Ultrasensitive electrochemical detection of digoxin using graphite oxide and Au-NPs composites

Abstract

Digoxin is a cardiac glycoside which is widely used as medication in treatment of congestive heart failure and arrhythmias. Unfortunately, digoxin has small therapeutic range (2 ng/mL), excess digoxin concentration in blood plasma can cause intoxication. Therefore, simple and sensitive procedure is required for strict monitoring of digoxin in blood level to minimize the risk of toxicity. In this paper, we report detection of digoxin using Au-NPs and GO composites synthesized with wet chemistry. X-ray diffraction (XRD), scanning electron microscopy (SEM) and Raman spectroscopy were employed for the confirmation of Au-NPs attachment on the surface of GO. The synthesized Au-NPs-GO composites were deposited on the surface of glassy carbon electrode (GCE) for electrochemical characterization. The electrodes were further incubated with mercaptoacetic acid (MAA) and digoxin antibody (Ab) for the formation of Ab-MAA-Au-NPs-GO modified electrode. MAA conjugation resulted in a 35 % increase in Ipc and 63 % decrease in charge transfer resistance (Rct). Antibody immobilization on MAA modified electrode resulted a sudden drop in both the cathodic peak (anodic peak) currents Ipc(Ipa). Increase in Rct (940 Ω) after Ab functionalization was due to its proteinic nature, which confirmed the formation of Ab-MAA-Au-NPs-GO modified GCE sensors. Work was further extended to probe the charge transfer characteristics in different dilution of digoxin. 17 % (10 %) decrease in Ipc(Ipa) as the digoxin drug was increased from 0.1 ng/mL to 1000 ng/mL. Linear sweep voltammetry (LSV) was also performed at the end for analytic performance of Ab modified sensor for various digoxin drug dilutions. Two linear regressions for current response against digoxin drug dilution were recorded, which confirmed sensitivity of the sensor was governed by interaction between Ab and digoxin drug coordinated by potassium ions at the electroactive sites. The sensitivity was 154.81 μAcm−2 ng-1 for 2-0.1 ng range and 10.71 μAcm−2 ng-1 in the range of 1000−2 ng. The limit of detection (LoD) was 0.19 ng/mL, which suggested that proposed Ab-MAA-Au-NPs-GO modified GCE electrochemical sensor can be successfully applied for future digoxin drug detection applications.