Lanthanide-Based Upconversion Nanoparticles for Bioimaging Applications

Lanthanide-based upconversion nanoparticles (UCNPs), which are capable of converting longer wavelength (e.g., near-infrared (NIR), 700–900 nm) radiation into high energy and shorter-wavelength emissions spanning from the visible to NIR spectrum region, are vitally important for application in fields as imaging of biological cells and tissues. As unique fluorescence probes, lanthanide-based UCNPs have provided several advantages over traditional biological labels, including low autofluorescence background, narrow band emission, low photo-bleaching, low toxicity, high sensitivity, and larger penetration depth in bio-tissue under NIR excitation. Especially, lanthanide-based multiphoton-excited fluorescence imaging techniques via multiphonon assistant frequency upconversion (UC) process is more beneficial for deep tissue imaging due to its greatly enhanced penetration depth and improved signal-noise ratio. Thus, these attractive features make the UCNPs promising as the next potential candidates for cell tracking, tumor-targeted imaging, and vascular imaging. In this chapter, we will summarize the design, properties, and application of the UCNPs for biomedical cell imaging.