Optoelectronic Properties of
Nanostructured Ensembles Controlled by
Biomolecular Logic Systems
Marcos Pita,
†
Melina Kra ¨ mer,
†,‡
Jian Zhou,
†
Arshak Poghossian,
‡
Michael J. Scho ¨ ning,
‡
Vı´ctor M. Ferna ´ ndez,
§
and Evgeny Katz
†,
*
†
Department of Chemistry and Biomolecular Science, and NanoBio Laboratory (NABLAB), Clarkson University, Potsdam, New York 13699-5810,
‡
Institute of Nano- and
Biotechnologies (INB), Aachen University of Applied Sciences, Ginsterweg 1, D-52428 Ju ¨lich, Germany, and Institute of Bio- and Nanosystems (IBN2), Research Centre Ju ¨lich,
D-52425 Ju ¨lich, Germany, and
§
Instituto de Cata ´lisis y Petroleoquı ´mica, CSIC, C/Marie Curie 2, 28049 Cantoblanco, Madrid, Spain
E
xperimental and theoretical studies
of optoelectronic properties of nano-
structured materials
1
and, particu-
larly, ensembles of metallic nanoparticles
(NPs) in solutions and on surfaces
2
have at-
tracted much recent attention. Localized
surface plasmon resonance (LSPR) in metal
NPs, which controls their optical properties,
depends on the metal nature, shape, size,
and environment of the NPs.
3
Minor
changes in the distances between the NPs,
charges localized on them, or alteration of
charging/dielectric properties in their
nearby environment (particularly changes
of charges in the organic shells)
4
might be
substantially amplified by the variation of
the optoelectronic properties of NPs (i.e.,
LSPR) yielding a shift of their absorbance
band. Functional coupling of metal NPs
with biomolecular systems
5
and high sensi-
tivity of the optoelectronic properties of
metal NPs to the environment changes are
used in various sensors and biosensors,
6,7
specifically in DNA and protein sensors,
8
and enzyme-based biosensors.
9
Most of the
observed optical effects and the applica-
tions based on them originate from the dis-
tance variation between metal NPs result-
ing in the change of their plasmon coupling
and consequently in the absorbance shift
in the NPs spectra.
10
The distance variation
could be caused by cross-linking of the
biomolecular-functionalized NPs through
biospecific interactions (usually upon DNA
hybridization
11
or protein-affinity bind-
ing
12
). Charging effects on the LSPR energy
and therefore on the optical properties of
metal NPs are much less studied and rarely
used in biosensors and optobioelectronic
systems. The charge directly associated with
the metallic cores of NPs or distributed on
a short distance from them (e.g., associated
with the organic shell) could be changed by
chemical,
13
biochemical,
14
electrochemical,
15,16
or photochemical
17
means. However, the charge effect on the
NPs absorbance band shift was reported
only in a few papers,
15
while other studies
used surface plasmon resonance to observe
the charge effects on the optical properties
of surface-confined NPs.
14,17
Functional
coupling of metal NPs with biomolecular
systems through the charge transfer pro-
cesses resulting in the optical properties
variation is a challenging aim yet.
*Address correspondence to
ekatz@clarkson.edu.
Received for review July 20, 2008
and accepted September 19, 2008.
Published online October 1, 2008.
10.1021/nn8004558 CCC: $40.75
© 2008 American Chemical Society
ABSTRACT A nanostructured system composed of enzyme-functionalized silica microparticles, ca. 74 m,
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.
KEYWORDS: functional nanoparticles · magnetic nanoparticles · enzyme logic · logic
gate · signal-responsive material · localized surface plasmon resonance · LSPR ·
switchable optical properties · optoelectronic properties · nanostructured materials
ARTICLE
VOL. 2 ▪ NO. 10 ▪ PITA ET AL. www.acsnano.org 2160