Remarkable NIR Enhancement of Multifunctional Nanoprobes for In Vivo Trimodal Bioimaging and Upconversion Optical/T2-Weighted MRI-Guided Small Tumor Diagnosis

Effective nanoprobes and contrast agents are urgently sought for early-stage cancer diagnosis. Upconversion nanoparticles (UCNPs) are considerable alternatives for bioimaging, cancer diagnosis, and therapy. Yb3+/ Tm3+ co-doping brings both emission and excitation wavelengths into the near-infrared (NIR) region, which is known as optical transmission window and ideally suitable for bioimaging. Here, NIR emission intensity is remarkably enhanced by 113 times with the increase of Yb3+ concentration from 20% to 98% in polyethylene glycol ( PEG) modified NaYF4:Yb3+/ Tm3+ UCNPs. PEG-UCNPs-5 (98% Yb3+) can act as excellent nanoprobes and contrast agents for trimodal upconversion (UC) optical/CT/T-2-weighted magnetic resonance imaging (MRI). In addition, the enhanced detection of lung in vivo long-lasting tracking, as well as possible clearance mechanism and excretion routes of PEG-UCNPs-5 have been demonstrated. More significantly, a small tumor down to 4 mm is detected in vivo via intravenous injection of these nanoprobes under both UC optical and T-2-weighted MRI modalities. PEG-UCNPs-5 can emerge as bioprobes for multi-modal bioimaging, disease diagnosis, and therapy, especially the early-stage tumor diagnosis.