Single molecules

Studies of single molecules in cryogenic solids, while limited to a relatively small number of cliromophore/ matrix combinations (and small variations tliereupon), have covered a wide range of spectroscopic and dynamic processes [66,62]. 

Xie X S 1996 Single-molecule spectroscopy and dynamics at room temperature Acc. Chem. Res. 29 598-606 

Nie S and Emory S R 1997 Probing single molecules and single nanoparticles by surface-enhanced Raman scattering Science 275 1102-6 

Betzig E and Chichester R J 1993 Single molecules observed by near-field scanning optical microscopy Science 262 1422 

Stipe B C, Rezaei M A and Flo W 1998 Single-molecule vibrational spectroscopy and microscopy Science 280 1732 

At the linear level, the microscopic induced dipole vector on a single molecule in the local Cartesian 

Figure Cl.5.3. Near-field fluorescence image 4.5 p.m square) of single oxazine 720 molecules dispersed on die surface of a PMMA film. Each peak (fwhm 100 nm) is due to a single molecule. The different intensities are due to different molecular orientations and spectra. Reprinted widi pennission from Xie 11221. Copyright 1996 American Chemical Society.

The approach to, and finally tire achievement of, detection and spectroscopy of single molecules proceeded almost independently from tliree separate directions. 

Trautman J K, Macklin J J, Brus L E and Betzig E 1994 Near-field spectroscopy of single molecules at room temperature Nature 369 40 

Kasas S, Thompson N FI, Smith B L, Flansma P K, Miklossy J and Flansma FI G 1997 Biological applications of the AFM from single molecules to organs Int. J. Im. Syst. Technol. 8 151 

Figure Cl.5.4. Comparison of near-field and far-field fluorescence images, spectra and lifetimes for the same set of isolated single molecules of a carbocyanine dye at a PMMA-air interface. Note the much higher resolution of the near-field image. The spectmm and lifetime of the molecule indicated with the arrow were recorded with near-field excitation and with far-field excitation at two different excitation powers. Reproduced with pennission from Trautman and Macklin [125].

It now seems clear tliat, under certain conditions, massive enhancements of what is nonnally a very weak process can be achieved. The ability to obtain vibrational spectra would be a great advance in tlie characterization of single molecules if metliods could be found to reproducibly observe all molecules in a sample, not only tliose tliat happen to bind to special sites on tlie colloid. 

Many of the most interesting current developments in electronic spectroscopy are addressed in special chapters of their own in this encyclopedia. The reader is referred especially to sections B2.1 on ultrafast spectroscopy. Cl.5 on single molecule spectroscopy, C3.2 on electron transfer, and C3.3 on energy transfer. Additional topics on electronic spectroscopy will also be found in many other chapters. 

Ribbe A E 1997 Laser scanning confocal microscopy in polymer science Trends Polym. Sc/. 5 333-7 Oliveira M J and Hemsiey D A 1996 Optical microscopy of polymers Sonderb. Prakt. Metallogr. 27 13-22 Nie Sh and Zare R N 1997 Optical detection of single molecules Ann. Rev. Biophys. Biomol. Struct. 26 567-96 Masters B R 1994 Confocal redox imaging of cells Adv. Mol. Cell Biol. 8 1-19 

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