Separation multiplexed

Lekowska-Kochaniak, A. Czajkowska, D. Popowski, J. Detection of Escherichia coli 0157 H7 in raw meat by immunomagnetic separation and multiplex PCR. Acta Microbiol. Polon. 2002,51, 327-337. 

Spectral multiplexing or multicolor detection is typically performed at a single excitation wavelength, and relies on the discrimination between different fluorescent labels by their emission wavelength. Desirable optical properties of suitable fluoro-phores are a tunable Stokes shift and very narrow, preferably well-separated emission bands of simple shape. 

Multiplex CARS microspectroscopy, in conjunction with appropriate spectral analysis tools, was successfully applied to the study of phospholipid bilayer model systems [120, 121, 142, 70, 143], lipids within cells [144, 127, 145-147, 141], a single pollen grain [148], a single bacterial endophore [140], a molecular J-aggregate microcrystal [149], silicon components on a wafer [130], separated phases in polymer blends [123, 135], and concentration profiles in a microreactor [150]. 

While in the frequency domain all the spectroscopic information regarding vibrational frequencies and relaxation processes is obtained from the positions and widths of the Raman resonances, in the time domain this information is obtained from coherent oscillations and the decay of the time-dependent CARS signal, respectively. In principle, time- and frequency-domain experiments are related to each other by Fourier transform and carry the same information. However, in contrast to the driven motion of molecular vibrations in frequency-multiplexed CARS detection, time-resolved CARS allows recording the Raman free induction decay (RFID) with the decay time T2, i.e., the free evolution of the molecular system is observed. While the non-resonant contribution dephases instantaneously, the resonant contribution of RFID decays within hundreds of femtoseconds in the condensed phase. Time-resolved CARS with femtosecond excitation, therefore, allows the separation of nonresonant and vibrationally resonant signals [151]. 

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