Nanoporous metals by alloy corrosion: Bioanalytical and biomedical applications
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ntroduction Numerous nanoporous materials can be obtained via dealloying. Among these, nanoporous gold (NPG) has stood apart for use in bioanalytical and biomedical applications. This can be attributed to its many desirable properties, including high effective surface area, good electrical conductivity, easy surface modification via thiol-gold linker chemistry, tunable pore morphology, and compatibility with conventional microfabrication. Initial interest in NPG has centered on its use as a versatile material to study structure–property relationships in the context of size-dependent mechanical properties, as well as catalytic and energy-storage applications. Recently, there has been a surge of interest in NPG’s applications in biomedical sciences, as it has offered unique solutions to standing issues in the fields of biosensors and neural interfaces. This article aims to provide a review of NPG-based biosensor and neural interface operation and challenges, as well as opportunities offered by NPG formed by dealloying.
Bioanalytical applications In most bioanalytical systems, the goal is to sense and extract molecule(s) of interest with high sensitivity and selectivity. We initially describe the considerations for sensing and later extend the discussion to bioseparation applications, as both have significant mechanistic commonalities.
A typical biosensor architecture can be generalized to a capture probe immobilized on a solid support, a target biomarker in liquid or gas medium, and a reporter molecule that mediates the transduction of the capture event to an easily measurable signal (e.g., optical, electrical) (Figure 1a). For example, in the case of a nucleic acid-based sensor, the capture probe could be a short nucleic acid with a sequence complementary to the target nucleic acid biomarker (e.g., DNA or RNA). In this case, the solid support (e.g., nanoporous gold) would be decorated with the capture probe. In order for the sensing event to occur, the target biomarker would need to react with the capture probe, which requires transport of the target biomarker to the capture probe on the electrode from the solution (e.g., blood sample). This capture reaction may be transduced via additional reporter molecules (e.g., doublestranded specific fluorescent markers) that bind to DNA only in its double-stranded form and emit a fluorescence signal that can be captured by an optical detector. The transport and reaction processes, as well as the effectiveness of the transduction component, constitute the key underlying mechanisms for sensor operation and performance. Much work has been devoted to enhancing various aspects of these processes. There are some performance metrics common to most sensors, with the limit of detection and selectivity/ specificity generally being more important ones. In this section,
Erkin S¸eker, Department of Electrical and Computer Engineering, Multifunctional Nanoporous Metals Group, University of California, Davis, USA; [email protected] Wei-Chuan Shih, Nanobiophotonics Laboratory, and Nanosyst
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