Biomedical Engineering Reference
In-Depth Information
Fig. 1.6.
Two-photon fluorescence images of a Ca
2+
wave in the whole heart of
the rat
1.3
Nonstaining Molecular Imaging (CARS)
Single-photon excitation confocal fluorescence microscopy is widely used be-
cause of the capability of 3D (three-dimensional) imaging of living cells [16].
Recently, multi-photon excitation fluorescence microscopy has been succes-
sfully developed owing to the progress of ultra-fast laser technology [17].
However, both microscopies fundamentally require a staining procedure with
a suitable fluorophore. The ability for molecular discrimination depends on
the dye. The staining procedure affects the biological sample, and hence the
function of the cell is often lost. In addition, staining requires technical skill.
In analytical chemistry, vibrational spectroscopy observing molecular vi-
brations (Raman and infrared spectroscopy) is widely used for molecular
identification, since the frequency of the molecular vibration is extremely
sensitive to the molecular structure. Molecular mapping without staining,
with micrometer or sub-micrometer resolution, is expected to be achieved
through a combination of vibrational spectroscopy and microscopy. However,
this combination is not so widely used for biological applications. Infrared
microscopy suffers from the problems of strong absorption of water in the
