A research team led by Prof LIU Xiaogang from the Department of Chemistry, National University of Singapore has developed a new generation of near infra-red (NIR)-emitting nanoprobes for super-resolution imaging in deep tissues. These nanoprobes are based on lanthanide-doped nanomaterials with rich energy levels, high photostability and programmable optical kinetics.
The team discovered that a series of neodymium (Nd3+)-doped lanthanide nanoparticles can act as more effective nanoprobes for STED imaging applications, enabling autofluorescence-free, low-power, super-resolution imaging in NIR optical windows. Upon excitation by a 808 nm wavelength laser beam, these Nd3+-doped nanoparticles emit strong luminescence around the 860 nm NIR region with more than 20% efficiency. When co-illuminated with a 1064 nm wavelength laser, this NIR luminescence is immediately switched off. The research team found that a near-unity efficiency (98.8%) in luminescence suppression can be achieved by increasing the depletion power. In comparison to organic dye-mediated STED microscopy, the amount of power required to reduce the luminescence intensity by half, known as the saturation intensity, is more than two orders of magnitude lower. This ability of the Nd3+-doped nanoparticles to be turned on and off by using different laser beam wavelengths at low power conditions enabled the STED process to achieve a lateral resolution of about 19 nm for a single nanoparticle. The research team also demonstrated high-contrast deep-tissue (~50 mm) imaging with approximately 70 nm spatial resolution. Importantly, these nanoprobes showed no sign of photobleaching even after 2 hours of irradiation.
Prof Liu said, “In recent years, many researchers have been taking on challenges in long term, deep tissue, high resolution imaging. This new generation of lanthanide nanoprobes may potentially find important applications in bioimaging and molecular detection.”
The figure above (a) shows the proposed optical emission depletion mechanism of the near infra-red (NIR) downshifting luminescence in the neodymium-mediated stimulated-emission depletion (STED) process. Figure (b) compares the images obtained from conventional confocal imaging and STED imaging using the lanthanide nanoparticles, with better contrast in the latter technique. [Credit: LIANG Liangliang]. Read the full story here.
