Optothermal effect

Some detectors employ the optothermal effect the absorbed modulated infrared radiation heats the sample and its environment, thus producing sound waves which are recorded with a microphone. They can be combined with scanning spectrometers and interferometers. A Golay cell (Golay, 1949) measures the optothermal pressure change by a light beam which is deflected by a reflecting membrane. The first infrared process spectrometer, the URAS, alieady employed the absorption bands of a detector gas to specifically analyze the concentration of this particular gas in a sample. This is a non-dispersive spectrometer already mentioned in Sec. 1. 

Optical devices (optodes) Absorbance Reflectance Luminescence Refractive index Optothermal effect Light scattering... 

Optothermal effect caused by concentration-dependent light absorpti(Hi on the sensor surface... 

Optical devices Changes in light intensity, color, or emission spectra Absorbance Reflectance Luminescence Refractive index Optothermal effect Light scattering (Raman scattering, plasmon resonance)... 

Optical sensors, following absorbance, reflectance, luminescence, fluorescence, refractive index, optothermal effect and light scattering... 

Optical devices transform changes of optical phenomena, which are the result of an interaction of the analyte with the receptor part. This group may be further subdivided according to the type of optical properties which have been applied in the chemical sensors absorbance, reflectance, luminescence, and fluorescence, refractive index including the surface plasmon resonance effect, the optothermal effect, and light scattering. 

Thermometric devices based on the measurement of the heat effects of a specific chemical reaction or adsorption which involve the analyte. Examples of this group are the so-called catalytic sensors. The devices based on measuring optothermal effects can alternatively be included in this group. 

The very large absorption cross-sections of Au nanoparticles give rise to photothermal effects, that is, an increase in local temperature upon plasmon resonance excitation. The concept of Au nanoparticles as photothermal transducers has inspired numerous efforts to develop biomedical applications such as localized hyperthermal therapy,63-65 photothermal contrast agents,66 and optothermally controlled drug release,67-69 and also novel platforms for information storage.70... 

Peterson, E.N., The hydrating effect of a cream and white petrolatum measured by optothermal infrared spectrometry in vivo, Acta Derm. Venereol., 71, 373, 1991. 

There has recently been considerable interest in the detection and identification of air-borne volatile compounds in such diverse areas as quality control of perfume to detection of toxic gases. Miniaturization, the potential low cost of sensors and the variety of applications promise an enormous market (29, 30), Chemical sensors (29) for volatile compounds operate on varied principles and can be classified according to the method of functioning into basic groups such as electrical (field-effect transistors, metal oxide semiconductors and organic semiconductors), optical (spectrophotometric, luminescence, optothermal) and sensors that are sensitive to a change of mass (piezoelectric and acoustosurface). 

---