Imaging Of Single-walled Carbon Nanotubes Research Articles

Preclinical Imaging and Spectroscopy in the NIR-II Window with Indocyanine Green (ICG) and Single-Walled Carbon Nanotubes

We developed a near-infrared small animal imaging system, IR VIVO, that provides real-time images, videos and spectral imaging in the NIR-I and shortwave infrared (SWIR or NIR-II) regions. We found that SWIR wavelengths can give optimal resolution for in vivo optical imaging of deep organs in mice up to 3 cm due to the low tissue autofluorescence, scattering and absorption of light at these wavelengths. We also showed how this higher penetration depth can enable the detection of small wavelength changes in the emission of carbon nanotube-based sensors implanted in vivo using a continuously tunable filter.First, we demonstrated superior image clarity and penetration depth at NIR-II wavelengths (1000-1700 nm) in vivo using an FDA approved dye, indocyanine green (ICG) in a mouse. We used 780 nm excitation, detection using a Zephir 1.7 InGaAs camera and 1250 nm long-pass emission filter. We found low tissue autofluorescence at 1250 nm. The ICG dye imaging resulted in superior visualization of microvasculature, perfusion, measurement of hearst rate, respiratory rate, hepatobiliary and intestinal contractions. Further anatomical and functional imaging was carried out by looking at the kinetics of ICG, resulting in the identification of different organs.Second, In vivo near-infrared hyperspectral imaging of carbon nanotubes was conducted using a continuously-tunable filter in the imager. A diffraction volume Bragg grating (VBG), was used to provide narrow-band wavelength selection. Coupled with a homogeneous global illumination, spectrally-defined images were acquired in the entire field of view. The result was a dataset containing both 2D spatial information and the full spectrum for each point in the image. We conducted near-infrared hyperspectral imaging of single-walled carbon nanotubes to measure small wavelength changes of the nanotubes implanted into live mice. Hyperspectral measurements of carbon nanotube sensors for lipids in the liver as well as implantable sensors for doxorubicin were conducted, facilitating liver disease monitoring and drug pharmacokinetics measurements.Finally, we believe wide-area NIR-II imaging and spectral/hyperspectral measurements have broad potential applications for the use of carbon nanotubes and other NIR-I/II materials in basic materials/biology, translational, and clinical work, including sensor arrays, point-of-care measurements, implants, whole small animal imaging and intraoperative/surgical imaging.

Facilitating Hotspot Alignment in Tip-Enhanced Raman Spectroscopy via the Silver Photoluminescence of the Probe.

A tip-enhanced Raman spectroscopy (TERS) system based on an atomic force microscope (AFM) and radially polarized laser beam was developed. A TERS probe with plasmon resonance wavelength matching the excitation wavelength was prepared with the help of dark-field micrographs. The intrinsic photoluminescence (PL) from the silver (Ag)-coated TERS probe induced by localized surface plasmon resonance contains information about the near-field enhanced electromagnetic field intensity of the probe. Therefore, we used the intensity change of Ag PL to evaluate the stability of the Ag-coated probe during TERS experiments. Tracking the Ag PL of the TERS probe was helpful to detect probe damage and hotspot alignment. Our setup was successfully used for the TERS imaging of single-walled carbon nanotubes, which demonstrated that the Ag PL of the TERS probe is a good criterion to assist in the hotspot alignment procedure required for TERS experiments. This method lowers the risk of contamination and damage of the precious TERS probe, making it worthwhile for wide adoption in TERS experiments.

Preclinical Imaging and Spectroscopy in the NIR-II Window with Single-Walled Carbon Nanotubes

We developed a near-infrared small animal imaging system, IR VIVO, that provides real-time images, videos, and spectral imaging in the NIR-I and shortwave infrared (SWIR or NIR-II) regions. We found that SWIR wavelengths can give optimal resolution for in vivo optical imaging of deep organs in mice due to the low tissue autofluorescence, scattering and absorption of light at these wavelengths. We also show how this higher penetration depth can enable the detection of small wavelength changes in the emission of carbon nanotube-based sensors implanted in vivo using a continuously tunable filter.First, we demonstrated superior image clarity and penetration depth at NIR-II wavelengths (1000-1700 nm) in vivo using an FDA approved dye, indocyanine green (ICG). We used 780 nm excitation and detection using a Zephir 1.7 InGaAs camera and 1250 nm long-pass emission filter. We found low tissue autofluorescence at 1250 nm. The ICG dye imaging resulted in superior visualization of microvasculature, perfusion, measurement of heart rate, respiratory rate, hepatobiliary, and intestinal contractions. Further anatomical and functional imaging was carried out by looking at the kinetics of ICG, resulting in identification of different organs.In vivo near-infrared hyperspectral imaging of carbon nanotubes was conducted using a continuously-tunable filter in the imager. A diffraction volume Bragg grating (VBG), was used to provide narrow-band wavelength selection. Coupled with a homogeneous global illumination, spectrally-defined images were acquired in the entire field of view. The result was a dataset containing both 2D spatial information and the full spectrum for each point in the image. We conducted near-infrared hyperspectral imaging of single-walled carbon nanotubes to measure small wavelength changes of the nanotubes implanted into live mice. Hyperspectral measurements of carbon nanotube sensors for lipids in the liver as well as implantable sensors for doxorubicin were conducted, facilitating liver disease monitoring and drug pharmacokinetics measurements.We believe wide-area NIR-II imaging and spectral/hyperspectral measurements have broad potential applications for the use of carbon nanotubes and other NIR-I/II materials in basic materials/biology, translational, and clinical work, including sensor arrays, point-of-care measurements, implants, whole-animal imaging, and intraoperative/surgical imaging.

Scanning electron microscopy imaging of single-walled carbon nanotubes on substrates

Scanning electron microscopy (SEM) plays an indispensable role in nanoscience and nanotechnology because of its high efficiency and high spatial resolution in characterizing nanomaterials. Recent progress indicates that the contrast arising from different conductivities or bandgaps can be observed in SEM images if single-walled carbon nanotubes (SWCNTs) are placed on a substrate. In this study, we use SWCNTs on different substrates as model systems to perform SEM imaging of nanomaterials. Substantial SEM observations are conducted at both high and low acceleration voltages, leading to a comprehensive understanding of the effects of the imaging parameters and substrates on the material and surface-charge signals, as well as the SEM imaging. This unified picture of SEM imaging not only furthers our understanding of SEM images of SWCNTs on a variety of substrates but also provides a basis for developing new imaging recipes for other important nanomaterials used in nanoelectronics and nanophotonics.

The impact of subcellular location on the near infrared-mediated thermal ablation of cells by targeted carbon nanotubes

Single-walled carbon nanotubes (SWNTs) are used in the near infrared (NIR)-mediated thermal ablation of tumor cells because they efficiently convert absorbed NIR light into heat. Despite the therapeutic potential of SWNTs, there have been no published studies that directly quantify how many SWNTs need be associated with a cell to achieve a desired efficiency of killing, or what is the most efficient subcellular location of SWNTs for killing cells. Herein we measured dose response curves for the efficiency of killing correlated to the measured amounts of folate-targeted SWNTs that were either on the surface or within the vacuolar compartment of normal rat kidney cells. Folate-targeted SWNTs on the cell surface were measured after different concentrations of SWNTs in medium were incubated with cells for 30 min at 4 °C. Folate-targeted SWNTs within the vacuolar compartments were measured after cells were incubated with different concentrations of SWNTs in medium for 6 h at 37 °C. It was observed that a SWNT load of ∼13 pg/cell when internalized was sufficient to kill 90% of the cells under standardized conditions of NIR light irradiation. When ∼3.5 pg/cell of SWNTs were internalized within the endosomal/lysosomal compartments, ∼50% of the cells were killed, but when ∼3.5 pg/cell of SWNTs were confined to the cell surface only ∼5% of the cells were killed under the same NIR irradiation conditions. The SWNT subcellular locations were verified using Raman imaging of SWNTs merged with fluorescence images of known subcellular markers. To our knowledge, this is the first time that SWNT amounts at known subcellular locations have been correlated with a dose-normalized efficacy of thermal ablation and the results support the idea that SWNTs confined to the plasma membrane are not as effective in NIR-mediated cell killing as an equivalent amount of SWNTs when internalized within the endosomal/lysosomal vesicles.

Effect of Competitive Surface Functionalization on Dual-Modality Fluorescence and Magnetic Resonance Imaging of Single-Walled Carbon Nanotubes.

It is well-known that ionic surfactant coated single-walled carbon nanotubes (SWNTs) possess higher near-infrared fluorescence (NIRF) quantum yield than nonionic polymer functionalized SWNTs. However, the influence of surface functionalization on the magnetic properties of SWNTs for T2-weighted magnetic resonance imaging (MRI) has not been reported. Here, we demonstrate that SWNTs functionalized by nonionic polymers display superior T2 relaxivity for MRI as compared to those coated by ionic surfactants. This difference may indicate that micelle structures formed by ionic surfactants are sufficiently tight to partially exclude water protons from the iron catalysts attached to the ends of SWNTs. On the basis of the different effects of the two types of suspension agents on NIRF and MRI of functionalized SWNTs, we further explore the competitive surface functionalization between ionic surfactants and nonionic polymers by stepwise replacing ionic surfactant molecules in a nanotube suspension with nonionic polymers. The superior NIRF of ionic surfactant coated SWNTs gradually quenches whereas no improvement on T2 relaxivity is observed during this replacement process. This result may indicate that nonionic polymers wrap around the outside of micelle structures to form small nanotube bundles rather than replacing ionic surfactants in the micelle structures to directly interact with the SWNT surface. Finally, we demonstrate the feasibility of dual-modality NIRF and MRI of nonionic polymer functionalized SWNTs in brain cells.

Preparation of carbon nanotube bioconjugates for biomedical applications

Biomedical applications of carbon nanotubes have attracted much attention in recent years. Here, we summarize our previously developed protocols for functionalization and bioconjugation of single-walled carbon nanotubes (SWNTs) for various biomedical applications including biological imaging; using nanotubes as Raman, photoluminescence and photoacoustic labels; sensing using nanotubes as Raman tags and drug delivery. Sonication of SWNTs in solutions of phospholipid-polyethylene glycol (PL-PEG) is our most commonly used protocol of SWNT functionalization. Compared with other frequently used covalent strategies, our non-covalent functionalization protocol largely retains the intrinsic optical properties of SWNTs, which are useful in various biological imaging and sensing applications. Functionalized SWNTs are conjugated with targeting ligands, including peptides and antibodies for specific cell labeling in vitro or tumor targeting in vivo. Radio labels are introduced for tracking and imaging of SWNTs in real time in vivo. Moreover, SWNTs can be conjugated with small interfering RNA (siRNA) or loaded with chemotherapy drugs for drug delivery. These procedures take various times ranging from 1 to 5 d.

Direct imaging of single-walled carbon nanotubes in cells

The development of single-walled carbon nanotubes for various biomedical applications is an area of great promise. However, the contradictory data on the toxic effects of single-walled carbon nanotubes highlight the need for alternative ways to study their uptake and cytotoxic effects in cells. Single-walled carbon nanotubes have been shown to be acutely toxic in a number of types of cells, but the direct observation of cellular uptake of single-walled carbon nanotubes has not been demonstrated previously due to difficulties in discriminating carbon-based nanotubes from carbon-rich cell structures. Here we use transmission electron microscopy and confocal microscopy to image the translocation of single-walled carbon nanotubes into cells in both stained and unstained human cells. The nanotubes were seen to enter the cytoplasm and localize within the cell nucleus, causing cell mortality in a dose-dependent manner.

Nanoscale optical imaging of single-walled carbon nanotubes

In this contribution, we apply a microscopic technique that relies on the enhanced electric field near a sharp, laser-irradiated metal tip that acts as a highly confined light source. The tip is used for the local excitation of the optical response of single-walled carbon nanotubes (SWNT) deposited on glass. We demonstrate photoluminescence and Raman imaging of the same SWNTs with a spatial resolution of about 10 nm.

Nanoscale Optical Imaging of Excitons in Single-Walled Carbon Nanotubes

We present simultaneous near-field photoluminescence (PL) and Raman imaging of single-walled carbon nanotubes (SWNTs) with a spatial resolution better than 15 nm. Highly localized excitation is used to visualize the spatial extent of the contributing excited states. For SWNTs on glass, we typically observe highly confined PL from short segments of about 20 nm in length. The PL from micelle-encapsulated SWNTs on mica is extended along the tube up to several hundreds of nanometers. We find that near-field enhancement is much stronger for photoluminescence than for Raman scattering, an observation that is explained by the low intrinsic quantum yield of SWNTs.

Electron-microscopic imaging of single-walled carbon nanotubes grown on silicon and silicon oxide substrates

Direct imaging of single-walled carbon nanotubes (SWNTs) suspended on pillar-patterned Si or SiO2 substrates is investigated using transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The suspended nanotubes are successfully observed by direct TEM imaging and it is seen that they have either individual or bundles of SWNTs. Low energy (< or =2 keV) SEM produces high contrast images of suspended SWNTs. On the contrary, when SWNTs contact a SiO2 substrate, they are imaged using electron-beam induced current. The image brightness depends on the length of SWNTs.

Mechanism of bright selective imaging of single-walled carbon nanotubes on insulators by scanning electron microscopy

Individual single-walled carbon nanotubes (SWNTs) produce highly bright images of the insulator surface around them when observed by scanning electron microscopy at low primary-electron voltage. We found that the insulator surface near SWNTs emits more secondary electrons due to electrons supplied through SWNTs connecting to the outside area of the primary-electron beam scanning. SWNTs are thus highlighted as bright lines corresponding to the electron-beam-induced current range around them. This technique provides a useful and effective way to investigate lateral growth morphology of SWNTs on the substrate.

Material contrast by combined scanning tunneling and force microscopy imaging of single-walled carbon nanotubes

A newly developed combination of tunneling and force microscopy enables near-atomic point resolution, and tubes can be identified without the need of a conducting substrate. This is a crucial step for the characterization of electronic devices based on individual single-wall tubes. Images of the spatial current distribution taken in constant force mode show strongly enhanced contrast between tubes and gold or silicon dioxide substrates, respectively, which is attributed to the unusual elastic properties of the nanotubes.