formulations to supplement the current typical diet which is deficient in vegetables. Improper metabolization of Trp may lead to a waste product in the brain or cause hallucination and delusion [3]. Hence, the sensitive and selective determination of Trp is highly essential. Several methods have been reported for the determination of Trp in biological and pharmaceutical samples such as high-performance liquid chromatography [4], spectrophotometry [5], fluorimetry [6] and capillary electrophoresis [7]. Although these methods are successfully used to determine Trp, they have several drawbacks including long analysis time, poor reproducibility, pre-cleaning of the matrix, pre-treatment of the sample and low detection limits. On the other hand, electrochemical method of determination is less expensive, more convenient, easy in handling, as well as with high sensitivity and selectivity. Several studies have been conducted in this area [8][9][10][11][12][13][14]. The results of such studies have revealed that the voltammetric response of the electrochemical process is not satisfactory due to slow heterogeneous electron transfer on the electrode surface and consequent high overpotentials of the electrochemical oxidation [15,16]. Therefore, one of the main challenges in this field is to select the suitable materials for the electrode surface modification that can increase the direct electron transfer between the electrode surface and redox molecule.Among different nanomaterials, carbon nanomaterials have attracted great interest in electroanalytical investigations because of their chemical and mechanical properties, wide potential window, and suitability for different types of analysis [17,18]. Given these unique properties, carbon nanomaterials such as carbon nanotubes (CNTs) [19][20][21], fullerene-C 60 [22], carbon nanofibers (CNFs) [23][24][25], and CNDs [26] have been widely used for modification of the electrode's surface. As new and interesting members of carbon family, CNDs have attracted great attention due to their Abstract A modified glassy carbon electrode (GCE) was prepared by incorporating carbon nanodots (CNDs) and chitosan (CS) for the determination of tryptophan (Trp). In this method, the electrochemical response of Trp was examined and the irreversible electrochemical oxidation and two electrons involved in the process of Trp were demonstrated. Because of good conductivity, large surface area, and excellent catalytic activity of CNDs, the CS and CNDs hybrid film extremely increased the electrochemical response of Trp, offering a highly sensitive electrochemical sensor for determination of Trp. The sensor showed a low detection limit of 90 nM and high sensitivity of 4 nA µM −1 . The high stability and simplicity of prepared nanohybrid combined with excellent sensitivity and selectivity of the sensor may bring novel and interesting applications for different diagnoses. As a way forward, the proposed methodology is promised for fabrication of the other effective and sensitive sensors
