CNT-modified ink as a simple way to generate flexible paper-based electrodes for dopamine determination in presence of uric and ascorbic acids

FEDERICO FIGUEREDO; EDUARDO CORTÓN; MARÍA JESÚS GONZÁLEZ'PABÓN

Washington D.C.

Conferencia; SLAS 2017; 2017

Society for Laboratory Automation and Screening

Nanostructured nanomaterials have gained an increasing interest in the construction of sensors. During the past few years, modification of cellulosic paper with carbon nanotubes (CNT) have been studied for the development of analytical devices mostly proposed to point of care (POC) diagnosis devices. Last reports showed how a CNT aqueous solution (CNT ink) could be used to make conductive paper, supercapacitors, potentiometric electrodes and chemometric sensors. In this report, we developed a CNT ink solution prepared with multi-wall CNT, chitosan (CS) and sodium dodecyl sulfate (SDS) named as CS-CNT ink and we made a comparison with the recently published CNT ink, containing CNT and SDS (CNT ink). Conductive papers were made by impregnation of just CNT (as a control) or CS-CNT inks. As a proof of principle, dopamine in the presence of uric acid and ascorbic acid was successfully detected for CS-CNT ink modified paper electrodes. Basically, filter paper Whatman grade 1 was cut with a CO2 laser engraver machine. The paper strips (2x10 mm) were soaked in CNT or CS-CNT inks for 30 s and let to dry (usually a few minutes at 25ºC), then soaked again in alkaline solution (NaOH 100 mM) for 30 s (only for CS-CNT ink). After dry, strips were washed with phosphate buffer saline (PBS 10 mM, pH 7). This procedure was considered one cycle, and was repeated until the sheet resistance of the dried papers reaches a constant value below 40 Ω sq-1. Scanning electron microscopy (SEM) and cyclic voltammetry (CV) were applied to investigate the properties of the electrodes. Electroactive surface area calculated from Randle-Sevcik slope showed to be approximately 5.25 and 3.17 times higher than the geometrical area for electrodes constructed with CNT and CS-CNT inks respectively. CVs (K3Fe(CN)6, 50 mV s-1) have shown good reversibility (ΔE = 131 mV) and excellent reproducibility (RSD 6.8%), when CS-CNT ink was used. The values obtained when CNT ink was used where ΔE = 249 mV and RSD of 6.8 % between different electrodes. We tested the oxidation current after electrodes were folded at 90° angle; better results were obtained for CS-CNT paper electrodes (RSD < 5 %, 4 fold cycles) in comparison to CNT paper electrodes (RSD between 10 and 30 %, 4 fold cycles). In conclusion, we show for the first time a new methodology for the construction of flexible paper-based amperometric CNT electrode for sensing applications.