Theranostics 2020; 10(6):2509-2521. doi:10.7150/thno.39403

Research Paper

Deep tissue photoacoustic imaging of nickel(II) dithiolene-containing polymeric nanoparticles in the second near-infrared window

Byullee Park1*, Kyung Min Lee2,6*, Suhyeon Park3, Misun Yun4, Hak-Jong Choi4, Jeesu Kim1, Changho Lee3,5✉, Hyungwoo Kim6✉, Chulhong Kim1✉

1. Departments of Creative IT Engineering, Electrical Engineering, and Mechanical Engineering, Pohang University of Science and Technology (POSTECH), 77 Cheongam-ro, Pohang 37673, Republic of Korea.
2. Department of Materials Science and Engineering, College of Engineering, Seoul National University, Seoul 08826, Republic of Korea.
3. Interdisciplinary Program of Molecular Medicine, Chonnam National University, 77 Yongbong‐ro, Buk‐gu, Gwangju 61186, Republic of Korea.
4. Microbiology and Functionality Research Group, World Institute of Kimchi, 86 Kimchi-ro, Gwangju 61755, Republic of Korea.
5. Department of Nuclear Medicine, Chonnam National University Medical School & Hwasun Hospital, 264, Seoyang-ro, Hwasun-eup, Hwasun-gun, Jeollanam-do 58128, Republic of Korea.
6. School of Polymer Science and Engineering, Chonnam National University, 77 Yongbong-ro, Buk-gu, Gwangju 61186, Republic of Korea.
* These authors contributed equally to this work.

This is an open access article distributed under the terms of the Creative Commons Attribution License ( See for full terms and conditions.
Park B, Lee KM, Park S, Yun M, Choi HJ, Kim J, Lee C, Kim H, Kim C. Deep tissue photoacoustic imaging of nickel(II) dithiolene-containing polymeric nanoparticles in the second near-infrared window. Theranostics 2020; 10(6):2509-2521. doi:10.7150/thno.39403. Available from

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Photoacoustic imaging is gaining great attention in the medical world due to its significant potential for clinical translation. Light excitation in the second near-infrared (NIR-II) window (1000-1350 nm) has resolution and penetration depth suitable for several clinical applications. However, the significant challenge exists for clinical translation because of the absence of notable intrinsic chromophores in this clinically significant optical range to generate diagnostic images.

Methods: We present newly developed a biocompatible nickel dithiolene-based polymeric nanoparticle (NiPNP), which have a strong and sharp absorption peak at 1064 nm, as a photoacoustic contrast agent to boost specific absorbance in the NIR-II window for in vivo deep tissue imaging.

Results: We confirm the enhanced PA signal by NiPNP's strong light absorption in the NIR-II window (287% higher than that of NIR-I) and deep tissue imaging capability (~5.1 cm) through in vitro experiment. We have successfully acquired diagnostic-quality in vivo photoacoustic images in deep tissue (~3.4 cm) of sentinel lymph nodes, gastrointestinal tracts, and bladders of live rats by using clinically viable imaging system.

Conclusions: Our results prove that with strong absorption in the NIR-II window and with deeper imaging depth, the clinical translation of photoacoustic imaging with NiPNP is feasible for preclinical studies and thus would facilitate further clinical investigations.

Keywords: Photoacoustic imaging, Deep tissue imaging, Nickel dithiolene complex, Polymeric nanoparticle, Second near-infrared window.