analyzed the electrochemical behavior of melatonin at the FeCo@CNFs electrode. Compared with previous reports on melatonin detection, this sensor has a lower detection limit and a wider detection range.
Characterization of FeCo@CNFs
In Fig. 1A, the SEM image FeCo@CNFs have a homogeneous fiber structure with a diameter of approximately 100~200 nm. And it can be seen from its HRTEM images that the FeCo@CNFs are porous structure and decorated with nanoparticles (Fig. 1B). Moreover, it can be seen from Fig. 1C that the obvious lattice fringes are 0.19 nm and 0.33 nm, corresponding to (110) crystalline facet of FeCo alloy and (002) crystalline facet of graphitized carbon layer respectively, indicating that FeCo is wrapped by graphitized carbon fibers. It is well known that transition metals such as Fe and Co can not only promote the transformation of adjacent amorphous carbon to graphitized carbon, but also change the electron interaction between host and guest, reduce the local work function of carbon layer and promote the electrocatalytic reaction[3].
Results and Conclusions
Fig. 1D shows the I-T curve of detection of MT in the stirring PB solution (pH 5.0) at FeCo@CNFs/GCE with the concentration ranging from 0.08μM to 400μM. It can be seen that the current response increases linearly with the increase of MT. The current response increased linearly with successive addition of MT and the linear relationship is Ip (μA) = 0.537 + 0.038C (μM) (R = 0.997) (Fig. 1E). The detection limit is estimated to be 2.7×10-9 mol L-1 (S/N=3).
References
[1] B. Claustrat, J. Brun, G. Chazot, The basic physiology and pathophysiology of melatonin, Sleep medicine reviews, 9 (2005) 11-24.
[2] A. Lerchl, S. Schlatt, Influence of Photoperiod on Pineal Melatonin Synthesis, Fur Color, Body Weight, and Reproductive Function in the Female Djungarian Hamster, Phodopus sungorus, Neuroendocrinology, 57 (1993) 359-364.
[3] X. Zou, X. Huang, A. Goswami, R. Silva, B.R. Sathe, E. Mikmekova, T. Asefa, Cobalt-embedded nitrogen-rich carbon nanotubes efficiently catalyze hydrogen evolution reaction at all pH values, Angewandte Chemie, 53 (2014) 4372-4376.

Figure 1