A simple electroanalytical method was developed to detect dopamine (DA) neurotransmitter by using carbon quantum dots (CQDs) modified electrode. To synthesis CQDs, a green electrochemical method was adopted and graphite rods were used as anode and cathodes in 0.1 M NaOH/ethanol (EtOH) as the electrolyte solution. As-synthesized CQD showed different particle sizes depending on the applied current with time as characterized by UV-visible spectroscopy. The particle size, lattice structure and functional groups of CQDs were analyzed by the HR-TEM, XRD and FT-IR, respectively. The CQD exhibited a green fluorescence under UV light (365 nm). Moreover, CQD dispersion was used to modify glassy carbon electrode (GCE) and screen-printed carbon electrode (SPCE) to study their electrochemical and electrocatalytic properties. The both GCE/CQD and SPCE/CQD showed higher electrocatalytic activity toward oxidation of dopamine (DA) in phosphate buffered saline (PBS) solution (pH = 7.4). In order to avoid interferences, Nafion (Nf) layer was coated on the CQD film modified electrode. The effect of scan rate on DA oxidation was studied from 10 to 150 mV/s. The calibration curve was recorded for DA from 1 to 7 μM using a SPCE/CQD and the limit of detection was found to be 0.099 μM. The observed electro-catalytic activity of the CQD was attributed to their negatively charged functional groups which attracted positively charged DA in 0.1 M PBS. In addition, detection of DA in spiked human urine sample was demonstrated with satisfactory recovery analysis.

Reduced graphene oxide (rGO) dispersion was obtained by ultrasonication of rGO powder using dodecanethiol (-SH) as an exfoliating agent. Using thiol chemistry, the gold nanoparticles (Au-NPs) were assembled onto the rGO-SH modified glassy carbon electrode (GCE) which showed a strong binding with the surface of the coated electrode. Furthermore, the GCE/rGO-SH/Au-NPs electrode was used to detect mercury (Hg 2+ ) ions in the aqueous solution. When employed as a working electrode, Hg 2+ ions get adsorbed on the electrode surface which was later electrochemically oxidized by differential pulse voltammetry (DPV) with the enhanced oxidation current at +0.172 V. Moreover, this sensor platform showed linear response for Hg detection from 1-10 μM in phosphate buffer saline (PBS) solution and the detection limit was found to be 0.2 μM (S/N = 3). The characterization of the Au-NPs and rGO-SH films were studied by Fourier-transform infrared spectroscopy (FT-IR), UV-Visible spectroscopy, transmission electron microscopy (TEM) and field emission scanning electron microscopy (FE-SEM). The application of the prepared sensor was also demonstrated in detecting mercury ions in tap water samples with satisfactory recovery analysis.

We synthesized an MoS2/f-MWCNTs/ZnO composite and successfully used it to prepare an electrochemical sensor for the selective detection of AA in blood serum samples.

L-cysteine (Cys) is one of the main amino acid and its deficiency could cause several diseases and biological disorders in our body. Thus, it is important to accurately detect Cys level in biological samples. Herein, we reported a facile strategy to fabricate novel electrode material consisting of conductive hybrid film made of copper oxide-boron nitride nanosheets (CuO/BN). Powdered X-ray diffraction (PXRD) and Fourier transform infrared (FT-IR) spectroscopy results confirmed the successful formation of CuO/BN hybrid nanocomposite. Next, electrochemical and electro-catalytic properties of CuO/BN hybrid film is studied by cyclic voltammetry and amperometry. Interestingly, CuO/BN coated glassy carbon electrode (GCE) showed excellent electro-catalytic activity towards Cys oxidation in phosphate buffer solution (0.1 M PBS). Newly developed CuO/BN film modified electrode is exhibited high oxidation peak current at lower potential of + 0.45 V compared to bare GCE. CuO/BN/GCE sensor is also utilized for the detection of Cys from 1 to 10 μM and limit of detection (LOD) was found to be 0.58 μM. The selectivity of the sensor is determined by detecting 5 μM Cys in the presence of different interferent molecules. Furthermore, repeatability, reproducibility and stability of the CuO/BN/GCE sensor are also investigated. Finally, CuO/BN/GCE sensor is successfully applied to detect spiked Cys in human blood serum samples with good recovery.

To face the change in energy paradigm, we need to devise technology that utilizes renewable resources and eventually realizes sustainability. Fuel cells generate electricity in a greener way, the efficiency and its cost-effectiveness depend mainly on the electrode material. Biochar serves as the promising electrode material, fuel, and separator membrane for fuel cells by being cheap, renewable, and possessing excellent electrochemical performance. The chapter is expected to provide a database of knowledge on how biochar with diversified physical and chemical features and functionalities can be effectively utilized for the possible application as electrode material for energy systems. The chapter appreciates the immense wealth of choice of biochar available with us for an important application in the area of energy as electrode material, fuel, and separator membrane for fuel cells.