Abstract
A graphene sample (EGr) was prepared by electrochemical exfoliation of graphite rods in solution containing 0.05 M (NH4)2SO4 + 0.1 M H3BO3 + 0.05 M NaCl. The exfoliation was performed by applying a constant voltage (12 V) between the graphite rods, while the temperature was kept constant (18 °C) with a temperature-controlled cryostat. The structural investigation of the graphene sample, performed by X-ray powder diffraction (XRD), revealed that the sample consists of a mixture of few-layer (69%), multi-layer graphene (14%) and graphene oxide (17%). In addition, XPS analysis proved that the sample was triple-doped with heteroatoms such as nitrogen (1.7 at%), sulfur (2.5 at%), and boron (3 at%). The sample was deposited onto the surface of a clean, glassy carbon electrode (GC) and investigated for the non-enzymatic electrochemical detection of L-tryptophan (TRP). The electrocatalytic properties of the EGr/GC electrode led to a considerable decrease in the oxidation potential from +0.9 V (bare GC) to +0.72 V. In addition, the EGr/GC electrode has higher sensitivity (two times) and a lower detection limit (ten times) in comparison with the bare GC electrode.
Highlights
Biosensors 2021, 11, 36. https://In the last few years, intensive research has been devoted to the development of analytical methods useful for the detection of biomolecules present in living species
The nonenzymatic electrochemical methods may be useful for the detection of important biomolecules (e.g., L-tryptophan, ascorbic acid, dopamine, uric acid) based on the fact that they have different oxidation potentials
Multiple doping is more efficient in comparison with mono-heteroatom doping since co-doped graphene materials have revealed a range of unique properties due to the synergistic effect of multiple-element doping [5]
Summary
In the last few years, intensive research has been devoted to the development of analytical methods useful for the detection of biomolecules present in living species. The nonenzymatic electrochemical methods may be useful for the detection of important biomolecules (e.g., L-tryptophan, ascorbic acid, dopamine, uric acid) based on the fact that they have different oxidation potentials. Co-doped carbon materials potentially possess promising properties for various applications, there are only a few reports about graphene that is simultaneously doped with nitrogen, sulfur, and boron [12]. Among the methods used for the determination of tryptophan, chromatographic [17], chemiluminescence [18], capillary electrophoresis [19], and electrochemical techniques [20] were highly sensitive, accurate, and simple to use. To the best of our knowledge, no study has been published on tryptophan determination using nitrogen-, sulfur-, and boron-doped graphene. Incorporating N, S, B into the electrochemically exfoliated graphene sheets showed favorable electrocatalytic activity towards tryptophan detection
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