Surface-enhanced optical absorption

The basis of surface enhanced optical absorption is the so-called "anomalous absorption". To observe anomalous absorption an absorbing colloid or colloid layer is positioned in a defined distance to a metal mirror and illuminated from the colloid side. At a certain distance of the colloid or absorbing layer to the mirror the incident fields has the same phase as the electromagnetic field that is reflected by the mirror at the position of the absorbing colloid particle (or colloid particle layer). The set-up is described as a reflection interference system, which feedback mechanism strongly enhances the absorption coefficient of the absorbing colloid (layer). 

The broadband analysis was confirmed by the experimental results mentioned in Sect. 5.4.1. This method can also be further enhanced by some of the techniques described in Sects. 5.4.2 and 5.4.3. The conclusion is that these methods of microcavity-enhanced optical absorption sensing provide compact, inexpensive, and sensitive detectors for molecular species in the ambient gas or liquid, and that further increases in sensitivity can be implemented to make them even more competitive. The molecular-transition specificity that is implicit in absorption spectroscopy is a limiting restriction, but the surface-enhanced Raman sensing that is enabled by metallic nanoparticles on the microresonator surface can significantly increase the number of molecular species that could be detected. 

Osawa, M., Surface enhanced infrared absorption, In Near Field Optics and Plasmon Polar itons Kawata, S., Ed. Springer, Berlin, 2001, 163 187... 

Instrumentation. In order to employ local enhancement of infrared absorption by surface plasmon polaritons that cause locally enhanced surface electromagnetic fields, a suitable optical arrangement is needed [295]. Surface enhanced infrared absorption spectroscopy can also be observed in the transmission mode [285, 296]. However, since no application of this approach in spectroelectrochemistry has been reported so far, it is not discussed further. 

Two of the many enhanced optical phenomena in surface-enhanced spectroscopy are surface-enhanced Raman scattering (SERS) and surface-enhanced infrared absorption (SEIRA). These two phenomena and now analytical techniques can be described as a new branch of vibrational spectroscopy that deals with the spectra of molecules on specially fabricated nanostructures with the... 

More complicated dependences are observed when two layers are located on the surface of the ATR element. The optical properties of a hemicylin-drical IRE-thin (d < 50 nm) metal hhn-hlm system, called the Kretschmann configuration [84] (Fig. 2.36a), were actively investigated in the seventies and eighties (see, e.g.. Ref. [85]) regarding the possibility of SEW excitation at the metal-outer layer interface. However, even without exploiting this and surface-enhanced infrared absorption (SEIRA) (Section 3.9.4) effects, optical enhancement may be achieved in the ATR spectrum of a layer deposited on metal. Because of this, the Kretschmann configuration has found wide application in the investigation of nanolayers located on the metal surfaces, especially at the metal-solution interface (Section 4.6.3). 

Interaction of an EM field with a nanostructured metal surface also strongly influences other optical phenomena, namely absorption and luminescence. Surface-enhanced infrared absorption (SEIRA) of monolayers of benzoic acids on thin Ag island films was first observed in 1980s (Hartstein et al. 1980). The EM mechanisms is attributed to a local field enhancement and, correspondingly, to an enhancement of the absorption cross-section. Absorption can be enhanced generally by a factor of 10 -10 (Osawa 2001 Aroca 2006) and SEIRA is used as a complementary technique to SERS in some cases (Aroca 2006). 

Probing Metalloproteins Electronic absorption spectroscopy of copper proteins, 226, 1 electronic absorption spectroscopy of nonheme iron proteins, 226, 33 cobalt as probe and label of proteins, 226, 52 biochemical and spectroscopic probes of mercury(ii) coordination environments in proteins, 226, 71 low-temperature optical spectroscopy metalloprotein structure and dynamics, 226, 97 nanosecond transient absorption spectroscopy, 226, 119 nanosecond time-resolved absorption and polarization dichroism spectroscopies, 226, 147 real-time spectroscopic techniques for probing conformational dynamics of heme proteins, 226, 177 variable-temperature magnetic circular dichroism, 226, 199 linear dichroism, 226, 232 infrared spectroscopy, 226, 259 Fourier transform infrared spectroscopy, 226, 289 infrared circular dichroism, 226, 306 Raman and resonance Raman spectroscopy, 226, 319 protein structure from ultraviolet resonance Raman spectroscopy, 226, 374 single-crystal micro-Raman spectroscopy, 226, 397 nanosecond time-resolved resonance Raman spectroscopy, 226, 409 techniques for obtaining resonance Raman spectra of metalloproteins, 226, 431 Raman optical activity, 226, 470 surface-enhanced resonance Raman scattering, 226, 482 luminescence... 

In principle, optical chemosensors make use of optical techniques to provide analytical information. The most extensively exploited techniques in this regard are optical absorption and photoluminescence. Moreover, sensors based on surface plasmon resonance (SPR) and surface enhanced Raman scattering (SERS) have recently been devised. 

Schaadt DM, Feng B, Yu ET (2005) Enhanced semiconductor optical absorption via surface plasmon excitation in metal nanoparticles. Appl Phys Lett 86(6) 063106... 

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