Optoelectronic properties of nanostructured ensembles controlled by biomolecular logic systems.

A nanostructured system composed of enzyme-functionalized silica microparticles, ca. 74 microm, and gold-coated magnetic nanoparticles, 18 +/- 3 nm, modified with pH-sensitive organic shells was used to process biochemical signals and transduce the output signal into the changes of the optoelectronic properties of the assembly. The enzymes (glucose oxidase, invertase, esterase) covalently bound to the silica microparticles performed Boolean logic operations AND/OR processing biochemical information received in the form of chemical input signals resulting in changes of the solution pH value. Dissociation state of the organic shells on the gold-coated magnetic nanoparticles was controlled by pH changes generated in situ by the enzyme logic systems. The charge variation on the organic shells upon the reversible protonation/dissociation process resulted in the changes of the gold layer localized surface plasmon resonance energy (LSPR), thus producing optical changes in the system. The proton transfer process allowed the functional coupling of the information processing enzyme systems with the signal transducing gold-coated magnetic nanoparticles providing their cooperative performance. Magnetic properties of the gold-coated magnetic nanoparticles allowed separation of the signal-transducing nanoparticles from the enzyme-modified signal processing silica microparticles. The reversible system operation was achieved by the Reset function, returning the pH value and optical properties of the system to the initial state. This process was biocatalyzed by another immobilized enzyme (urease) activated with a biochemical signal. The studied approach opens the way to novel optical biosensors logically processing multiple biochemical signals and "smart" multisignal responsive materials with logically switchable optical properties.