Boron-Doped Reduced Graphene Oxide (B-RGO) and Its Application to L-Cysteine Sensing

In this study, we prepare a boron-doped reduced graphene oxide thin film on the screen printed carbon electrode (SPCE) for the electrochemical sensing of L-cysteine (L-cys). L-cysteine, a sulfur containing amino acid, plays a crucial role in regulating the biological activity of certain proteins, peptides and enzymes. Low level of L-cys is related to myriad of diseases, including slow growth in children, depigmentation of hair, lethargy, liver damage, loss of muscle and fat, skin lesions, and weakness.^[1]  However, current L-cys sensing techniques require intensive pretreatments^[2,3]as well as purifications. As a result, developing a relatively easy, selective and sensitive L-cys biosensor in physiological study and clinical diagnosis is highly demanded.

In the electron energy loss spectroscopy (Fig. 1 (a)), the peaks of π*(~190 eV) and σ*(~200 eV) anti-bonding orbitals on the K-edge of boron (B) revealed the hybridized sp²-bonded B atoms in the graphene nanosheet. These two peaks indicates that the substitution doping is the dominate type of doping. The STEM-EELS mapping of B-RGO (Fig. 1 (b)) confirms that dopant B (green) is uniformly distributed on the reduced graphene oxide.

Electrochemical characterization shows different performances among bare SPCE, RGO/SPCE and B-RGO/SPCE in Fig. 1(c). The results show that with the help of boron, B-RGO (B=9.6%) possesses good electrocatalytic ability to L-cys by decreasing the overpotential and increasing the current density of the irreversible oxidation reaction. Fig. 1(d) shows a plot of the current density of the B-RGO/SPCE as a function time at various L-cys concentrations. The current density increases linearly with the increased L-cys concentration, as shown in the inset. The sensitivity of the B-RGO/SPCE is 20.7 mAcm⁻²M⁻¹. The limit of detection (LOD), based on a signal-to-noise ratio of 3, for the B-RGO/SPCE is 0.07 μM.  

[1] S. Shahrokhian, Anal. Chem. 73 (2001), 5972

[2] G. Chwatko, E. Bald, Talanta,52 (2000) 509.

[3] K. Arlt, S. Brandt, J. Kehr, Journal of Chromatography A, 926 (2001) 319.