Electroanalysis of urinary l-dopa using tyrosinase immobilized on gold nanoelectrode ensembles

Abstract

The performance of an amperometric biosensor constructed by associating tyrosinase (Tyr) enzyme with the advantages of a 3D gold nanoelectrode ensemble (GNEE) is evaluated in a flowinjection analysis (FIA) system for the analysis of Levodopa (Ldopa). GNEEs were fabricated by electroless deposition of the metal within the pores of polycarbonate track-etched membranes. A simple solvent etching procedure based on the solubility of polycarbonate membranes is adopted for the fabrication of the 3D GNEE. Afterwards, enzyme was immobilized onto preformed self-assembled monolayers of cysteamine on the 3D GNEEs (GNEE-Tyr) via cross-linking with glutaraldehyde. The experimental conditions of the FIA system, such as the detection potential (-0.200 V (vs. Ag/ AgCl)) and flow rates (1.0 mL min -1 ) were optimized. Analytical responses for L-dopa were obtained in a wide concentration range between 1 9 10 -8 mol L -1 and 1 9 10 -2 mol L -1 . The limit of quantification was found to be 1 9 10 -8 mol L -1 with a resultant % RSD of 7.23% (n = 5). The limit of detection was found to be 1 9 10 -9 mol L -1 (S/N = 3). The common interfering compounds namely, glucose (10 mmol L -1 ), ascorbic acid (10 mmol L -1 ), and urea (10 mmol L -1 ) were studied. The recovery of L-dopa (1 9 10 -7 mol L -1 ) from spiked urine samples was found to be 96%. Therefore, the developed method is adequate to be applied in the clinical analysis.

Electroanalytical Overview: The Determination of Levodopa (L-DOPA)

“…A schematic representation of how the biosensor is prepared is shown in Figure A, which comprises of 4 steps involving the electroless gold deposition in polycarbonate membranes, followed by partial etching exposing gold nanoarrays. Figure B shows an SEM image of the 3D GNEE which shows that the gold nanowires have an average diameter of 50 nm and a length of 180 (±20) nm which also shows the absence of voids on surface, which suggest that this method produces 3D GNEEs with protruding gold wires . The 3D GNEE was explored toward the sensing of L-DOPA using a flow-injection analysis system, as shown in Figure C where a linear current response for L-DOPA between 10 nM and 10 mM was achieved.…”

“…Pinho et al reported the use of a 3D gold nanoelectrode ensemble (GNEE) in a flow-injection analysis system for the sensing of L-DOPA. A schematic representation of how the biosensor is prepared is shown in Figure A, which comprises of 4 steps involving the electroless gold deposition in polycarbonate membranes, followed by partial etching exposing gold nanoarrays.…”

“…Inset a, linear fit of L-DOPA from 10 –8 to 10 –5 mol L –1 ; insets b and c, FIA responses for consecutive injections of L-DOPA solutions (10 –3 –10 –8 mol L –1 ) in PBS (pH 6.5). Reproduced with permission from ref . Copyright 2012 Springer.…”

“…22 The authors were able to show that their composite achieved the determination of L-DOPA from 0.1 μM to 1.9 μM, with a low LOD of 40 nM, but only in model solutions; despite this the authors noted that their sensor has advantages such as rapid response, high stability, and reproducibility. Pinho et al 49 reported the use of a 3D gold nanoelectrode ensemble (GNEE) in a flow-injection analysis system for the sensing of L-DOPA. A schematic representation of how the biosensor is prepared is shown in Figure 5A, which comprises of 4 steps involving the electroless gold deposition in polycarbonate membranes, followed by partial etching exposing gold nanoarrays.…”

Electrical Chips for Biological Point-of-Care Detection

“…Carbon nanotube sensors improve the sensitivity of detection by increasing the available surface area and potentially by altering the activity and electron transport of the targeted biomolecule by bringing the electrode surface closer to the enzyme's active site (105,106). The use of nanoelectrodes confers unique advantages on amperometric biosensors, as shown recently by the detection of glucose (107,108) and L-dopa (109). The increased surface area and small dimensions of nanoelectrodes increase the sensors' sensitivity and enhance mass transport through the use of hemispherical diffusion fields (110).…”