Three-dimensional mid-infrared tomographic imaging of endogenous and exogenous molecules in a single intact cell with subcellular resolution

Microscopy in the mid-infrared spectral range provides detailed chemical information on a sample at moderate spatial resolution and is being used increasingly in the characterization of biological entities as challenging as single cells. However, a conventional cellular 2D imaging measurement is limited in its ability to associate specific compositional information to subcellular structures because of the interference from the complex topography of the sample. Herein we provide a method and protocols that overcome this challenge in which tilt-series infrared tomography is used with a standard benchtop infrared microscope. This approach gives access to the quantitative 3D distribution of molecular components based on the intrinsic contrast provided by the sample. We demonstrate the method by quantifying the distribution of an exogenous metal carbonyl complex throughout the cell and by reporting changes in its coordination sphere in different locations in the cell.

Metal-carbonyl units for vibrational and luminescence imaging: towards multimodality

Metal-carbonyl complexes are attractive structures for bio-imaging. In addition to unique vibrational properties due to the CO moieties enabling IR and Raman cell imaging, the appropriate choice of ancillary ligands opens up the opportunity for luminescence detection. Through a classification by techniques, past and recent developments in the application of metal-carbonyl complexes for vibrational and luminescence bio-imaging are reviewed. Finally, their potential as bimodal IR and luminescent probes is addressed.

Enhanced Cytotoxicity through Conjugation of a "Clickable" Luminescent Re(I) Complex to a Cell-Penetrating Lipopeptide

Re(I) tricarbonyl polypyridine-based complexes are particularly attractive metal complexes in the field of inorganic chemical biology due to their luminescent properties, ease of conjugation to targeting biomolecules, and the possibility to prepare their "hot" (99m)Tc analogues for radioimaging. In this study, we prepared and characterized a novel, "clickable" complex, [Re(2,2'-bipyridine)(3-ethynylpyridine)(CO)3](BF4) ([Re(CO) 3 (bipy)(py-alkyne)](BF 4 )), exhibiting the characteristic luminescent properties and moderate cytotoxicity of this general class of compound. Using Cu(I)-catalyzed "click" chemistry, the complex was efficiently attached to a lipidated peptide known to increase cell permeability, namely, the myristoylated HIV-1 Tat peptide (myr-Tat), to give Re-myr-Tat. Fluorescence microscopy localization in human cervical cancer cells (HeLa) confirmed enhanced cellular uptake of Re-myr-Tat compared with [Re(CO) 3 (bipy)(py-alkyne)](BF 4 ), and cytotoxicity studies showed that this resulted in an increase in potency to a level comparable with cisplatin (13.0 ± 2.0 μM).

Fourier transform infrared (FT-IR) spectromicroscopy to identify cell organelles: correlation with fluorescence staining in MCF-7 breast cancer cells

Biomolecules display specific vibrational signatures in the infrared (IR) range, and organelles that concentrate these biomolecules can be identified by these IR signatures. Subcellular identification and location of cell organelles using IR signatures is attractive as it does not require the use of any specific trackers and is thus non-invasive and non-destructive. We show here that endogenous IR absorptions are relevant to detecting and imaging the nucleus, the cytoplasm, and the Golgi apparatus/endoplasmic reticulum in MCF-7 breast cancer cells, and we compare these results with our previous work on the HeLa cell line. We correlate maps of fixed and dried cells obtained by synchrotron radiation Fourier transform infrared (SR FT-IR) spectromicroscopy with epifluorescence images using fluorescent trackers for Golgi apparatus and nucleus, namely BODIPY TR C5-ceramide complexed to BSA and DAPI, respectively. Interestingly, the ratios of the IR bands CH2 : CH3 (both asymmetric and symmetric) and CO((ester)):amide I were shown to be reliable gauges of the lipidic character of a cellular compartment, the -CH2 and the CO((ester)) absorptions increasing with the presence of inner membranes like in the Golgi apparatus.

Opportunities for live cell FT-infrared imaging: macromolecule identification with 2D and 3D localization

Infrared (IR) spectromicroscopy, or chemical imaging, is an evolving technique that is poised to make significant contributions in the fields of biology and medicine. Recent developments in sources, detectors, measurement techniques and speciman holders have now made diffraction-limited Fourier transform infrared (FTIR) imaging of cellular chemistry in living cells a reality. The availability of bright, broadband IR sources and large area, pixelated detectors facilitate live cell imaging, which requires rapid measurements using non-destructive probes. In this work, we review advances in the field of FTIR spectromicroscopy that have contributed to live-cell two and three-dimensional IR imaging, and discuss several key examples that highlight the utility of this technique for studying the structure and chemistry of living cells.