Biomedical Engineering Reference
In-Depth Information
of its unique stability and biocompatibility for use in various i elds [9].
Owing to the inherent hydrophilic nature of gold and the capillary force
of nanopores, NPG can be easily penetrated by molecules and solutions.
NPG is broadly used in the i eld of catalysis [10], sensors [11], actuators
[12], optics [13], and numerous areas. For this reason, researchers have
devoted extensive studies to the preparation, properties and applica-
tions of NPG [14-18]. h is perspective focuses on the application of the
NPG i lms in biosensors including nucleic acid based and protein-based
biosensors.
11.2
Fabrication of Nanoporous Gold
Since tunable structure of NPG is a key parameter for its properties and
application, preparation methods of NPG have always been a concern of
researchers. h e fabrication procedures include three main categories:
dealloying, templating and electrochemical method.
11.2.1 Dealloying Procedure
h e most common fabrication procedure for NPG is dealloying corrosion.
Both chemical and electrochemical dealloying has been used for the etch-
ing process [4, 14]. During the dealloying process, more reactive constitu-
ents of the alloy are dissolved in a suitable corrosive solution, resulting in
the formation of a three-dimensional porous network, composed almost
entirely of the most noble alloy components and with pores 5-100 nm
in size [4, 19-20]. For specii c applications in nanotechnology, it is not
only important to reduce the length scale but also to tune the length scale
of nanomaterials. Pore sizes in NPG can be tuned over a wide range by
changing the compositions of starting alloys, varying the electrochemi-
cal potential, or employing thermal annealing at er dealloying [21]. It has
been found that commercially available 12-carat white gold sheets (Ag/Au
alloy, 50:50 wt%) either 100 nm or 1 mm in thickness can be etched to gen-
erate NPG structures that are inexpensive and crack-free over 80 cm
2
[21].
h e structure of dealloyed 100-nm-thick NPG sheet is shown in Figure
11.1. h e pore size is roughly 15 nm. Dealloying is done under free corro-
sion; the sheet is l oated on concentrated nitric acid for 1 h for the etching
process. During dealloying, silver atoms are selectively corroded, and the
gold atoms are assembled into the 3D porous network. h e NPG architec-
ture can be manipulated to increase its pore size by annealing at increased
temperature [22].
