Fluorescent imaging of biological systems in the second near-infrared window (NIR-II) can probe tissue at centimetre depths and achieve micrometre-scale resolution at depths of millimetres. Unfortunately, all current NIR-II fluorophores are excreted slowly and are largely retained within the reticuloendothelial system, making clinical translation nearly impossible. Here, we report a rapidly excreted NIR-II fluorophore (∼90% excreted through the kidneys within 24 h) based on a synthetic 970-Da organic molecule (CH1055). The fluorophore outperformed indocyanine green (ICG)-a clinically approved NIR-I dye-in resolving mouse lymphatic vasculature and sentinel lymphatic mapping near a tumour. High levels of uptake of PEGylated-CH1055 dye were observed in brain tumours in mice, suggesting that the dye was detected at a depth of ∼4 mm. The CH1055 dye also allowed targeted molecular imaging of tumours in vivo when conjugated with anti-EGFR Affibody. Moreover, a superior tumour-to-background signal ratio allowed precise image-guided tumour-removal surgery.

Photoacoustic imaging of living subjects offers higher spatial resolution and allows deeper tissues to be imaged compared with most optical imaging techniques 1-7 . As many diseases do not exhibit a natural photoacoustic contrast, especially in their early stages, it is necessary to administer a photoacoustic contrast agent. A number of contrast agents for photoacoustic imaging have been suggested previously 8-15 , but most were not shown to target a diseased site in living subjects. Here we show that single-walled carbon nanotubes conjugated with cyclic Arg-Gly-Asp (RGD) peptides can be used as a contrast agent for photoacoustic imaging of tumours. Intravenous administration of these targeted nanotubes to mice bearing tumours showed eight times greater photoacoustic signal in the tumour than mice injected with non-targeted nanotubes. These results were verified ex vivo using Raman microscopy. Photoacoustic imaging of targeted single-walled carbon nanotubes may contribute to non-invasive cancer imaging and monitoring of nanotherapeutics in living subjects 16 .Recently, we reported on the conjugation of cyclic RGD containing peptides to single-walled carbon nanotubes 17 (SWNT-RGD) that is stable in serum. The single-walled carbon nanotubes, which were 1-2 nm in diameter and 50-300 nm in length were coupled to the RGD peptides through polyethylene glycol-5000 grafted phospholipid (PL-PEG 5000 ). These SWNT-RGD conjugates bind with high affinity to α v β 3 integrin, which is overexpressed in tumour neovasculature, and to other integrins expressed by tumours but with lower *e-mail: sgambhir@stanford.edu. Author contributions A.D. built the photoacoustic instrument, designed and performed the experiments and wrote the paper. C.Z. designed, performed and analysed the Raman experiments. S.K. built the photoacoustic instrument and designed the experiments. S.V. designed and built the photoacoustic instrument. S.B. performed the experiments and helped write the paper. Z.L. synthesized the single-walled carbon nanotube conjugates. J.L. performed the cell uptake studies. B.R.S. helped write the paper. T.M. and O.O. helped design the photoacoustic instrument. Z.C. helped perform the comparison to fluorescence imaging. X.C. provided the RGD peptides, performed the fluorescence imaging of QD-RGD conjugates and helped write the manuscript. H.D. was responsible for single-walled carbon nanotube conjugation synthesis. B.T.K. was responsible for building the photoacoustic instrument. S.S.G. was responsible for experimental design and wrote the paper.Author information Reprints and permission information is available online at http://npg.nature.com/reprintsandpermissions/. Correspondence and requests for materials should be addressed to S.S.G. (Fig. 1a). Our photoacoustic instrument 20 used a single-element focused transducer to raster scan the object under study, which was illuminated through a fibre head (see Methods and Supplementary Information, Fig. S1). In a phantom study we measured the photoacoustic signal of pla...

The design and use of materials in the nanoscale size range for addressing medical and health-related issues continues to receive increasing interest. Research in nanomedicine spans a multitude of areas, including drug delivery, vaccine development, antibacterial, diagnosis and imaging tools, wearable devices, implants, high-throughput screening platforms, etc. using biological, nonbiological, biomimetic, or hybrid materials. Many of these developments are starting to be translated into viable clinical products. Here, we provide an overview of recent developments in nanomedicine and highlight the current challenges and upcoming opportunities for the field and translation to the clinic.

The development of fluorophores and molecular probes for the second near-infrared biological window (NIR-II, 1000-1700 nm) represents an important, newly emerging and dynamic field in molecular imaging, chemical biology and materials chemistry. Because of reduced scattering, minimal absorption and negligible autofluorescence, NIR-II imaging provides high resolution, a high signal-to-noise ratio, and deep tissue penetration capability. Among various state-of-the-art bioimaging modalities, one of the greatest challenges in developing novel probes is to achieve both high resolution and sensitivity. The chemical design and synthesis of NIR-II fluorophores suitable for multimodal imaging is thus emerging as a new and powerful strategy for obtaining high-definition images. NIR-II fluorophores may convert NIR-II photons into heat for photothermal therapy and be excited by NIR-II light to produce singlet oxygen for photodynamic therapy. The presence of simultaneous diagnostic and therapeutic capabilities in a single probe can be used for precise treatment. In this review, we have focused on recent advances in the chemical design and synthesis of NIR-II fluorophores from small organic molecules to organic and inorganic nanoparticles, and we have further discussed recent advances and key operational differences in reported NIR-II imaging systems and biomedical applications based on NIR-II imaging, such as multimodal imaging, photothermal and photodynamic therapy, guidance for intraoperative surgery, and drug delivery.

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Molecular imaging of living subjects continues to rapidly evolve with bioluminescence and fluorescence strategies, in particular being frequently used for small-animal models. This article presents noninvasive deep-tissue molecular images in a living subject with the use of Raman spectroscopy. We describe a strategy for small-animal optical imaging based on Raman spectroscopy and Raman nanoparticles. Surface-enhanced Raman scattering nanoparticles and single-wall carbon nanotubes were used to demonstrate whole-body Raman imaging, nanoparticle pharmacokinetics, multiplexing, and in vivo tumor targeting, using an imaging system adapted for small-animal Raman imaging. The imaging modality reported here holds significant potential as a strategy for biomedical imaging of living subjects.nanotubes ͉ SERS nanoparticles M olecular imaging of living subjects provides the ability to study cellular and molecular processes that have the potential to impact many facets of biomedical research and clinical patient management (1-4). Imaging of small-animal models is currently possible by using positron emission tomography (PET), single photon emission computed tomography, magnetic resonance imaging, computed tomography, optical bioluminescence and fluorescence, high frequency ultrasound, and several other emerging modalities. However, no single modality currently meets the needs of high sensitivity, high spatial and temporal resolution, high multiplexing capacity, low cost, and high-throughput.Fluorescence imaging, in particular, has significant potential for in vivo studies but is limited by several factors (5, 6), including a limited number of fluorescent molecular imaging agents available in the near infra-red (NIR) window with large spectral overlap between them, which restricts the ability to interrogate multiple targets simultaneously (multiplexing). In addition, background autofluorescence emanating from superficial tissue layers restricts the sensitivity and the depth to which fluorescence imaging can be used. Moreover, rapid photobleaching of fluorescent molecules limits their useful lifetime and prevents studies of prolonged duration. Therefore, we have attempted to develop new strategies that may solve some of the limitations of fluorescence imaging in living subjects.Raman spectroscopy can differentiate the spectral fingerprint of many molecules, resulting in very high multiplexing capabilities. Narrow spectral features are easily separated from the broadband autofluorescence, because Raman is a scattering phenomenon as opposed to absorption/emission in fluorescence, and Raman active molecules are more photostable compared with fluorophores, which are rapidly photobleached. Unfortunately, the precise mechanism for photobleaching is not well understood. However, it has been linked to a transition from the excited singlet state to the excited triplet state. Photobleaching is significantly reduced for single molecules adsorbed onto metal particles because of the rapid quenching of excited electrons by the metal surface...

Fluorescence imaging in the second near-infrared window (NIR-II) allows visualization of deep anatomical features with an unprecedented degree of clarity. NIR-II fluorophores draw from a broad spectrum of materials spanning semiconducting nanomaterials to organic molecular dyes, yet unfortunately all water-soluble organic molecules with >1,000 nm emission suffer from low quantum yields that have limited temporal resolution and penetration depth. Here, we report tailoring the supramolecular assemblies of protein complexes with a sulfonated NIR-II organic dye (CH-4T) to produce a brilliant 110-fold increase in fluorescence, resulting in the highest quantum yield molecular fluorophore thus far. The bright molecular complex allowed for the fastest video-rate imaging in the second NIR window with ∼50-fold reduced exposure times at a fast 50 frames-per-second (FPS) capable of resolving mouse cardiac cycles. In addition, we demonstrate that the NIR-II molecular complexes are superior to clinically approved ICG for lymph node imaging deep within the mouse body.

This study evaluates the influence of particle size, PEGylation, and surface coating on the quantitative biodistribution of near-infrared-emitting quantum dots (QDs) in mice. Polymer- or peptide-coated 64Cu-labeled QDs 2 or 12 nm in diameter, with or without polyethylene glycol (PEG) of molecular weight 2000, are studied by serial micropositron emission tomography imaging and region-of-interest analysis, as well as transmission electron microscopy and inductively coupled plasma mass spectrometry. PEGylation and peptide coating slow QD uptake into the organs of the reticuloendothelial system (RES), liver and spleen, by a factor of 6–9 and 2–3, respectively. Small particles are in part renally excreted. Peptide-coated particles are cleared from liver faster than physical decay alone would suggest. Renal excretion of small QDs and slowing of RES clearance by PEGylation or peptide surface coating are encouraging steps toward the use of modified QDs for imaging living subjects.