In Situ Characterizations of Porous Media for Applications in Biofuel Cells: Issues and Challenges - Porous Media: Applications in Biological Systems and Biotechnology - page 514

Nivens et al. (1993) have used this technique in the study of microbial
biofilm growth. Since the observation was conducted over a long period of
time, they have to remove the baseline drift due to the fluctuations of hydro-
static pressure and temperature in the liquid test cell. They thus generated a
calibration curve for the frequency shift corresponding to the number of bac-
teria within the biofilm with a detection limit of 3 10 5 cells cm − 2 . With this

calibration curve, they can study the number of attached cells versus time and
derive the rate of biofilm formation. Marx (2003) published a recent review on
QCM for studying thin polymer films and complex biomolecular systems at
the solution-surface interface. The wide detection range makes QCM attractive
for studies ranging from detection of monolayer surface coverage to measuring
much larger mass bound to surface in solution that contains either biopolymers
or biomacromolecules. The QCM technique also provides information about
the energy dissipating properties of the bound surface mass. In combination
with electrochemical techniques, one can study the ion or solute transport in a
film during changes in the film environment or (chemical and/or electrochem-
ical) state. The molecular systems include micellar systems, self-assembling
monolayers (and their phase transition behavior), molecularly imprinted poly-
mers, chemical sensing systems, films made by layer-by-layer (LBL) assembly
technique, and biopolymer films.
There are numerous attempts in the past to use various combinations of
these in situ techniques (even with other spectroscopic techniques) to inves-
tigate film deposition and the resulting film properties. For example, Ham-
nett and Hillman used spectroscopic ellipsometry to study electrodeposition
of poly-thionine and -thiophene in solutions (Hamnett and Hillman 1985,
1987). They were able to calculate film composition and thickness with optical
parameters ( n , k ) accounted for solvent ingress in the film development, thus
fully explored the utility of the spectroscopic ellipsometry with electrochem-
ical techniques. They, however, did not use QCM to help them reap out the
adsorption effect that should be accounted for in the optical model. Gottes-
feld and his coworkers (Redondo et al. 1988; Rishpon et al. 1990; Rubinstein
et al. 1990; Rishpon and Gottesfeld 1991; Sabatani et al. 1993a,b; Gottesfeld
et al. 1995) and many others (e.g., Tjaernhage and Sharp 1994; Severin and
Lewis 2000; McMillan et al. 2005; Richter and Brisson 2005) attempted to uti-
lize various combinations of these techniques to study conjugated conductive
polymers. In general, it is important to point out that the ellipsometric angles
not only change with a material's thickness but also reflect its optical, elec-
trical, and other physical property changes. Probing evolutions of ellipsomet-
ric angles simultaneously with imaging of surface morphological development
and synchronously with nanoscale measurement of mass changes in relation
to other experimental parameters and conditions (such as those imposed by
electrochemical cyclic voltammetry [Rusling and Suib 1994]) to reduce the
information into detailed temporal and spatial resolutions is a very power-
ful tool to probe reaction kinetics or surface phenomena at a (solid-liquid or
solid-gas) interface.

×