Picomolar sensitivity MRI and photoacoustic imaging of cobalt nanoparticles

Abstract

Multimodality imaging based on complementary detection principles has broad clinical applications and promises to improve the accuracy of medical diagnosis. This means that a tracer particle advantageously incorporates multiple functionalities into a single delivery vehicle. In the present work, we explore a unique combination of MRI and photoacoustic tomography (PAT) to detect picomolar concentrations of nanoparticles. The nanoconstruct consists of ferromagnetic (Co) particles coated with gold (Au) for biocompatibility and a unique shape that enables optical absorption over a broad range of frequencies. The end result is a dual-modality probe useful for the detection of trace amounts of nanoparticles in biological tissues, in which MRI provides volume detection, whereas PAT performs edge detection.dual-modality imaging ͉ ferromagnetic nanoparticle ͉ molecular imaging ͉ MRI contrast ͉ photoacoustic tomography W e have synthesized nanoparticles for dual-modality (1-7)MRI and photoacoustic tomography (PAT). The incorporation of MRI and PAT into a single probe offers the unique possibility of combining the complementary strategies of contrastbased volume imaging and edge detection. Our nanoconstruct consists of zero-valence ferromagnetic cobalt (Co) particles (8) with a gold (Au) coating for biocompatibility and a unique shape rendering increased optical absorption over a broad range of frequencies (9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19). This research theme follows the rapid developments in nanotechnology, diagnostic radiology, and targeted molecular imaging (20), whereby nanoparticulate contrast agents, with the desirable properties of high chemical specificity, biocompatibility, and a reasonable half-life, are administered within a specific region of interest. In nanoparticle-based imaging studies, higher particle concentrations lead to better signal-to-noise contrasts, but this also poses a tradeoff with the toxicity. Therefore, one of the most important parameters when developing particle-based contrast is the safest and lowest nanoparticle concentration that offers sufficient contrast sensitivity.In MRI, magnetic materials such as gadolinium chelates and magnetic nanoparticles are often used (21-23) to enhance image contrast. The magnetic nanoparticles are passivated by biocompatible coatings such as dextrin, citrate, polystyrene/divinylbenzene, and elemental gold. These coatings also detoxify the particles, resulting in enhanced lifetimes in vivo. Typical examples of magnetic nanoparticulate core-shell configurations include magnetitedextrin, magnetite-silica (24) and iron-gold (25).Laser-based PAT (9-19) is a hybrid imaging modality [see supporting information (SI) Fig. S1]. It uses a pulsed laser source to illuminate a biological sample. Light absorption by the tissue results in a transient temperature rise on the order of 10 mK. The rapid thermoelastic expansion excites ultrasonic waves that are measured by using broadband ultrasonic transducers conformally arranged around the sample. Finally, a modif...

Functionalized nanomaterials: their use as contrast agents in bioimaging: mono- and multimodal approaches

“…This dual-modality probe revealed very useful for the detection of trace amounts of NPs in the biological tissues in which MRI provides volume detection, whereas PAT performs edge detection [110] . Water-soluble cobalt oxide nanocrystals (CoO NCs) were obtained via a phase-transfer method with amphiphilic surfactants, such as anionic (sodium dodecyl sulfate (SDS)), neutral (Pluronic F127, PF127), and cationic (cetyltrimethyl ammonium bromide, CTAB) [111] .…”

“…Some of those commonly used for PAT include spherical gold NPs [304, 314 -320] , nanorods [321 -327] , nanostars [328] , nanocages [305, 329 -334] , hollow nanoshells [335] , and composite materials with gold nanoshells: SiO 2 @Au, [306,336,337] Fe 3 O 4 @Au, [314] cobalt@gold NPs, [110] gold-speckled silica [316,320] , and gold nanobeacons [338,339] . The reasons for such an attention to gold nanosystems are many fold: they have tunable size-and shape-dependent plasmonic properties [340,341] , which allow them to absorb and scatter light from the visible to NIR region and make them suitable for image-guided therapy [325, 342 -344] and PTA of tumors [345 -347] .…”

Magnetic Nanoparticles: Its Effect on Cellular Behaviour and Potential Applications

“…The signal intensity of these MNP is related to the size of the particle, its position, its concentration within a given voxel, data acquisition parameters, the magnetic field, and dosage of the SPIO (Wang et al, 2001). In order to achieve higher relaxivity, types of MNPs have also been designed and included those doped with alternative metals such as CoFe 2 O 4 , NiFe 2 O 4 , MnFe 2 O 4 , Gd 2 O 3 and gold-coated cobalt nanoparticles (Bouchard, et al, 2009;Bridot et al, 2007;. Magnetism in MNPs is highly sensitive to its size because it arises from the collective interaction of atomic magnetic dipoles.…”

Functionalized nanomaterials: their use as contrast agents in bioimaging: mono- and multimodal approaches

“…This dual-modality probe revealed very useful for detection of trace amounts of nanoparticles in biological tissues, in which MRI provides volume detection, whereas PAT performs edge detection [110]. Water-soluble cobalt oxide nanocrystals (CoO NCs) were obtained via a phase-transfer method with amphiphilic surfactants, such as anionic (sodium dodecyl sulfate, SDS), neutral (Pluronic F127, PF127) and cationic (cetyltrimethyl ammonium bromide, CTAB) [111].…”