Abstract
Reflectometric interference spectroscopy (RIfS), which is well-established in the visual regime, measures the optical thickness change of a sensitive layer caused, e.g., by binding an analyte. When operated in the mid-infrared range the sensor provides additional information via weak absorption spectra (fingerprints). The originally poor spectra are magnified by surface-enhanced infrared absorption (SEIRA). This is demonstrated using the broad complex fluid water band at 3300 cm−1, which is caused by superposition of symmetric, antisymmetric stretching vibration, and the first overtone of the bending vibration under the influence of H-bonds and Fermi resonance effect. The results are compared with a similar experiment performed with an ATR (attenuated total reflectance) set-up.
Highlights
Optical biosensors play an important role in the detection and quantification of analytes
The originally poor spectra are magnified by surface-enhanced infrared absorption (SEIRA)
A subfield of optical biosensors are those operated through direct optical detection
Summary
Optical biosensors play an important role in the detection and quantification of analytes. Optical biosensors are used in basic research and life science, for example, to study protein–protein interactions [1,2]. A subfield of optical biosensors are those operated through direct optical detection. Direct optical sensing relates to the detection of analyte molecules without the use of labels. They lack the disadvantages of fluorescence technologies such as photodegradation, loss of bioactivity or costs of labeling. An early overview in the field of direct optical sensors, including optical principles and assay formats for selective detection, is given in [3] and updated in [4]
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