detection limits of 100 fg/mm
2 . In addition, it can make multiple measurements per second, which allows it to monitor surface alterations in
real time.
DPI has been marketed as a biosensor to measure the interactions
between proteins and their substrates and to study the formation of
membranes, supported lipid bilayers, and the interaction of surfaces
with lipid vesicles. A nonbiological application of DPI is the characterization of the physisorption of nanospheres to hard surfaces. Because it is
able to simultaneously determine both thickness and refractive index
(and consequently density and mass), DPI is also used to monitor the
changes in surface morphology of various thin films. For example, DPI
can be used to estimate the shape of a protein adsorbed to a surface under
conditions of differing pH.
8.5 SURFACE-SENSITIVE SPECTROSCOPIC
METHODS
Several of the spectroscopic methods discussed in Chapter 6 can be
adapted for studying surface phenomena by using experimental geometries that rely on principles discussed in the previous sections, such as
total internal reflection or surface plasmons, to restrict the region of
observation to within a few hundred nanometers of a surface. Several of
these techniques will be discussed in the following sections.
8.5.1 Attenuated total reflection IR spectroscopy
ATR-FTIR spectroscopy is a powerful spectroscopic technique used to
investigate the structure of adsorbates confined to the solid–air or solid–
liquid interface. The technique is essentially IR spectroscopy of molecules
present at the surface of a solid. It offers several advantages over its
counterpart transmittance-mode IR absorption spectroscopy, which was
discussed in Chapter 6. ATR-FTIR offers near-surface selectivity with only
a minimal amount of sample and allows for the detection of samples of
mass on the order of nanograms. Furthermore, using an infrared polarizer, it is easy to determine the orientation of anisotropic (well-ordered)
samples such as self-assembled surfactant or lipid monolayers. The
sample can also be exposed to external conditions (e.g., various solvents
or different pH conditions), making in situ studies feasible.
CHAPTER 8: Surface Characterization and Imaging Methods
290
2 . In addition, it can make multiple measurements per second, which allows it to monitor surface alterations in
real time.
DPI has been marketed as a biosensor to measure the interactions
between proteins and their substrates and to study the formation of
membranes, supported lipid bilayers, and the interaction of surfaces
with lipid vesicles. A nonbiological application of DPI is the characterization of the physisorption of nanospheres to hard surfaces. Because it is
able to simultaneously determine both thickness and refractive index
(and consequently density and mass), DPI is also used to monitor the
changes in surface morphology of various thin films. For example, DPI
can be used to estimate the shape of a protein adsorbed to a surface under
conditions of differing pH.
8.5 SURFACE-SENSITIVE SPECTROSCOPIC
METHODS
Several of the spectroscopic methods discussed in Chapter 6 can be
adapted for studying surface phenomena by using experimental geometries that rely on principles discussed in the previous sections, such as
total internal reflection or surface plasmons, to restrict the region of
observation to within a few hundred nanometers of a surface. Several of
these techniques will be discussed in the following sections.
8.5.1 Attenuated total reflection IR spectroscopy
ATR-FTIR spectroscopy is a powerful spectroscopic technique used to
investigate the structure of adsorbates confined to the solid–air or solid–
liquid interface. The technique is essentially IR spectroscopy of molecules
present at the surface of a solid. It offers several advantages over its
counterpart transmittance-mode IR absorption spectroscopy, which was
discussed in Chapter 6. ATR-FTIR offers near-surface selectivity with only
a minimal amount of sample and allows for the detection of samples of
mass on the order of nanograms. Furthermore, using an infrared polarizer, it is easy to determine the orientation of anisotropic (well-ordered)
samples such as self-assembled surfactant or lipid monolayers. The
sample can also be exposed to external conditions (e.g., various solvents
or different pH conditions), making in situ studies feasible.
CHAPTER 8: Surface Characterization and Imaging Methods
290