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Chemical Sensors
Published in John G Webster, Minimally Invasive Medical Technology, 2016
Electrochemical sensors convert a chemical quantity into electric potential or electric current, based on electrochemical principles. Figure 1.1 shows the fundamental electrochemical measurement system. It consists of two electrodes (one as a reference electrode), electrolyte solution and the electronic circuits. When the electrolyte is dissolved in solution, it dissociates into ions. If an electric field is applied in the solution, the ions move in the electrolyte and form an electric current in the solution. However, the electronic circuit cannot measure the ion current directly, because the current in the circuit is due to the movement of the free electrons instead of chemical ions. Hence a pair of electrodes converts the ionic current into the electric current. In electrochemistry, an electrode is defined as the interface between the electrolyte and the electric conductor. The electrolyte concentration can either be reflected by the potential between the two electrodes or the current flowing between the two electrodes. When the concentration is expressed as a potential difference, the electrochemical sensor is called a potentiometric sensor. When the quantity is expressed as current, it is named an amperometric sensor.
Integrated Biosensors for Rapid and Point-of-Care Biomedical Diagnosis
Published in Raju Khan, Chetna Dhand, S. K. Sanghi, Shabi Thankaraj Salammal, A. B. P. Mishra, Advanced Microfluidics-Based Point-of-Care Diagnostics, 2022
Electrochemistry is a powerful device that has the ability to obtain information from enzymatic compounds, redox mechanisms of enzymatic interactions, and metabolic mechanisms. It is applied in different fields including medical, environmental, and pharmaceutical, etc. because of its cost-effective, miniaturized, and simple analysis systems, and it is easy to fabricate. It is divided into three electrochemical techniques such as amperometry, potentiometry, and impedance spectroscopy [45]. The potentiometric sensor is simple and fabricated easily but exhibits limited sensitivity in comparison to the amperometric sensor. It consists of a two or three-electrode system. In two-electrode systems, the working and the reference (counter) electrodes are used but, in three-electrode systems, the working, reference and counter electrodes are used [46]. A biosensor-based electrochemical sensor is comprised of two parts, one is a transducer, and another is recognition elements for example enzymes or enzyme-labeled antibodies [47]. Shabaninejad et al. developed electrochemical-modified biosensors for microRNA detection. The microRNA is called single-stranded RNA molecules, containing 22 nucleotides in length which regulate the biological function by cellular proliferation, and cause death to cancer development and progression. Moreover, the diagnostic value of miRNAs in different diseases has been analyzed. Therefore, the prepared biosensor can be used for the analysis of nucleic acid in the future [48]. Kilic et al. discovered an electrochemical-modified biosensor for the analysis of microRNA, miR21, in breast cancer cells. The prepared biosensor has several important advantages as being accurate, reproducible, robust, and the short time taken. They are also applied to the detection of total RNA, and microRNAs from various cancer tissues or cell lines[49].
Nanomaterials A Way to Chemical Sensor and Biosensor—Fundamentals
Published in Jayeeta Chattopadhyay, Nimmy Srivastava, Application of Nanomaterials in Chemical Sensors and Biosensors, 2021
Jayeeta Chattopadhyay, Nimmy Srivastava
An electrochemical sensor is composed of a sensing or working electrode, a reference electrode and in many cases a counter electrode. These electrodes are typically placed in contact with either a liquid or a solid electrolyte. In the low-temperature range (< 140º C), electrochemical sensors are used to monitor pH, conductivity, dissolved ions and dissolved gases. For measurements at high temperatures (> 500º C), such as the measurement of exhaust gases and molten metals, solid electrolyte sensors are used (Guth et al. 2009). Electrochemical sensors work on the principle of measuring an electrical parameter of the sample of interest. They can be categorized based on the measurement-approach employed. Electrochemical sensors present a number of advantages, including low power consumption, high sensitivity, good accuracy and resistance to surface-poisoning effects. However, their sensitivity, selectivity and stability are highly influenced by environmental conditions, particularly temperature. Environmental conditions also have a strong influence on operational lifespan; for example, a sensor’s useful life will be significantly reduced in hot and dry environments. Cross-sensitivity to other gases can be a problem for gas sensors. Oversaturation of the sensor to the species of interest can also reduce the sensor’s lifespan. The potentiometric sensor measures differences in potential (voltage) between the working electrode and a reference electrode. The working electrode’s potential depends on the concentration (more exactly, the ion activity) of the species of interest (Banica 2012). For example, in a pH sensor, the electric potential, created between the working electrode and the reference electrode, is a function of the pH value of the solution being measured. Other applications of potentiometric sensors include ion-selective electrodes for both inorganic (for example, monitoring of metal ion contamination in environmental samples or profiling of blood electrolytes) and organic ions (such as aromatic aldehyde or ibuprofen in human serum samples).
Novel polymeric sensor for ultra-trace determination of cerium (III) based on CoNiFe2O4 nanocomposite
Published in Inorganic and Nano-Metal Chemistry, 2023
Fatemeh Sabeti Ghahfarokhi, Arezoo Ghaemi, Roya Mohammadzadeh Kakhki
A novel sensitive and selective electrochemical sensor was proposed based on CoNiFe2O4 nanocomposite as a new additive to measure of Ce (III) ions. CoNiFe2O4 nanocomposite probably increases the consistency, durability, conductivity, and adsorption of the electrode membrane and therefore can increase the sensitivity of the potentiometric sensor. The fabricated sensor with an optimized structure has interesting characteristics such as a good Nernstian slope, a wide linear range, a low detection limit, a short response time, a long lifetime, high selectivity and functionality in a wide pH range from 2 to 10. As well, it was successfully used for complexometric titration and also the determination of Ce (III) in environmental samples. This proposed sensor manifested superior aspects in comparison to previous reports (Table 6).
Review of pH sensing materials from macro- to nano-scale: Recent developments and examples of seawater applications
Published in Critical Reviews in Environmental Science and Technology, 2022
Roberto Avolio, Anita Grozdanov, Maurizio Avella, John Barton, Mariacristina Cocca, Francesca De Falco, Aleksandar T. Dimitrov, Maria Emanuela Errico, Pablo Fanjul-Bolado, Gennaro Gentile, Perica Paunovic, Alberto Ribotti, Paolo Magni
Platinum electrodes, realized by photolithography, have been modified with polypyrrole and used by Lakard et al. (2007); the potentiometric response of these sensors was tested in the pH range 2–11, showing a nearly linear dependence of potential with pH. The sensitivity, however, showed a progressive decrease over 30 days of monitoring, attributed to the degradation of the silver pseudo-reference electrode. Ppy polymerized onto PEI modified electrodes showed improved stability, due to the adhesion granted by the imine layer (Segut et al., 2007). As a more recent example of a potentiometric sensor made by electropolymerization, it is worth mentioning the device proposed by Li et al. (2011). By polymerization of bisphenol A (BPA) onto indium tin oxide (ITO) coated glass, the authors developed an electrode that was tested in either potentiostatic or potentiometric setup, in a wide pH range (1 to 14) showing a sensitivity close to the Nernst limit and a reasonable stability of the response up to 12 days.
Progress on electrochemical sensors for the determination of heavy metal ions from contaminated water
Published in Journal of the Chinese Advanced Materials Society, 2018
Xiangzi Dai, Shuping Wu, Songjun Li
Meanwhile, Jing et al. have developed IIPs using cadmium ions as the template which were directly grafted on the surface of low-cost print paper based on the reversible addition–fragmentation chain transfer polymerization.[82] It can be applied as a recognition element to selectively capture the target ions in the complex samples owning to the selective recognition, formation of dithizone-cadmium complexes and light transmission ability. IIPs-paper has response to Cd(II) in the linear range from 1 to 100 nM and the limit of detection was 0.4 nM. Rezvani Ivari et al. also prepared a novel IIP based potentiometric sensor for the trace determination of Cd(II).[83] The Cd(II)-IIP electrode was fabricated by dispersing cadmium (II) IIP particles in 2-nitrophenyloctyl ether as a plasticizer and then embedding them in a polyvinylchloride polymeric matrix. The obtained IIP sensor showed a Nernstian response for Cd(II) over the concentration range of 2.0 × 10−7–1.0 × 10−2 M and the detect limit of 1.0 × 10−7 M. The proposed electrode was successfully applied in the analysis of spiked water samples. Lai et al. synthesized an Pb(II) imprinted polymer (Pb-IIP) using methacrylic acid as a monomer, Pb(II) as template ions, ethylene glycol dimethacrylate (EGDMA) as a crosslinker, 8-hydoxyquinoline as a ligand and azobisisobutyronitrile as initiator.[84] The polymer was applied to voltammetric sensor for Pb(II) adsorption and trace detection. Compared to other heavy metal ions, such as Hg(II), Cd(II) and Cu(II), the polymer has shown a delightful selectivity for Pb(II) and used to detect trace levels of Pb(II) in food and water samples with linear range of 0.05–60 mμ M of Pb(II) concentrations and a limit of detection at 0.01 mμ M.