Fluorescence Imaging In Vivo at Wavelengths beyond 1500 nm

Abstract

These authors contribute to the work equally.Key words: Imaging Agents, cancer, fluorescence, imaging agents, nanotechnology, near Fluorescence-based optical imaging is indispensable to investigating biological systems with high spatial and temporal resolution. [1] However, a formidable challenge to in vivo fluorescence imaging of live animals has been the limited depth of penetration and inability of high-resolution imaging through live tissues owing to both the absorption and scattering of photons. To circumvent this problem, we and others have recently explored in vivo fluorescence imaging in the second near-infrared window (NIR-II, 1000-1700 nm) to benefit from reduced photon scattering and achieve higher imaging resolution deeper in the body than with traditional NIR imaging (NIR-I, 750-900 nm). [2] Nevertheless, the NIR-II fluorophores used thus far mainly emit below about 1400 nm, which is still not optimal from the tissue scattering point of view. Although in vivo fluorescence imaging at longer wavelengths would further reduce scattering, increased water absorption upon approaching the infrared region could diminish the intensity of light passing through biological tissues, which is a valid concern that has deterred in vivo fluorescence imaging in the long wavelength NIR region. Another consideration for the development of in vivo fluorescence imaging in the long NIR window is the lack of biocompatible emitters with sufficient brightness. To date, most NIR-II in vivo fluorescence imaging has been based on highpressure carbon monoxide conversion (HiPCO) single-walled nanotubes (SWNTs) with a small diameter distribution of 0.7--1.1 nm, emitting band-gap fluorescence in the range of 1000-1400 nm. [2c,g,h,3] We expect that SWNTs with larger diameters, such as SWNTs grown by the laser vaporization method originally developed by Smalley, [4] could enable highresolution fluorescence imaging in the longer-wavelength region.The long wavelength NIR-II region near 1600 nm offers a balance of photonscattering and water-absorption effects, promising to significantly enhance the performance of fluorescence imaging in vivo, by achieving both improved penetration depth and imaging resolution. As shown in the absorption spectrum of water and the extinction spectra of biological tissues (Figure 1a), the near 1600 nm region resides in a local valley between a water vibrational OH stretching overtone absorption peak at approximately 1450 nm and the edge of an increasing water absorption combination band beyond 1700 nm. Thus, the fluorescence imaging window near 1600 nm offers a local minimum in the water absorption spectrum to minimize attenuation of the fluorescence signal caused by water dominant in biological tissues. On the other hand, as photon scattering scales as λ -α (α=0.2--4 for different tissues), [5] the near 1600 nm window provides the lowest photon scattering in the entire NIR-II window (without water absorption dominance), useful for high-resolution, deep-tissue biological imaging.We herein report the succ...

Molecular imaging of biological systems with a clickable dye in the broad 800- to 1,700-nm near-infrared window

“…We also developed an NIR-IIb >1,500-nm-emitting molecular imaging agent based on laser-vaporization SWCNTs enriched in fluorescent, semiconducting SWCNTs. The nanotubes were first coated with amine-terminated polymers (22,40,41) and then conjugated to SA before purification via DGU (SI Appendix, Figs. S6 and S7).…”

“…Although the imaging depth increased marginally in the NIR-II nuclear stain compared with the shorterwavelength NIR-I nuclear stain, many factors other than the imaging wavelength contribute to the maximum attainable staining depth. These factors include the limited probe diffusion depths of smallmolecule vs. nanomaterial-labeled proteins into tissues, receptorligand binding strength, variable fluorophore QYs [>10% for Deep Red (45, 46), 1.9% for IR-FGP, and 0.01-0.05% for SWCNTs (22)], as well as NIR-II detector and integrated optical path conditions of the home-built confocal setup (47). Therefore, to achieve deeper scanning depths with high spatial resolution for one-photon-based systems, NIR-II conjugates with higher QYs, improved staining conditions allowing deeper probe diffusion into fixed tissues, as well as optimized NIR-II confocal setups are needed.…”

“…The increased photon penetration depth allows for visualization of deeper physiological structures, opening the possibility of layer-by-layer fluorescence imaging for 3D molecular imaging using simple one-photon techniques (9,20,21). Furthermore, the low NIR-II tissue autofluorescence that eventually could reach near-zero levels in the NIR-IIb (1,500-1,700 nm) window could facilitate a marked increase in fluorescent probe signal-to-background ratios and imaging specificity for fluorescent probes (22)(23)(24).…”

Layer-by-layer assembled fluorescent probes in the second near-infrared window for systemic delivery and detection of ovarian cancer

“…Current NIR-II emissive materials, including rare-earthbased down-conversion nanoparticles (DCNPs), quantum dots (QDs), single-walled carbon nanotubes (SWNTs), and small organic molecules, have been incorporated into diagnostic probes using a single lipid, polymer, protein, or bacteriophage (6)(7)(8)(9)(10)(11)(12). However, these delivery carriers lack the modularity and versatility to include drugs effectively for theranostic platforms and do not as readily enable the incorporation of complex or multiple drug payloads.…”

Construction of a photothermal Venus flytrap from conductive polymer bimorphs

“…44,45 Because of the large absorption, the PP-PEDOT surface was heated upon exposure to a NIR light, as shown in the thermal image in Figure 2c. The maximum temperature (T max ) of the PP-PEDOT surface on a PDMS (t 1 = 70 μm) was 96, 117 and 131°C, for t 2 of 130, 290 and 400 nm, respectively, upon exposure to a 198 mW NIR source for 10 s (Figure 2b and c).…”