Studies On Electrochemical Immunesensors Based On Functional Carbon Nanomaterials For Signal Amplification

It is important and valuable to develop highly sensitive and accurate assay in the immuno-analytical field. Electrochemical immunosensor, combined immunologic methods with electrochemical sensing technique, is an analytical method which which hold the advantages of high sensitivity, good selectivity, rapid response, simple operation, and so on. Recently, electrochemical immunosensor detection of tumor markers has been received much attention, which achieved by nanomaterials, biomolecule immobilization technology and signal enhancement technique. This research focuses on the preparation of functionalized nanocomposite, the construction of sensitive interface, the application of novel signal amplification strategies, and were further used to prepare high sensitivity electrochemical immunosensors. The research details are described as follows:1 Ultrasensitive electrochemical immunosensors for clinical immunoassay using gold nanoparticle coated multi-walled carbon nanotubes as labels and horseradish peroxidase as an enhancerA novel electrochemical immunosensor for ultrasensitive detection of a-fetoprotein (AFP) is described with use of the gold nanoparticles/(3-Mercaptopropyl) trimethoxysilane (AuNP/MPTS) modified electrode as desirable platform and gold nanoparticles functionalized multi-walled carbon nanotubes (MWCNT) nanocomposites labeled secondary antibodies (Ab2) as signal tag. At first, gold nanoparticles (AuNP) were attached on the MWCNT surface by using poly(diallyldimethylammoniumchloride) (PDDA) as linkage reagent to obtain AuNPs/MWCNTs nanocomposites. Subsequently, horseradish peroxidase (HRP) and thionine (Thi) labeled secondary antibodies (Thi-Ab2) were used to bind AuNP/MWCNT nanocomposites with high load amount and good biological activity. Moreover, the immunosensor can provide amplified signals because of the increased surface area and biocompatibility of AuNP/MWCNT nanocomposites. On the other hand, the AuNP/MPTS were used for the biosensor platform for increasing the surface area as well as improving the electronic transmission rate to capture a large amount of primary antibodies (Ab1). Thus, amplified signals can be obtained by an electrochemical sandwich immunoassay protocol in presence of H2O2. The proposed sensing strategy provides a wide linear dynamic range from 0.01 to 50 ng-mL-1 with a low detection limit of 3 pg·mL-1 (S/N= 3). Significantly, the developed immunoassay method showed a good stability, selectivity and reproducibility.2 Highly sensitive impedimetric immunosensor based on single-walled carbon nanohorns as labels and bienzyme biocatalyzed precipitation as enhancer for cancer biomarker detectionA novel sandwich-type electrochemical immunosensor based on functionalized nanomaterial labels and bienzyme biocatalyzed precipitation was developed for the detection of AFP. The enzymes linked to functionalized nanomaterials as a biocatalyst could accelerate the oxidation of 4-chloro-l-naphthol (4-CN) by H2O2 to yield the insoluble product on the electrode surface, the mass loading of the precipitates on the device led to a significant enhancement signal. Cyclic voltammetry and electrochemical impedance spectroscopy techniques were used to monitor the enhanced precipitation of 4-CN that accumulated on the electrode surface and subsequent decrement in the electrode surface area by monitoring the reduction process of the Fe(CN)63-/Fe(CN)64-redox couple. Under the optimal conditions, the proposed immunosensor showed a high sensitivity and a wide linear range from 0.001 to 60 ng-mL"1 with a low detection limit of 0.33 p g-mL-1. Moreover, the immunosensor exhibited good selectivity, acceptable stability and reproducibility. The amplification strategy performed good promise for clinical screening of tumor biomarkers.3 Ultrasensitive electrochemical immunosensor for carbohydrate antigen 19-9 using Au/porous graphene nanocomposites as platform and Au@Pd core/shell bimetallic functionalized graphene nanocomposites as signal enhancersA facile and feasible sandwich-type electrochemical immunosensor for ultrasensitive determination of Carbohydrate antigen 19-9 (CA19-9) was designed by using Au nanoparticles functionalized porous graphene (Au-PGO) as sensing platform and Au@Pd core/shell bimetallic functionalized graphene nanocomposites (Au@Pd-Gra) as signal enhancers. Herein, Au@Pd-Gra with large surface area was prepared for immobilizing plentiful of redox probe-thionine (Thi), HRP and secondary antibodies (Ab2), leading to the formation of Au@Pd-Gra/Thi-Ab2/HRP bioconjugate wexhibited satisfying electrochemical redox activity, highly electrocatalytic activity and friendly biocompatibility. With the synergistic effect between Au@Pd-Gra and HRP, an almost triple amplified detection signal was achieved in the present of H2O2, so as to improve the detection limit of the proposed immunosensor effectively. Furthermore, Au-PGO was utilized as the biosensor platform which could greatly enhance the surface area to immobilize a large amount of capture primary antibodies (Ab 1) leading a further enhanced the sensitivity of immunosensor. Under optimal conditions, the electrochemical immunosensor exhibited desirable performance for determination of CA19-9 with a wide linearity in the range from 0.015 to 150 U-mL-1 and a relatively low detection limit of 0.006 U·mL-1. Importantly, the resulted immunosensor displayed good specificity and high sensitivity, implying potential applications in clinical research.