Here, a highly sensitive electrochemical sensor for detection
of
tryptophan (Trp) using a nitrogen defect graphitic carbon nitride-modified
glassy carbon electrode (ND-CN/GCE) was introduced. ND-CN/GCE showed
a higher oxidation current for Trp than the graphitic carbon nitride-modified
glassy carbon electrode (
g
-CN/GCE) and bare glassy
carbon electrode (BGCE). The synthesized nitrogen defect-rich graphitic
carbon nitride (ND-CN) was characterized using X-ray photoelectron
spectroscopy, X-ray diffraction spectroscopy, Fourier-transform infrared
spectroscopy, scanning electron microscopy, and transmission electron
microscopy. Electrochemical impedance spectroscopy and cyclic voltammetry
were used to further analyze the electrochemical properties of BGCE,
g
-CN/GCE, and ND-CN/GCE. The oxidation of Trp at ND-CN/GCE
is a diffusion-controlled process at pH 3.0. It was calculated that
the transfer coefficient, rate constant, and diffusion coefficient
of Trp were 0.53, 2.24 × 10
3
M
–1
s
–1
, and 8.3 × 10
–3
cm
2
s
–1
, respectively, at ND-CN/GCE. Trp was
detected using square wave voltammetry, which had a linear range from
0.01 to 40 μM at pH 3.0 and a limit of detection of about 0.0034
μM (3σ/
m
). Analyzing the presence of
Trp in a milk and multivitamin tablet sample with a percentage recovery
in the range of 97.0–108% satisfactorily demonstrated the practical
usability of the electrochemical sensor. The ND-CN/GCE additionally
displays good repeatability and reproducibility and satisfactory selectivity.