Fluorescence-based in vivo imaging of MSP. Fluorescence-based in vivo imaging of MSP. (A) Fluorescence of 100 μl of MSP-72h with varied concentrations in the subcutaneous tissue of nude Balb/c athymic mice at three residence times. The residence time is 0 min unless otherwise specified. Fluorescence of 300 μl of (B) MSP-72h, (C) MSP-24h, and (D) MSP-6h (all 800 μg/ml) in the intraperitoneal cavity at various residence times. Image sequences of (C) and (D) were recorded at the same time intervals with (B). The magnetic needle was placed at t = 3 min. Xiaohui Yan et al. Sci. Robotics 2017;2:eaaq1155 Copyright © 2017 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works