Biosensors based on direct electron transfer of protein - Electrochemical Sensors, Biosensors and Their Biomedical Applications - page 534

to incorporate proteins into fi lms. In the fi rst, a solution of surfactant in chloroform
is spread onto the electrode surface, and solvent is evaporated. The coated electrode
is then placed into an electrochemical cell containing a solution of protein, which is
taken up into the fi lm. This works best with fi lms in the liquid crystal phase. An alter-
native preparation controls the amount of protein in the fi lm. An aqueous vesicle dis-
persion of surfactant is made and then mixed with a solution containing protein. A
precise volume of this mixture is spread onto an electrode and dried. The vesicles fl at-
ten as they dry, resulting in multiple stacks of bilayers.
Didodecyldimethylammonium bromide (DDAB) is a kind of surfactant, which
can form stable fi lm. DDAB fi lm is lamellar liquid crystals at room temperature
and this fl uid state facilitates good mass and charge transport necessary for catalytic
applications. Rusling and Nasser [8] reported the preparation of stable myoglobin
(Mb)-DDAB fi lms on pyrolytic graphite (PG) electrodes, which was by spontaneous
insertion of Mb from solution into water-insoluble cast fi lms of DDAB. The hetero-
geneous electron-transfer rate on pyrolytic graphite for the Mb Fe(III)/Fe(II) redox
couple in these fi lms was enhanced up to 1000-fold over those in aqueous solution.
Electron-transfer rates of Mb were also enhanced in fi lms of soluble cationic and ani-
onic surfactants adsorbed on PG. The resulting fi lms were stable for a month in pH
5.5-7.5 buffers containing 50 mM NaBr. Spectroscopic, thermal, and electrochemical
characterizations suggested that the fi lms consist of lamellar liquid crystal DDAB con-
taining preferentially oriented myoglobin with the iron heme in a high spin state. Mb-
DDAB fi lms showed good charge-transport rate, which allowed Mb to be used as a
redox catalyst. Reductions of the organohalide acid and ethylene dibromide were cata-
lyzed by Mb-DDAB fi lms on PG electrodes at voltages 1.0-1.3 V less negative than
direct reductions.

17.2.1.5 Nanoparticles embedment of protein
Nanoparticles of metals and metal oxides have been investigated extensively in
recent years due to their novel material properties, which differ greatly from the
bulk substances [9-10]. Very small clusters (

50 metal atoms) act like large mol-

ecules, whereas large ones ( 300 atoms) exhibit characteristics of a bulk sample of

those atoms [11]. Between these extremes, the materials (usually nanomaterial) have
largely unknown chemical and physical properties, which is also the reason why a
glut of research activities has been focused on nanoparticles. Materials in the nano-
metric size category display size-dependent optical, electronic, and chemical proper-
ties. Nanoparticles can be applied to many fi elds, such as optical devices, electronic
devices, catalysis, sensor technology, biomolecular labeling [12-13], etc. Considering
the virtues of nanoparticles, such as large surface area, high powered catalysis and
excellent affi nity, nowadays, varied material nanoparticles have been used to embed
proteins. Carbon nanotubes (CNTs) [14], Au colloid [15-16], quantum dots [17-18],
and nano TiO 2 [19] are generally used.
Since their discovery in 1991 [20], CNTs have generated a frenzy of excitement [21].
CNTs, consisting of cylindrical graphitic sheets with nanometer diameters, possess superb