Quantum dot imaging for embryonic stem cells

Murine embryonic stem (ES) cells were labeled with six different QDs using Qtracker. ES cell viability, proliferation, and differentiation were not adversely affected by QDs compared with non-labeled control cells (P = NS). Afterward, labeled ES cells were injected subcutaneously onto the backs of athymic nude mice. These labeled ES cells could be imaged with good contrast with one single excitation wavelength. With the same excitation wavelength, the signal intensity, defined as (total signal-background)/exposure time in millisecond was 11 ± 2 for cells labeled with QD 525, 12 ± 9 for QD 565, 176 ± 81 for QD 605, 176 ± 136 for QD 655, 167 ± 104 for QD 705, and 1,713 ± 482 for QD 800. Finally, we have shown that QD 800 offers greater fluorescent intensity than the other QDs tested.In summary, this is the first demonstration of in vivo multiplex imaging of mouse ES cells labeled QDs. Upon further improvements, QDs will have a greater potential for tracking stem cells within deep tissues. These results provide a promising tool for imaging stem cell therapy non-invasively in vivo.Quantum dots (QDs) are emerging as an exciting new class of fluorescent probes for non-invasive in vivo imaging [1-5]. Compared to conventional organic dyes, QDs offer a number of fascinating optical and electronic properties. QDs are semiconductor nanocrystals that can be excited by a wide range of light, ranging from ultraviolet to near-infrared, and can emit different wavelengths of light, depending on their size and composition. QDs have broad excitation spectra and narrow emission spectra (Figure 1). Because QDs can be excited by one single wavelength and can emit light of different wavelengths, they are ideal probes for multiplex imaging [6]. By contrast, conventional organic dyes cannot be easily synthesized to emit different colors and have narrow excitation spectra and broad emission spectra that often cross into the red wavelengths, making it difficult to use these dyes for multiplex