Ring-shaped silica nanoparticles are synthesized with a high tetrakis(4-carboxyphenyl)porphyrin (TCPP) content or silica/TCPP hybrid nanorings (HNRs) using a one-pot sol-gel reaction with a TCPP-binding silica precursor for fluorescence imaging of tumor. The shape of the HNRs is a reflection of abundant ring-shaped TCPP aggregates in the silica matrix. The HNRs are of a size that makes them susceptible to the enhanced permeability and retention effect. For comparison, the TCPP-doped silica nanoparticles are synthesized using a conventional method. The nanoparticles are spherical in shape because little TCPP is contained in the silica matrix and are designated as TCPP-containing silica nanospheres (NSs). The absorption bands of the HNRs shift by about 20 nm toward longer wavelengths compared with the TCPP bands. This redshift leads the excitation wavelength of the HNRs into the near-infrared (NIR) region. Therefore, the HNRs are excited by NIR light to emit strong fluorescence, although the NSs emit no fluorescence. The PEGylated HNRs (PEG-HNRs) are uncharged and possess a significantly longer blood circulation time than PEG-NSs. The PEG-HNRs accumulate in tumor through multiple factors including their size, uncharged surface, unique shape, and long circulation time in blood, resulting in the acquisition of clear images of tumor.
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