Millimeter-Deep Detection of Single Shortwave-Infrared-Emitting Polymer Dots through Turbid Media

• Published in: Nano letters Vol. 20; no. 12; pp. 8803 - 8810
• Main Authors: Piwoński, Hubert, Wang, Yang, Li, Wei, Michinobu, Tsuyoshi, Habuchi, Satoshi
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 09.12.2020
• Subjects: tissue phantoms; single-molecule; time-gated fluorescence detection; fluorescence imaging; conjugated polymer nanoparticles; fluorescent probes; shortwave infrared
• ISSN: 1530-6984; 1530-6992
• DOI: 10.1021/acs.nanolett.0c03675

Fluorescence imaging at longer wavelengths, especially in the shortwave-infrared (SWIR: 1000–1700 nm) region, leads to a substantial decrease in light attenuation, scattering, and background autofluorescence, thereby enabling enhanced penetration into biological tissues. The limited selection of fluorescent probes is a major bottleneck in SWIR fluorescence imaging. Here, we develop SWIR-emitting nanoparticles composed of donor–acceptor-type conjugated polymers. The bright SWIR fluorescence of the polymer dots (primarily attributable to their large absorption cross-section and high fluorescence saturation intensity (as high as 113 kW·cm–2)) enables the unprecedented detection of single particles as small as 14 nm through millimeter-thick turbid media. Unlike most SWIR-emitting nanomaterials, which have an excited-state lifetime in the range of microseconds to milliseconds, our polymer dots exhibit a subnanosecond excited-state lifetime. These characteristics enable us to demonstrate new time-gated single-particle imaging with a high signal-to-background ratio. These findings expand the range of potential applications of single-particle deep-tissue imaging.