The electroconductive or electrocatalytic properties of cond

The electroconductive or electrocatalytic properties of conductive moieties including polymers in combination with carbon or metal-based nanomaterials have also been explored. For example, Dong et al. (2017) developed a portable electrochemical immunosensor by creating a film of Prussian blue chitosan-AuNPs (PB-CS-AuNP) nanocomposite on the screen-printed electrode (Dong et al., 2017). The immunodetection was based on the typical competitive assay, where histamine-antigen (HA-Ag) (the coating antigen) competes with free histamine to combine with HRP-labeled histamine antibody (HRP-HA-Ab) (i.e. detector antibody) as shown in Fig. 10. After the interaction of histamine sample with the detector antibody, the mixture is introduced onto the electrode, where the free detector antibody forms a complex with the pre-immobilized HA-Ag. Subsequently, the electrochemical signal is generated by introducing the hydroquinone (HQ) and H2O2 solution, which serves as a substrate for the HRP enzyme. The sensor response was observed to be inversely proportional to the concentration of histamine. This method showed a higher sensitivity and faster response due to the combination of (i) electrocatalytic activity of Prussian blue and (ii) facilitated Pentylenetetrazole mg transfer by means of AuNPs. The developed immunosensor showed a linear range from 0.09 μM to 0.90 mM (0.01–100 μg/mL) 0.01 to 100 μg/mL for HA in fish samples with an average rate of recovery ranging from 97.25 to 105%. Geto, Tessema, and Admassie (2014) developed a nanocomposite of multi-walled carbon nanotubes (MWCNTs) and poly (4-amino-3-hydroxynaphthalenesulfonic acid) MWCNTs/p-(AHNSA) for electrochemical sensing of histamine (Geto et al., 2014). The nanocomposite was coated onto the GCE to form the nanosensor matrix which showed 34-fold enhancement in the peak current response compared to the bare electrode response. The higher performance of the polymer modified electrode could be explained by the existence of an electrostatic interaction between the protonated histamine and anionic functional units of polymer film which eventually electrocatalytically oxidize the histamine. Under optimum conditions, the oxidation peak current increased linearly with the concentration of histamine over a range of 0.1 to 100 μM. The calculated limit of detection and limit of quantitation were found to be 7.62 nM and 254 nM, respectively. In addition, recovery measurements were conducted by spiking the sample with 5.0 × 10−6 M, 10.0 × 10−6 M and 25.0 × 10−6 M histamine standards. The method was also successfully applied for the determination of histamine in fish muscle extract and spiked samples with satisfactory recovery limits from 96.6 to 102.9%. Polyaniline (PANI) is a conductive polymer and its optical and electrochemical properties can be controlled by charge transfer doping and deprotonation. It has been widely used for optical signal processing, energy conversion (photovoltaic cells), electrochemical and optical sensors and electrocatalysis (Sainz et al., 2005). The electrochemical properties of PANI have been utilized to develop a histamine sensor by forming its composite with CeO2 nanoparticles (Bhargavi, Nesakumar, Sethuraman, Maheswari Krishnan, & Rayappan, 2014). The electrochemical sensor matrix was fabricated by coating the CeO2-PANI on GCE followed by immobilization of diamine oxidase (DAO). The DAO catalyzes the oxidative deamination of histamine into imidazole acetaldehyde and peroxide, which eventually generates electrons and produces the electrochemical signal (Burger, 1967). The nano-interface of CeO2-PANI increases the direct electron transfer between the electrode and enzyme, which in turn, enhances the sensitivity of the biosensor. The sensor exhibited a linear response in the concentration range from 0.45 to 1.05 mM with a sensitivity of 724.94 μA cm−2 mM−1. The developed method exhibited a LOD value of 48.7 μM, and limit of quantification (LOQ) of 132.4 μM with a response time of <1 s and a sufficiently long shelf life of 18 days with a recovery rate of almost 86%.