Immunosensor Based on Zinc Oxide Nanocrystals Decorated with Copper for the Electrochemical Detection of Human Salivary Alpha-Amylase

Abstract

(1) Background: Nanocrystals (NCs)-based electrochemical sensors have been proposed for biomarkers detection, although immunosensors using ZnO NCs decorated with copper are still scarce. (2) Methods: Electrochemical immunodetection of human salivary alpha-amylase (HSA) used ZnO, CuO, and ZnO:xCu (x = 0.1, 0.4, 1.0, 4.0, and 12.0) NCs. (3) Results: Substitutional incorporation of Cu2+ in the crystalline structure of ZnO and formation of nanocomposite were demonstrated by characterization. Graphite electrodes were used and the electrochemical signal increased by 40% when using ZnO:1Cu and 4Cu (0.25 mg·mL−1), in an immunosensor (0.372 mg·mL−1 of anti-alpha-amylase and 1% of casein). Different interactions of HSA with the alpha-amylase antibody were registered when adding the NCs together, either before or after the addition of saliva (4 μL). The immunosensor changed specificity due to the interaction of copper. The ZnO:1Cu and ZnO:4Cu samples showed 50% interference in detection when used before the addition of saliva. The immunosensor showed 100% specificity and a sensitivity of 0.00196 U·mL−1. (4) Conclusions: Results showed that the order of NCs addition in the sensors should be tested and evaluated to avoid misinterpretation in detection and to enable advances in the validation of the immunosensor.

Electrochemical Immunosensors Based on Zinc Oxide Nanorods for Detection of Antibodies Against SARS-CoV-2 Spike Protein in Convalescent and Vaccinated Individuals

“…Some successful examples of practical device enhancement are the manufacturing of miniaturized micro–nano electrodes in glucose and urea sensors, 37 − 39 bacterial meningitis detection, 40 cholesterol biosensing, 41 H1N1 influenza detection, 42 legionella pneumophila diagnosis, 43 grapevine virus detection, 44 cancer diagnosis, 45 , 46 and many other devices employed as promising immunosensors. 47 − 52 …”

“…Indeed, ZnO can now be grown as bulk crystals, thin films, and nanostructures with various techniques such as wet chemical method, microwaves, sputtering, vapor deposition, − and electrodeposition. − This advancement has enabled its usage as a biosensor component, offering a high degree of reproducibility, scalability, design flexibility, and multiplexing of operational features. Some successful examples of practical device enhancement are the manufacturing of miniaturized micro–nano electrodes in glucose and urea sensors, − bacterial meningitis detection, cholesterol biosensing, H1N1 influenza detection, legionella pneumophila diagnosis, grapevine virus detection, cancer diagnosis, , and many other devices employed as promising immunosensors. − …”

Electrochemical Synthesis of Zinc Oxide Nanostructures on Flexible Substrate and Application as an Electrochemical Immunoglobulin-G Immunosensor

“…To date few papers have reported data on ZnO-based immunosensors. Legionella pneumophila [61], cortisol [62], ovarian cancer antigen CA-125/MUC126 [63], human salivar alpha-amylase [64], and urine albumin [65] have been detected using ZnO-based immunosensors. In the case of H-IgG detection, ZnO was used to build field-effect transistor [66] and electrochemical sensors [67].…”

Highly Stable Buffer-Based Zinc Oxide/Reduced Graphene Oxide Nanosurface Chemistry for Rapid Immunosensing of SARS-CoV-2 Antigens

“…Several approaches have been examined for immobilizing bioreceptors on ZnO-contained electrodes. Physical adsorption was tested for immobilizing antibodies on ZnO for immunosensing of human salivary cortisol and α-amylase . Also, carboxyl functional groups existing on graphene form covalent amide bonding with the amine group of antibodies upon their surface deposition, creating more stable bonds and increasing the stability and sensitivity of the immunosensors.…”

“…Physical adsorption was tested for immobilizing antibodies on ZnO for immunosensing of human salivary cortisol 63 and α-amylase. 64 Also, carboxyl functional groups existing on graphene 65 form covalent amide bonding with the amine group of antibodies upon their surface deposition, creating more stable bonds and increasing the stability and sensitivity of the immunosensors. To this end, the accompanying elements such as gold nanoparticles have been used to hybridize DNA probe strands 66 on ZnO−Gr nanocomposites to connect the crosslinkers needed for immobilizing the carboxylic groups.…”