Electrochemical biosensors CNTs-based

CNTs offer an exciting possibility for developing ultrasensitive electrochemical biosensors because of their unique electrical properties and biocompatible nanostructures. Luong et al. have fabricated a glucose biosensor based on the immobilization of GOx on CNTs solubilized in 3-aminopropyltriethoxysilane (APTES). The as-prepared CNT-based biosensor using a carbon fiber has achieved a picoamperometric response current with the response time of less than 5 s and a detection limit of 5-10 pM [109], When Nation is used to solubilize CNTs and combine with platinum nanoparticles, it displays strong interactions with Pt nanoparticles to form a network that connects Pt nanoparticles to the electrode surface. The Pt-CNT nanohybrid-based glucose biosensor... 

Other enzymes have also been immobilized on CNTs for the construction of electrochemical biosensors. Deo et al. [115] have described an amperometric biosensor for organophosphorus (OP) pesticides based on a CNT-modified transducer and OP hydrolase, which is used to measure as low as 0.15 pM paraoxon and 0.8 pM parathion with... 

Layer-by-layer (LBL) technique was used for assembling AChE on a CNT transducer (Figure 2). The principle of the biosensor is based on the inhibition of enzyme activity by OPs. The inhibition can be electroehemieally measured. Positively charged poly(diallyldimethylammonium chloride) (PDDA) and negatively charged AChE enzyme were assembed on the CNT surface by LBL technique. Here, CNTs play dual significant roles in the transduction and enzyme-immobilization events. As carriers, CNTs provide a suitable microenviromnent to retain the AChE activity. As a transducer, CNTs amplify the electrochemical signal of the product of the enzymatic reaction. 

Electrochemical biosensor performance such as sensitivity, protein stability, selectivity or reproducibility have been improved due to the use of different carbonaceous materials and combination of them. To improve the sensitivity of a electrochemical biosensor is necessaiy to increase the enzyme amount in a proper immobilization manner. CNTs are good candidates and in this regard, some authors combine carbon nanomaterials with conducting polymers, which gives rise the biosensor special properties due to the synergic effect of the individual components. The electrochemical determination of lactate by the use of lactate oxidase (LOx) based SPE platform takes advantages of the combination of MW-CNT and conductive polysulfone polymer, and such an electrochemical biosensor was successfully applied for the quantification of lactate in wine and beer. In some cases, the inconvenient is the low stability associated with the deleterious interaction of the enzyme LOx with the composite CNT/polymer substrate. 

Monoamine oxidase amperometric biosensor based on SPE were also modified with MWCNT by using the drop casting technique for the determination of antidepressants in model solutions and dosage forms. The authors used BSA protein which provided a matrix for the immobilization of the enzyme and protection of the enzyme activity when glutaraldehyde is used as a linker. Serafin et aZ. developed a label free dual immunosensor for the determination of human growth and prolactin hormones. The electrochemical immunosensor was based on CNT modify carbon SPE platform with the presence of poly(ethylene-dioxythiophene) (PEDOT) and gold nanoparticles. Again, the hybrid nano-material composite facilitated a proper immobilization of the antibody on the electrode matrix. 

In addition to the previously described dehydrogenase-based CNT electrodes, electrochemical biosensors that employ other types of enzyme-modified CNTs have also been reported. Kowalewska and Kulesza applied CNTs with adsorbed redox mediator tetrathiafulvalene (TTF) for electrochemical detection of glucose." TTF-modified CNTs were found to facilitate electron transfer between GOx and the electrode surface for glucose detection. Jia et al. reported a similar strategy for the detection of lactate using MWCNTs modified with TTF and lactate oxidase. Since TTF does not cause skin irritation and the CNT/TTF platform also enables low-potential sensing of lactate, CNT/ TTF/lactate oxidase-based electrochemical biosensors conld be used to detect lactate in perspiration directly on human skin. This was accomplished by preparing temporary tattoos from CNT/ TTF/lactate oxidase-conductive carbon ink that was transferred onto a human subject s skin. ... 

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