The metal nanoparticles of gold Au silver Ag Platinum Pt
The metal nanoparticles of gold (Au), silver (Ag), Platinum (Pt), Palladium (Pd) and/or their composites are also being widely used to develop electrochemical sensors because of their unique advantages such as (i) ease in immobilization of receptor molecules, (ii) catalysis of electrochemical reactions, (iii) enhancement of adenosine 5 triphosphate disodium receptor transfer, and (iv) easy labeling of analyte or receptor molecules (Luo, Morrin, Killard, & Smyth, 2006). For example, Carralero, González, Yáñez Sedeño, and Pingarrón (2004) developed an amperometric sensor for histamine detection by using AuNPs modified glassy carbon electrodes (AuNPs-GCE) (Carralero et al., 2004). The presence of AuNPs on GCE enhances the catalytic activity and thereby the signal response compared to the response obtained from the conventional gold electrode disk. Authors explained that at a sufficiently positive potential value, oxidation of histamine occurs with concomitant formation of gold oxides, which upon application of cathodic potential gets reduced in order to regenerate the sensor. This method showed a LOD value of 0.6 μM for histamine detection. However, this method has limited field deployability as it essentially requires purification of the sample using a chromatographic technique such as HPLC, because tyramine, tryptamine and indole can generate amperometric signals higher than that of histamine. Recently, bimetallic [email protected] core-shell nanostructures have been utilized to develop histamine sensors in order to enhance the electrocatalytic ability of electrochemical sensors (Gajjala & Palathedath, 2018). The core-shell nanostructures deposited pencil graphite electrodes exhibited greater electrochemically active surface area (43.2 m2/g) compared to other bimetallic nanomaterials reported in the literature. This high active surface area was attributed to the uniform distribution of Pd with an excellent coverage on the electrode surface. Under optimized conditions, the amperometry sensor could detect histamine at a very low oxidation potential of +0.55 V vs. Ag/AgCl without any interference from oxygen evolution reactions. The sensor exhibited a sensitivity of 0.082 μA/μM/cm2 with a LOD value as low as 3.2 ± 0.1 nM. The developed sensor demonstrated an excellent selectivity towards histamine even in the presence of many other common interfering biogenic agents such as tyramine, cadaverine, putrescine, urea, ammonia, and uric acid. In another interesting approach, Ye et al. (2016) developed an impedimetric biosensor by utilizing a biofunctionalized nanoporous alumina membrane and magnetic nanoparticles (Fig. 8) (Ye et al., 2016). In this method, anti-histamine antibody modified magnetic nanoparticles (size = 10 nm) served as pre-concentrator and assisted in signal amplification by capturing the histamine specifically at their surface (Fig. 8a). After concentrating the histamine, the magnetic nanoparticles are transferred to the modified nanoporous membrane (pore size = 100 nm), where they interact with the anti-histamine antibody, resulting in blocking of the pores, which is further amplified due to a relatively large size of the magnetic nanoparticles (Fig. 8b). The blockage signal could increase the impedance across the nanoporous membrane. The rate of impedance change is found to be linearly increased as a function of the logarithmic concentration of histamine in the range of 5 nM to 10 μM with a LOD value of 3 nM. The developed method was useful for histamine detection in surrey fish sample. Since metal nanoparticles and carbon-based nanomaterials possess excellent electroconductive or electrocatalytic properties, a few research groups explored the use of their composites to improve the performance of electrochemical sensors. For example, Apetrei and Apetrei (2016) developed an amperometric biosensor using a screen-printed carbon electrode modified with diamine oxidase/platinum nanoparticles/graphene/chitosan (DAO-nPt/GPH/chitosan/CSPE) for the detection of histamine in freshwater fish samples (Apetrei & Apetrei, 2016). The diamine oxidase immobilized onto the nanostructured surface of the sensor matrix, catalyzes the oxidative deamination of histamine and generates H2O2 (Fig. 9). The liberated H2O2 is catalyzed by platinum nanoparticles (which act as an anode) to form water and eventually generates the electrochemical signal. The nanobiosensor showed a high sensitivity (0.0631 μA.μM), low detection limit (2.54 × 10−8 M) and a broad linear domain from 0.1 to 300 μM. In a different approach, Kumar et al. (2018) designed a voltammetric sensor based on a nanocomposite of graphene nanoribbons and AgNPs (GNRs-AgNPs) for histamine detection (Kumar & Goyal, 2018). The GNRs were chosen as supporting material to grow AgNPs in order to get superior electrical conductivity. The nanocomposite-modified sensor demonstrated a linear calibration plot in the concentration range of 1–500 μM with a sensitivity of 0.158 μA/μM with a LOD value of 0.049 μM. The GNRs-AgNPs sensor showed high selectivity in the presence of common interfering compounds present in biological fluids. Good levels of recovery (> 99%) were found in blood plasma samples.