Photoacoustic imaging of living mouse brain vasculature using hollow gold nanospheres
Introduction
Noninvasive molecular and functional imaging techniques show promise for detecting and monitoring various physiological and pathological conditions in animals and, ultimately, humans. Among these imaging modalities, photoacoustic imaging offers higher spatial resolution and allows deeper tissues to be imaged than most optical imaging techniques [1], [2], [3], [4], [5], [6], [7], [8]. Photoacoustic tomography (PAT) referred to as optoacoustic tomography (OAT) is a hybrid, nonionizing imaging modality that combines the merits of both optical and ultrasonic imaging methods [6]. PAT detects absorbed photons ultrasonically through the photoacoustic effect: a short-pulsed laser irradiates biological tissues and induces wideband ultrasonic waves (photoacoustic waves) as a result of transient thermoelastic expansion [8]. Owing to the optical absorption of hemoglobin, PAT has been successfully applied to the visualization of different structures in biological tissues, especially to imaging of the cerebral cortex in small animals [9], [10], human blood vessels [10], [11], microvasculature of tumors [4], [12] and quantifying oxygen hemoglobin saturation in tumors [2], [5], [9], [13].
PAT is capable of monitoring exogenous optical contrast agents with high sensitivity and specificity [5], [11], [14]. Optical contrast allowed spectroscopic separation of signal contributions from multiple optical absorbers such as oxyhemoglobin, deoxyhemoglobin, and molecular contrast agents, thus enabling simultaneous molecular and functional imaging [5]. Recently, gold nanoparticles such as gold nanoshells [7], nanocages [15], [16], nanorods [17], [18], [19], [20], [21], [22], [23], and nanobeacons [24], as well as carbon nanotubes [25], [26], [27], have been employed as molecular contrast enhancement agents in the near-infrared (NIR) range, where intrinsic optical absorption in tissue is minimal and penetration is optimal [28]. These gold nanoparticles can generate greater photoacoustic signals due to light excitation in the NIR spectral region, where the signal ratio of gold nanoparticles to hemoglobin is higher, thus showing greater contrast to endogenous chromophores [14], [26]. Moreover, the gold nanoparticles are not susceptible to photobleaching, a problem commonly associated with the use of organic dyes. These nanoparticles showed enhanced photoacoustic mapping of cerebral vasculature [7], [15], sentinel lymph node [16], [18], [27] and tumor in vivo [25], [26], joint tissue ex vivo [29], and macrophages in atherosclerotic plaques [30]. PAT also can noninvasively image the progressive extravasation of gold nanoshells through solid tumor vasculature in vivo [31]. In addition, gadolinium (Gd)-doped, gold-speckled silica nanoparticles were synthesized as multimodal nanoparticulate contrast agents for noninvasive imaging using both magnetic resonance imaging (MRI) and PAT [32].
Hollow gold nanospheres (HAuNS) have the unique combination of small size (outer diameter, 40–50 nm), spherical shape, and a hollow interior that results from their highly uniform structure [33], [34], [35]. The HAuNS have a strong and precisely tunable absorption band peaked at ∼800 nm and are coated with polyethylene glycol (PEG, MW 5000) to increase their blood circulation half-life. The purpose of this study was to evaluate the use of these HAuNS as a new molecular contrast agent for PAT. The accuracy of PAT with pegylated HAuNS (PEG-HAuNS) of mouse brain vasculature was confirmed through histological analysis. The pharmacokinetics, biodistribution, and acute toxicity of PEG-HAuNS were assessed to provide preliminary data for future translation in clinical applications.
Section snippets
Materials
Biotinylated secondary antibody, straptavidin-horseradish peroxidase (straptavidin-HRP), 3,3′-diaminobensidine (DAB), hematoxylin, luciferin, and 4% paraformaldehyde were purchased from Fisher Scientific (Waltham, MA). Rat anti-mouse CD31 monoclonal antibody was purchased from Millipore (Billerica, MA). Alexa Fluor 594-tagged goat anti-rat IgG and RPMI-1640 phenol red free cell culture medium were purchased from Invitrogen (Carlsbad, CA). Rat anti-mouse CD 68 antibody was obtained from AbD
PEG-HAuNS characterizations
A transmission electron microscopy (TEM) image of PEG-HAuNS shows that the nanoparticles had a mean outer diameter of 43–46 nm and a mean shell thickness of 2–4 nm (Fig. 1A). The resonance absorbance of these nanoparticles was tuned to peak at 800 nm (Fig. 1B). The optical absorption and scattering coefficients of gold nanospheres (i.e., absorption and scattering cross-sections per unit volume) were calculated (Fig. 1C). Our calculations showed that HAuNS with an outer diameter of 45 nm and
Conclusion
In this study, we evaluated a new nanoparticulate optical contrast agent based on HAuNS for photoacoustic imaging. The particles can be fabricated with surface plasmon resonance tunable at the NIR wavelength (∼800 nm), which allows deeper penetration of laser light and lowers the intrinsic background noise. The photoacoustic efficiency of HAuNS is significantly greater than that of blood. The pegylated HAuNS showed the mouse brain vasculature with greater clarity and more detailed structures,
Acknowledgements
We thank Dawn Chalaire for editing the manuscript. This work was supported in part by a grant from the National Institutes of Health (R01 CA119387 and R44 CA110137), a Seed Grant through the Alliance for NanoHealth by the Department of Army Telemedicine and Advanced Technology Research Center (W81XWH-07-2-0101), and by the John S. Dunn Foundation.
References (48)
- et al.
Bioconjugated gold nanoparticles as a molecular based contrast agent: implications for imaging of deep tumors using optoacoustic tomography
Mol Imaging Biol
(2004) - et al.
Noninvasive in vivo spectroscopic nanorod-contrast photoacoustic mapping of sentinel lymph nodes
Eur J Radiol
(2009) - et al.
Influence of anchoring ligands and particle size on the colloidal stability and in vivo biodistribution of polyethylene glycol-coated gold nanoparticles in tumor-xenografted mice
Biomaterials
(2009) - et al.
Brain delivery property and accelerated blood clearance of cationic albumin conjugated pegylated nanoparticle
J Control Release
(2007) - et al.
Stealth Me.PEG-PLA nanoparticles avoid uptake by the mononuclear phagocytes system
J Pharm Sci
(1995) - et al.
Photoacoustic imaging in biomedicine
Rev Sci Instrum
(2006) - et al.
Noninvasive imaging of hemoglobin concentration and oxygenation in the rat brain using high-resolution photoacoustic tomography
J Biomed Opt
(2006) - et al.
Functional photoacoustic microscopy for high-resolution and noninvasive in vivo imaging
Nat Biotechnol
(2006) - et al.
Initial results of in vivo non-invasive cancer imaging in the human breast using near-infrared photoacoustics
Opt Express
(2007) - et al.
Simultaneous molecular and hypoxia imaging of brain tumors in vivo using spectroscopic photoacoustic tomography
Proc IEEE
(2008)
Time-resolved optoacoustic imaging in layered biological tissues
Photoacoustic tomography of a nanoshell contrast agent in the in vivo rat brain
Nano Lett
Optoacoustic tomography
Noninvasive laser-induced photoacoustic tomography for structural and functional in vivo imaging of the brain
Nat Biotechnol
Three-dimensional photoacoustic imaging of blood vessels in tissue
Opt Lett
Noninvasive photoacoustic angiography of animal brains in vivo with near-infrared light and an optical contrast agent
Opt Lett
Laser optoacoustic imaging system for detection of breast cancer
J Biomed Opt
In vivo imaging and characterization of hypoxia-induced neovascularization and tumor invasion
Int J Oncol
Photoacoustic tomography of a rat cerebral cortex in vivo with au nanocages as an optical contrast agent
Nano Lett
Near-infrared gold nanocages as a new class of tracers for photoacoustic sentinel lymph node mapping on a rat model
Nano Lett
Targeted gold nanorod contrast agent for prostate cancer detection by photoacoustic imaging
J Appl Phys
In vivo photoacoustic molecular imaging with simultaneous multiple selective targeting using antibody-conjugated gold nanorods
Opt Express
Photoacoustic imaging of multiple targets using gold nanorods
IEEE Trans Ultrason Ferroelectr Freq Control
Photoacoustic imaging of early inflammatory response using gold nanorods
Appl Phys Lett
Cited by (0)
- 1
Present address: Grodno State University, Grodno, Belarus.