Two-dimensional fluorescence correlation in capillary electrophoresis for peak resolution and species identification

Cell cycle-dependent characterization of single MCF-7 breast cancer cells by 2-D CE

The composition of single MCF-7 breast cancer cells is characterized using 2-D CE. Individual MCF-7 cells were aspirated into a 30 mum inner diameter fused-silica capillary and lysed by contact with an SDS-containing buffer. Proteins and other primary amines were fluorescently labeled on-column using the fluorogenic dye 3-(2-furoyl)quinoline-2-carboxaldehyde. Labeled components were separated first according to molecular weight using capillary sieving electrophoresis (CSE) and then by MEKC. Analytes were detected in a sheath-flow cuvette using LIF. The expression profiles for MCF-7 cellular homogenate and a single MCF-7 cell are compared. As a proof-of-principle investigation, variation in expression was also compared within and between G1 and G2/M cell cycle phases for MCF-7 cells. Following their treatment with the viable nuclear stain Hoechst 33342, MCF-7 cells were sorted by flow cytometry on the basis of their ploidy. Sorted cells were then analyzed by 2-D CE. The degree of variability was >2.5 times larger between cells of different phases than between cells of the same phase. In typical 1 h 2-D CE separations using MCF-7 cells, over 100 components are resolved.

Two-dimensional fluorescence correlation spectroscopy IV: resolution of fluorescence of tryptophan residues in alcohol dehydrogenase and lysozyme

Generalized two-dimensional (2D) fluorescence correlation spectroscopy has been used to resolve the fluorescence spectra of two tryptophan (Trp) residues in alcohol dehydrogenase and lysozyme. In each protein, one Trp residue is buried in a hydrophobic domain of the protein matrix and the other Trp residue is located at a hydrophilic domain close to the protein-water interface. Fluorescence quenching by iodide ion, a hydrophilic quencher, was employed as a perturbation to induce the intensity change in the spectra. The Trp residue which is located at the hydrophilic domain is effectively quenched by the quencher, while the Trp residue located at the hydrophobic domain is protected from the quenching. Therefore, the fluorescence of these two Trp residues have a different sensitivity to the quenching, showing a different response to the concentration of the quencher. Fluorescence spectra of the two Trp residues in alcohol dehydrogenase, which are heavily overlapped in conventional one-dimensional spectra, have been successfully resolved by the 2D correlation technique. From the asynchronous correlation map, it was revealed that the quenching of Trp located at the hydrophobic part was brought about after that of Trp located at the hydrophilic part. In contrast, the fluorescence spectra of the two Trp residues could not be resolved after the alcohol dehydrogenase was denatured with guanidine hydrochloride. These results are consistent with the well-known structure of alcohol dehydrogenase. Furthermore, it was elucidated that the present 2D analysis is not interfered by Raman bands of the solvent, which sometimes bring difficulty into the conventional fluorescence analysis. Fluorescence spectra of the Trp residues in lysozyme could not be resolved by the 2D correlation technique. The differences between the two proteins are attributed to the fact that the Trp residue in the hydrophobic site of lysozyme is not sufficiently protected from the quenching.

Single-cell protein analysis of a single mouse embryo by two-dimensional capillary electrophoresis

The characterization of protein expression from a single-cell mouse embryo using two-dimensional capillary electrophoresis (2D-CE) is described. These zygotes were obtained from Hsf1 gene knockout mice. Single zygotes were lysed off-column and proteins were fluorescently labeled using the fluorogenic dye 3-(2-furoyl)quinoline-2-carboxaldehyde (FQ). After injection, analytes were separated first according to molecular weight using capillary sieving electrophoresis (CSE) and then by micellar electrokinetic capillary chromatography (MEKC) to obtain protein expression fingerprints. Analytes were detected in a sheath flow cuvette using laser-induced fluorescence. In a 1-h 2D-CE separation, over 100 components were resolved with a spot capacity of 380.

Minimizing urine autofluorescence under multi-photon excitation conditions

We report on the effects of excitation wavelength, laser power, and phase resolution on the multi-photon-excited autofluorescence (background) from human urine. When compared to the autofluorescence under one-photon excitation conditions (lambda(ex) = 260-480 nm), the urine multi-photon-excited autofluorescence (lambda(ex) = 725-950 nm) can be less complicated. However, at higher laser powers, the multi-photon-excited autofluorescence spectra that are produced by excitation above ~775 nm are more complex in comparison to the corresponding one-photon-excited autofluorescence. The origin of these more complex spectra arises from simultaneous two- and three-photon-driven excitation of intrinsic luminescent species within the urine. At lower laser powers, three-photon-driven processes are minimized and the autofluorescence spectrum is simplified. Phase resolution is used to further minimize the urine autofluorescence, but it cannot fully eliminate autofluorescence even when excitation is performed under multi-photon conditions at 950 nm. For detecting 250 nM Rhodamine 6G (a mock analyte) dissolved in urine, we find that the two-photon excitation is superior in comparison to one-photon excitation by 5- to 70-fold, depending on the excitation wavelength. Phase resolution combined with two-photon excitation leads to an additional 5- to 7-fold improvement in signal-to-background ratios in comparison to steady-state two-photon excitation.

Two-dimensional fluorescence correlation spectroscopy II: spectral analysis of derivatives of anthracene and pyrene in micellar solutions

Generalized two-dimensional (2D) correlation spectroscopy has been applied to the analysis of fluorescence spectra in two micellar systems: (1) a mixture of pyrene and 1,3,6,8-pyrenetetrasulfonic acid in the cationic micellar solutions of cetyltrimethylammonium chloride (CTAC) and (2) a mixture of pyrene and 9-anthracencepropionic acid in anionic micellar solutions of sodium dodecyl sulfate (SDS). Fluorescence quenching is employed as a perturbation mode for causing intensity changes in fluorescence bands (quenching perturbation). Iodide ion (I-) is used as a quencher in the former system, and cetyl pridinium chloride (CPC) is used in the latter. Vibronic bands in the complicated fluorescence spectra of the mixture of the analytes were successfully resolved. It is shown that asynchronous maps are especially useful for spectral resolution enhancement when the quenching perturbation is employed in 2D fluorescence correlation spectroscopy. Furthermore, the information about the order of response of the bands to quenching is obtained by comparing the signs of synchronous and asynchronous cross-peaks.