Metallic nanoparticles enzyme immobilization

Here, we review the use of microgel particles as reactors for the immobilization of catalytically active metal nanoparticles or enzymes. The composite particles of microgels and the metal nanoparticles can be used for catalysis in aqueous media, that is, under very mild conditions [24-28], Thus, the composite systems allow us to do green chemistry [29] and conduct chemical reactions in a very efficient way. 

All results reviewed herein demonstrate that the microgel particles may serve as nanoreactors for the immobilization of catalytically active nanostructures, namely for metal nanoparticles and enzymes. In both cases, the resulting composites particles are stable against coagulation and can be easily handled. Moreover, the catalytic activity of metal nanoparticles can be modulated through the volume transition that takes place within the thermosensitive microgel carrier system. Similar behavior has been also observed for the temperature dependence of enzymatic activity. Thus, the microgel particles present an active carrier system for applications in catalysis. 

Enzyme sensors are another important application of metal nanoparticles in CMEs besides nonenzyme sensors. Many enzymes can keep their activity when anchored onto gold nanoparticles. A novel method for fabrication of a biosensor based on the combination of sol-gel and self-assembled techniques has been introduced very recently. For example, the gold nanoparticles and enzyme horseradish peroxidase (HRP) can be successfully immobilized on gold electrode by the help of sol-gel with thiol groups, and the direct electrochemistry of HRP has been achieved and the biosensor thus prepared exhibits fast response, good reproducibility, and long-term stability. 

There are a variety of methods to detect the DNA content of food, which can be used to unequivocally identify the nature of the product [4]. Among the various systems for nucleic acid detection, electrochemical DNA analysis can involve direct detection based on a guanine signal (label-free) [5] or an electrocatalytic mechanism (label-based). Quantum dots (QDs) [6,7], metal nanoparticles (NPs) [8,9], enzymes [10,11], and metal complexes [12, 13] can be employed as labels. This chapter focuses on electrochemical biosensing systems based on DNA hybridization events, which offer novel routes for food safety and security applications. Particularly, it describes in detail different approaches reported in the latest years on the immobilization of oligonucleotides on electrochemical transducers for sensing of various compounds with interest in food industry. In addition, some interesting applications in other fields that can easily be extended to that of food are also included. 

The above studies suggest that electrochemical deposition provides a versatile, yet simple route for immobilizing proteins, enzymes, and bacteria in silane sol-gel films. The biological species remained active in the electrodeposited composite films, allowing their applications for biosensing. More sophisticated films with redox mediators, metal nanoparticles, and CNTs have also been constructed via the sol-gel co-electrodeposition approach. 

The performance of the films can be further improved by co-electrodeposition with other species such as metals, nanoparticles, and carbon nanotubes. Moreover, electrodeposited sol-gel films may also serve as a platform for embedding fiuictional materials. Specifically, the sol-gel system is ideal for immobilizing bioactive species, such as enzymes and bacteria thus, electrodeposition approach allows simple one-step fobrication of biosensors. Electrodeposition also yields selective deposition of silane/CNT antireflective coatings on conductive patterns. Molecularly imprinted films are prepared by co-electrodeposition of the target molecule with sol-gel followed by its removal. 

This chapter has addressed recent advances in the application biomolcules immobilized onto metal oxide nanoparticles for fabrication of biosensors. Electrochemical contacting of redox enzymes or proteins with electrode surfaces is a key step in construction of third generation reagent-free biosensors. We have described a variety of metal oxide nanoparticles... 

---