(a) Schematic illustration of the molecular structure of the DTPA and Nd-DTPA, along with the synthesis process of Nd-DTPA. (b) UV–vis absorption spectrum (600–900 nm) and photoluminescent spectrum of the Nd-DTPA complex under the excitation of 808 nm laser, demonstrating the efficient narrow-band emissions centered at 1,050 and 1,330 nm. (c) NIR-II imaging of the mouse in the supine position, revealing the rapid excretion of Nd-DTPA molecule via kidney. The digital photograph (upper-right end) and the NIR-II imaging (lower-right end) of the urine sample are also collected after 2 h post-injection. Reproduced with permission from Ref. [101], © Elsevier Ltd 2018.