Multi-photon excitation

Quack M 1998 Multi photon excitation Encyclopedia of Computational Chemistry o 3, ed P v R Schleyer et al (New York Wiley) pp 1775-91... 

The NIR femtosecond laser microscope realized higher order multi photon excitation for aromatic compounds interferometric autocorrelation detection of the fluorescence from the microcrystals of the aromatic molecules confirmed that their excited states were produced not via stepwise multiphoton absorption but by simultaneous absorption of several photons. The microscope enabled us to obtain three-dimensional multiphoton fluorescence images with higher spatial resolution than that limited by the diffraction theory for one-photon excitation. 

VELOCITY MAPPING OF MULTI PHOTON EXCITED MOLECULES... 

In the direct effect of ionizing radiation on DNA, radical cations are the primary products (Chap. 12). For this reason, their reactions are of considerable interest. Obviously, photoionization (e.g., at 193 nm) and laser multi-photon excitation leads to such species (e.g., Candeias and Steenken 1992b Malone et al. 1995 Chap. 2.2). Base radical cation electron pairs have been proposed to be the first observable intermediates with a lifetime of 10 ps for Ade and four times longer for the other nucleobases (Reuther et al. 2000). Radical cations are also assumed to be intermediates in the reactions of photosensitization reactions with qui-nones, benzophenone, phthalocyanine and riboflavin (Cadet et al. 1983a Decar-roz et al. 1987 Krishna et al. 1987 Ravanat et al. 1991, 1992 Buchko et al. 1993 Douki and Cadet 1999 Ma et al. 2000). Nucleobase radical cations may be produced by electrochemical oxidation (Nishimoto et al. 1992 Hatta et al. 2001) or with strongly oxidizing radicals (for a compilation of their reduction potentials see Chap. 5.3). Rate constants are compiled in Table 10.3. 

Masters BR, So PTC. Multi-photon excitation microscopy and confocal microscopy imaging of in vivo human skin a comparison. Microscopy and Microanalysis 1999, 5, 282-289. 

Lakowicz JR, Gryczynski I, Tolosa L, Dattelbaum JD, Castellano FN, Li L, Rao G. Advances in fluorescence spectroscopy multi-photon excitation, engineered proteins, modulation sensing and microsecond rhenium metal-ligand complexes. Acta Physica Polonica A 1999, 95, 179-196. 

Several articles and reviews on different aspects of multi-photon excitation of biomolecule system are available. For example, Birch [11] consideraticms concentrate mainly on the impact of multi-photon techniques to the time-resolved fluorescence spectroscopy. Lakowicz and Gryczynski [12] have discussed examples of three-photon excited fluorescence. Rehms and Callis studied the two-photon excited fluorescence emission of aromatic amino acids [13]. Kierdasz et al analyzed emission spectra of Tyrosine- and Tryptophan-containing proteins using one-photon (270-3 10 nm) and two-photon (565-6 10 nm) excitation [14]. 

This chapter is devoted to describe the impact of metallic nanosphere to the multi-photon excitation fluorescence of Tryptophan, and little further consideration to multi-photon absorption process will be given, as the reader can find several studies in [11-14]. In section II, the nonlinear light-matter interaction in composite materials is discussed through the mechanism of nonlinear susceptibilities. In section III, experimental results of fluorescence induced by multi-photon absorption in Tryptophan are reported and analyzed. Section IV described the main results of this chapter, which is the effect of metallic nanoparticles on the fluorescent emission of the Tryptophan excited by a multi-photon process. Influence of nanoparticle concentration on the Tryptophan-silver colloids is observed and discussed based coi a nonlinear generalization of the Maxwell Garnett model, introduced in section II. The main conclusion of the chapter is given in secticHi IV. 

Fluorescence emission is just one, but probably the most convenient, of several methods available for observing multi-photon absorption. In a multi-photon excited fluorescence process, the fluorescence intensity Iji does not increase linearly with increasing of the excitation intensity, lac- Instead, Iji and la are related by... 

MULTI-PHOTON EXCITATION OF TRYPTOPHAN-SILVER COLLOID... 

Buehler C, Dreessen J, Mueller K, So PTC, Schilb A, Hassiepen U, Stoeckli KA, Auer M. Multi-photon excitation of intrinsic protein fluorescence and its appUcation to pharmaceutical drug screening. Assay Drug Devel. Technol. 2005 3 155-167. 

The basic idea of this method is to investigate the dependence of the fluorescence intensity on the excitation intensity because this relation determines the order of the non-linearity [8, 38-40]. For example, a quadratic dependence corresponds to a two-photon absorption process and a cubic dependence refers to a three-photon absorption. By means of a tunable excitation light source, one can also map the dispersion of the multi-photon transition, the resulting multi-photon excitation... 

Multi-photon excitation imaging of dynamic processes in living cells and tissues... 

More recently, confocal fluorimetry itself has been impressively extended. In particular, the implementation of multi-photon excitation opened the potential to excite different fluorescent labels by a single laser line [47]. This considerably simplified the optical setup of confocal instruments. For example, Heinze et al. [48] described a setup for two-photon excitation confocal fluorimetry where three molecular species were quantified simultaneously using a single laser. When included in screening systems, these spectroscopic advancements enable the quantification of enzymatic reaction rates on several substrates in parallel or, when applied for peptide or protein ligands, the simultaneous measurement of binding affinities on different target receptors. In this way, biopharmaceuticals can be selected on the basis of their specificity and selectivity. As a consequence, undesired side activities can be controlled very early in the hit identification process. 

---