This
is the first comprehensive review on methods and materials
for use in optical sensing of pH values and on applications of such
sensors. The Review starts with an introduction that contains subsections
on the definition of the pH value, a brief look back on optical methods
for sensing of pH, on the effects of ionic strength on pH values and
p
K
a
values, on the selectivity, sensitivity,
precision, dynamic ranges, and temperature dependence of such sensors.
Commonly used optical sensing schemes are covered in a next main chapter,
with subsections on methods based on absorptiometry, reflectometry,
luminescence, refractive index, surface plasmon resonance, photonic
crystals, turbidity, mechanical displacement, interferometry, and
solvatochromism. This is followed by sections on absorptiometric and
luminescent molecular probes for use pH in sensors. Further large
sections cover polymeric hosts and supports, and methods for immobilization
of indicator dyes. Further and more specific sections summarize the
state of the art in materials with dual functionality (indicator and
host), nanomaterials, sensors based on upconversion and 2-photon absorption,
multiparameter sensors, imaging, and sensors for extreme pH values.
A chapter on the many sensing formats has subsections on planar, fiber
optic, evanescent wave, refractive index, surface plasmon resonance
and holography based sensor designs, and on distributed sensing. Another
section summarizes selected applications in areas, such as medicine,
biology, oceanography, bioprocess monitoring, corrosion studies, on
the use of pH sensors as transducers in biosensors and chemical sensors,
and their integration into flow-injection analyzers, microfluidic
devices, and lab-on-a-chip systems. An extra section is devoted to
current challenges, with subsections on challenges of general nature
and those of specific nature. A concluding section gives an outlook
on potential future trends and perspectives.
