Academic Appointments

Research & Scholarship

Current Research and Scholarly Interests

Biomedical Engineering and Nanotechnology with a focus on Fluorescence and Raman Spectroscopy for Early Cancer Detection and Surgical Guidance.

•Development and evaluation of novel tumor targeting nanoparticles for either diagnostic, therapeutic or combination applications.

Development and evaluation of new molecular imaging devices including both preclinical and clinically translatable optical imaging devices for ultrasensitive cancer detection.

•Evaluating biodistribution patterns and pharmacokinetics of various clinically translatable nanoparticles after various routes of administration (Intravenous, Intraperitoneal, Intrarectal, Oral or Topical Application).


Stanford Advisees


All Publications

  • A Clinical Wide-Field Fluorescence Endoscopic Device for Molecular Imaging Demonstrating Cathepsin Protease Activity in Colon Cancer. Molecular imaging and biology Sensarn, S., Zavaleta, C. L., Segal, E., Rogalla, S., Lee, W., Gambhir, S. S., Bogyo, M., Contag, C. H. 2016; 18 (6): 820-829


    Early and effective detection of cancers of the gastrointestinal tract will require novel molecular probes and advances in instrumentation that can reveal functional changes in dysplastic and malignant tissues. Here, we describe adaptation of a wide-field clinical fiberscope to perform wide-field fluorescence imaging while preserving its white-light capability for the purpose of providing wide-field fluorescence imaging capability to point-of-care microscopes.We developed and used a fluorescent fiberscope to detect signals from a quenched probe, BMV109, that becomes fluorescent when cleaved by, and covalently bound to, active cathepsin proteases. Cathepsins are expressed in inflammation- and tumor-associated macrophages as well as directly from tumor cells and are a promising target for cancer imaging. The fiberscope has a 1-mm outer diameter enabling validation via endoscopic exams in mice, and therefore we evaluated topically applied BMV109 for the ability to detect colon polyps in an azoxymethane-induced colon tumor model in mice.This wide-field endoscopic imaging device revealed consistent and clear fluorescence signals from BMV109 that specifically localized to the polypoid regions as opposed to the normal adjacent colon tissue (p?

    View details for PubMedID 27154508

  • A hyperspectral method to assay the microphysiological fates of nanomaterials in histological samples ELIFE SoRelle, E. D., Liba, O., Campbell, J. L., Dalal, R., Zavaleta, C. L., de la Zerda, A. 2016; 5


    Nanoparticles are used extensively as biomedical imaging probes and potential therapeutic agents. As new particles are developed and tested in vivo, it is critical to characterize their biodistribution profiles. We demonstrate a new method that uses adaptive algorithms for analysis of hyperspectral dark-field images to study the interactions between tissues and administered nanoparticles. This non-destructive technique quantitatively identifies particles in ex vivo tissue sections and enables detailed observations of accumulation patterns arising from organ-specific clearance mechanisms, particle size, and the molecular specificity of nanoparticle surface coatings. Unlike nanoparticle uptake studies with electron microscopy, this method is tractable for imaging large fields of view. Adaptive hyperspectral image analysis achieves excellent detection sensitivity and specificity and is capable of identifying single nanoparticles. Using this method, we collected the first data on the sub-organ distribution of several types of gold nanoparticles in mice and observed localization patterns in tumors.

    View details for DOI 10.7554/eLife.16352

    View details for Web of Science ID 000385437600001

    View details for PubMedID 27536877

  • A correlative optical microscopy and scanning electron microscopy approach to locating nanoparticles in brain tumors MICRON Kempen, P. J., Kircher, M. F., de la Zerda, A., Zavaleta, C. L., Jokerst, J. V., Mellinghoff, I. K., Gambhir, S. S., Sinclair, R. 2015; 68: 70-76


    The growing use of nanoparticles in biomedical applications, including cancer diagnosis and treatment, demands the capability to exactly locate them within complex biological systems. In this work a correlative optical and scanning electron microscopy technique was developed to locate and observe multi-modal gold core nanoparticle accumulation in brain tumor models. Entire brain sections from mice containing orthotopic brain tumors injected intravenously with nanoparticles were imaged using both optical microscopy to identify the brain tumor, and scanning electron microscopy to identify the individual nanoparticles. Gold-based nanoparticles were readily identified in the scanning electron microscope using backscattered electron imaging as bright spots against a darker background. This information was then correlated to determine the exact location of the nanoparticles within the brain tissue. The nanoparticles were located only in areas that contained tumor cells, and not in the surrounding healthy brain tissue. This correlative technique provides a powerful method to relate the macro- and micro-scale features visible in light microscopy with the nanoscale features resolvable in scanning electron microscopy.

    View details for DOI 10.1016/j.micron.2014.09.004

    View details for Web of Science ID 000348016500011

    View details for PubMedID 25464144

  • A real-time clinical endoscopic system for intraluminal, multiplexed imaging of surface-enhanced Raman scattering nanoparticles. PloS one Garai, E., Sensarn, S., Zavaleta, C. L., Loewke, N. O., Rogalla, S., Mandella, M. J., Felt, S. A., Friedland, S., Liu, J. T., Gambhir, S. S., Contag, C. H. 2015; 10 (4)


    The detection of biomarker-targeting surface-enhanced Raman scattering (SERS) nanoparticles (NPs) in the human gastrointestinal tract has the potential to improve early cancer detection; however, a clinically relevant device with rapid Raman-imaging capability has not been described. Here we report the design and in vivo demonstration of a miniature, non-contact, opto-electro-mechanical Raman device as an accessory to clinical endoscopes that can provide multiplexed molecular data via a panel of SERS NPs. This device enables rapid circumferential scanning of topologically complex luminal surfaces of hollow organs (e.g., colon and esophagus) and produces quantitative images of the relative concentrations of SERS NPs that are present. Human and swine studies have demonstrated the speed and simplicity of this technique. This approach also offers unparalleled multiplexing capabilities by simultaneously detecting the unique spectral fingerprints of multiple SERS NPs. Therefore, this new screening strategy has the potential to improve diagnosis and to guide therapy by enabling sensitive quantitative molecular detection of small and otherwise hard-to-detect lesions in the context of white-light endoscopy.

    View details for DOI 10.1371/journal.pone.0123185

    View details for PubMedID 25923788

  • Evaluation of s-1 receptor radioligand 18F-FTC-146 in rats and squirrel monkeys using PET. Journal of nuclear medicine : official publication, Society of Nuclear Medicine James, M. L., Shen, B., Nielsen, C. H., Behera, D., Buckmaster, C. L., Mesangeau, C., Zavaleta, C., Vuppala, P. K., Jamalapuram, S., Avery, B. A., Lyons, D. M., McCurdy, C. R., Biswal, S., Gambhir, S. S., Chin, F. T. 2014; 55 (1): 147-153


    The noninvasive imaging of ?-1 receptors (S1Rs) could provide insight into their role in different diseases and lead to novel diagnostic/treatment strategies. The main objective of this study was to assess the S1R radiotracer (18)F-FTC-146 in rats. Preliminary squirrel monkey imaging and human serum/liver microsome studies were performed to gain information about the potential of (18)F-FTC-146 for eventual clinical translation.The distribution and stability of (18)F-FTC-146 in rats were assessed via PET/CT, autoradiography, ? counting, and high-performance liquid chromatography (HPLC). Preliminary PET/MRI of squirrel monkey brain was conducted along with HPLC assessment of (18)F-FTC-146 stability in monkey plasma and human serum.Biodistribution studies showed that (18)F-FTC-146 accumulated in S1R-rich rat organs, including the lungs, pancreas, spleen, and brain. Pretreatment with known S1R compounds, haloperidol, or BD1047, before radioligand administration, significantly attenuated (18)F-FTC-146 accumulation in all rat brain regions by approximately 85% (P < 0.001), suggesting radiotracer specificity for S1Rs. Similarly, PET/CT and autoradiography results demonstrated accumulation of (18)F-FTC-146 in rat brain regions known to contain S1Rs and that this uptake could be blocked by BD1047 pretreatment. Ex vivo analysis of (18)F-FTC-146 in the brain showed that only intact radiotracer was present at 15, 30, and 60 min, whereas rapid metabolism of residual (18)F-FTC-146 was observed in rat plasma. Preliminary monkey PET/MRI studies demonstrated specific accumulation of (18)F-FTC-146 in the brain (mainly in cortical structures, cerebellum, and vermis) that could be attenuated by pretreatment with haloperidol. HPLC of monkey plasma suggested radioligand metabolism, whereas (18)F-FTC-146 appeared to be stable in human serum. Finally, liver microsome studies revealed that (18)F-FTC-146 has a longer half-life in human microsomes, compared with rodents.Together, these results indicate that (18)F-FTC-146 is a promising tool for visualizing S1Rs in preclinical studies and that it has potential for mapping these sites in the human brain.

    View details for DOI 10.2967/jnumed.113.120261

    View details for PubMedID 24337599

  • A Scanning Transmission Electron Microscopy Approach to Analyzing Large Volumes of Tissue to Detect Nanoparticles MICROSCOPY AND MICROANALYSIS Kempen, P. J., Thakor, A. S., Zavaleta, C., Gambhir, S. S., Sinclair, R. 2013; 19 (5): 1290-1297


    The use of nanoparticles for the diagnosis and treatment of cancer requires the complete characterization of their toxicity, including accurately locating them within biological tissues. Owing to their size, traditional light microscopy techniques are unable to resolve them. Transmission electron microscopy provides the necessary spatial resolution to image individual nanoparticles in tissue, but is severely limited by the very small analysis volume, usually on the order of tens of cubic microns. In this work, we developed a scanning transmission electron microscopy (STEM) approach to analyze large volumes of tissue for the presence of polyethylene glycol-coated Raman-active-silica-gold-nanoparticles (PEG-R-Si-Au-NPs). This approach utilizes the simultaneous bright and dark field imaging capabilities of STEM along with careful control of the image contrast settings to readily identify PEG-R-Si-Au-NPs in mouse liver tissue without the need for additional time-consuming analytical characterization. We utilized this technique to analyze 243,000 ?m3 of mouse liver tissue for the presence of PEG-R-Si-Au-NPs. Nanoparticles injected into the mice intravenously via the tail vein accumulated in the liver, whereas those injected intrarectally did not, indicating that they remain in the colon and do not pass through the colon wall into the systemic circulation.

    View details for DOI 10.1017/S143192761300192X

    View details for Web of Science ID 000324550900022

    View details for PubMedID 23803218

  • High-sensitivity, real-time, ratiometric imaging of surface-enhanced Raman scattering nanoparticles with a clinically translatable Raman endoscope device. Journal of biomedical optics Garai, E., Sensarn, S., Zavaleta, C. L., Van de Sompel, D., Loewke, N. O., Mandella, M. J., Gambhir, S. S., Contag, C. H. 2013; 18 (9): 096008-?


    ABSTRACT. Topical application and quantification of targeted, surface-enhanced Raman scattering (SERS) nanoparticles offer a new technique that has the potential for early detection of epithelial cancers of hollow organs. Although less toxic than intravenous delivery, the additional washing required to remove unbound nanoparticles cannot necessarily eliminate nonspecific pooling. Therefore, we developed a real-time, ratiometric imaging technique to determine the relative concentrations of at least two spectrally unique nanoparticle types, where one serves as a nontargeted control. This approach improves the specific detection of bound, targeted nanoparticles by adjusting for working distance and for any nonspecific accumulation following washing. We engineered hardware and software to acquire SERS signals and ratios in real time and display them via a graphical user interface. We report quantitative, ratiometric imaging with nanoparticles at pM and sub-pM concentrations and at varying working distances, up to 50 mm. Additionally, we discuss optimization of a Raman endoscope by evaluating the effects of lens material and fiber coating on background noise, and theoretically modeling and simulating collection efficiency at various working distances. This work will enable the development of a clinically translatable, noncontact Raman endoscope capable of rapidly scanning large, topographically complex tissue surfaces for small and otherwise hard to detect lesions.

    View details for DOI 10.1117/1.JBO.18.9.096008

    View details for PubMedID 24008818

  • A small animal Raman instrument for rapid, wide-area, spectroscopic imaging PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Bohndiek, S. E., Wagadarikar, A., Zavaleta, C. L., Van de Sompel, D., Garai, E., Jokerst, J. V., Yazdanfar, S., Gambhir, S. S. 2013; 110 (30): 12408-12413


    Raman spectroscopy, amplified by surface enhanced Raman scattering (SERS) nanoparticles, is a molecular imaging modality with ultra-high sensitivity and the unique ability to multiplex readouts from different molecular targets using a single wavelength of excitation. This approach holds exciting prospects for a range of applications in medicine, including identification and characterization of malignancy during endoscopy and intraoperative image guidance of surgical resection. The development of Raman molecular imaging with SERS nanoparticles is presently limited by long acquisition times, poor spatial resolution, small field of view, and difficulty in animal handling with existing Raman spectroscopy instruments. Our goal is to overcome these limitations by designing a bespoke instrument for Raman molecular imaging in small animals. Here, we present a unique and dedicated small-animal Raman imaging instrument that enables rapid, high-spatial resolution, spectroscopic imaging over a wide field of view (> 6 cm(2)), with simplified animal handling. Imaging of SERS nanoparticles in small animals demonstrated that this small animal Raman imaging system can detect multiplexed SERS signals in both superficial and deep tissue locations at least an order of magnitude faster than existing systems without compromising sensitivity.

    View details for DOI 10.1073/pnas.1301379110

    View details for Web of Science ID 000322112300062

    View details for PubMedID 23821752

  • A Raman-based endoscopic strategy for multiplexed molecular imaging. Proceedings of the National Academy of Sciences of the United States of America Zavaleta, C. L., Garai, E., Liu, J. T., Sensarn, S., Mandella, M. J., Van de Sompel, D., Friedland, S., Van Dam, J., Contag, C. H., Gambhir, S. S. 2013; 110 (25): E2288-97


    Endoscopic imaging is an invaluable diagnostic tool allowing minimally invasive access to tissues deep within the body. It has played a key role in screening colon cancer and is credited with preventing deaths through the detection and removal of precancerous polyps. However, conventional white-light endoscopy offers physicians structural information without the biochemical information that would be advantageous for early detection and is essential for molecular typing. To address this unmet need, we have developed a unique accessory, noncontact, fiber optic-based Raman spectroscopy device that has the potential to provide real-time, multiplexed functional information during routine endoscopy. This device is ideally suited for detection of functionalized surface-enhanced Raman scattering (SERS) nanoparticles as molecular imaging contrast agents. This device was designed for insertion through a clinical endoscope and has the potential to detect and quantify the presence of a multiplexed panel of tumor-targeting SERS nanoparticles. Characterization of the Raman instrument was performed with SERS particles on excised human tissue samples, and it has shown unsurpassed sensitivity and multiplexing capabilities, detecting 326-fM concentrations of SERS nanoparticles and unmixing 10 variations of colocalized SERS nanoparticles. Another unique feature of our noncontact Raman endoscope is that it has been designed for efficient use over a wide range of working distances from 1 to 10 mm. This is necessary to accommodate for imperfect centering during endoscopy and the nonuniform surface topology of human tissue. Using this endoscope as a key part of a multiplexed detection approach could allow endoscopists to distinguish between normal and precancerous tissues rapidly and to identify flat lesions that are otherwise missed.

    View details for DOI 10.1073/pnas.1211309110

    View details for PubMedID 23703909

  • A comparison of noise models in a hybrid reference spectrum and principal components analysis algorithm for Raman spectroscopy JOURNAL OF RAMAN SPECTROSCOPY Van de Sompel, D., Garai, E., Zavaleta, C., Gambhir, S. S. 2013; 44 (6): 841-856

    View details for DOI 10.1002/jrs.4258

    View details for Web of Science ID 000319935700009

  • High-resolution, serial intravital microscopic imaging of nanoparticle delivery and targeting in a small animal tumor model NANO TODAY Smith, B. R., Zavaleta, C., Rosenberg, J., Tong, R., Ramunas, J., Liu, Z., Dai, H., Gambhir, S. S. 2013; 8 (2): 126-137
  • Comparison of Gaussian and Poisson Noise Models in a Hybrid Reference Spectrum and Principal Component Analysis Algorithm for Raman Spectroscopy SINGLE MOLECULE SPECTROSCOPY AND SUPERRESOLUTION IMAGING VI Van de Sompel, D., Garai, E., Zavaleta, C., Gambhir, S. S. 2013; 8590

    View details for DOI 10.1117/12.2005455

    View details for Web of Science ID 000321741600011

  • A Brain Tumor Molecular Imaging Strategy using a New Triple-Modality MRI-Photoacoustic-Raman Nanoparticle PHOTONS PLUS ULTRASOUND: IMAGING AND SENSING 2013 de la Zerda, A., Kircher, M. F., Jokerst, J. V., Zavaleta, C. L., Kempen, P. J., Mittra, E., Pitter, K., Huang, R., Campos, C., Habte, F., Sinclair, R., Brennan, C. W., Mellinghoff, I. K., Holland, E. C., Gambhir, S. S. 2013; 8581

    View details for DOI 10.1117/12.2001719

    View details for Web of Science ID 000322832800007

  • New Positron Emission Tomography (PET) Radioligand for Imaging sigma-1 Receptors in Living Subjects JOURNAL OF MEDICINAL CHEMISTRY James, M. L., Shen, B., Zavaleta, C. L., Nielsen, C. H., Mesangeau, C., Vuppala, P. K., Chan, C., Avery, B. A., Fishback, J. A., Matsumoto, R. R., Gambhir, S. S., McCurdy, C. R., Chin, F. T. 2012; 55 (19): 8272-8282


    ?-1 receptor (S1R) radioligands have the potential to detect and monitor various neurological diseases. Herein we report the synthesis, radiofluorination, and evaluation of a new S1R ligand 6-(3-fluoropropyl)-3-(2-(azepan-1-yl)ethyl)benzo[d]thiazol-2(3H)-one ([(18)F]FTC-146, [(18)F]13). [(18)F]13 was synthesized by nucleophilic fluorination, affording a product with >99% radiochemical purity (RCP) and specific activity (SA) of 2.6 ± 1.2 Ci/?mol (n = 13) at end of synthesis (EOS). Positron emission tomography (PET) and ex vivo autoradiography studies of [(18)F]13 in mice showed high uptake of the radioligand in S1R rich regions of the brain. Pretreatment with 1 mg/kg haloperidol (2), nonradioactive 13, or BD1047 (18) reduced the binding of [(18)F]13 in the brain at 60 min by 80%, 82%, and 81%, respectively, suggesting that [(18)F]13 accumulation in mouse brain represents specific binding to S1Rs. These results indicate that [(18)F]13 is a promising candidate radiotracer for further evaluation as a tool for studying S1Rs in living subjects.

    View details for DOI 10.1021/jm300371c

    View details for Web of Science ID 000309643500008

    View details for PubMedID 22853801

  • A Hybrid Least Squares and Principal Component Analysis Algorithm for Raman Spectroscopy PLOS ONE Van de Sompel, D., Garai, E., Zavaleta, C., Gambhir, S. S. 2012; 7 (6)


    Raman spectroscopy is a powerful technique for detecting and quantifying analytes in chemical mixtures. A critical part of Raman spectroscopy is the use of a computer algorithm to analyze the measured Raman spectra. The most commonly used algorithm is the classical least squares method, which is popular due to its speed and ease of implementation. However, it is sensitive to inaccuracies or variations in the reference spectra of the analytes (compounds of interest) and the background. Many algorithms, primarily multivariate calibration methods, have been proposed that increase robustness to such variations. In this study, we propose a novel method that improves robustness even further by explicitly modeling variations in both the background and analyte signals. More specifically, it extends the classical least squares model by allowing the declared reference spectra to vary in accordance with the principal components obtained from training sets of spectra measured in prior characterization experiments. The amount of variation allowed is constrained by the eigenvalues of this principal component analysis. We compare the novel algorithm to the least squares method with a low-order polynomial residual model, as well as a state-of-the-art hybrid linear analysis method. The latter is a multivariate calibration method designed specifically to improve robustness to background variability in cases where training spectra of the background, as well as the mean spectrum of the analyte, are available. We demonstrate the novel algorithm's superior performance by comparing quantitative error metrics generated by each method. The experiments consider both simulated data and experimental data acquired from in vitro solutions of Raman-enhanced gold-silica nanoparticles.

    View details for DOI 10.1371/journal.pone.0038850

    View details for Web of Science ID 000305583300060

    View details for PubMedID 22723895

  • A brain tumor molecular imaging strategy using a new triple-modality MRI-photoacoustic-Raman nanoparticle NATURE MEDICINE Kircher, M. F., de la Zerda, A., Jokerst, J. V., Zavaleta, C. L., Kempen, P. J., Mittra, E., Pitter, K., Huang, R., Campos, C., Habte, F., Sinclair, R., Brennan, C. W., Mellinghoff, I. K., Holland, E. C., Gambhir, S. S. 2012; 18 (5): 829-U235


    The difficulty in delineating brain tumor margins is a major obstacle in the path toward better outcomes for patients with brain tumors. Current imaging methods are often limited by inadequate sensitivity, specificity and spatial resolution. Here we show that a unique triple-modality magnetic resonance imaging-photoacoustic imaging-Raman imaging nanoparticle (termed here MPR nanoparticle) can accurately help delineate the margins of brain tumors in living mice both preoperatively and intraoperatively. The MPRs were detected by all three modalities with at least a picomolar sensitivity both in vitro and in living mice. Intravenous injection of MPRs into glioblastoma-bearing mice led to MPR accumulation and retention by the tumors, with no MPR accumulation in the surrounding healthy tissue, allowing for a noninvasive tumor delineation using all three modalities through the intact skull. Raman imaging allowed for guidance of intraoperative tumor resection, and a histological correlation validated that Raman imaging was accurately delineating the brain tumor margins. This new triple-modality-nanoparticle approach has promise for enabling more accurate brain tumor imaging and resection.

    View details for DOI 10.1038/nm.2721

    View details for Web of Science ID 000303763500053

    View details for PubMedID 22504484

  • Raman's "Effect" on Molecular Imaging JOURNAL OF NUCLEAR MEDICINE Zavaleta, C. L., Kircher, M. F., Gambhir, S. S. 2011; 52 (12): 1839-1844


    Raman spectroscopy is an optical technique that offers unsurpassed sensitivity and multiplexing capabilities to the field of molecular imaging. In the past, Raman spectroscopy had predominantly been used as an analytic tool for routine chemical analysis, but more recently, researchers have been able to harness its unique properties for imaging and spectral analysis of molecular interactions in cell populations and preclinical animal models. Additionally, researchers have already begun to translate this optical technique into a novel clinical diagnostic tool using various endoscopic strategies.

    View details for DOI 10.2967/jnumed.111.087775

    View details for Web of Science ID 000298162500016

    View details for PubMedID 21868625

  • Gold Nanoparticles: A Revival in Precious Metal Administration to Patients NANO LETTERS Thakor, A. S., Jokerst, J., Zavaleta, C., Massoud, T. F., Gambhir, S. S. 2011; 11 (10): 4029-4036


    Gold has been used as a therapeutic agent to treat a wide variety of rheumatic diseases including psoriatic arthritis, juvenile arthritis, and discoid lupus erythematosus. Although the use of gold has been largely superseded by newer drugs, gold nanoparticles are being used effectively in laboratory based clinical diagnostic methods while concurrently showing great promise in vivo either as a diagnostic imaging agent or a therapeutic agent. For these reasons, gold nanoparticles are therefore well placed to enter mainstream clinical practice in the near future. Hence, the present review summarizes the chemistry, pharmacokinetics, biodistribution, metabolism, and toxicity of bulk gold in humans based on decades of clinical observation and experiments in which gold was used to treat patients with rheumatoid arthritis. The beneficial attributes of gold nanoparticles, such as their ease of synthesis, functionalization, and shape control are also highlighted demonstrating why gold nanoparticles are an attractive target for further development and optimization. The importance of controlling the size and shape of gold nanoparticles to minimize any potential toxic side effects is also discussed.

    View details for DOI 10.1021/nl202559p

    View details for Web of Science ID 000295667000001

    View details for PubMedID 21846107

  • Preclinical Evaluation of Raman Nanoparticle Biodistribution for their Potential Use in Clinical Endoscopy Imaging SMALL Zavaleta, C. L., Hartman, K. B., Miao, Z., James, M. L., Kempen, P., Thakor, A. S., Nielsen, C. H., Sinclair, R., Cheng, Z., Gambhir, S. S. 2011; 7 (15): 2232-2240


    Raman imaging offers unsurpassed sensitivity and multiplexing capabilities. However, its limited depth of light penetration makes direct clinical translation challenging. Therefore, a more suitable way to harness its attributes in a clinical setting would be to couple Raman spectroscopy with endoscopy. The use of an accessory Raman endoscope in conjunction with topically administered tumor-targeting Raman nanoparticles during a routine colonoscopy could offer a new way to sensitively detect dysplastic lesions while circumventing Raman's limited depth of penetration and avoiding systemic toxicity. In this study, the natural biodistribution of gold surface-enhanced Raman scattering (SERS) nanoparticles is evaluated by radiolabeling them with (64) Cu and imaging their localization over time using micropositron emission tomography (PET). Mice are injected either intravenously (IV) or intrarectally (IR) with approximately 100 microcuries (?Ci) (3.7 megabecquerel (MBq)) of (64) Cu-SERS nanoparticles and imaged with microPET at various time points post injection. Quantitative biodistribution data are obtained as % injected dose per gram (%ID g(-1)) from each organ, and the results correlate well with the corresponding microPET images, revealing that IV-injected mice have significantly higher uptake (p < 0.05) in the liver (5 h = 8.96% ID g(-1); 24 h = 8.27% ID g(-1)) than IR-injected mice (5 h = 0.09% ID g(-1); 24 h = 0.08% ID g(-1)). IR-injected mice show localized uptake in the large intestine (5 h = 10.37% ID g(-1); 24 h = 0.42% ID g(-1)) with minimal uptake in other organs. Raman imaging of excised tissues correlate well with biodistribution data. These results suggest that the topical application of SERS nanoparticles in the mouse colon appears to minimize their systemic distribution, thus avoiding potential toxicity and supporting the clinical translation of Raman spectroscopy as an endoscopic imaging tool.

    View details for DOI 10.1002/smll.201002317

    View details for Web of Science ID 000294361200015

    View details for PubMedID 21608124

  • The Fate and Toxicity of Raman-Active Silica-Gold Nanoparticles in Mice SCIENCE TRANSLATIONAL MEDICINE Thakor, A. S., Luong, R., Paulmurugan, R., Lin, F. I., Kempen, P., Zavaleta, C., Chu, P., Massoud, T. F., Sinclair, R., Gambhir, S. S. 2011; 3 (79)


    Raman spectroscopy is an optical imaging method that is based on the Raman effect, the inelastic scattering of a photon when energy is absorbed from light by a surface. Although Raman spectroscopy is widely used for chemical and molecular analysis, its clinical application has been hindered by the inherently weak nature of the Raman effect. Raman-silica-gold-nanoparticles (R-Si-Au-NPs) overcome this limitation by producing larger Raman signals through surface-enhanced Raman scattering. Because we are developing these particles for use as targeted molecular imaging agents, we examined the acute toxicity and biodistribution of core polyethylene glycol (PEG)-ylated R-Si-Au-NPs after different routes of administration in mice. After intravenous administration, PEG-R-Si-Au-NPs were removed from the circulation by macrophages in the liver and spleen (that is, the reticuloendothelial system). At 24 hours, PEG-R-Si-Au-NPs elicited a mild inflammatory response and an increase in oxidative stress in the liver, which subsided by 2 weeks after administration. No evidence of significant toxicity was observed by measuring clinical, histological, biochemical, or cardiovascular parameters for 2 weeks. Because we are designing targeted PEG-R-Si-Au-NPs (for example, PEG-R-Si-Au-NPs labeled with an affibody that binds specifically to the epidermal growth factor receptor) to detect colorectal cancer after administration into the bowel lumen, we tested the toxicity of the core nanoparticle after administration per rectum. We observed no significant bowel or systemic toxicity, and no PEG-R-Si-Au-NPs were detected systemically. Although additional studies are required to investigate the long-term effects of PEG-R-Si-Au-NPs and their toxicity when carrying the targeting moiety, the results presented here support the idea that PEG-R-Si-Au-NPs can be safely used in living subjects, especially when administered rectally.

    View details for DOI 10.1126/scitranslmed.3001963

    View details for Web of Science ID 000292976700004

    View details for PubMedID 21508310

  • Affibody-Functionalized Gold-Silica Nanoparticles for Raman Molecular Imaging of the Epidermal Growth Factor Receptor SMALL Jokerst, J. V., Miao, Z., Zavaleta, C., Cheng, Z., Gambhir, S. S. 2011; 7 (5): 625-633


    The affibody functionalization of fluorescent surface-enhanced Raman scattering gold-silica nanoparticles as multimodal contrast agents for molecular imaging specific to epidermal growth factor receptor (EGFR) is reported. This nanoparticle bioconjugate reports EGFR-positive A431 tumors with a signal nearly 35-fold higher than EGFR-negative MDA-435S tumors. The low-level EGFR expression in adjacent healthy tissue is 7-fold lower than in the positive tumors. Validation via competitive inhibition reduces the signal by a factor of six, and independent measurement of EGFR via flow cytometry correlates at R(2) = 0.92.

    View details for DOI 10.1002/smll.201002291

    View details for Web of Science ID 000288081900013

    View details for PubMedID 21302357

  • Oxidative Stress Mediates the Effects of Raman-Active Gold Nanoparticles in Human Cells SMALL Thakor, A. S., Paulmurugan, R., Kempen, P., Zavaleta, C., Sinclair, R., Massoud, T. F., Gambhir, S. S. 2011; 7 (1): 126-136


    Polyethylene glycol (PEG)ylated Raman-active gold nanoparticles (PEG-R-AuNPs) consist of an interchangeable Raman organic molecule layer held onto a gold nanocore by a silica shell. PEG-R-AuNPs have been shown preclinically to increase the sensitivity and specificity of Raman spectroscopy, with picomolar sensitivity and multiplexing capabilities. Although clinical trials are being designed to use functionalized PEG-R-AuNPs in various applications (e.g., to target dysplastic bowel lesions during colonoscopy), the effects of these nanoparticles on human cells remain unknown. The occurrence and mechanisms underlying any potential cytotoxicity induced by these nanoparticles (0-1000 PEG-R-AuNPs/cell) are investigated in immortalized human HeLa and HepG2 cell lines at several time points (0-48 h) after exposure. Using fluorometric assays, cell viability (MTT), reactive oxygen species (ROS) generation (dichlorofluorescein diacetate), protein oxidation (protein carbonyl content), and total cellular antioxidant concentrations the concentrations (metmyoblobin-induced oxidation of ABTS) are assessed. Analysis of lipid oxidation using an enzyme immunoassay (8-isoprostane concentrations), gene expression of antioxidant enzymes using quantitative reverse transcription polymerase chain reactions, and the intracellular location of PEG-R-AuNPs using transmission electron microscopy is also undertaken. PEG-R-AuNPs cause no cytotoxicity in either HeLa or HepG2 cells in the acute setting as ROS generation is balanced by antioxidant enzyme upregulation. Following prolonged exposures (48 h) at relatively high concentrations (1000 PEG-R-AuNPs/cell), nanoparticles are found within vesicles inside cells. Under these conditions, a minimal amount of cytotoxicity is seen in both cell lines owing to increases in cellular oxidative stress, most likely due to ROS overwhelming the antioxidant defenses. Evidence of oxidative stress-induced damage includes increased lipid and protein oxidation. Although further in vivo toxicity studies are necessary, these initial encouraging results show that PEG-R-AuNPs cause minimal toxicity in human cells in the acute setting, which bodes well for potential future applications of these nanoparticles in living subjects.

    View details for DOI 10.1002/smll.201001466

    View details for Web of Science ID 000285794100015

    View details for PubMedID 21104804

  • A Hybrid Least Squares and Principal Component Analysis Algorithm for Raman Spectroscopy Van de Sompel, D., Garai, E., Zavaleta, C., Gambhir, S. S. IEEE. 2011: 6971-6974


    The least squares fitting algorithm is the most commonly used algorithm in Raman spectroscopy. In this paper, however, we show that it is sensitive to variations in the background signal when the signal of interest is weak. To address this problem, we propose a novel algorithm to analyze measured spectra in Raman spectroscopy. The method is a hybrid least squares and principal component analysis algorithm. It explicitly accounts for any variations expected in the reference spectra used in the signal decomposition. We compare the novel algorithm to the least squares method with a low-order polynomial residual model, and demonstrate the novel algorithm's superior performance by comparing quantitative error metrics. Our experiments use both simulated data and data acquired from an in vitro solution of Raman-enhanced gold nanoparticles.

    View details for Web of Science ID 000298810005123

    View details for PubMedID 22255942

  • Multiplexed imaging of surface enhanced Raman scattering nanotags in living mice using noninvasive Raman spectroscopy PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Zavaleta, C. L., Smith, B. R., Walton, I., Doering, W., Davis, G., Shojaei, B., Natan, M. J., Gambhir, S. S. 2009; 106 (32): 13511-13516


    Raman spectroscopy is a newly developed, noninvasive preclinical imaging technique that offers picomolar sensitivity and multiplexing capabilities to the field of molecular imaging. In this study, we demonstrate the ability of Raman spectroscopy to separate the spectral fingerprints of up to 10 different types of surface enhanced Raman scattering (SERS) nanoparticles in a living mouse after s.c. injection. Based on these spectral results, we simultaneously injected the five most intense and spectrally unique SERS nanoparticles i.v. to image their natural accumulation in the liver. All five types of SERS nanoparticles were successfully identified and spectrally separated using our optimized noninvasive Raman imaging system. In addition, we were able to linearly correlate Raman signal with SERS concentration after injecting four spectrally unique SERS nanoparticles either s.c. (R(2) = 0.998) or i.v. (R(2) = 0.992). These results show great potential for multiplexed imaging in living subjects in cases in which several targeted SERS probes could offer better detection of multiple biomarkers associated with a specific disease.

    View details for DOI 10.1073/pnas.0813327106

    View details for Web of Science ID 000268877300066

    View details for PubMedID 19666578

  • Enhanced Sensitivity Carbon Nanotubes as Targeted Photoacoustic Molecular Imaging Agents PHOTONS PLUS ULTRASOUND: IMAGING AND SENSING 2009 de la Zerda, A., Liu, Z., Zavaleta, C., Bodapati, S., Teed, R., Vaithilingam, S., Ma, T., Oralkan, O., Chen, X., Khuri-Yakub, B. T., Dai, H., Gambhir, S. S. 2009; 7177

    View details for DOI 10.1117/12.809601

    View details for Web of Science ID 000285714100080

  • Photoacoustic Molecular Imaging using Single Walled Carbon Nanotubes in Living Mice PHOTONS PLUS ULTRASOUND: IMAGING AND SENSING 2009 de la Zerda, A., Zavaleta, C., Keren, S., Vaithilingam, S., Bodapati, S., Teed, R., Liu, Z., Levi, J., Smith, B. R., Ma, T., Oralkan, O., Cheng, Z., Chen, X., Dai, H., Khuri-Yakub, B. T., Gambhir, S. S. 2009; 7177

    View details for DOI 10.1117/12.806497

    View details for Web of Science ID 000285714100066

  • Noninvasive Raman spectroscopy in living mice for evaluation of tumor targeting with carbon nanotubes NANO LETTERS Zavaleta, C., de la Zerda, A., Liu, Z., Keren, S., Cheng, Z., Schipper, M., Chen, X., Dai, H., Gambhir, S. S. 2008; 8 (9): 2800-2805


    An optimized noninvasive Raman microscope was used to evaluate tumor targeting and localization of single walled carbon nanotubes (SWNTs) in mice. Raman images were acquired in two groups of tumor-bearing mice. The control group received plain-SWNTs, whereas the experimental group received tumor targeting RGD-SWNTs intravenously. Raman imaging commenced over the next 72 h and revealed increased accumulation of RGD-SWNTs in tumor ( p < 0.05) as opposed to plain-SWNTs. These results support the development of a new preclinical Raman imager.

    View details for DOI 10.1021/nl801362a

    View details for Web of Science ID 000259140200034

    View details for PubMedID 18683988

  • Carbon nanotubes as photoacoustic molecular imaging agents in living mice NATURE NANOTECHNOLOGY de la Zerda, A., Zavaleta, C., Keren, S., Vaithilingam, S., Bodapati, S., Liu, Z., Levi, J., Smith, B. R., Ma, T., Oralkan, O., Cheng, Z., Chen, X., Dai, H., Khuri-Yakub, B. T., Gambhir, S. S. 2008; 3 (9): 557-562


    Photoacoustic imaging of living subjects offers higher spatial resolution and allows deeper tissues to be imaged compared with most optical imaging techniques. 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, 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.

    View details for DOI 10.1038/nnano.2008.231

    View details for Web of Science ID 000259013100014

    View details for PubMedID 18772918

  • Noninvasive molecular imaging of small living subjects using Raman spectroscopy PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Keren, S., Zavaleta, C., Cheng, Z., de la Zerda, A., Gheysens, O., Gambhir, S. S. 2008; 105 (15): 5844-5849


    Molecular imaging of living subjects continues to rapidly evolve with bioluminescence and fluorescence strategies, in particular being frequently used for small-animal models. This article presents noninvasive deep-tissue molecular images in a living subject with the use of Raman spectroscopy. We describe a strategy for small-animal optical imaging based on Raman spectroscopy and Raman nanoparticles. Surface-enhanced Raman scattering nanoparticles and single-wall carbon nanotubes were used to demonstrate whole-body Raman imaging, nanoparticle pharmacokinetics, multiplexing, and in vivo tumor targeting, using an imaging system adapted for small-animal Raman imaging. The imaging modality reported here holds significant potential as a strategy for biomedical imaging of living subjects.

    View details for DOI 10.1073/pnas.0710575105

    View details for Web of Science ID 000255237200036

    View details for PubMedID 18378895

  • Imaging of Re-186-liposome therapy in ovarian cancer xenograft model of peritoneal carcinomatosis JOURNAL OF DRUG TARGETING Zavaleta, C. L., Goins, B. A., Bao, A., McManus, L. M., McMahan, C. A., Phillips, W. T. 2008; 16 (7-8): 626-637
  • Use of avidin/biotin-lipo some system for enhanced peritoneal drug delivery in an ovarian cancer model INTERNATIONAL JOURNAL OF PHARMACEUTICS Zavaleta, C. L., Phillips, W. T., Soundararajan, A., Goins, B. A. 2007; 337 (1-2): 316-328


    The goal of this study was to determine the distribution of the avidin/biotin-liposome system in an ovarian cancer xenograft model. Optimal avidin/biotin-liposome injection sequence with enhanced liposome accumulation to the peritoneum was determined. Two weeks after NIH:OVCAR-3 cell inoculation, rats were divided into three groups. Group 1 (B-A) (n=4), received an intraperitoneal injection of (99m)Tc-blue-biotin-liposomes 30 min before an intraperitoneal injection of avidin. Group 2 (A-B) (n=4), received an intraperitoneal injection of avidin 30 min before an intraperitoneal injection of (99m)Tc-blue-biotin-liposomes. Group 3 (A-B 2h) (n=5), received an intraperitoneal injection of avidin 2h before an intraperitoneal injection of (99m)Tc-blue-biotin-liposomes. Three additional non-tumor nude rats served as controls in each group, and were subjected to the same injection sequences. Scintigraphic imaging commenced at various times post (99m)Tc-blue-biotin-liposome injection. After imaging, rats were euthanized at 23 h post-liposome injection for tissue biodistribution. Images showed no apparent difference in liposome distribution between control and tumor animals. Regional uptake analysis at 4h for tumor rats showed significantly higher lymphatic channel uptake in the A-B 2h group (p<0.05) and a trend of increased peritoneal uptake in A-B group. By 22 h, peritoneal and lymphatic channel uptake was similar for all groups. At necropsy, most activity was found in blue-stained omentum, diaphragm, mediastinal and abdominal nodes. Bowel activity was minimal. These results correlate with previous normal rat studies, and demonstrate potential use of this avidin/biotin-liposome system for prolonging drug delivery to the peritoneal cavity and associating lymph nodes in this ovarian cancer xenograft model.

    View details for DOI 10.1016/j.ijpharm.2007.01.010

    View details for Web of Science ID 000247355800037

    View details for PubMedID 17276633

  • Characterization of an intraperitoneal ovarian cancer xenograft model in nude rats using noninvasive microPET imaging INTERNATIONAL JOURNAL OF GYNECOLOGICAL CANCER Zavaleta, C. L., Phillips, W. T., Bradley, Y. C., McManus, L. M., Jerabek, P. A., Goins, B. A. 2007; 17 (2): 407-417


    MicroPET is a noninvasive imaging modality that can potentially track tumor development in nude rats using the radiotracer fluorine 18-fluorodeoxyglucose ((18)F-FDG). Our goal was to determine whether microPET, as opposed to more invasive techniques, could be used to noninvasively monitor the development of ovarian cancer in the peritoneal cavity of nude rats for monitoring treatment response in future studies. Female nude rats were inoculated intraperitoneally with 36 million NIH:OVCAR-3 cells. Imaging was carried out at 2, 4, 6, or 8 weeks postinoculation. Each rat was fasted overnight and intravenously injected with 11.1 MBq (300 microCi) of (18)F-FDG in 0.2 mL of saline. Thirty minutes following injection, the rats were placed in the microPET and scanned for 30 min. After imaging, rats were euthanized for ascites and tissue collection for biodistribution and histopathologic correlation. Standard uptake values (SUVs) of (18)F-FDG within the peritoneal cavity were also calculated from regions of interest analysis of the microPET images. MicroPET images showed diffuse increased uptake of (18)F-FDG throughout the peritoneal cavity of tumor rats (mean SUV=4.64) compared with control rats (mean SUV=1.03). Ascites gathered from tumor-bearing rats had increased (18)F-FDG uptake as opposed to the peritoneal fluid collected from control rats. Biodistribution data revealed that the percent injected dose per gram (% ID/g) was significantly higher in tumor-bearing rats (6.29%) than in control rats (0.59%) in the peritoneal lymph nodes. Pathology verified that these lymph nodes were more reactive in tumor-bearing rats. By 6 weeks, some rats developed solid masses within the peritoneum, which could be detected on microPET images and confirmed as tumor by histopathology. (18)F-FDG uptake in these tumors at necropsy was 2.83% ID/g. These results correlate with previous invasive laparoscopic studies of the same tumor model and demonstrate that microPET using (18)F-FDG is a promising noninvasive tool to localize and follow tumor growth in an intraperitoneal ovarian cancer model.

    View details for DOI 10.1111/j.1525-1438.2007.00814.x

    View details for Web of Science ID 000244885300014

    View details for PubMedID 17362319

  • Potential use of drug carried-liposomes for cancer therapy via direct intratumoral injection INTERNATIONAL JOURNAL OF PHARMACEUTICS Bao, A., Phillips, W. T., Goins, B., Zheng, X., Sabour, S., Natarajan, M., Woolley, F. R., Zavaleta, C., Otto, R. A. 2006; 316 (1-2): 162-169


    Liposomes have recognized advantages as nano-particle drug carriers for tumor therapy. In this study, the pharmacokinetics and distribution of intratumorally administered liposomes were investigated as drug carriers for treating solid tumors via direct intratumoral administration. 99mTc-liposomes were administered intratumorally to nude rats bearing human head and neck squamous cell carcinoma xenografts. Planar gamma camera images were analyzed to evaluate the local retention of the intratumorally administered liposomes. Co-registered pinhole micro-single photon emission computed tomography (SPECT)/computed tomography (CT) images were acquired of the whole animal as well as the dissected tumors to determine intratumoral distribution of the 99mTc-liposomes. For 99mTc-liposomes, there was an initial retention of 47.4 +/- 11.0% (n = 4) in tumors and surrounding tissues. At 20 h, 39.2 +/- 10.6% (n = 4) of 99mTc-activity still remained in the tumor. In contrast, only 18.7 +/- 3.3% (n = 3) of the intratumoral 99mTc-activity remained for unencapsulated 99mTc-complex at 20 h. Pinhole micro-SPECT images demonstrated that 99mTc-liposomes also have a superior intratumoral 99mTc-activity diffusion compared with unencapsulated 99mTc-complex. Higher intratumoral retention of 99mTc-liposomes accompanied by an improved intratumoral diffusion suggests that intratumorally administered liposomal drugs are potentially promising agents for solid tumor local therapy.

    View details for DOI 10.1016/j.ijpharm.2006.02.039

    View details for Web of Science ID 000238551100023

    View details for PubMedID 16580161

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