Plasmon resonance coupling of metal nanoparticles for molecular imaging of carcinogenesis in vivo

Abstract

An effective cancer control strategy requires improved early detection methods, patient-specific drug selection, and the ability to assess response to targeted therapeutics. Recently, plasmon resonance coupling between closely spaced metal nanoparticles has been used to develop ultrasensitive bioanalytical assays in vitro. We demonstrate the first in vivo application of plasmon coupling for molecular imaging of carcinogenesis. We describe molecular-specific gold bioconjugates to image epidermal growth factor receptor (EGFR); these conjugates can be delivered topically and imaged noninvasively in real time. We show that labeling with gold bioconjugates gives information on the overexpression and nanoscale spatial relationship of EGF receptors in cell membranes, both of which are altered in neoplasia. EGFR-mediated aggregation of gold nanoparticles in neoplastic cells results in more than a 100-nm color shift and a contrast ratio of more than tenfold in images of normal and precancerous epithelium in vivo, dramatically increasing contrast beyond values reported previously for antibody-targeted fluorescent dyes.

Detection of TiO2 nanoparticles in cells by flow cytometry

“…For example, gold scatters more light than silver (12,32). It is conceivable that metal ions like gold, silver, or titanium will exhibit surface plasmon resonance, resulting in the scattering of a large amount of laser light (12,20,(36)(37)(38)(39)(40)(41). It may be possible to detect using flow cytometry other nanoparticles that scatter less light than TiO 2 by increasing the detection optics of the scatter signal and using a lower wavelength laser (405 or 372 nm) to excite the particles instead of the standard 488-nm signals.…”

“…The SSC signal is affected by the RI of the cytoplasm and the number and type of organelles present in the cell. SSC has been used to show differences in the physical state of the cell, including mitosis, particle uptake, and sperm decondensation (20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30)(31)(32). Cell populations can be defined by their specific light-scattering clusters in a cytogram (plot of FSC vs. SSC), and then the amount of fluorescence from specific probes in various channels can be correlated to the scatter patterns of the specific cell populations.…”

“…Most flow cytometers measure the small angle forward scatter (FSC) intensity with a photodiode and side scatter (SSC) intensity with a photomultiplier tube. Generally, it is considered that the FSC provides information on the overall size of cells while the SSC provides information on internal structures and organelles (20)(21)(22)(23)(24).…”

Plasmonic flow cytometry by immunolabeled nanorods

“…As the number of bound nanoparticles increases, there is initially a linear increase in scattering intensity (9). At higher concentrations, however, the distances between membrane-bound nanoparticles decreases, causing plasmonic coupling and a subsequent quadratic increase in scattering intensity (10). On average, EGFR-expressing cells contain between 2 3 10 4 and 2 3 10 5 EGFR proteins per cell (30).…”

“…Protocols have also been developed for facile conjugation of noble metal nanoparticles to antibodies, DNA probes, and small-molecule ligands, which makes them useful for targeting applications (4). Immunolabeled nanoparticles are comparable with fluorescence tags in quantifying receptor expression levels, but provide the additional benefit that they are also sensitive to the local refractive index within the cell (9)(10)(11).…”