Electrochemical Sensor for Bilirubin Detection Using Screen Printed Electrodes Functionalized with Carbon Nanotubes and Graphene

Abstract

Practice oriented point-of-care diagnostics require easy-to-handle, miniaturized, and low-cost analytical tools. In a novel approach, screen printed carbon electrodes (SPEs), which were functionalized with nanomaterials, are employed for selective measurements of bilirubin, which is an important biomarker for jaundice. Multi-walled carbon nanotubes (MWCNT) and graphene separately deposited on SPEs provide the core of an electrochemical sensor for bilirubin. The electrocatalytic activity towards bilirubin oxidation (bilirubin to biliverdin) was observed at +0.25 V. In addition, a further peak corresponding to the electrochemical conversion of biliverdin into purpurin appeared at +0.48 V. When compared to MWCNT, the graphene type shows a 3-fold lower detection limit (0.3 ± 0.022 nM and 0.1 ± 0.018 nM, respectively), moreover, the graphene type exhibits a larger linear range (0.1-600 µM) than MWCNT (0.5-500 µM) with a two-fold better sensitivity, i.e., 30 nA µM^-1 cm^-2, and 15 nA µM^-1 cm^-2, respectively. The viability is validated through measurements of bilirubin in blood serum samples and the selectivity is ensured by inhibiting common interfering biological substrates using an ionic nafion membrane. The presented approach enables the design and implementation of low cost and miniaturized electrochemical sensors.

Keywords: bilirubin; carbon nanotubes (CNT); electrochemical analysis; electrochemical sensor; graphene; nanomaterials; screen printed electrode (SPE).

Figure A1

Effect of the pH value on the voltammetric potential responses of Er-GR-SPE in 0.1 M PBS containing 100 µM BR at scan rate of 50 mV s⁻¹.

Figure 1

Schematic drawing of the preparation of the multi-walled carbon nanotubes (MWCNT) based (top row) or electrochemically reduced graphene oxide (Er-GR) based (bottom row) bilirubin sensors.

Figure 2

SEM images of the morphology of the (A) screen printed carbon electrodes (SPE), (B) MWCNT-SPE, and graphene oxide (GO)-SPE before (C) and after electrochemical reduction (D).

Figure 3

(A) Electrochemical responses of the GO-SPE (a) before and (b) after electrochemical reduction in 0.1 M PBS (pH 7.2) at a scan rate of 50 mV s⁻¹. (B) Typical electrochemical responses of the (a) bare SPE, (b) MWCNT–SPE, and (c) Er-GR-SPE in 0.1 M PBS (pH 7.2) and (C) in 0.1 M PBS containing 2.5 mM K₃[Fe(CN)₆] at a scan rate of 50 mV s⁻¹. (D) Effect of the pH value on the voltammetric current responses (at +0.48 V) of the bare SPE, MWCNT-SPE, and Er-GR-SPE in 0.1 M PBS containing 100 µM BR at scan rate of 50 mV s⁻¹.

Figure 4

(A) Electrochemical responses of the (a) bare SPE, (b) MWCNT-SPE, and (c) Er-GR-SPE in the presence of 100 µM BR in 0.1 M PBS (pH 7.2) at a scan rate of 50 mV s⁻¹. (B) Electrochemical responses of the Er-GR-SPE in the presence of (a) 10, (b) 50, (c) 100, (d) 150, (e) 200, (f) 250, and (g) 300 µM of BR in 0.1 M PBS (pH 7.2) at a scan rate of 50 mV s⁻¹. (C) Zoomed in to +0.48 V. (D) Calibration plot for BR using MWCNT-SPE (a) Er-GR-SPE (b).

Figure 5

Histograms representing Bilirubin (BR) oxidation current for the Er-GR-SPE (A) and MWCNT-SPE (B) before and after nafion coating, upon addition of 50 µM of UA, AsA, GSH and glucose in 0.1 M PBS containing 100 µM BR. (C) Relative BR oxidation current responses of the MWCNT-SPE and Er-GR-SPE over long term storage. (D) Electrochemical current responses of the Er-GR-SPE at +0.48 V in 0.1 M PBS containing 0, 50, 100, 150, 200, and 400 µM of albumin in the absence and presence of 100 µM BR.