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WIREs Nanomed Nanobiotechnol
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Identification of nanoparticles and nanosystems in biological matrices with scanning probe microscopy

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Identification of nanoparticles and nanosystems into cells and biological matrices is a hot research topic in nanobiotechnologies. Because of their capability to map physical properties (mechanical, electric, magnetic, chemical, or optical), several scanning probe microscopy based techniques have been proposed for the subsurface detection of nanomaterials in biological systems. In particular, atomic force microscopy (AFM) can be used to reveal stiff nanoparticles in cells and other soft biomaterials by probing the sample mechanical properties through the acquisition of local indentation curves or through the combination of ultrasound‐based methods, like contact resonance AFM (CR‐AFM) or scanning near field ultrasound holography. Magnetic force microscopy can detect magnetic nanoparticles and other magnetic (bio)materials in nonmagnetic biological samples, while electric force microscopy, conductive AFM, and Kelvin probe force microscopy can reveal buried nanomaterials on the basis of the differences between their electric properties and those of the surrounding matrices. Finally, scanning near field optical microscopy and tip‐enhanced Raman spectroscopy can visualize buried nanostructures on the basis of their optical and chemical properties. Despite at a still early stage, these methods are promising for detection of nanomaterials in biological systems as they could be truly noninvasive, would not require destructive and time‐consuming specific sample preparation, could be performed in vitro, on alive samples and in water or physiological environment, and by continuously imaging the same sample could be used to dynamically monitor the diffusion paths and interaction mechanisms of nanomaterials into cells and biological systems. This article is categorized under: Diagnostic Tools > In Vivo Nanodiagnostics and Imaging Nanotechnology Approaches to Biology > Nanoscale Systems in Biology
Sketch of the working principle of SPM methods for NPs detection in cells. (a) The tip is sensitive to nontopographical properties (e.g., mechanical, electric, magnetic, etc.) of the sample in a volume under the tip. Therefore, simultaneously to the topography (b), a map of the nontopographical properties (c) is reconstructed in which NPs buried under the surface of the cell are visible
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(a) EFM phase image of SWCNTs embedded in a SWCNT/PMMA composite film. (b) Dependence of the EFM phase shift (measured in correspondence of the points T1 and T2 on the tip–sample lift height for the two SWCNTs). (c) 3D visualization of the two SWCNTs in the PMMA matrix. (Reprinted with permission from Jespersen and Nygård (). Copyright 2007 AIP Publishing)
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(a) Topographic and phase images obtained from (A) iron‐poor and (B–D) iron‐rich regions on unstained optimal cutting temperature (OCT) compound embedded spleen sections. (Reprinted with permission from Blissett et al. (). Copyright 2017 Elsevier) (b) AFM topography and MFM phase shift image of an empty niosome, the latter revealing a small positive phase shift in correspondence of the niosome. (c) AFM topography and the corresponding MFM phase shift images vesicular systems encapsulating magnetite NPs. (Reprinted with permission from Dong et al. (). Copyright 2015 AIP Publishing)
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(a) Stiffness tomography images of living neurons, in which harder inclusions under the membrane are visualized. (Reprinted with permission from Roduit et al. (). Copyright 2009, Elsevier) (b) Isosurface volume image and (c) cross section reconstructed from normalized stiffness maps of elastomeric polypropylene, in which stiffer crystalline lamellae buried into softer amorphous material. (Reprinted with permission from Spitzner et al. (). Copyright 2010 American Chemical Society)
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(a) Topography and phase images revealing the presence of silica NPs in alveolar macrophages. (Reprinted with permission from Tetard et al. (). Copyright 2010, Elsevier) (b) Topography and phase images revealing the presence of single‐walled carbon nanohorns in red blood cells. (Reprinted with permission from Tetard, Passian, Venmar, et al. (). Copyright 2008 Springer Nature) (c) Nanomechanical maps revealing the presence of aggregates of magnetite NPs in microglial cells from cerebral cortices of mouse embryos. (Reprinted with permission from Passeri et al. (). Copyright 2017 Royal Society of Chemistry)
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(a) Sketch of the experimental configuration used in SNFUH. While the tip scans the sample surface in contact mode, the cantilever and the sample are set into oscillation at ultrasonic frequencies fc and fs, respectively, the difference of which is close to the first CRF of the system and is mapped to image the mechanical properties of the sample. (b) Sketch of the experimental configuration used in CR‐AFM. The sample (or the cantilever) is excited at ultrasonic frequency, fs (or fc), close to one of the CRFs of the system. The oscillation amplitude or, more often, the values of the CRFs (and the corresponding quality factors, Q) are mapped to image the mechanical properties of the sample
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(a) Sketch of the experimental configuration used in MFM and EFM. After having scanned the sample surface in tapping mode, the tip is lifted at lift height Δz which is maintained constant during the second‐pass scan in which the phase or frequency shift of the oscillating cantilever is recorded. Using a magnetically coated tip, the long‐range magnetic tip–sample interactions are recorded in MFM. Using a nonmagnetic conductive tip and applying a tip‐sample bias Vbias, the long‐range electric tip–sample interactions are recorded in EFM. (b) Sketch of the experimental configuration used in KPFM. After having scanned the sample surface in tapping mode, the tip is lifted at lift height Δz which is maintained constant during the second‐pass scan. An AC tip–sample voltage sets the cantilever into oscillation the amplitude of which is nullified by applying a variable DC tip–sample bias Vbias = −VCPD. The latter is mapped to reconstruct the image of the tip–sample contact potential difference VCPD and, thus, of the sample surface potential. (Adapted with permission from Passeri, Angeloni, Reggente, and Rossi (). Copyright 2017 Springer Nature)
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Nanotechnology Approaches to Biology > Nanoscale Systems in Biology
Diagnostic Tools > In Vivo Nanodiagnostics and Imaging

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