Abstract
Near infrared wavelength region is known to have the most transparency of live body for electromagnetic wave with wavelength around the visible wavelength. Namely, the near infrared with a wavelength longer than 1000 nm (OTN-NIR) shows more transparency than that with shorter wavelength. The observation depth can be several centimeters with the OTN-NIR fluorescence, while that is limited to be only several millimeters with visible fluorescence. As OTN-NIR fluorescent agents, dyes, quantum dots, carbon nanotubes and rare-earth doped ceramic nanoparticles (RED-CNP) are known. A special feature of the RED-CNP is to show infrared-to-visible upconversion to emit visible light with a near infrared excitation, simultaneously with the OTN-NIR fluorescence. As a theranostic approach, nanomaterials for achieving photodynamic therapy with the near infrared excitation are introduced. Another special feature of the RED-CNP is the potential use for fluorescence nanothermometry. A scheme for ratiometric fluorescence nanothermometry with the OTN-NIR fluorescence is described. By using a RED-CNP with holomium and erbium co-doping, ratiometric fluorescence nanothermometry was successfully demonstrated. As shown with the case of photodynamic therapy with near infrared excitation, by applying an upconversion excitation scheme, visible light emission for photochemical reaction is possible with a near infrared excitation with high transparency in a live body. By constructing these multiple functions on the RED-CNP, various theranostic approach can be achieved. The size and bio distribution controls are important issues for applications of the RED-CNP for medical applications.
