showing the adhesion of these cells to be most likely derived from chemical factors. The long-term culture of hepatocytes on porous silicon closely resembled that
from tissue culture polystyrene, evidenced by comparison of their viable populations and productions of albumin and urea.
These studies of cell growth upon porous silicon indicate that the fabrication of
bioactive silicon implants may be achieved in the near future. The coupling of cellular and tissue structures to the optoelectronic properties of porous silicon may
allow the implantation of biocompatible, intelligent, and fully integrated devices
for controlled release of drugs, diagnostics of bodily functions, and replacement of
failed bodily processes. The interfacing of neural cells (substantia nigra) to siliconbased electronics may be the next step in this area of research [81].
16.4.2
Micro Enzyme Reactors (mIMERS) and Total Analysis Systems (mTAS)
For separation- and catalysis-based technologies, interfacial characteristics are critical. There has been considerable research to understand the effects of different
surface terminations on non-specific binding of biological molecules, such as proteins, to surfaces based on thiol-on-gold self assembly [82]. It is expected that the
results of these studies can be generalized to silicon-based monolayers; thus, tailoring of the nanocrystalline porous silicon interface will allow versatility and optimization of properties for specific applications. This desire for control over surface
chemistry has extended to size as well. Interest in the miniaturization of analytical
substrates and the conservation of analyte samples has driven the development of
compact integrated platforms for biochemical analysis. Recent work from Bengtsson et al. outlined the use of high-aspect ratio porosified silicon enzyme microreactors with immobilized glucose oxidase and trypsin reagents [83]. Colorimetric
assay and mass spectrometry of the trypsin digests were used to assess the catalytic
turnovers of these mIMERS; the greatest activity was measured for silicon substrates that had been etched to form porous layers of equal thickness throughout
the full length of the microreactor channels (Figure 16.10). In contrast, non-porous
substrates functionalized with these enzymes, lacking the expansive surface area
of the etched, porous reactors, show substantially smaller turnover numbers, as
evidenced by preceding work [84–87]. The inferior performance of mIMERS with
variable porous layer thicknesses was ascribed to the relatively inefficient transport
properties of the inhomogeneous pore morphology of these systems; the smaller,
incongruous sizes of such pores hinder the diffusion of chemical substrates into
the enzyme-derivatized material and thus limit the efficiency of these microreactors. In addition to etching conditions, variation in the dimensions of the microreactor channels and walls was also found to affect catalytic turnover; however,
thicker porous layers did not generally increase enzymatic activity, suggesting the
existence of an optimal thickness. Although the physical attributes of these systems and their effects upon enzymatic activity have been investigated, the surface
chemistry remains to be more fully researched. In other work, development of
reliable and stable immunoassays based upon antibody-modified porous silicon
16.4 Chemical Applications Based on Porous Silicon 531
from tissue culture polystyrene, evidenced by comparison of their viable populations and productions of albumin and urea.
These studies of cell growth upon porous silicon indicate that the fabrication of
bioactive silicon implants may be achieved in the near future. The coupling of cellular and tissue structures to the optoelectronic properties of porous silicon may
allow the implantation of biocompatible, intelligent, and fully integrated devices
for controlled release of drugs, diagnostics of bodily functions, and replacement of
failed bodily processes. The interfacing of neural cells (substantia nigra) to siliconbased electronics may be the next step in this area of research [81].
16.4.2
Micro Enzyme Reactors (mIMERS) and Total Analysis Systems (mTAS)
For separation- and catalysis-based technologies, interfacial characteristics are critical. There has been considerable research to understand the effects of different
surface terminations on non-specific binding of biological molecules, such as proteins, to surfaces based on thiol-on-gold self assembly [82]. It is expected that the
results of these studies can be generalized to silicon-based monolayers; thus, tailoring of the nanocrystalline porous silicon interface will allow versatility and optimization of properties for specific applications. This desire for control over surface
chemistry has extended to size as well. Interest in the miniaturization of analytical
substrates and the conservation of analyte samples has driven the development of
compact integrated platforms for biochemical analysis. Recent work from Bengtsson et al. outlined the use of high-aspect ratio porosified silicon enzyme microreactors with immobilized glucose oxidase and trypsin reagents [83]. Colorimetric
assay and mass spectrometry of the trypsin digests were used to assess the catalytic
turnovers of these mIMERS; the greatest activity was measured for silicon substrates that had been etched to form porous layers of equal thickness throughout
the full length of the microreactor channels (Figure 16.10). In contrast, non-porous
substrates functionalized with these enzymes, lacking the expansive surface area
of the etched, porous reactors, show substantially smaller turnover numbers, as
evidenced by preceding work [84–87]. The inferior performance of mIMERS with
variable porous layer thicknesses was ascribed to the relatively inefficient transport
properties of the inhomogeneous pore morphology of these systems; the smaller,
incongruous sizes of such pores hinder the diffusion of chemical substrates into
the enzyme-derivatized material and thus limit the efficiency of these microreactors. In addition to etching conditions, variation in the dimensions of the microreactor channels and walls was also found to affect catalytic turnover; however,
thicker porous layers did not generally increase enzymatic activity, suggesting the
existence of an optimal thickness. Although the physical attributes of these systems and their effects upon enzymatic activity have been investigated, the surface
chemistry remains to be more fully researched. In other work, development of
reliable and stable immunoassays based upon antibody-modified porous silicon
16.4 Chemical Applications Based on Porous Silicon 531