Electrochemical Biosensors

Ali A. Ensafi

• Publisher: Elsevier
• Year: 2019
• ISBN:
  9780128164921
• Topic: Physical Sciences
• Subtopic: Analytic Chemistry

Electrochemical Biosensors summarizes fundamentals and trends in electrochemical biosensing. It introduces readers to the principles of transducing biological information to measurable electrical signals to identify and quantify organic and inorganic substances in samples. The complexity of devices related to biological matrices makes this challenging, but this measurement and analysis are critically valuable in biotechnology and medicine. Electrochemical biosensors combine the sensitivity of electroanalytical methods with the inherent bioselectivity of the biological component. Some of these sensor devices have reached the commercial stage and are routinely used in clinical, environmental, industrial and agricultural applications.

• Describes several electrochemical methods used as detection techniques with biosensors
• Discusses different modifiers, including nanomaterials, for preparing suitable pathways for immobilizing biomaterials at the sensor
• Explains various types of signal monitoring, along with several recognition systems, including antibodies/antigens, DNA-based biosensors, aptamers (protein-based), and more

Chapter 1

An introduction to sensors and biosensors

Ali A. Ensafi, PhD Professor, Department of Chemistry, Isfahan University of Technology, Isfahan, Iran

Abstract

In this chapter, I have a brief introduction to sensors and biosensors, different detection methods that have been used in biosensors technology, and important parameters that affect in electrochemical biosensors responses.

Keywords

Biosensors; Characterization; Introduction; Sensors

1.1. Sensors

A sensor may be defined as a device to convert an input of physical quantity into a functionally related output usually in the form of an electrical or optical signal that can be read or detected either by human users or by electronic instruments. Sensors and their associated interface are used to detect and measure different physical and chemical properties of compounds including temperature, pH, force, odor, and pressure, the presence of special chemicals, flow, position, and light intensity (Ensafi and Kazemzadeh, 1999; Zhu et al., 2018).

A sensor is mainly characterized as one that (1) is solely sensitive to the chemical or physical quantity to be measured, whereas it is insensitive to all other parameters likely to be encountered in its application and (2) while in operation, does not influence the properties of the input chemical and/or physical quantities. The sensitivity of a sensor indicates the degree of variation of the output relative to the change in the measured chemical or physical property. Selection of a sensor should be based on such essential features as its selectivity (Fraden, 2004), sensitivity, accuracy, calibration range, resolution, cost-effectiveness, and repeatability as well as the prevailing environmental conditions (Vetelino and Reghu, 2010; Ensafi et al., 2011; Grandke and Ko, 2008; Gründler, 2007).

1.2. Classification of sensors

Depending on the properties of the substance or analyte to be measured, sensors may be broadly classified into physical and chemical types, with the physical one referring to the device detecting and/or measuring such physical responses as temperature, pressure, magnetic field, force, absorbance, refractive index, conductivity, and mass change (Gründler, 2007). Moreover, the devices do not have any chemical interface.

A chemical sensor has a chemically selective layer that responds selectively to a special analyte (Janata, 2009). It deals specifically with the chemical information obtained from the chemical reaction of the analyte or a physical property of the system being probed. Such information may include the concentration of a specific component or the analysis of a total composition, which is then transformed into such signals of analytical use as conductance change, light, voltage, current, or sound.

Chemical sensors are gaining a leading position among the presently commercially available ones with a wide array of clinical, industrial, environmental, and agricultural applications.

1.3. Biosensors

A biological component, a bioreceptor, and a physicochemical detector, and a transducer, may be combined to form a biosensor (Buerk, 1993). A biomolecule, such as an antibody, aptamer, enzyme, nucleic acid, or cell, capable of detecting or identifying the target analyte is used as the bioreceptor. These sensors offer such advantages as high selectivity to the target analyte mainly due to the specific interaction of the bioreceptor present in their structure with the target analyte (biorecognition) (Buerk, 1993). More important, this specific interaction prevents the interference of signals from other substances with the desired biosensor signal. Finally, the event recognized by the bioreceptor is transformed by a transducer into a measurable signal (Fig. 1.1).

The prerequisite to a stable biosensor is the immobilization of the bioreceptor at the surface of the transducer using a reversible or irreversible immobilization method. To achieve this, different strategies may be used, which are classified into surface adsorption, covalence binding, cross-liking, entrapment (beads or fibers), bioaffinity, and chelation or metal binding based on such criteria as a type of sample, desired selectivity, difficulty, and ranging (Buerk, 1995).

Being an element for converting one form of energy produced by a physical change accompanying a reaction into another, the transducer in a biosensor transforms the biorecognition event into a measurable signal in a process called “signalization.” Transducers come in a variety of optical, electrochemical, quartz crystal piezoelectric, calorimetric (heat output or absorbed by the reaction), and thermal types (Karunakaran et al., 2015). Most transducers, however, produce either optical or electrical signals in proportion to the analyte-bioreceptor interactions. A schematic diagram of the main components of a biosensor is shown in Fig. 1.1.

Figure 1.1 Schematic diagram of a biosensor.

Originally, Clark and Lyons (1962) introduced the first biosensor in 1962. Using the enzyme glucose oxidase (GOx) as a recognition element, it was indeed an amperometric oxygen electrochemical sensor for detecting glucose. The term “biosensor” was coined as the shortened form of the so-called “bioselective sensor” proposed by Rechnitz et al. (1977) for arginine selective electrode that used living organisms as its recognition elements.

Biosensors have gone viral as analytical and diagnostic tools of widespread use, as they outperformance any other presently in use. Thanks to their operational simplicity, low cost, and no skills requirements, they have become the ordinary man's tools of everyday use. These advantages have won them increasingly wide applications in such varied areas as diabetic and cardiac self-monitoring, forensic investigations such as drug discovery, agricultural and environmental detection systems, the food industry, and biodefense (Scott, 1998). No doubt, further commercialization of biosensors rely much on such improved features as enhanced selectivity, sensitivity, stability, reproducibility, and portability, all at lower costs.

A variety of transducer-based output signals have been used in biosensors (Fig. 1.1). These include optical (such as absorbance, luminescence, chemiluminescence, and surface plasmon) (Ligler and Taitt, 2008), mass (piezoelectric and magnetoelectric) (Steinem and Janshoff, 2007), thermometric (Zhou et al., 2013), and electrochemical signals (Cosnier, 2013). From among these, the electrochemical ones are more prominently important, as they are not only economical and user-friendly but also allow robust, portable, and miniaturized devices to be fabricated for particular applications. Moreover, their excellent capacity for detecting and monitoring any changes in the electrical parameters of electrode potential, current, and charge transfer impedance or capacitance as a function of analyte concentration has made them suitable for many commercial applications (Ensafi et al., 2014). Based on the signal monitored, electrochemical biosensors may be classified into amperometric, potentiometric, voltammetric, impedimetric/conductometric, and capacitive sensors (Fig. 1.2).

1.4. Electrochemical biosensors

IUPAC defines an electrochemical biosensor as a self-contained and integrated device that uses a biological recognition element (biochemical receptor) in direct spatial contact with an electrochemical transducer to produce certain quantitative or semiquantitative analytical information on an analyte of interest (Theâvenot et al., 1999).

As already mentioned, a wide variety of electrochemical detection techniques are available that include amperometry, potentiometry, v...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Contributors
• Preface
• Chapter 1. An introduction to sensors and biosensors
• Chapter 2. Electrochemical detection techniques in biosensor applications
• Chapter 3. Surface modification methods for electrochemical biosensors
• Chapter 4. Typically used carbon-based nanomaterials in the fabrication of biosensors
• Chapter 5. Typically used nanomaterials-based noncarbon materials in the fabrication of biosensors
• Chapter 6. Types of monitoring biosensor signals
• Chapter 7. Enzyme-based electrochemical biosensors
• Chapter 8. Aptamer-based electrochemical biosensors
• Chapter 9. Nucleic acid–based electrochemical biosensors
• Chapter 10. Peptide-based electrochemical biosensors
• Chapter 11. Receptor-based electrochemical biosensors for the detection of contaminants in food products
• Index