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Fabrication of Electrochemical Sensors for the Sensing of Hazardous Compounds

  • Khursheed AhmadEmail author
  • Waseem Raza
Living reference work entry
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Abstract

Environmental pollution is a big threat for the world. There are various inorganic/organic pollutants which derailed out from the different industries and have toxic nature. Many compounds such as toluene, hydrazine, nitrite, hydrogen peroxide, resorcinol, 4-chlorophenol, hydroquinone, catechol, phenol, nitro-phenol, and nitrobenzene are widely used in the industries and these compounds are showed hazardous effects on humans, animals, as well as environments. Some of these compounds even in trace amount may harm the human beings. Therefore, the determinations of such compounds are of great importance. Previously various approaches have been made to detect these organic/inorganic compounds. Various research groups have employed different detection techniques which showed good results. Recently, electrochemical approach attracted much attention of the researchers due to its excellent sensitivity, good detection limit, reproducibility, repeatability, simple fabrication procedure, low cost, and high selectivity. In this chapter, fabrication and advantages of electrochemical sensor for the sensing of different analytes have been discussed. Moreover, the role of newly designed and different electrode modifiers for the fabrication of electrochemical sensors has also been discussed.

Introduction

In present time environmental pollution is a great threat for the whole world [1, 2, 3, 4, 5, 6, 7, 8, 9]. Environmental pollution rapidly increasing, and various factors are responsible for this enhanced environment pollution. There are various organic, inorganic, or other toxic compounds which possess hazardous impact on animals as well as humans and environment [8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25]. Phenol family is toxic in nature and widely used in various applications. Catechol has been used in chemical, textiles, oil refinements, plastic industries, and agricultural fields [26]. Similarly, hydroquinone which is also isomer of catechol has been applied in various applications such as paints, cosmetics, antioxidants, pesticides, oil industries, photography and pharmaceuticals etc. [26]. There is also another form of phenol derivative known as resorcinol (1,2-benzenediol) has been used in food, dye, and pharmaceutical industries. These phenolic compounds such as catechol and resorcinol have hazardous impact on the environment as well as plants, animals, and human beings. Another form of phenol family is 2-phenylphenol and 4-chlorophenol [1, 5] which also has toxic nature. These phenolic compounds are also used as disinfectant in nursing homes, households, fungicides, food processing plants, hospitals, barbershops, industries, and laundries [5]. These phenolic compounds are also hazardous to the skin, eyes, and responsible for other health issues. Nitrite is another source of nitrogen for green plants and known as intermediate byproduct in the nitrogen cycles. Nitrite is also present in soil, water, and environment. Nitrite is also employed in food industries as preservative. Although nitrite does not cause harmful effects in moderate concentrations but at higher concentrations it may interact with hemoglobin to produce methemoglobin which inhibited the hemoglobin to transport the oxygen throughout the human body and can cause tissue hypoxia [27]. Nitrite may also interact with amide, secondary amines, and tertiary amines to produce nitrosamines which are a carcinogenic compound. Thus, detection of nitrite is important for human as well as environmental concerns. Another compound urea is an organic compound which is used as fertilizer and converted to ammonia and polluted the environment. Urea is also present in protein metabolism and its presence in high concentration in the blood or urine may cause urinary tract obstruction, dehydration, shock, burn, kidney damage, and gastrointestinal bleeding. However, its presence in low concentration may also cause nephritic syndrome, cachexia, and hepatic failure. Urea is also used in milk and its higher concentration in the milk can causes ulcers, indigestion, acidity, etc. Therefore, the detection of urea is important for its use in dairy products, clinical diagnostics, fertilizer plants, or environment monitoring. Hydrazine is also an unstable and highly toxic compound and widely used in rocket fuels, duel cells, chemical reactions, catalyst, and other applications [7]. The long-term contact with hydrazine may have carcinogenic effects due to containing of neurotoxin. Hydrogen peroxide (H2O2) plays crucial role physiological processes. H2O2 is an analyte used in clinics, drugs, chemical, and food industry [4]. H2O2 also has negative impacts on the environments and human beings. So, the detection of H2O2 is also a necessary task. The nitro group containing aromatic compounds such as nitrophenol and picric acid (2,4,6 trinitrophenol) are highly toxic and explosive in nature [15, 17]. Picric acid is used in pharmaceutical, dye, and leather industries [15]. It has toxic nature and has hazardous effects on the environment, plants, and human beings due to its bio-toxicity. Thus, the above-discussed compounds are highly toxic and have hazardous effects. Therefore, the determinations of such compounds are important task. In previous reports, various approaches have been used to the determination of such toxic compounds. The conventional methods such as high-performance liquid chromatography, spectrophotometry, quartz crystal microbalance, spectrofluorometry, surface plasmon resonance, electrophoresis, and flow injection chemiluminescence have been employed for the determination of toxic compounds [9, 28]. In last few years, electrochemical methods have attracted the scientific community for the sensing of toxic and hazardous compounds due to its simple fabrication, cost effectiveness, high sensitivity, selectivity, and repeatability [29, 30, 31]. Hence, in this chapter, we have discussed the recent advances in the sensing of different toxic and hazardous compound employing electrochemical methods.

How to Prepare the Electrochemical Sensors?

The fabrication of the electrochemical sensors is a simple task. Generally a glassy carbon electrode (GCE) or screen printed electrode (SPE) has been widely used as electrode substrate. The working area of the screen printed or glassy carbon electrode cleaned with alumina slurry and the electrode modifier has to be deposited on to the cleaned active area of the working electrode substrate. Further, this modified electrode to be dry in air for several hours and further used as working electrode.

In general, screen-printed electrode is used as working electrode whereas two other electrodes (reference electrode = Ag/AgCl and counter electrode = platinum wire) also used in the three electrode assembly for the determination of the toxic compounds using electrochemical approach. The schematic illustration of the fabrication of the electrochemical sensor using screen-printed electrode substrate has been presented in Scheme 1.
Scheme 1

Schematic illustration of the fabrication of the electrochemical sensor and three electrode system

Electrochemical Sensing of Hazardous Compounds

There are numerous toxic and hazardous compounds which are harmful to the humans, plants, animals, and environment. Herein, we have summarized the recent advances in the field of electrochemical sensing of different toxic compound using electrochemical methods.

Sensing of Catechol

Catechol is a derivative of the phenol and is highly toxic in nature. Nazari et al. prepared an electrochemical sensor for the sensing of catechol using ZnO-Al2O3 ceramic nanofibers electrode modifier while glassy carbon electrode was used as working substrate [32]. The prepared ZnO-Al2O3 ceramic nanofiber was checked by scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and Energy-dispersive X-ray spectroscopy (EDX).

The surface was calculated using Brunauer–Emmett–Teller (BET) investigations. Further electrochemical investigation were carried out in presence of 5 mM K3Fe(CN)6 in 0.1 M KCl. The cyclic voltammograms (CVs) of the AuNP/GO/chit/GCE (a), ZnO/Al2O3/GO/chit/GCE (b), and AuNP/ZnO/Al2O3/GO/chit/GCE (c) in 5 mM K3Fe(CN)6 in 0.1 M KCl have been displayed in Fig. 1. The recorded CV curves showed the high current activity for the AuNP/ZnO/Al2O3/GO/chit/GCE compare to the AuNP/GO/chit/GCE or ZnO/Al2O3/GO/chit/GCE. Further, the differential pulse voltammetry (DPV) curves of the bare GCE (a), GO/chit/GCE (b), AuNP/GO/chit/GCE (c), and AuNP/ZnO/Al2O3/GO/chit/GCE (d) in catechol (1 mM) have been displayed in Fig. 2a. The higher current was appeared for the AuNP/ZnO/Al2O3/GO/chit/GCE in 1 mM catechol. Further the DPV curves in presence of 50 μM catechol were also recorded at different pH (Fig. 2b). The recorded DPV graphs showed the shifting in the potential with change in the pH values.
Fig. 1

CV curve of the AuNP/GO/chit/GCE (a), ZnO/Al2O3/GO/chit/GCE (b), and AuNP/ZnO/Al2O3/GO/chit/GCE (c) in 5 mM K3Fe(CN)6 in 0.1 M KCl. (Adopted with permission [32])

Fig. 2

DPV (a) of the bare GCE (a), GO/chit/GCE (b), AuNP/GO/chit/GCE (c), and AuNP/ZnO/Al2O3/GO/chit/GCE (d) in catechol (1 mM) and effect of pH (b) on the DPV curves in 50 μM catechol. (Adopted with permission [32])

The obtained results showed good electrochemical activity of the AuNP/ZnO/Al2O3/GO/chit/GCE towards determination of catechol. The detection limit of 3.1 μM was obtained for catechol sensing using AuNP/ZnO/Al2O3/GO/chit/GCE.

In another report, Liu et al. employed F, N-doped carbon dots/laccase composite for the sensing of catechol [33]. The authors of this work have prepared F, N-doped carbon dots decorated laccase using benign approach. The formation of the F, N-doped carbon dots/laccase composite was confirmed by transmission electron microscopy (TEM), ultraviolet-visible (UV-vis) absorption spectroscopy, and photoluminescence (PL) spectroscopy which clearly showing the formation of F, N-doped carbon dots/laccase composite.

The X-ray photoelectron spectroscopy (XPS) measurements were also carried out for the F, N-doped carbon dots. The recorded XPS curve of the F, N-doped carbon dots has been displayed in Fig. 3. The full survey scan of the F, N-doped carbon dots has been shown in Fig. 3a whereas the high resolution scan of the C1s, N1s, and F1s have been depicted in Fig. 3cd. The observations confirmed the presence of F and N elements in the carbon dots and this suggested the formation of F, N-doped carbon dots. Furthermore, electrochemical was fabricated, and electrochemical detection of catechol was investigated using cyclic voltammetry.
Fig. 3

XPS of the F, N-doped carbon dots: Survey scan (a), high resolution C1s (b), N1s (c), and F1s (d). (Adopted with permission [33])

The CV curves of the F, N-CDs/lac/GCE in presence of catechol (1 mM) at different scan were recorded. The obtained CV results have been displayed in Fig. 4a whereas the linear calibration plot has been depicted in Fig. 4b. The obtained results revealed good electrochemical activity of the F, N-CDs/lac/GCE and the electrochemical current response increases linearly. The excellent detection limit of 0.014 μM was obtained using F, N-CDs/lac/GCE. The fabricated F, N-CDs/lac/GCE also exhibited high sensitivity of 219.17 μM μAcm−2 mM−1 towards the sensing of catechol.
Fig. 4

CV (a) curves of F,N-CDs/lac/GCE in presence of catechol (1 mM) at different scan rates (10-250 mV/s) and linear calibration plot (b). (Adopted with permission [33])

Sensing of Hydroquinone

Hydroquinone is another isomer form of catechol and derivative of phenol compound which is also toxic in nature and widely used in cosmetics. The accurate detection is necessary to avoid the carcinogenic effect of the hydroquinone.

Yao et al. prepared a composite of copper nanoparticles (CuNPs)/multi-walled carbon nanotubes (MWCNTs) using microwave method [34]. The confirmation of the formation of the CuNPs/MWCNTs composite was carried out by X-ray diffraction (XRD) and SEM analysis (Fig. 5).
Fig. 5

XRD patterns of CNT and Cu-CNT. (Adopted with permission [34])

The recorded XRD pattern of the CNT showed the diffraction planes of (002) and (100) while the XRD pattern of the Cu-CNT exhibited the diffraction planes of (002), (111), (200), and (220) which confirmed the formation of CNT and Cu-CNT composite. Further, SEM images were also recorded to observe the morphological features of the CNT and Cu-CNT composite. The electrochemical sensor was prepared using GCE as working electrode. Since, electrochemical impedance spectroscopy (EIS) is an important tool to know the electrochemical activity of the electrode materials. Thus, Nyquist plot of the bare GCE, MWCNTs, and Cu-MWCNTs in 5 mM [Fe(CN)6]3−/4- in 0.1 M KCl were recorded and presented in Fig. 6.
Fig. 6

Nyquist plots of the bare GCE, MWCNTs, and Cu-MWCNTs in 5 mM [Fe(CN)6]3−/4- in 0.1 M KCl. Inset: equivalent circuit. (Adopted with permission [34])

The equivalent circuit for the plotted EIS result has been presented in inset of Fig. 6. The EIS results revealed that Cu-MWCNTs modified electrode has higher electrochemical activity compare to the other two electrodes. This may be due to the synergistic effects between MWCNTs and CuNPs. Furthermore, the chitosan (Chi) was also used in the fabrication of electrodes for the sensing of hydroquinone using cyclic voltammetry. The CV curves of the bare (a) GCE, (b) MWCNTs@Chi/GCE, and (c) Cu-MWCNTs@Chi/GCE in the presence of hydroquinone have been displayed in Fig. 7.
Fig. 7

CV curves of the bare (a) GCE, (b) MWCNTs@Chi/GCE, and (c) Cu-MWCNTs@Chi/GCE in the presence of hydroquinone. (Adopted with permission [34])

The CV pattern of the bare GCE showed least current whereas Cu-MWCNTs@Chi/GCE exhibited the highest current towards the sensing of hydroquinone using cyclic voltammetry. This higher current activity or electrochemical behavior of the Cu-MWCNTs@Chi/GCE may be due to the synergistic interactions. The lowest detection limit of 0.04 μM was obtained with excellent reproducibility. The prepared Cu-MWCNTs@Chi/GCE was also employed for real sample analysis and obtained results showed satisfactory performance for practical applications.

Sensing of Hydrazine

Hydrazine is a hazardous compound and the determination of hydrazine is an important tool. Therefore, Beduk et al. have designed and fabricated a novel sensor for the detection of hydrazine [35]. In this work, authors developed inkjet-printed paper using poly(3,4- ethylenedioxythiophene):poly(styrene sulfonate) = PEDOT:PSS decorated ZnO with nafion matrix sensor for the sensing of hydrazine.

The obtained results showed increased current response with increasing concentration of hydrazine. The schematic diagram of the developed sensor has been displayed in Fig. 8a while the digital picture of the sensor has been displayed in Fig. 8b. Further CV investigations were carried out in different concentrations of hydrazine in 0.1 M PBS (Fig. 8c). The fabricated sensor showed good electrochemical activity with improved hydrazine detection. The current was enhanced with increased concentration of the hydrazine. The sensitivity and stability of the developed sensor was also improved with the decoration of the PEDOT:PSS by ZnO particles. The layer by layer deposition method was applied for the fabrication of the electrode which was characterized by XRD, SEM, and atomic force microscopy (AFM) techniques. The developed sensor exhibited the lower detection limit of 5 μM with a wide linear range (10 to 500 μM). This printed electrode (sensor) was also applied for real sample analysis using mineral, sea, and tap water for further explore in the practical applications.
Fig. 8

Schematic of the sensor (a), digital image of the developed sensor (b), and CV curves of PEDOT:PSS/ZnO/nafion in 0, 0.1, 0.5, 1, 5 mM of hydrazine in 0.1 M phosphate buffer solution (PBS). pH = 7.4. (Adopted with permission [35])

Sensing of 2-Phenylphenol and Chlorophenol

Karimi-Maleh et al. developed the electrochemical sensor for the sensing of 2-phenylphenol (water pollutant) in presence of 4-chlorophenol using voltammetric measurements [36].

Karimi-Maleh et al. synthesized Fe3O4 nanoparticles decorated n-hexyl-3-methylimidazolium hexafluorophosphate composite. The n-hexyl-3-methylimidazolium hexafluorophosphate is denoted with HMPF6 whereas carbon paste electrode denoted with CPE. The CPE was modified with Fe3O4-NPs/HMPF6 denoted as Fe3O4-NPs/HMPF6/CPE. This modified Fe3O4-NPs/HMPF6/CPE was further employed for the sensing of 2-phenylphenol using voltammetry investigations. The fabricated sensor showed descent electrochemical performance.

In another work, Zhu et al. [37] also demonstrated the role of electrochemical sensor for the detection of 4-chlorophenol. A novel composite was prepared composed of hydroxylated carbon nanotubes (CNTs-OH) decorated with platinum nanoparticles (PtNPs)/rhodamine B (RhB) composite. The schematic illustration for the fabrication of electrode modifier CNTs-OH/PtNP/RhB has been displayed in Scheme 2.
Scheme 2

Schematic illustration of the synthesis of CNTs-OH/PtNP/RhB. (Adopted with permission [37])

Further the electrochemical sensor with electrode modifier (CNTs-OH/PtNP/RhB) was developed and its electrochemical activity was checked in a redox electrolyte solution (5 mM K3[Fe(CN)6] in 0.1 M KCl). The CV curves of GCE (a), CNTs-OH/GCE (b), CNTs-OH/RhB/GCE (c), CNTs-OH/PtNPs/GCE (d), and CNTs-OH/PtNP/RhB/GCE in 5 mM K3[Fe(CN)6] in 0.1 M KCl at scan rate = 50 mV/s have been shown in Fig. 9.
Fig. 9

CV curves of GCE (a), CNTs-OH/GCE (b), CNTs-OH/RhB/GCE (c), CNTs-OH/PtNPs/GCE (d), and CNTs-OH/PtNP/RhB/GCE in 5 mM K3[Fe(CN)6] in 0.1 M KCl at scan rate = 50 mV/s. (Adopted with permission [37])

The electrode modified with CNTs-OH/PtNP/RhB showed the highest electrochemical activity compare to the other four electrodes (GCE, CNTs-OH/GCE, CNTs-OH/RhB/GCE, and CNTs-OH/PtNPs/GCE). This improved electrochemical activity attributed to the synergistic effects.

Furthermore, the prepared electrodes GCE (a), CNTs-OH/GCE (b), CNTs-OH/RhB/GCE (c), CNTs-OH/PtNPs/GCE (d), and CNTs-OH/PtNP/RhB/GCE (e) was explore to the sensing of 4-chlorophenol and 2,4,6-trichlorophenol. The recorded DPV curve of GCE (a), CNTs-OH/GCE (b), CNTs-OH/RhB/GCE (c), CNTs-OH/PtNPs/GCE (d), and CNTs-OH/PtNPs/RhB/GCE (e) in 50 μM 2,4,6 TCP and 100 μM 4-CP in 0.1 M PBS (pH = 6.0) have been displayed in Fig. 10.
Fig. 10

DPV curve of GCE (a), CNTs-OH/GCE (b), CNTs-OH/RhB/GCE (c), CNTs-OH/PtNPs/GCE (d), and CNTs-OH/PtNPs/RhB/GCE (e) in 50 μM 2,4,6 TCP and 100 μM 4-CP in 0.1 M PBS (pH = 6.0). (Adopted with permission [37])

The CNTs-OH/PtNPs/RhB/GCE exhibited higher current response compare to the other four electrodes (GCE, CNTs-OH/GCE, CNTs-OH/RhB/GCE, and CNTs-OH/PtNPs/GCE). However, GCE showed the least current response which is due to the poor and bare surface area of the electrode. The developed sensor showed the detection limit of 3.69 μM for 4-CP whereas 1.55 μM for 2,4,6-TCP, respectively. This electrode CNTs-OH/PtNPs/RhB/GCE also showed potential for real sample analysis. Thus it can be said the proposed electrode CNTs-OH/PtNPs/RhB/GCE possess excellent electrochemical activity and can be further employed in the detection of other hazardous compounds.

Sensing of Hydrogen Peroxide

Hydrogen peroxide (H2O2) has an important role in physiological processes. The determination of H2O2 is an important task [4]. Thus, Hang et al. developed the hierarchical graphene/nanorods-based hydrogen peroxide sensor applying electrochemical method [38]. The developed sensor showed reasonable detection limit and sensitivity. In other work, Dang et al. have prepared a novel electrode material to prepare the electrochemical electrode for the detection of H2O2 [39]. The author has synthesized copper (Cu) metal-organic-framework (Cu-MOF) decorated ammoniated Au nanoparticles (AuNPs-NH2). The schematic representation for the preparation of AuNPs-NH2/Cu-MOF has been illustrated in Scheme 3.
Scheme 3

Schematic synthesis process of the AuNPs-NH2/Cu-MOF. (Adopted with permission [39])

The XRD pattern of simulated and experimental of Cu-MOF, standard XRD of AuNPs and experimental XRD of AuNPs-NH2/Cu-MOF (a) and FTIR spectra of Cu-MOF and AuNPs-NH2/Cu-MOF (b) have been presented in Fig. 11. The simulated and experimental XRD patterns of the Cu-MOF were well-matched which suggested the successful formation of the Cu-MOF in bulk. Further, the standard XRD of the AuNPs was also compared with the experimental XRD data of the AuNPs (Fig. 11a). The obtained results were well matched which also confirmed the successful synthesis of AuNPs. The XRD of AuNPs-NH2/Cu-MOF showed the diffraction peaks corresponded to the Cu-MOF and AuNPs. This suggested the formation of XRD of AuNPs-NH2/Cu-MOF composite. The FTIR of the Cu-MOF and AuNPs-NH2/Cu-MOF also showed the vibration bands corresponded to the OH-C=O, C=O, C=C, and C-H groups. However, the absorption band at 1650 cm−1 was attributed to the NH2 groups (Fig. 11b).
Fig. 11

XRD pattern of simulated and experimental of Cu-MOF, standard XRD of AuNPs and experimental XRD of AuNPs-NH2/Cu-MOF (a). FTIR spectra of Cu-MOF and AuNPs-NH2/Cu-MOF (b). (Adopted with permission [39])

Furthermore, electrochemical sensor was developed using AuNPs-NH2/Cu-MOF as electrode material. The amperometric current responses were recorded to evaluate the performance of the electrochemical sensors. For comparison, Cu-MOF was also deposited on the working substrate and its electrochemical performance was also checked using amperometric measurements. The amperometric curves of the Cu-MOF and AuNPs-NH2/Cu-MOF in 0.5 mM H2O2 in 0.1 M PBS at pH = 7.4 and amperometric curve of the AuNPs-NH2/Cu-MOF with different concentration of H2O2 have been presented in Fig. 12ab. The observation showed that the lower current was appeared for the Cu-MOF modified electrode whereas the higher current response was obtained for the AuNPs-NH2/Cu-MOF modified electrode (Fig. 12a). Furthermore, authors also recorded the amperometric curve using AuNPs-NH2/Cu-MOF electrode with successive addition of H2O2. The current enhanced with spike of the H2O2 as shown in Fig. 12b.
Fig. 12

Amperometric curves of the Cu-MOF and AuNPs-NH2/Cu-MOF in 0.5 mM H2O2 in 0.1 M PBS at pH = 7.4 (a) and amperometric curve of the AuNPs-NH2/Cu-MOF with different concentration of H2O2 (b). (Adopted with permission [39])

The modified electrode with AuNPs-NH2/Cu-MOF showed the wide linear range from 5 μM to 850 μM. The detection limit using AuNPs-NH2/Cu-MOF modified electrode was calculated to be 1.2 μM. The obtained results were really impressive and could be further employed for practical applications.

Sensing of Nitrite

Nitrite ions NO2 which is also known as preservative are usually used in the drink and food industries. The NO2 may discharge to the environment and has hazardous effects on human health and ecosystem. The detection of NO2 is important and many approaches have been used to detect the NO2 ions. Han et al. prepared a novel composite (rose-like AuNPs/MoS2/graphene) using hydrothermal method [40]. The formation of the rose-like AuNPs/MoS2/graphene composite was checked using XRD, XPS, and TEM measurements. The schematic illustration of the preparation of rose-like AuNPs/MoS2/graphene has been shown in Scheme 4. The TEM results showed that MoS2 possess flower-like surface morphology.
Scheme 4

Schematic representation of the synthesis of rose-like AuNPs/MoS2/graphene and working of modified electrode towards the sensing of nitrite. (Adopted with permission [40])

The survey scan XPS spectrum (a), C1s (b), O1s (c), Mo3d (d), S2p (e), and Au4f (f) XPS spectrum of the rose-like AuNPs/MoS2/graphene have been displayed in Fig. 13af. The XPS data clearly showed the presence of C1s, O1s, Mo3d, S2p, and Au4f which indicated the formation of AuNPs/MoS2/graphene composite.
Fig. 13

XPS full scan spectrum (a), C1s (b), O1s (c), Mo3d (d), S2p (e), and Au4f (f) XPS spectrum of the rose-like AuNPs/MoS2/graphene. (Adopted with permission [40])

Further, the electrodes were prepared using different electrode modifier to investigate the effects of the materials. The CV curves of the bare GCE, GN/GCE, MoS2NF/GCE, and AuNPs/MoS2/GN/GCE in 1 mM NaNO2 in 0.1 M PBS were recorded and the obtained results have been depicted in Fig. 14a.
Fig. 14

CV curves of the bare GCE, GN/GCE, MoS2NF/GCE, and AuNPs/MoS2/GN/GCE in 1 mM NaNO2 in 0.1 M PBS at scan rate = 50 mV/s: pH = 4.0 (a). CV curves of the AuNPs/MoS2/GN/GCE in 1 mM NaNO2 at different scan rates (b). (Adopted with permission [40])

The observations revealed that bare GCE has poor electrochemical activity while the AuNPs/MoS2/GN/GCE possesses excellent electrochemical activity. The highest current response was obtained for the AuNPs/MoS2/GN/GCE in 1 mM NaNO2 in 0.1 M PBS at pH = 4. Further the effect of different scan rates was also investigated in 1 mM NaNO2 in 0.1 M PBS. The recorded CV graphs have been inserted in Fig. 14b. The obtained results showed that the current enhanced in a linear way with increase in the scan rate. This suggested the diffusion controlled process for the sensing of nitrite. The detection limit of 1 μM was obtained with wide linear range using AuNPs/MoS2/GN/GCE. The obtained detection limit for the sensing of nitrite was quite interesting and showed the potential use of AuNPs/MoS2/GN/GCE as a suitable electrode material for electrochemical sensing applications.

Conclusions and Further Outlook

There are so many toxic and hazardous compounds which are frequently used in various industries, cosmetics, and also used as preservatives. These compounds like catechol, hydroquinone, hydrazine, hydrogen peroxide, nitrite, chlorophenol etc. has negative impacts on the human beings and environment including animals and plants. There were conventional approaches to detect these toxic compounds but electrochemical has shown excellent performance with good detection limit and sensitivity. However, there are few challenges for the electrochemical approaches for the sensing of such hazardous compounds. Since the performance of the electrochemical detecting devices depends on the working substrate and electrode modifier, a highly efficient sensor needs to be developed.

The electrochemical sensitivity and detection limit can also be improved by applying new electrode materials such as highly conducting metal oxides, two-dimensional materials such MXene decorated metal oxides or polymer decorated metal oxides. Moreover, some new working electrode substrate consists of highly conducting materials are desirable for the construction of the sensors for electrochemical sensing of toxic or hazardous compounds.

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Copyright information

© Springer Nature Switzerland AG 2020

Authors and Affiliations

  1. 1.Discipline of ChemistryIndian Institute of Technology Indore, Simrol, Khandwa RoadIndoreIndia
  2. 2.Department of ChemistryIndian Institute of Technology DelhiNew DelhiIndia

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