Enzyme-Based Electrochemical Biosensors for Microfluidic Platforms to Detect Pharmaceutical Residues in Wastewater

Abstract

Emerging water pollutants such as pharmaceutical contaminants are suspected to induce adverse effects to human health. These molecules became worrisome due to their increasingly high concentrations in surface waters. Despite this alarming situation, available data about actual concentrations in the environment is rather scarce, as it is not commonly monitored or regulated. This is aggravated even further by the absence of portable and reliable methods for their determination in the field. A promising way to tackle these issues is the use of enzyme-based and miniaturized biosensors for their electrochemical detection. Here, we present an overview of the latest developments in amperometric microfluidic biosensors that include, modeling and multiphysics simulation, design, manufacture, testing, and operation methods. Different types of biosensors are described, highlighting those based on oxidases/peroxidases and the integration with microfluidic platforms. Finally, issues regarding the stability of the biosensors and the enzyme molecules are discussed, as well as the most relevant approaches to address these obstacles.

Keywords: biosensors; electrochemistry; enzymes; microfluidics; pharmaceutical residues.

Figure 1

Schematic of a typical biosensor system architecture. The target analyte is detected by the bioreceptor and translated into a signal for analysis with the aid of a transducer. (A) Sample. (B) Biosensor electrode: composed by the bioreceptor, the immobilization surface and the transducer element. (C) Physicochemical reaction. (D) Data analysis.

Figure 2

Three electrode sensor configuration. (a) reference, (b) working and (c) counter electrodes.

Figure 3

Enzyme immobilization onto electrodes. (A) Physically adsorbed through electrostatic interactions, (B) covalently bound to the surface, (C) entrapped within a film, (D) encapsulated within a porous surface and (E) cross-linked within the surface.

Figure 4

Example of momentum transport and velocity profile generated in a microfluidic channel.

Figure 5

Circuit approach for modeling fluid flow in microsystems: (A) pressure and flow ratio in a microchannel, (B) relationship for voltages and currents in a circuit, (C,D) examples of different microsystems configurations and their corresponding circuit analog.

Figure 6

Simulation of microfluidic system in Comsol Multiphysics ^® (A) Simulation domain with the corresponding boundary conditions (inlet speed, outlet pressure and non-slip in the walls), (B) discretization of the domain by a meshing process and the list of physical properties of the fluid, (C) velocity profile in the channel as recovered from Computational Fluid Dynamics (CFD) simulations.

Figure 7

(A) Manufacturing process by photolithographic techniques and (B) manufacturing process by laser cutting.

Figure 8

Functional groups catalyzed in redox reactions by oxidase and peroxidase enzymes.

Figure 9

Laccase-based biosensors categories according to the transduction method used. (A) Electrochemical biosensor, (B) optical biosensor, and (C) thermal biosensor.