TMTP1 is a polypeptide independently screened in our laboratory, which can target tumors in situ and metastases. In previous work, we have successfully developed a near-infrared (NIR) probe TMTP1-PEG4-ICG for tumor imaging. However, the limited ability to target tumor micrometastases hinders its further clinical application. Multimerization of peptides has been extensively demonstrated as an effective strategy to increase receptor binding affinity due to "multivalent effect" or "apparent cooperative affinity". In this study, a novel TMTP1 homodimer-directed NIR probe (TMTP1-PEG4)(2)-ICG was successfully constructed and synthesized. The cyclic TMTP1 peptides were bridged by two PEG4 linkers and then labeled with ICG-NHS for tumor imaging and photothermal therapy. In vivo biodistribution were assessed in normal BALB/c mice, and tumor targeting abilities of (TMTP1-PEG4)(2)-ICG and its monomer were evaluated and compared in 4T1-bearing subcutaneous tumor and lymph node metastasis model mice. Biodistribution analysis in vivo revealed that (TMTP1-PEG4)(2)-ICG was cleared mainly in both liver and kidney dependent way. Comparing with free ICG dye or TMTP1-PEG4-ICG probe, this improved (TMTP1-PEG4)(2)-ICG dimer showed more sensitive tumor imaging and could clearly identify tumors at a minimum volume of 10 mm(3). Additionally, when compared to its monomer, lymph node (LN) metastases could also be apparently visualized and easily distinguished from normal LN by the novel dimer at 24 h post-injection. The blocking study revealed that the tumor accumulation of this probe was specifically medicated by receptor-ligand interaction. Furthermore, with the increase in stability and tumor targeting ability of ICG in vivo, the probe could also be an attractive photothermal agent to significantly inhibit tumor growth under 808 nm NIR laser irradiation. In conclusion, our work revealed that the novel (TMTP1-PEG4)(2)-ICG dimer could be a promising theranostic agent for sensitive tumor imaging and imaging-guided photothermal therapy, indicating its broad prospects for further clinical transformation. (C) 2021 The Authors. Published by Elsevier Masson SAS.