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

Abstract

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.

Organic J-Aggregate Nanodots with Enhanced Light Absorption and Near-Unity Fluorescence Quantum Yield

“…The heavy-metal-free organic Jdots constitute a promising biocompatible alternative to semiconductor nanomaterials for one- and two-photon fluorescence imaging applications. Careful design and synthesis of carbazole-based symmetric D-π- A -π-D molecules with different acceptor moieties could enable researchers to tune the fluorescence into the near-infrared (NIR) and shortwave infrared (SWIR) spectral regions, , which is more desirable in biological imaging. Utilization of self-assembled J-aggregates nanostructures could solve the common problem of limited brightness of NIR/SWIR-emitting fluorescent probes.…”

The Pursuit of Shortwave Infrared-Emitting Nanoparticles with Bright Fluorescence through Molecular Design and Excited-State Engineering of Molecular Aggregates

“…(b) Schematic illustration describing the experimental configuration of single-particle fluorescence imaging of the PSN Pdots through tissue phantoms. (c) Fluorescence images of individual PSN Pdots deposited onto the tissue phantoms with varied thickness, as captured by the visible/NIR-I detector (left) and the SWIR detector (right) . Reproduced with permission from ref , copyright 2020 American Chemical Society.…”

“…The solid lines show fitting of the data to a two-state model. (g) Saturation intensities and (h) maximum fluorescence count rates obtained for the SWIR-emitting fluorophores determined by fitting the excitation power-dependent fluorescence intensity displayed in (a–f) . Reproduced with permission from ref , copyright 2020 American Chemical Society.…”

“…The blue arrows show the applied time gate of the detection. Fluorescence images of individual (d) PSN Pdots deposited onto a 40-μm-thick tissue phantom captured at varied time gates with signal-to-background ratios at applied time gate depicted . Reproduced with permission from ref , copyright 2020 American Chemical Society.…”

Highly Efficient Luminescence from Charge-Transfer Gold Nanoclusters Enabled by Lewis Acid

“…Intramolecular charge transfer (ICT), namely, charge transfer from the electron-rich part to conjugated electron-deficient one in a molecule, can alter molecule structure and electron distribution. − The occurrence of ICT commonly generates two drastically different states, i.e., local excited (LE) state and the ICT state. − Precisely controlling the proportion of LE and ICT states in the excited process will endow organic molecules and inorganic–organic complexes with tunable luminescence. − Such a unique feature is appealing for their subsequent applications in sensing, biological imaging, and optical switches. − However, the rational design of ICT-based fluorescence probes in aqueous solution remains a serious challenge because the flexible intramolecular rotation in a polar solvent favors nonradiative decay and greatly weakens ICT emission . In recent years, the restriction of intramolecular motion (RIM) has been demonstrated to be a promising approach to strengthen the emission from the ICT state owing to its ability to significantly suppress the ultrafast nonradiative relaxation following an ICT process. , Unfortunately, this strategy usually suffers from some typical problems, such as producing large size of architectures with poor water-solubility and involving a cumbersome modification procedure …”