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

FIGUEREDO FEDERICO; GONZALEZ PABON MARIA JESUS; CORTÓN, EDUARDO

Washington

Congreso; Society for Laboratory Automation and Screening (SLAS 2017); 2017

SLAS

NOTA: FF es becado por los organizadores cubriendo todos los gastos, con la única beca otorgada a la Argentina (total de 62 a nivel mundial). SLAS Tony B. Academic Travel Awards Program.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 (CNTink) 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), an anionic surfactant (CS-SDS-CNT ink) and we made a comparison with the recently published CNT ink, containing CNT and SDS.  Conductive papers were made by impregnation of just CNT (as a control) or CS-SDS-CNT inks. As a proof of principle, dopamine in the presence of uric acid and ascorbic acid was successfully detected for CS-SDS-CNT ink modified paper electrodes. Basically, filter paper Whatman grade 1 was cut with a CO2 laser engraver machine. The paperstrips (2x10 mm) were soaked in CNT or CS-SDS-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-SDS-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 resistance of the dried papers reaches a stable value, usually around 40 Ωcm. The number of cycles needed for a correct stabilization was 5 and 9 for CS-SDS-CNT and CNT inks, respectively. Scanning electron microscopy (SEM), cyclic voltammetry (CV), differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy were applied to investigate the properties of the electrodes. Electroactive surface area calculated from Randle-Sevcik slope showed to be 4 times higher than the geometrical area for electrodes constructed with both inks. CVs (ferrycyanide, 50 mV s-1) shown good reversibility (Δp = 130.3 mV) and excellent reproducibility (oxidation peak of 0.06 mA, RSD 5%), when CS-SDS-CNT ink was used. The values obtained when CNT ink was used where Δp = 250 mV and 0.07 mA (RSD 10 %) for the oxidation peak. We tested the oxidation current after electrodes were folded at 90° angle; better results were obtained for CS-SDS-CNT ink electrodes (RSD 5 %,4 fold cycles) in comparison to CNT ink electrodes (RSD 30 %, 4 fold cycles).Based on the excellent results achieved, CS-SDS-CNT ink paper electrodes were selected for dopamine determination. By applying DPV, and using a mixture of uric acid (0.4 mM), ascorbic acid (0.08 mM) and dopamine (0.01 to 0.1 mM), we observed a separation between peaks for the three species in PBS solution. In conclusion, we show for the first time a new methodology for the construction of flexible paper-based amperometric CNT based electrodes for sensing applications.