Biomolecule-functionalized nanoparticles

In recent years, there has been a lot of research in the utilization of biomolecule-functionalized nanoparticles for the formation of hybrid nanostructures. While much effort was spent on solution systems, there are some examples that exploit the binding specificity of the biomolecules, for example, proteins, peptides, and DNA to assemble nanoparticles on surfaces. 

The strong and specific biotin-streptavidin binding was used to assemble biomolecule-functionalized nanoparticles in multilayered structures.67 Application of an electrical field allowed the assembly of multilayer structures by using extremely low concentrations of nanoparticles with minimal nonspecific binding. A microelectrode array was used to facilitate the rapid parallel electrophoretic transport and binding of biotin- and streptavidin-functionalized fluorescent nanoparticles to specific sites. By controlling the current, voltage, and activation time at each nanoparticle adsorption step, the directed assembly of more than 50 layers of nanoparticles was accomplished within an hour. 

Biomolecule-Functionalized Nanoparticles for Controlled Chemical Reactivity... 

Wet preparation of metal nanoparticles and their covalent immobilization onto silicon surface has been surveyed in this manuscript. Thiol-metal interaction can be widely used in order to functionalize the surface of metal nanoparticles by SAM formation. Various thiol molecules have been used for this purpose. The obtained functionalized particles can be purified to avoid the effect of unbounded molecules. On the other hand, hydrogen-terminated silicon surface is a good substrate to be covered by Si-C covalently bonded monolayer and can be functionalized readily by this link formation. Nanomaterials, such as biomolecules or nanoparticles, can be immobilized onto silicon surface by applying this monolayer formation system. 

The fast, sensitive, reliable, and reproducible detection of (bio)molecules including quantification as well as biomolecule localization, the measurement of their interplay with one another or with other species, and the assessment of biomolecule function in bioassays as well as in vitro and in vivo plays an ever increasing role in the life sciences. The vast majority of applications exploit extrinsic fluorophores like organic dyes, fluorescent proteins, and also increasingly QDs, as the number of bright intrinsic fluorophores emitting in the visible and NIR is limited. In the near future, the use of fluorophore-doped nanoparticles is also expected to constantly increase, with their applicability in vivo being closely linked to the intensively discussed issue of size-related nanotoxicity [88]. 

Li Wang, Xian-Xue Gan (2009) Biomolecule-functionalized magnetic nanoparticles for flowthrough quartz crystal microbalance immunoassay of aflatoxin Bl. Bioprocess Biosyst Eng 32 109-116... 

Another approach consists in functionalizing nanoparticles with target-specific biomolecules for controlling the navigation under in vivo conditions. 

In 1994, thiols were firstly used as stabilizers of gold nanoparticles [6a]. Thiols form monolayer on gold surface [18] and highly stable nanoparticles could be obtained. Purification of nanoparticles can be carried out, which makes chemical method of metal nanoparticles a real process for nanomaterial preparation. Various thiol derivatives have been used to functionalize metal nanoparticles [6b, 19]. Cationic and anionic thiol compounds were used to obtain hydrosols of metal nanoparticles. Quaternary ammonium-thiol compounds make the nanoparticle surface highly positively charged [20]. In such cases, cationic nanoparticles were densely adsorbed onto oppositely charged surfaces. DNA or other biomolecule-attached gold nanoparticles have been proposed for biosensors [21]. 

The branched polysaccharide dextran is assembled with alkanethiol-modified gold nanoparticles and the resulting nanocomposite is then functionalized to facilitate the specific binding of target biomolecules. This biorecognition process can be easily detected by particle plasmon resonance (PPR), based on the optical properties of gold nanoparticles [163]. 

Nanoparticle surface modification is of tremendous importance to prevent nanoparticle aggregation prior to injection, decrease the toxicity, and increase the solubility and the biocompatibility in a living system [20]. Imaging studies in mice clearly show that QD surface coatings alter the disposition and pharmacokinetic properties of the nanoparticles. The key factors in surface modifications include the use of proper solvents and chemicals or biomolecules used for the attachment of the drug, targeting ligands, proteins, peptides, nucleic acids etc. for their site-specific biomedical applications. The functionalized or capped nanoparticles should be preferably dispersible in aqueous media. 

The applications of nanoparticles in biosensors can be classified into two categories according to their functions (1) nanoparticle-modified transducers for bioanalytical applications and (2) biomolecule-nanoparticle conjugates as labels for biosensing and bioassays. We intend to review some of the major advances and milestones in biosensor development based upon nanoparticle labels and their roles in biosensors and bioassays for nucleic acids and proteins. Moreover, we focus on some of the key fundamental properties of certain nanoparticles that make them ideal for different biosensing applications. 

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