Photothermal spectroscopy with femtojoule sensitivity using a micromechanical device

• Published in: Nature (London) 1994-11, Vol.372 (6501), p.79-81
• Main Authors: Barnes, J. R, Stephenson, R. J, Welland, M. E, Gerber, Ch, Gimzewski, J. K
• Format: Article
• Language: English
• Subjects: Engineering; Exact sciences and technology; Heat; Humanities and Social Sciences; Instruments, apparatus, components and techniques common to several branches of physics and astronomy; letter; multidisciplinary; Other topics in instruments, apparatus, components and techniques common to several branches of physics and astronomy; Physics; Science; Science (multidisciplinary); Sensors; Spectroscopy
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/372079a0

WHEN a material absorbs a photon, a fraction of the energy may be transformed into heat. A measurement of photothermal heating as a function of wavelength can provide an absorption spectrum of the material. We have recently 1,2 developed a micromechanical sensor capable of detecting heat changes of the order of picojoules (10 -12 J). The instrument incorporates a bilayer cantilever of micrometre dimensions which bends in response to heating. Here we show that this device can be used for photothermal spectroscopy with a power sensitivity of 100 pW—two orders of magnitude better than the sensitivity of conventional photothermal deflection spectroscopy 3 . The small size of the sensor allows picogram quanti-ties of material to be studied, opening up the possibility of spectro-scopic studies on individual cells and bacteria. Being based on silicon technology, the sensor should be compatible with micro-electronic circuitry.