Advanced Characterization Techniques for Nanoparticles for Cancer Research: Applications of SEM and NanoSIMS for Locatin
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Advanced Characterization Techniques for Nanoparticles for Cancer Research: Applications of SEM and NanoSIMS for Locating Au Nanoparticles in Cells Paul J Kempen1, Chuck Hitzman2, Laura S Sasportas3, Sanjiv S Gambhir3 and Robert Sinclair1 1 Department of Material Science and Engineering, Stanford University, 496 Lomita Mall, Stanford, CA 94305-4034 U.S.A. 2 Stanford Nanocharacterization Laboratory, Stanford University, 476 Lomita Mall, Stanford, CA 94305-4035 U.S.A. 3 Molecular Imaging Program at Stanford, Department of Radiology, Stanford University, 318 Campus Drive, Stanford, CA 94305-5427 U.S.A. ABSTRACT The ability of nano secondary ion mass spectrometry (NanoSIMS) to locate and analyze Raman active gold core nanoparticles (R-AuNPs) in a biological system is compared with the standard analysis using the scanning electron microscope (SEM). The same cell with R-AuNPs on and inside the macrophage was analyzed with both techniques to directly compare them. SEM analysis showed a large number of nanoparticles within the cell. Subsequent NanoSIMS analysis showed fewer R-AuNPs with lower spatial resolution. SEM was determined to be superior to NanoSIMS for the analysis of inorganic nanoparticles in complex biological systems. INTRODUCTION With the continuing and growing use of nanoparticles for biological applications [1-3] it is becoming increasingly important to be able to accurately locate and characterize them on and within a cell. Owing to their small size it is necessary to utilize advanced characterization techniques to study them. The scanning electron microscope (SEM), capable of sub-nanometer spatial resolution [4] and good depth of field, is commonly utilized for this purpose [5]. Moreover, it is possible to distinguish materials by atomic number through the use of backscattered electron (BSE) imaging [6]. This atomic number sensitivity creates contrast in the image where higher atomic number inorganic nanoparticles appear bright against a dark low atomic number, organic matrix background. This enables the ready identification of inorganic nanoparticles both on the surface and in the cytoplasm of cell samples [7]. Recently there have been advances in secondary ion mass spectrometry (SIMS), combining SIMS with a focused scanning ion beam, allowing for the creation of high spatial resolution, ca 50 nm, compositional maps [8]. The NanoSIMS combines reasonably good spatial resolution with high atomic sensitivity, down to the ppm regime [8] and is powerful because it is capable of distinguishing between isotopes of the same material while analyzing up to seven distinct elements or species at the same time [9]. This technique has been increasingly utilized to study and analyze complex biological systems including the use of isotope labeling [10, 11]. Gold-core silica-shell nanoparticles (R-AuNPs) are promising as a multimodality surface enhanced Raman spectroscopy (SERS) and photoacoustic nanoparticle for diagnostic purposes [12-14]. R-AuNPs, produced by Oxonica Materials Inc (now owned by Cabot Corporation), cons
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