Matthew A. Wall

Surface-Enhanced Resonance Raman Scattering Nanostars for High Precision Cancer Imaging

Surface-enhanced resonance Raman scattering gold nanostars allow detection of macro- and microscopic foci of premalignant and cancerous lesions in vivo. Seeing Nanostars Microscopic tumors may be difficult for the naked eye to see, but they are no match for nanosized imaging agents, which home in on cancerous tissues to signal the presence of disease. Harmsen and colleagues created a new generation of cancer imaging agents, called “surface-enhanced resonance Raman scattering (SERRS) nanostars” −75-nm star-shaped gold cores wrapped in Raman reporter molecule-containing silica. When hit by a near-infrared laser, these nanostars emit a unique photonic signature (Raman “fingerprint”). The authors used a new silica encapsulation method and a reporter molecule that was “in resonance” with the laser, which meant that they shone nearly 400 times brighter than their “nonresonant” counterparts during Raman imaging. The SERRS nanostars were used to image macro- and microscopic malignant lesions in animal models of pancreatic cancer, breast cancer, prostate cancer, and sarcoma with high precision. As endoscopic and handheld Raman imaging devices are further developed for the clinic, the SERRS nanostars are sure to find a place in human tumor detection. The inability to visualize the true extent of cancers represents a significant challenge in many areas of oncology. The margins of most cancer types are not well demarcated because the cancer diffusely infiltrates the surrounding tissues. Furthermore, cancers may be multifocal and characterized by the presence of microscopic satellite lesions. Such microscopic foci represent a major reason for persistence of cancer, local recurrences, and metastatic spread, and are usually impossible to visualize with currently available imaging technologies. An imaging method to reveal the true extent of tumors is desired clinically and surgically. We show the precise visualization of tumor margins, microscopic tumor invasion, and multifocal locoregional tumor spread using a new generation of surface-enhanced resonance Raman scattering (SERRS) nanoparticles, which are termed SERRS nanostars. The SERRS nanostars feature a star-shaped gold core, a Raman reporter resonant in the near-infrared spectrum, and a primer-free silication method. In genetically engineered mouse models of pancreatic cancer, breast cancer, prostate cancer, and sarcoma, and in one human sarcoma xenograft model, SERRS nanostars enabled accurate detection of macroscopic malignant lesions, as well as microscopic disease, without the need for a targeting moiety. Moreover, the sensitivity (1.5 fM limit of detection) of SERRS nanostars allowed imaging of premalignant lesions of pancreatic and prostatic neoplasias. High sensitivity and broad applicability, in conjunction with their inert gold-silica composition, render SERRS nanostars a promising imaging agent for more precise cancer imaging and resection.

Rational Design of a Chalcogenopyrylium-Based Surface-Enhanced Resonance Raman Scattering-Nanoprobe with Attomolar Sensitivity

High sensitivity and specificity are two desirable features in biomedical imaging. Raman imaging has surfaced as a promising optical modality that offers both. Here, we report the design and synthesis of a group of near infrared absorbing 2-thienyl-substituted chalcogenopyrylium dyes tailored to have high affinity for gold. When adsorbed onto gold nanoparticles, these dyes produce biocompatible SERRS-nanoprobes with attomolar limits of detection amenable to ultrasensitive in vivo multiplexed tumor and disease marker detection.

Silica Nanoparticles as Substrates for Chelator-free Labeling of Oxophilic Radioisotopes

Chelator-free nanoparticles for intrinsic radiolabeling are highly desirable for whole-body imaging and therapeutic applications. Several reports have successfully demonstrated the principle of intrinsic radiolabeling. However, the work done to date has suffered from much of the same specificity issues as conventional molecular chelators, insofar as there is no singular nanoparticle substrate that has proven effective in binding a wide library of radiosotopes. Here we present amorphous silica nanoparticles as general substrates for chelator-free radiolabeling and demonstrate their ability to bind six medically relevant isotopes of various oxidation states with high radiochemical yield. We provide strong evidence that the stability of the binding correlates with the hardness of the radioisotope, corroborating the proposed operating principle. Intrinsically labeled silica nanoparticles prepared by this approach demonstrate excellent in vivo stability and efficacy in lymph node imaging.

Cancer imaging using surface-enhanced resonance Raman scattering nanoparticles

The unique spectral signatures and biologically inert compositions of surface-enhanced resonance Raman scattering (SERRS) nanoparticles make them promising contrast agents for in vivo cancer imaging. Our SERRS nanoparticles consist of a 60-nm gold nanoparticle core that is encapsulated in a 15-nm-thick silica shell wherein the resonant Raman reporter is embedded. Subtle aspects of their preparation can shift their limit of detection by orders of magnitude. In this protocol, we present the optimized, step-by-step procedure for generating reproducible SERRS nanoparticles with femtomolar (10−15 M) limits of detection. We provide ways of characterizing the optical properties of SERRS nanoparticles using UV/VIS and Raman spectroscopy, and their physicochemical properties using transmission electron microscopy and nanoparticle tracking analysis. We introduce several applications of these nanoprobes for biomedical research, with a focus on intraoperative cancer imaging via Raman imaging. A detailed account is provided for successful i.v. administration of SERRS nanoparticles such that delineation of cancerous lesions can be achieved in vivo and ex vivo on resected tissues without the need for specific biomarker targeting. This straightforward, yet comprehensive, protocol—from initial de novo gold nanoparticle synthesis to SERRS nanoparticle contrast-enhanced preclinical Raman imaging in animal models—takes ∼96 h.

Chelator-Free Radiolabeling of SERRS Nanoparticles for Whole-Body PET and Intraoperative Raman Imaging

A single contrast agent that offers whole-body non-invasive imaging along with the superior sensitivity and spatial resolution of surface-enhanced resonance Raman scattering (SERRS) imaging would allow both pre-operative mapping and intraoperative imaging and thus be highly desirable. We hypothesized that labeling our recently reported ultrabright SERRS nanoparticles with a suitable radiotracer would enable pre-operative identification of regions of interest with whole body imaging that can be rapidly corroborated with a Raman imaging device or handheld Raman scanner in order to provide high precision guidance during surgical procedures. Here we present a straightforward new method that produces radiolabeled SERRS nanoparticles for combined positron emission tomography (PET)-SERRS tumor imaging without requiring the attachment of molecular chelators. We demonstrate the utility of these PET-SERRS nanoparticles in several proof-of-concept studies including lymph node (LN) tracking, intraoperative guidance for LN resection, and cancer imaging after intravenous injection. We anticipate that the radiolabeling method presented herein can be applied generally to nanoparticle substrates of various materials by first coating them with a silica shell and then applying the chelator-free protocol.

Determination on the Structure of Au Nanorods with Pentagonal Cross-Sections by Various TEM Techniques

1. Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, NY, 11973, USA. 2. Department of Radiology, Memorial Sloan-Kettering Cancer Center, New York, NY, 10065, USA. 3. Department of Chemistry, Hunter College of the City University of New York, New York, NY. 10065, USA. 4. Nanotechnology Center, Memorial Sloan-Kettering Cancer Center, New York, NY, 10065, USA. 5. Department of Radiology, Weill, Cornell Medical College, New York, NY 10065, USA.