Studies On Immunosensors For Carcinoembryonic Antigen Based On Inorganic Nano-materials

Electrochemical immunosensors have been widely used for clinical diagnosis,environmental inspection,food analysis and bioassay due to their advantages high sensitivity, fast analytical time, intrinsic selectivity and good ability for real-time analysis. The method used to immobilize biomelecules effectively is the key factor in the construction of immunosensor while maintaining their bioactivity. Nano-materials, exhibiting good biocompatibility, large specific surface area and excellent adsorption capacity, are favorable for fabricating immunosensors, which not only enhance the adsorption and retain the biological activities, but also improve the sensitivity and serving life of the sensors. In this article, we have constructed three immunoelectrodes based on multi-walled carbon nanotubes (MWNT), prussion blue nanoparticles (PB), gold nanoparticles (nano-Au) as matrixes, and their electrochemical characteristics have been evaluated.1. An immunosensor for carcinoembryonic antigen based on gold nanoparticles and MWNT-Pt-CS Composite.A highly sensitive amperometric immunosensor for the determination of carcinoembryonic antigen (CEA) was developed. In the solution of nano-Pt doped chitosan (Pt-CS), multi-wall carbon nanotubes (MWNT) were ultrasonically dispersed to give a multi-wall carbon nanotubes-Pt-chitosan composite (MWNT-Pt-CS). This method offered some advantages as follows:(1) Nano-Au increased the amount of antibody; (2) H2O2 could be directly reduced by Nano-Pt and MWNT, thereby increasing the sensitivity of immunosensor; (3) In addition to block the possible remaining active sites of nano-Au layer, HRP could improve sensitivity by catalytic reduction of H2O2. Under the optimized conditions, the response current of the proposed immunosensor decreased linearly in two concentrations ranges of CEA from 0.5 to 10 ng/mL and from 10 to 120 ng/mL with a detection limit of 0.2 ng/mL.2. A novel immunosensor for carcinoembryonic antigen based on double-layer nanometer-sized gold particles and poly(diallyldimethylammonium chloride) protected prussian blue nanoparticlesA highly sensitive amperometric immunosensor has been developed for the detection of carcinoembryonic antigen (CEA) based on poly(diallyldimethylammonium chloride) (PDDA) protected prussian blue nanoparticles (P-PB) and double-layer nanometer-sized gold particles. Compared with traditional PB nanoparticles, P-PB was more stable in aqueous solution.The double-layer nanometer-sized gold particles were modified to offer large specific interface and desirable biocompatibility to adsorb amount of antibodies without losing their activities. This immunosensor was characterized by cyclic voltammetry (CV) and scanning electron microscope (SEM). Under the optimized conditions, this immunosensor showed good linearity, and the working ranges were in two concentration of CEA from 0.3 to 10 ng/mL and from 10 to 120 ng/mL with a detection limit of 0.1 ng/mL at 3 times the background noise.3. Bilayers HRP-coated carbon nanotubes as biolabel for electrical biosensing of cancer biomarker.A novel and ultrasensitive electrochemical immunosensor based on double enzyme layers assembled multiwall carbon nanotubes (MWNT) as signal amplification labels was developed for the detection of a cancer biomarker, as exemplified by the measurement of Carcinoembryonic Antigen (CEA) as a model protein. In this study, horseradish peroxidase (HRP) was assembled onto MWNT templates through electrostatic interactions with poly (diallyldimethylammonium chloride) (PDDA), and further conjugated with CEA secondary antibodies (Ab2) as the enzyme biolabel which could amplify the sensitivity greatly. Under the optimum conditions, a linear range from 0.05 to 45 ng/mL (R=0.9980) was obtained with the detection limit of 16.0 pg/mL (3δ).