Environmental Engineering Reference
In-Depth Information
frequencies are absorbed in the presence of a magnetic ield. The main drawback of
this technique is the cost of analysis [6].
PAS is relatively a new technique used in bioilm characterisation based on the
absorption of electromagnetic radiation. It allows a depth resolved analysis of
both optically and acoustically heterogeneous media that is not possible with other
spectroscopic techniques [43]. Although not a widely used technique, it can be used
to monitor detachment of bioilm.
Use of combined or coupled techniques to monitor bioilms is rapidly gaining
importance. Pradier and co-workers [44] combined three techniques: FTIR, XPS and
ToF secondary ion mass spectrometry, to determine and characterise the chemical
composition of the uppermost layers of the bioilm. Since the three techniques have
different sensitivities and provide different information, they can give us additive
information on bioilm composition and formation. Beech and co-workers [45] also
combined AFM with MS to gain insight into microbe and substrate interaction.
EIS is one of the eficient approaches for monitoring bioilm formation and is rapidly
gaining importance.
In situ
, real-time, and on-line monitoring of bioilms are easier.
Monitoring sensors can easily be installed and operated. An improved version of EIS
was used to monitor bacterial adhesion and bioilm maturation using double-layer
capacitance [46].
Piezoelectricity of a material is its property of deformation upon exposure to an
electric ield. A quartz crystal microbalance (QCM) is a piezoelectric sensor that
employs a quartz crystal, a broadband oscillator, and a frequency counter to examine
change in mass on the quartz resonator [47] It is a very sensitive mass sensing device
with a detection limit of 10
4
bacteria/cm
2
[48]. Many a times, random luctuations in
environmental conditions such as temperature and pressure may lead to baseline drift
and could be misunderstood as mass change. Surface roughness, chemical adsorption
and non-uniform mass sensitivity are other parameters that affect the response [6].
QCM could be employed as a low cost detector to monitor the formation of bioilms
if methods for compensation of pressure and temperature are devised. QCM could
also be used to examine the viscoelastic (non-rigid) properties of bioilms.
Molecular techniques including nucleic acid probes, pulse ield gel electrophoresis,
denaturing-gradient gel electrophoresis and PCR in combination with different
analytical methods, e.g., MS and microscopic techniques is gaining importance for
identifying microbes [43].
With ribosomal ribonucleic acid (rRNA) targeted and fluorescence tagged
oligonucleotides it is possible to detect microbes and study possible mechanisms of
