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...

These findings are of interest for the development of alpha7-nicotinic acetylcholine receptor agonists as a new class of anti-inflammatory therapeutics.

Photoacoustic tomography is a rapidly growing imaging modality that can provide images of high spatial resolution and high contrast at depths up to 5 cm. We report here the design, synthesis and evaluation of an activatable probe that shows great promise in enabling detection of the cleaved probe in the presence of the high levels of non-activated, un-cleaved probe, a difficult task to attain in absorbance-based modality. Before the cleavage by its target, proteolytic enzyme MMP-2, the probe, an activatable cell penetrating peptide, Ceeee[Ahx]PLGLAGrrrrrK, labeled with two chromophores, BHQ3 and Alexa750, shows photoacoustic signal of similar intensity at the two wavelengths corresponding to the absorption maxima of the chromophores, 675 and 750 nm. Subtraction of the images taken at these two wavelengths makes the probe effectively photoacoustically silent as the signals at these two wavelengths essentially cancel out. After the cleavage, the dye associated with the cell penetrating part of the probe(CPP), BHQ3, accumulates in the cells, while the other dye diffuses away, resulting in photoacoustic signal seen only at one of the wavelengths, 675 nm. The subtraction of the photoacoustic images at two wavelengths reveals the location of the cleaved (activated) probe. In the search for the chromophores that are best suited for photoacoustic imaging we have investigated photoacoustic signal of five chromophores absorbing in the NIR region. We have found that the photoacoustic signal did not correlate with the absorbance and fluorescence of the molecules, as the highest photoacoustic signal arose from the least absorbing quenchers BHQ3 and QXL 680.

Anisotropic colloidal hybrid nanoparticles exhibit superior optical and physical properties compared to their counterparts with regular architectures. We herein developed a controlled, stepwise strategy to build novel, anisotropic, branched, gold nanoarchitectures (Au-tripods) with predetermined composition and morphology for bioimaging. The resultant Au-tripods with size less than 20 nm showed great promise as contrast agents for in vivo photoacoustic imaging (PAI). We further identified Au-tripods with two possible configurations as high-absorbance nanomaterials from various gold multipods using a numerical simulation analysis. The PAI signals were linearly correlated with their concentrations after subcutaneous injection. The in vivo biodistribution of Au-tripods favorable for molecular imaging was confirmed using small animal positron emission tomography (PET). Intravenous administration of cyclic Arg-Gly-Asp-d-Phe-Cys (RGDfC) peptide conjugated Au-tripods (RGD-Au-tripods) to U87MG tumor-bearing mice showed PAI contrasts in tumors almost 3-fold higher than for the blocking group. PAI results correlated well with the corresponding PET images. Quantitative biodistribution data revealed that 7.9% ID/g of RGD-Au-tripods had accumulated in the U87MG tumor after 24 h post-injection. A pilot mouse toxicology study confirmed that no evidence of significant acute or systemic toxicity was observed in histopathological examination. Our study suggests that Au-tripods can be reliably synthesized through stringently controlled chemical synthesis and could serve as a new generation of platform with high selectivity and sensitivity for multimodality molecular imaging.

2-deoxy-2-[18F]fluoro-D-glucose ([18F]FDG) has extensively been used for clinical diagnosis, staging, and therapy monitoring of cancer and other diseases. Nonradioactive glucose analogues enabling the screening of the glucose metabolic rate of tumors are of particular interest for anticancer drug development. A nonradioactive fluorescent deoxyglucose analogue may have many applications for both imaging of tumors and monitoring therapeutic efficacy of drugs in living animals and may eventually translate to clinical applications. We found that a fluorescent 2-deoxyglucose analogue, 2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-2-deoxy-D-glucose (2-NBDG), can be delivered in several tumor cells via the glucose transporters (GLUTs). We therefore conjugated D-glucosamine with a near-infrared (NIR) fluorphor Cy5.5 and tested the feasibility of the Cy5.5-D-glucosamine (Cy5.5-2DG) conjugate for NIR fluorescence imaging of tumors in a preclinical xenograft animal model. Cy5.5-2DG was prepared by conjugating Cy5.5 monofunctional N-hydroxysuccinimide ester (Cy5.5-NHS) and D-glucosamine followed by high-performance liquid chromatography purification. The accumulation of Cy5.5-2DG and Cy5.5-NHS in different tumor cell lines at 37 and 4 degrees C were imaged using a fluorescence microscope. Tumor targeting and retention of Cy5.5-2DG and Cy5.5-NHS in a subcutaneous U87MG glioma and A375M melanoma tumor model were evaluated and quantified by a Xenogen IVIS 200 optical cooled charged-coupled device system. Fluorescence microscopy imaging shows that Cy5.5-2DG and Cy5.5-NHS are taken up and trapped by a variety of tumor cell lines at 37 degrees C incubation, while they exhibit marginal uptake at 4 degrees C. The tumor cell uptake of Cy5.5-2DG cannot be blocked by the 50 mM D-glucose, suggesting that Cy5.5-2DG may not be delivered in tumor cells by GLUTs. U87MG and A375M tumor localization was clearly visualized in living mice with both NIR fluorescent probes. Tumor/muscle contrast was clearly visible as early as 30 min postinjection (pi), and the highest U87MG tumor/muscle ratios of 2.81 +/- 0.10 and 3.34 +/- 0.23 were achieved 24 h pi for Cy5.5-2DG and Cy5.5-NHS, respectively. While as a comparison, the micropositron emission tomography imaging study shows that [18F]FDG preferentially localizes to the U87MG tumor, with resulting tumor/muscle ratios ranging from 3.89 to 4.08 after 30 min to 2 h postadministration of the probe. In conclusion, the NIR fluorescent glucose analogues, Cy5.5-2DG and Cy5.5-NHS, both demonstrate tumor-targeting abilities in cell culture and living mice. More studies are warranted to further explore their application for optical tumor imaging. To develop NIR glucose analogues with the ability to target GLUTs/hexokinase, it is highly important to select NIR dyes with a reasonable molecular size.