Design and Construction of Enzyme-Based Electrochemical Gas Sensors

Abstract

The demand for the ubiquitous detection of gases in complex environments is driving the design of highly specific gas sensors for the development of the Internet of Things, such as indoor air quality testing, human exhaled disease detection, monitoring gas emissions, etc. The interaction between analytes and bioreceptors can described as a "lock-and-key", in which the specific catalysis between enzymes and gas molecules provides a new paradigm for the construction of high-sensitivity and -specificity gas sensors. The electrochemical method has been widely used in gas detection and in the design and construction of enzyme-based electrochemical gas sensors, in which the specificity of an enzyme to a substrate is determined by a specific functional domain or recognition interface, which is the active site of the enzyme that can specifically catalyze the gas reaction, and the electrode-solution interface, where the chemical reaction occurs, respectively. As a result, the engineering design of the enzyme electrode interface is crucial in the process of designing and constructing enzyme-based electrochemical gas sensors. In this review, we summarize the design of enzyme-based electrochemical gas sensors. We particularly focus on the main concepts of enzyme electrodes and the selection and design of materials, as well as the immobilization of enzymes and construction methods. Furthermore, we discuss the fundamental factors that affect electron transfer at the enzyme electrode interface for electrochemical gas sensors and the challenges and opportunities related to the design and construction of these sensors.

Keywords: electrochemical gas sensor; enzyme electrode; interface; specificity.

Figure 2

(a) The structure schematic of the electrochemical gas sensor; (b) The image of the electrodes by optical microscope; (c) The current response of miniaturized planar electrochemical gas sensor to oxygen [16]; (d) The preparation process and working principle of a wearable origami-like paper-based electrochemical biosensor for sulfur mustard detection; (e) The detection results of origami-ePAD for the standard solution of SM in liquid phase (absence (black) and in presence of SM concentrations equal to 2 mM and 4 mM); (f) The detection results of origami-ePAD for the aerosolized SM(absence (black line) and in presence of SM concentrations equal to 0.019 g/m³ and 0.76 g/m³) [21].

Figure 1

The strategies to achieve high-performance enzyme-based electrochemical gas sensors.

Figure 3

(a) Schematic of the solution-gated graphene transistors (SGGT) modified with AOx/CNs in a polyacrylamide hydrogel-based system; (b) The change in potential between the gate and channel before (solid line) and after (dotted line) the addition of alcohol in PBS solution; (c) the detection of increasing H₂O₂ concentration in PBS solution by a bare Au gate; (d) the detection of increasing concentration of H₂O₂ in PBS solution by CN-modified Au gate; (e) Change in effective gate voltage of the SGGT with unmodified Au gate and CN-modified Au gate vs. the logarithm of H₂O₂ concentration; (f) The selectivity of the SGGT device with the AOx/CN-modified gate [25].

Figure 4

Physical and chemical methods for immobilization of enzymes.

Figure 5

(a) Schematic of sensing device containing graphite electrode, a network of polymer and AOx; (b) Amperometric response of the alcohol sensors to increasing ethanol concentrations; (c) Effect of interfering substances on biosensor performance [44]; (d) the immobilization of the formaldehyde dehydrogenase and the mechanism for catalyzing formaldehyde; (e) The FTIR spectra of formaldehyde dehydrogenase immobilized on pyrenyl carbon nanostructures; (f) Amperometric responses for various concentration of formaldehyde [37].

Figure 6

(a) The schematic of preparation alcohol oxidase-based methanol sensor; (b) FTIR spectra of PS-PAMAM, GA-PS-PAMAM, and AOX/PS-PAMAM ESNFs samples; (c) the response of sensor to a series concentration of gas-phase methanol [35]; (d) The schematic diagram of the process for preparing paper-based ethanol biosensor; (e) The calibration plot of ethanol concentration vs. current (The inset shows the chronoamperometric records with the concentration increase from 0–12 mM); (f) the evaluation of shelf-life at 4 °C of the ethanol sensor, fresh biosensor (black bar), 1 week (red bar), 2 weeks (green bar), 3 weeks (blue bar) and 4 weeks (violet bar) [19].

Figure 7

(a) Reduction of O₂ to H₂O by bilirubin oxidase via direct electron transfer (DET) or mediated electron transfer (MET); (b) Electrodes modified with naphthoquinone functionalized pyrene/carbon nanotubes can promote direct electron transfer to laccase and bilirubin oxidase, as well as PQQ-dependent glucose dehydrogenase-mediated electron transfer-dependent glucose dehydrogenase-mediated electron transfer [32].