Biomolecule–Nanoparticle Hybrid Systems
Authors: Zayats Maya , Willner Itamar 
Published: June 2010

Abstract
Biomolecule‐nanoparticle (NP) hybrid systems provide new materials that combine the unique electronic and optical properties of NPs with the recognition and catalytic functions of biomaterials. The biomolecule‐NP conjugates find growing interest as functional materials for designing biosensor systems, nanocircuitry and biomolecule‐templated nanoscale devices. Metallic NPs are applied as nanoscale electrodes for the electrical contacting of redox enzymes with electrodes and the development of amperometric biosensors. Similarly, metal NPs are implemented as electroactive or catalytic labels for the amplified detection of biorecognition events, such as DNA‐nucleic acid hybridization or the formation of aptamer‐protein complexes. The metal NPs are also employed as “weight‐labels” for the amplified detection of biorecognition processes. Semiconductor NPs are also used as labels for the electrochemical detection of biomolecular recognition complexes, and multiplexes analysis of different DNAs was accomplished with semiconductor NPs of different compositions.
Metal NPs provide a versatile optical label for the following of biorecognition complexes. The analyte‐induced aggregation of Au NPs results in an inter‐particle plasmon coupling and a red‐to‐blue color transition as a result of aggregation. This phenomenon was implemented in developing DNA sensors and aptasensors, and is used to characterize the activities of DNAzymes. Also, biomolecule‐metal NPs were used as optical labels of biorecognition events by the probing of the interactions of the localized plasmon of the particles with the surface plasmon waves.
Semiconductor NPs or quantum dots (QDs) exhibit unique size‐controlled luminescence properties. Semiconductor QDs were extensively used as fluorescence labels of biorecognition events. Recent activities demonstrated the use of semiconductor QDs in probing biocatalytic transformations, such as DNA replication or telomerization, and in assaying the activities of enzymes, such as tyrosinase or thrombin. Semiconductor NPs associated with biomolecules were also used for the generation of photocurrents. The resulting photocurrents provided readout signals for DNA recognition, biocatalytic transformations, and enzyme inhibition processes.
Biomolecules, and particularly different enzymes, were found to grow metallic NPs, such as Au or Ag NPs. The enzyme‐generated NPs were used as optical labels to probe the enzyme activities or to quantitatively analyze the substrates of the respective enzymes.
Biomolecule‐NP systems provide catalytic templates for the synthesis of metallic nanowires for future miniaturized electronics. Silver or gold nanowires on DNA templates were generated by the catalytic metallization of metal nanoparticles or metal nanoclusters associated with the templates. Similarly, metal nanowires were synthesized in the cavities of peptide nanotubules, or on peptide nanowires, such as actin. A different approach to generate metallic nanowires by biomolecule‐NP hybrid systems involved the use of enzyme‐NP conjugates as “biocatalytic ink” for the dip‐pen nanolithographic patterning of surfaces, and the subsequent growth of metallic nanopatterns. The metallic nanowires were used as components of nanoscale devices. The fabrication of nanoscale transistors or a fuel‐driven nanotransporter was already materialized.