Quantification of uptake and localization of bovine serum albumin-stabilized single-wall carbon nanotubes in different human cell types

Oxidative stress modulating nanomaterials and their biochemical roles in nanomedicine

Many pathological conditions are predominantly associated with oxidative stress, arising from reactive oxygen species (ROS); therefore, the modulation of redox activities has been a key strategy to restore normal tissue functions. Current approaches involve establishing a favorable cellular redox environment through the administration of therapeutic drugs and redox-active nanomaterials (RANs). In particular, RANs not only provide a stable and reliable means of therapeutic delivery but also possess the capacity to finely tune various interconnected components, including radicals, enzymes, proteins, transcription factors, and metabolites. Here, we discuss the roles that engineered RANs play in a spectrum of pathological conditions, such as cancer, neurodegenerative diseases, infections, and inflammation. We visualize the dual functions of RANs as both generator and scavenger of ROS, emphasizing their profound impact on diverse cellular functions. The focus of this review is solely on inorganic redox-active nanomaterials (inorganic RANs). Additionally, we deliberate on the challenges associated with current RANs-based approaches and propose potential research directions for their future clinical translation.

Cytometry in the Short-Wave Infrared

Cytometry plays a crucial role in characterizing cell properties, but its restricted optical window (400-850 nm) limits the number of stained fluorophores that can be detected simultaneously and hampers the study and utilization of short-wave infrared (SWIR; 900-1700 nm) fluorophores in cells. Here we introduce two SWIR-based methods to address these limitations: SWIR flow cytometry and SWIR image cytometry. We develop a quantification protocol for deducing cellular fluorophore mass. Both systems achieve a limit of detection of ∼0.1 fg cell-1 within a 30 min experimental time frame, using individualized, high-purity (6,5) single-wall carbon nanotubes as a model fluorophore and macrophage-like RAW264.7 as a model cell line. This high-sensitivity feature reveals that low-dose (6,5) serves as an antioxidant, and cell morphology and oxidative stress dose-dependently correlate with (6,5) uptake. Our SWIR cytometry holds immediate applicability for existing SWIR fluorophores and offers a solution to the issue of spectral overlapping in conventional cytometry.

Carbon Nanomaterial Fluorescent Probes and Their Biological Applications

Fluorescent carbon nanomaterials have broadly useful chemical and photophysical attributes that are conducive to applications in biology. In this review, we focus on materials whose photophysics allow for the use of these materials in biomedical and environmental applications, with emphasis on imaging, biosensing, and cargo delivery. The review focuses primarily on graphitic carbon nanomaterials including graphene and its derivatives, carbon nanotubes, as well as carbon dots and carbon nanohoops. Recent advances in and future prospects of these fields are discussed at depth, and where appropriate, references to reviews pertaining to older literature are provided.

Catechin-Albumin Conjugates: Enhanced Antioxidant Capacity and Anticancer Effects

(+)-Catechin conjugated with human serum albumin (CT–HSA) was prepared and evaluated as a drug carrier bearing anticancer effects. It was found that 2.4 mol of CT was conjugate to 1 mol HSA. The CT–HSA has an antioxidant capacity of about 3.3 times the amount of CT in the conjugate. Intracellular incorporation of the CT–HSA was analyzed by fluorescence-activated cell sorting (FACS) and confocal laser scanning microscopy (CLSM) measurements using fluorescein isothiocyanate (FITC)-labelled CT–HSA. The results indicated that the FITC-labelled CT–HSA was incorporated into HeLa cells in a concentration-dependent manner. The CT–HSA enhanced the binding of anticancer drugs (5-fluorouracil (5-Fu) and mitomycin C (MMC)) comparing with HSA, and the CT–HSA mixed with 5-Fu or MMC decreased significantly the HeLa cell viability as compared with the same concentration of each drug. In addition, intracellular reactive oxygen species (ROS) scavenging by the CT–HSA is likely to affect the anticancer effects. Thus, the CT–HSA enhanced anticancer drug efficacy in relation to controlling ROS-scavenging ability.

Carbon nanotube uptake in cyanobacteria for near-infrared imaging and enhanced bioelectricity generation in living photovoltaics

The distinctive properties of single-walled carbon nanotubes (SWCNTs) have inspired the development of many novel applications in the field of cell nanobiotechnology. However, studies thus far have not explored the effect of SWCNT functionalization on transport across the cell walls of prokaryotes. We explore the uptake of SWCNTs in Gram-negative cyanobacteria and demonstrate a passive length-dependent and selective internalization of SWCNTs decorated with positively charged biomolecules. We show that lysozyme-coated SWCNTs spontaneously penetrate the cell walls of a unicellular strain and a multicellular strain. A custom-built spinning-disc confocal microscope was used to image the distinct near-infrared SWCNT fluorescence within the autofluorescent cells, revealing a highly inhomogeneous distribution of SWCNTs. Real-time near-infrared monitoring of cell growth and division reveal that the SWCNTs are inherited by daughter cells. Moreover, these nanobionic living cells retained photosynthetic activity and showed an improved photo-exoelectrogenicity when incorporated into bioelectrochemical devices.

Cell cycle-dependent endocytosis of DNA-wrapped single-walled carbon nanotubes by neural progenitor cells

While exposure of C17.2 neural progenitor cells (NPCs) to nanomolar concentrations of carbon nanotubes (NTs) yields evidence of cellular substructure reorganization and alteration of cell division and differentiation, the mechanisms of NT entry are not understood. This study examines the entry modes of (GT)₂₀ DNA-wrapped single-walled carbon nanotubes (SWCNTs) into NPCs. Several endocytic mechanisms were examined for responsibility in nanomaterial uptake and connections to alterations in cell development via cell-cycle regulation. Chemical cell-cycle arrest agents were used to synchronize NPCs in early G₁, late G₁/S, and G₂/M phases at rates (>80%) aligned with previously documented levels of synchrony for stem cells. Synchronization led to the highest reduction in SWCNT internalization during the G₁/S transition of the cell cycle. Concurrently, known inhibitors of endocytosis were used to gain control over established endocytic machineries (receptor-mediated endocytosis (RME), macropinocytosis (MP), and clathrin-independent endocytosis (CIE)), which resulted in a decrease in uptake of SWCNTs across the board in comparison with the control. The outcome implicated RME as the primary mechanism of uptake while suggesting that other endocytic mechanisms, though still fractionally responsible, are not central to SWCNT uptake and can be supplemented by RME when compromised. Thereby, endocytosis of nanomaterials was shown to have a dependency on cell-cycle progression in NPCs.

The Blanket Effect: How Turning the World Upside Down Reveals the Nature of Graphene Oxide Cytocompatibility

Extensive cytocompatibility testing of 2D nanocarbon materials including graphene oxide (GO) has been performed, but results remain contradictory. Literature has yet to account for settling-although sedimentation is visible to the eye and physics suggests that even individual graphenic flakes will settle. To investigate settling, a series of functional graphenic materials (FGMs) with differing oxidation levels, functionalities, and physical dimensions are synthesized. Though zeta potential indicates colloidal stability, significant gravitational settling of the FGMs is theoretically and experimentally demonstrated. By creating a setup to culture cells in traditional and inverted orientations in the same well, a "blanket effect" is demonstrated in which FGMs settle out of solution and cover cells at the bottom of the well, ultimately reducing viability. Inverted cells protected from the blanket effect are unaffected. Therefore, these results demonstrate that settling is a crucial factor that must be considered for FGM cytocompatibility experiments.

Femtosecond pulsed laser microscopy: a new tool to assess the in vitro delivered dose of carbon nanotubes in cell culture experiments

Background

In vitro models are widely used in nanotoxicology. In these assays, a careful documentation of the fraction of nanomaterials that reaches the cells, i.e. the in vitro delivered dose, is a critical element for the interpretation of the data. The in vitro delivered dose can be measured by quantifying the amount of material in contact with the cells, or can be estimated by applying particokinetic models. For carbon nanotubes (CNTs), the determination of the in vitro delivered dose is not evident because their quantification in biological matrices is difficult, and particokinetic models are not adapted to high aspect ratio materials. Here, we applied a rapid and direct approach, based on femtosecond pulsed laser microscopy (FPLM), to assess the in vitro delivered dose of multi-walled CNTs (MWCNTs).

Methods and results

We incubated mouse lung fibroblasts (MLg) and differentiated human monocytic cells (THP-1) in 96-well plates for 24 h with a set of different MWCNTs. The cytotoxic response to the MWCNTs was evaluated using the WST-1 assay in both cell lines, and the pro-inflammatory response was determined by measuring the release of IL-1β by THP-1 cells. Contrasting cell responses were observed across the MWCNTs. The sedimentation rate of the different MWCNTs was assessed by monitoring turbidity decay with time in cell culture medium. These turbidity measurements revealed some differences among the MWCNT samples which, however, did not parallel the contrasting cell responses. FPLM measurements in cell culture wells revealed that the in vitro delivered MWCNT dose did not parallel sedimentation data, and suggested that cultured cells contributed to set up the delivered dose. The FPLM data allowed, for each MWCNT sample, an adjustment of the measured cytotoxicity and IL-1β responses to the delivered doses. This adjusted in vitro activity led to another toxicity ranking of the MWCNT samples as compared to the unadjusted activities. In macrophages, this adjusted ranking was consistent with existing knowledge on the impact of surface MWCNT functionalization on cytotoxicity, and might better reflect the intrinsic activity of the MWCNT samples.

Conclusion

The present study further highlights the need to estimate the in vitro delivered dose in cell culture experiments with nanomaterials. The FPLM measurement of the in vitro delivered dose of MWCNTs can enrich experimental results, and may refine our understanding of their interactions with cells.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12989-021-00402-5.

Clearance of single-wall carbon nanotubes from the mouse lung: a quantitative evaluation

Based on the characteristics of carbon nanotubes (CNTs) that absorb light in the near-infrared region, we have developed a method to quantify the biodistribution of CNTs in mouse tissues such as the liver, lungs and spleen. By using this method, the kinetic biodistribution of single-walled CNTs (SWNTs) after intravenous injection into mice for 60 days has been successfully investigated. The results show that the biodistribution of CNTs was diameter-dependent by comparing two different diameters of SWNTs. The SWNTs with larger diameters (1-5 nm) accumulated more in the liver or spleen but less in the lungs than those with smaller diameters (0.7-0.9 nm). The quantities of both SWNTs in the liver and lungs decreased with time and showed no significant change in the spleen, which is also confirmed by histological analysis. In particular, the results have demonstrated that both SWNTs are cleared from the lungs almost completely within 60 days, suggesting that the pulmonary toxicity of SWNTs would be low when low amounts of CNTs (<70 μg g^-1 of tissue) enter inside the lungs. In addition, no obvious inflammatory responses are found from the measurement of the cytokines TGF-β1, IL-6, INF-γ, and TNF-α in the plasma and organs after the injection of both SWNTs into mice.

The study of the interaction mechanism between bovine serum albumin and single-walled carbon nanotubes depending on their diameter and concentration in solid nanocomposites by vibrational spectroscopy

The results of the study of composites based on bovine serum albumin (BSA) and single-walled carbon nanotubes (SWCNT) are presented. Nanocomposites were created by evaporation of the water-albumin dispersion with nanotubes using diode laser with temperature control. Two types of nanotubes were used. SWCNT I were synthesized using the electric arc method, SWCNT II were synthesized using the gas phase method. SWCNT I had a diameter and length less than SWCNT II. The mechanism of interaction between BSA and SWCNT in solid nanocomposites is considered. An experimental and theoretical studies of the interaction between aspartic (Asp) and glutamic (Glu) amino acids located on the outer surface of BSA and nanotubes using of vibrational spectroscopy (Fourier-transform infrared (FTIR) and Raman spectroscopy) was carried out. The possibility of nanotubes functionalization by oxygen atoms of negative amino acid residues Asp and Glu, which are on the outer surface of BSA, is shown by molecular modeling. The formation of covalent bonds between BSA and SWCNT in nanocomposites with different concentrations of nanotubes (0.01, 0.1 and 1 g/l) was confirmed by vibrational spectra. The covalent interaction between BSA with SWCNT under the laser irradiation leads to the conformational changes in the secondary and tertiary structures of albumin. This is confirmed by a significant decrease in the intensity of the absorption bands in the high-frequency region. The calculation of the vibrational spectra of the three Glycine:Glycine, Glutamic acid:Threonine and Aspartic acid:Lysine complexes, which take into account hydrogen, ion-dipole and ion-ion bonds, showed that a disturbance in the intermolecular interaction between amino acid residues led to significant decrease in the intensity of absorption bands in the region of stretching vibrations bonds OH and NH. From the Raman spectra, it was found that a significant number of defects in SWCNT is caused by the covalent attachment of oxygen atoms to the graphene surface of nanotubes. An increase in the diameter of nanotubes (4 nm) has practically no effect on the absorption spectrum of nanocomposite, while measuring the concentration of SWCNT affects the FTIR spectra. This confirmed the hydrophobic interaction between BSA and SWCNT. Thus, it was shown that BSA solid nanocomposites with CNTs can interact either with the help of hydrophobic forces or with the formation of covalent bonds, which depends on the diameter of the used nanotubes. The viability of connective fibroblast tissue cells on nanocomposites with both types of SWCNT was demonstrated. It was found that nanocomposites based on SWCNT I provide slightly better compatibility of their structure with fibroblasts. It allows to achieve better cell adhesion to the nanocomposite surface. These criteria make extensive use of scaffold nanocomposites in biomedicine, depending on the requirements for their quality and application.

Quantification of Carbon Nanotube Doses in Adherent Cell Culture Assays Using UV-VIS-NIR Spectroscopy

The overt hazard of carbon nanotubes (CNTs) is often assessed using in vitro methods, but determining a dose–response relationship is still a challenge due to the analytical difficulty of quantifying the dose delivered to cells. An approach to accurately quantify CNT doses for submerged in vitro adherent cell culture systems using UV-VIS-near-infrared (NIR) spectroscopy is provided here. Two types of multi-walled CNTs (MWCNTs), Mitsui-7 and Nanocyl, which are dispersed in protein rich cell culture media, are studied as tested materials. Post 48 h of CNT incubation, the cellular fractions are subjected to microwave-assisted acid digestion/oxidation treatment, which eliminates biological matrix interference and improves CNT colloidal stability. The retrieved oxidized CNTs are analyzed and quantified using UV-VIS-NIR spectroscopy. In vitro imaging and quantification data in the presence of human lung epithelial cells (A549) confirm that up to 85% of Mitsui-7 and 48% for Nanocyl sediment interact (either through internalization or adherence) with cells during the 48 h of incubation. This finding is further confirmed using a sedimentation approach to estimate the delivered dose by measuring the depletion profile of the CNTs.

Electrostatic Assemblies of Single-Walled Carbon Nanotubes and Sequence-Tunable Peptoid Polymers Detect a Lectin Protein and Its Target Sugars

A primary limitation to real-time imaging of metabolites and proteins has been the selective detection of biomolecules that have no naturally occurring or stable molecular recognition counterparts. We present developments in the design of synthetic near-infrared fluorescent nanosensors based on the fluorescence modulation of single-walled carbon nanotubes (SWNTs) with select sequences of surface-adsorbed N-substituted glycine peptoid polymers. We assess the stability of the peptoid-SWNT nanosensor candidates under variable ionic strengths, protease exposure, and cell culture media conditions and find that the stability of peptoid-SWNTs depends on the composition and length of the peptoid polymer. From our library, we identify a peptoid-SWNT assembly that can detect lectin protein wheat germ agglutinin (WGA) with a sensitivity comparable to the concentration of serum proteins. To demonstrate the retention of nanosensor-bound protein activity, we show that WGA on the nanosensor produces an additional fluorescent signal modulation upon exposure to the lectin's target sugars, suggesting the lectin protein remains active and selectively binds its target sugars through ternary molecular recognition interactions relayed to the nanosensor. Our results inform design considerations for developing synthetic molecular recognition elements by assembling peptoid polymers on SWNTs and also demonstrate these assemblies can serve as optical nanosensors for lectin proteins and their target sugars. Together, these data suggest certain peptoid sequences can be assembled with SWNTs to serve as versatile optical probes to detect proteins and their molecular substrates.

Interaction of Gold Nanorods with Human Dermal Fibroblasts: Cytotoxicity, Cellular Uptake, and Wound Healing

Herein, the cytotoxicity, cellular uptake and wound healing of human dermal fibroblasts were investigated upon treatment with gold nanorods (GNR) decorated with different ligands. Neutral and cationic poly ethylene glycol (PEG)-decorated GNR demonstrated the least cytotoxicity and cellular internalization, while anionic- and bovine serum albumin (BSA)-coated GNR revealed significant cytotoxicity and cellular uptake into human dermal fibroblasts. The cell scratch test demonstrated that neutral, cationic PEGylated GNR and anionic-decorated GNR have accelerated the wound healing rate in vitro after 24 h of incubation with scratched human dermal fibroblasts compared to control, while there was a drastic retardation of wound healing rate of scratched fibroblasts upon exposure to BSA-GNR accompanied with a significant release of the inflammatory cytokine; interlukin-1β (IL-1β). The cytotoxicity of GNR against the dermal cells and their ability to enhance the wound healing in vitro are greatly linked to their surface modifications.

Analytical approaches for characterizing and quantifying engineered nanoparticles in biological matrices from an (eco)toxicological perspective: old challenges, new methods and techniques

To promote the safer by design strategy and assess environmental risks of engineered nanoparticles (ENPs), it is essential to understand the fate of ENPs within organisms. This understanding in living organisms is limited by challenges in characterizing and quantifying ENPs in biological media. Relevant literature in this area is scattered across research from the past decade or so, and it consists mostly of medically oriented studies. This review first introduces those modern techniques and methods that can be used to extract, characterize, and quantify ENPs in biological matrices for (eco)toxicological purposes. It then summarizes recent research developments within those areas most relevant to the context and field that are the subject of this review paper. These comprise numerous in-situ techniques and some ex-situ techniques. The former group includes techniques allowing to observe specimens in their natural hydrated state (e.g., scanning electron microscopy working in cryo mode and high-pressure freezing) and microscopy equipped with elemental microanalysis (e.g., energy-dispersive X-ray spectroscopy); two-photon laser and coherent anti-Stokes Raman scattering microscopy; absorption-edge synchrotron X-ray computed microtomography; and laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS). The latter group includes asymmetric flow field flow fractionation coupled with ICP-MS and single particle-ICP-MS. Our review found that most of the evidence gathered for ENPs actually focused on a few metal-based ENPs and carbon nanotube and points to total mass concentration but no other particles properties, such as size and number. Based on the obtained knowledge, we developed and presented a decision scheme and analytical toolbox to help orient scientists toward selecting appropriate ways for investigating the (eco)toxicity of ENPs that are consistent with their properties.

Advances in Carbon Nanotubes for Malignant Melanoma: A Chance for Treatment

Malignant melanoma is an aggressive skin cancer with limited therapeutic options. Cancer is the second largest cause of death in society and one of the most difficult diseases to treat. Advances in biotechnology have enabled the current use of nanotechnology via the application of nanomaterials, especially as drug delivery systems for the transportation of very small particles. In this context, carbon nanotubes, with a potential role in the diagnosis and treatment of melanoma, are still an emerging research field. Their properties have been extensively studied for the use of antineoplastics drugs, as well as for DNA and RNA interference for the treatment of cancer. However, the most important challenge in nanomedicine is to decrease the toxicity and increase the biocompatibility of the nanomaterials used to transport therapeutic molecules. In this sense, this article addresses the recent advances in the use of carbon nanotubes in melanoma therapy and highlights the opportunities and challenges in this area. The advances and challenges involving these topics are essential to the success of nanoconjugate systems, and studies improving the comprehension of these nanosystems contribute to the development of specific antitumor therapies.

Quantification of cellular associated graphene and induced surface receptor responses

The use of graphene for biomedical and other applications involving humans is growing and shows practical promise. However, quantifying the graphitic nanomaterials that interact with cells and assessing any corresponding cellular response is extremely challenging. Here, we report an effective approach to quantify graphene interacting with single cells that utilizes combined multimodal-Raman and photoacoustic spectroscopy. This approach correlates the spectroscopic signature of graphene with the measurement of its mass using a quartz crystal microbalance resonator. Using this technique, we demonstrate single cell noninvasive quantification and multidimensional mapping of graphene with a detection limit of as low as 200 femtograms. Our investigation also revealed previously unseen graphene-induced changes in surface receptor expression in dendritic cells of the immune system. This tool integrates high-sensitivity real-time detection and monitoring of nanoscale materials inside single cells with the measurement of induced simultaneous biological cell responses, providing a powerful method to study the impact of nanomaterials on living systems and as a result, the toxicology of nanoscale materials.

Adsorption of Plasma Proteins on Single-Walled Carbon Nanotubes Reduced Cytotoxicity and Modulated Neutrophil Activation

Proteins in the bloodstream bind to carbon nanotubes (CNTs) through noncovalent interactions to form a protein corona, thereby effectively influencing the biological properties and blood biocompatibility of the CNTs. Here, we investigated the binding of common plasma proteins (i.e., human immunoglobulin G (IgG), human serum albumin (HSA), and fibrinogen (FG)) to carboxylated single-walled CNTs (SWCNTs), and evaluated the effects of these different protein coronas on cytotoxicity to endothelial cells and immune response to neutrophils in the bloodstream. Measurements of adsorption parameters revealed tight binding of proteins to SWCNTs, and the SWCNTs adsorption capacities followed the order FG > HSA > IgG. In addition, the basic residues (Arg, Lys, His) were found to play an important role in the formation of protein-SWCNTs corona complexes and determine their adsorption capacity. Consistent with the higher protein adsorption capacity, FG more significantly reduced the cytotoxicity of CNTs to human umbilical vein endothelial cells than the other two proteins. However, only treatment of SWCNTs with IgG resulted in the enhancement of CNT-induced myeloperoxidase (MPO) release (i.e., neutrophil activation) in neutrophils, while MPO-dependent degradation of CNTs induced less cytotoxicity than initial nanomaterials. Consistent with these effects of protein coronas, the presence of serum attenuated the cytotoxicity of CNTs and CNTs could induce neutrophil activation in human blood plasma. Our study demonstrates the ability of adsorbed plasma proteins to influence cytotoxicity and neutrophil response caused by CNTs in the bloodstream.

Fibrinogen binding-dependent cytotoxicity and degradation of single-walled carbon nanotubes

Carbon nanotubes are widely used in the area of biomedicine, and the binding of protein to carbon nanotubes are believed to play an important role in the potential cytotoxicity of nanomaterials. In this work, we investigated the effects of human fibrinogen-surface coatings on the biodegradation and cytotoxicity of carboxylated single-walled carbon nanotubes (SWCNTs). It was found that the electrostatic and π-π stacking interactions might be the crucial factors in stabilizing the binding of fibrinogen with SWCNTs by both theoretical and experimental approaches. Although naked SWCNTs could induce significant toxicity to macrophages, coating these nanomaterials with fibrinogen could greatly attenuate their toxicity. On the other hand, although SWCNTs and fibrinogen-preincubated SWCNTs were resistant to biodegradation in resting macrophages, both naked and fibrinogen-coated SWCNTs could be effectively and similarly degraded through myeloperoxidase (MPO) and peroxynitrite (ONOO^-)-dependent pathways in activated macrophages, where NADPH oxidase played a determinant role in the biodegradation process. Importantly, degraded SWCNTs by ONOO^- pathway in vitro induced less cytotoxicity than non-degraded nanotubes. These findings demonstrated that the binding of fibrinogen to SWCNTs could reduce cytotoxicity without affecting the biodegradation of nanotubes in activated inflammatory cells, providing a new route to design the safer nanotubes for future biomedical applications.

A fundamental study of photoluminescence modulation from DNA-wrapped single-walled carbon nanotubes

In this study, we investigated the interaction of base sequence-assigned single-stranded DNA (ssDNA) molecules with the surfaces of single-walled carbon nanotube (SWNT)-thymine (T30)/cytosine (C30) hybrids (T30/C30-SWNT), by measuring the modulation of near-infrared (NIR) photoluminescence (PL). Significant PL shifts were observed when T30/C30-SWNTs were reacted with 30-mers of adenine (A30)/guanine (G30). In contrast, when non-complementary ssDNA was used, no significant energy shift was observed in the PL modulation except when T30-SWNTs were reacted with G30. Furthermore, atomic force microscopy (AFM) measurements revealed that the average heights of the T30-SWNTs and C30-SWNTs, after reaction with A30 were 2 ± 0.6 and 1.1 ± 0.3 nm, respectively. This result was in good agreement with the results of PL measurements. Our data reveal that DNA hybridization could be detected by measuring PL from SWNTs, without the use of fluorescent molecules. This leads to the possibility of developing nanotube-based photoelectric conversion or optical switch devices driven by organic molecules.

Quantitation of cell-associated carbon nanotubes: selective binding and accumulation of carboxylated carbon nanotubes by macrophages

To understand the influence of carboxylation on the interaction of carbon nanotubes with cells, the amount of pristine multi-walled carbon nanotubes (P-MWNTs) or carboxylated multi-walled carbon nanotubes (C-MWNTs) coated with Pluronic^® F-108 that were accumulated by macrophages was measured by quantifying CNTs extracted from cells. Mouse RAW 264.7 macrophages and differentiated human THP-1 (dTHP-1) macrophages accumulated 80-100 times more C-MWNTs than P-MWNTs during a 24-h exposure at 37 °C. The accumulation of C-MWNTs by RAW 264.7 cells was not lethal; however, phagocytosis was impaired as subsequent uptake of polystyrene beads was reduced after a 20-h exposure to C-MWNTs. The selective accumulation of C-MWNTs suggested that there might be receptors on macrophages that bind C-MWNTs. The binding of C-MWNTs to macrophages was measured as a function of concentration at 4 °C in the absence of serum to minimize the potential interference by serum proteins or temperature-dependent uptake processes. The result was that the cells bound 8.7 times more C-MWNTs than P-MWNTs, consistent with the selective accumulation of C-MWNTs at 37 °C. In addition, serum strongly antagonized the binding of C-MWTS to macrophages, suggesting that serum contained inhibitors of binding. Moreover, inhibitors of class A scavenger receptor (SR-As) reduced the binding of C-MWNTs by about 50%, suggesting that SR-As contribute to the binding and endocytosis of C-MWNTs in macrophages but that other receptors may also be involved. Altogether, the evidence supports the hypothesis that macrophages contain binding sites selective for C-MWNTs that facilitate the high accumulation of C-MWNTs compared to P-MWNTs.

Carbon nanotubes physicochemical properties influence the overall cellular behavior and fate

The unique properties of single walled carbon nanotubes (SWCNTs) make them viable candidates for versatile implementation in the next generation of biomedical devices for targeted delivery of chemotherapeutic agents or cellular-sensing probes. Such implementation requires user-tailored changes in SWCNT's physicochemical characteristics to allow for efficient cellular integration while maintaining nanotubes' functionality. However, isolated reports showed that user-tailoring could induce deleterious effects in exposed cells, from decrease in cellular proliferation, to changes in cellular adhesion, generation of reactive oxygen species or phenotypical variations, just to name a few. Before full implementation of SWCNTs is achieved, their toxicological profiles need to be mechanistically correlated with their physicochemical properties to determine how the induced cellular fate is related to the exposure conditions or samples' characteristics. Our study provides a comprehensive analysis of the synergistic cyto- and genotoxic effects resulted from short-term exposure of human lung epithelial cells to pristine (as manufactured) and user-tailored SWCNTs, as a function of their physicochemical properties. Specifically, through a systematic approach we are correlating the nanotube uptake and nanotube-induced cellular changes to the sample's physicochemical characteristics (e.g., metal impurities, length, agglomerate size, surface area, dispersion, and surface functionalization). By identifying changes in active hallmarks involved in cell-cell connections and maintaining epithelial layer integrity, we also determine the role that short-term exposure to SWCNTs plays in the overall cellular fate and cellular transformation. Lastly, we assess cellular structure-function relationships to identify non-apoptotic pathways induced by SWCNTs exposure that could however lead to changes in cellular behavior and cellular transformation. Our results show that the degree of cell transformation is a function of the physicochemical properties of the SWCNT, with the nanotube with higher length, higher metal content and larger agglomerate size reducing cell viability to a larger extent. Such changes in cell viability are also complemented by changes in cell structure, cycle and cell-cell interactions, all responsible for maintaining cell fate.

Strategies for Preparing Albumin-based Nanoparticles for Multifunctional Bioimaging and Drug Delivery

Biosafety is the primary concern in clinical translation of nanomedicine. As an intrinsic ingredient of human blood without immunogenicity and encouraged by its successful clinical application in Abraxane, albumin has been regarded as a promising material to produce nanoparticles for bioimaging and drug delivery. The strategies for synthesizing albumin-based nanoparticles could be generally categorized into five classes: template, nanocarrier, scaffold, stabilizer and albumin-polymer conjugate. This review introduces approaches utilizing albumin in the preparation of nanoparticles and thereby provides scientists with knowledge of goal-driven design on albumin-based nanomedicine.

Length-dependent intracellular bundling of single-walled carbon nanotubes influences retention

Single-walled carbon nanotubes (SWCNTs) are increasingly being investigated for biomedical imaging, sensing, and drug delivery. Cell types, cellular entry mechanisms, and SWCNT lengths dictate SWCNT uptake, subsequent intracellular trafficking, and retention. Specialized immune cells known as macrophages are capable of two size-dependent entry mechanisms: endocytosis of small particles (diameter < 200 nm) and phagocytosis of large particles (diameter > 500 nm). In comparison, fibroblasts uptake particles predominantly through endocytosis. We report dependence of cellular processing including uptake, subcellular distribution, and retention on the SWCNT length and immune cell-specific processes. We chose SWCNTs of three different average lengths: 50 nm (ultrashort, US), 150 nm (short) and 500 nm (long) to encompass two different entry mechanisms, and noncovalently dispersed them in water, cell culture media, and phosphate buffer (pH 5) with bovine serum albumin, which maintains the SWCNT optical properties and promotes their cellular uptake. Using confocal Raman imaging and spectroscopy, we quantified cellular uptake, tracked the intracellular dispersion state (i.e., individualized versus bundled), and monitored recovery as a function of SWCNT lengths in macrophages. Cellular uptake of SWCNTs increases with decreasing SWCNT length. Interestingly, short-SWCNTs become highly bundled in concentrated phase dense regions of macrophages after uptake and most of these SWCNTs are retained for at least 24 h. On the other hand, both US- and long-SWCNTs remain largely individualized after uptake into macrophages and are lost over a similar elapsed time. After uptake into fibroblasts, however, short-SWCNTs remain individualized and are exocytosed over 24 h. We hypothesize that aggregation of SWCNTs within macrophages but not fibroblasts may facilitate the retention of SWCNTs within the former cell type. Furthermore, the differential length-dependent cellular processing suggests potential applications of macrophages as live cell carriers of SWCNTs into tumors and regions of inflammation for therapy and imaging.

Nanoemitters and innate immunity: the role of surfactants and bio-coronas in myeloperoxidase-catalyzed oxidation of pristine single-walled carbon nanotubes

Single-walled carbon nanotubes (SWCNTs) are experimentally utilized in in vivo imaging and photothermal cancer therapy owing to their unique physicochemical and electronic properties. For these applications, pristine carbon nanotubes are often modified by polymer surfactant coatings to improve their biocompatibility, adding more complexity to their recognition and biodegradation by immuno-competent cells. Here, we investigate the oxidative degradation of SWCNTs catalyzed by neutrophil myeloperoxidase (MPO) using bandgap near-infrared (NIR) photoluminescence and Raman spectroscopy. Our results show diameter-dependence at the initial stages of the oxidative degradation of sodium cholate-, DNA-, and albumin-coated SWCNTs, but not phosphatidylserine-coated SWCNTs. Moreover, sodium deoxycholate- and phospholipid-polyethylene glycol coated SWCNTs were not oxidized under the same reaction conditions, indicating that a surfactant can greatly impact the biodegradability of a nanomaterial. Our data also revealed that possible binding between MPO and surfactant coated-SWCNTs was unfavorable, suggesting that oxidation is likely caused by a hypochlorite generated through halogenation cycles of free MPO, and not MPO bound to the surface of SWCNTs. The identification of SWCNT diameters and coatings that retain NIR fluorescence during the interactions with the components of an innate immune system is important for their applications in in vivo imaging.

Noncovalent Protein and Peptide Functionalization of Single-Walled Carbon Nanotubes for Biodelivery and Optical Sensing Applications

The exquisite structural and optical characteristics of single-walled carbon nanotubes (SWCNTs), combined with the tunable specificities of proteins and peptides, can be exploited to strongly benefit technologies with applications in fields ranging from biomedicine to industrial biocatalysis. The key to exploiting the synergism of these materials is designing protein/peptide-SWCNT conjugation schemes that preserve biomolecule activity while keeping the near-infrared optical and electronic properties of SWCNTs intact. Since sp² bond-breaking disrupts the optoelectronic properties of SWCNTs, noncovalent conjugation strategies are needed to interface biomolecules to the nanotube surface for optical biosensing and delivery applications. An underlying understanding of the forces contributing to protein and peptide interaction with the nanotube is thus necessary to identify the appropriate conjugation design rules for specific applications. This article explores the molecular interactions that govern the adsorption of peptides and proteins on SWCNT surfaces, elucidating contributions from individual amino acids as well as secondary and tertiary protein structure and conformation. Various noncovalent conjugation strategies for immobilizing peptides, homopolypeptides, and soluble and membrane proteins on SWCNT surfaces are presented, highlighting studies focused on developing near-infrared optical sensors and molecular scaffolds for self-assembly and biochemical analysis. The analysis presented herein suggests that though direct adsorption of proteins and peptides onto SWCNTs can be principally applied to drug and gene delivery, in vivo imaging and targeting, or cancer therapy, nondirect conjugation strategies using artificial or natural membranes, polymers, or linker molecules are often better suited for biosensing applications that require conservation of biomolecular functionality or precise control of the biomolecule's orientation. These design rules are intended to provide the reader with a rational approach to engineering biomolecule-SWCNT platforms, broadening the breadth and accessibility of both wild-type and engineered biomolecules for SWCNT-based applications.

Label-Free Molecular Imaging of Biological Cells and Tissues by Linear and Nonlinear Raman Spectroscopic Approaches

Raman spectroscopy is an emerging technique in bioanalysis and imaging of biomaterials owing to its unique capability of generating spectroscopic fingerprints. Imaging cells and tissues by Raman microspectroscopy represents a nondestructive and label-free approach. All components of cells or tissues contribute to the Raman signals, giving rise to complex spectral signatures. Resonance Raman scattering and surface-enhanced Raman scattering can be used to enhance the signals and reduce the spectral complexity. Raman-active labels can be introduced to increase specificity and multimodality. In addition, nonlinear coherent Raman scattering methods offer higher sensitivities, which enable the rapid imaging of larger sampling areas. Finally, fiber-based imaging techniques pave the way towards in vivo applications of Raman spectroscopy. This Review summarizes the basic principles behind medical Raman imaging and its progress since 2012.

Toward the suppression of cellular toxicity from single-walled carbon nanotubes

In the multidisciplinary fields of nanobiology and nanomedicine, single-walled carbon nanotubes (SWCNTs) have shown great promise due to their unique morphological, physical and chemical properties. However, understanding and suppressing their cellular toxicity is a mandatory step before promoting their biomedical applications. In light of the flourishing recent literature, we provide here an extensive review on SWCNT cellular toxicity and an attempt to identify the key parameters to be considered in order to obtain SWCNT samples with minimal or no cellular toxicity.

Facile fabrication of bioactive ultra-small protein–hydroxyapatite nanoconjugates via liquid-phase laser ablation and their enhanced osteogenic differentiation activity

Ultra-small protein–hydroxyapatite nanoconjugates promote the osteogenic differentiation of mesenchymal stem cells.

Dispersed single wall carbon nanotubes do not impact mitochondria structure or function, but technical issues during analysis could yield incorrect results

Mitochondria, which generate cellular energy, are not influenced by purified carbon nanotubes. Many traditional biological assays to determine mitochondria function give false results because of nanotube surface activity and optical interference.

Polymer cloaking modulates the carbon nanotube protein corona and delivery into cancer cells

Polycarbodiimide cloaking of photoluminescent single-walled carbon nanotubes modulates their surface chemistry, protein corona, and uptake in cancer cells.

Interactions and effects of BSA-functionalized single-walled carbon nanotubes on different cell lines

Functionalized carbon nanotubes (CNTs) have shown great promise in several biomedical contexts, spanning from drug delivery to tissue regeneration. Thanks to their unique size-related properties, single-walled CNTs (SWCNTs) are particularly interesting in these fields. However, their use in nanomedicine requires a clear demonstration of their safety in terms of tissue damage, toxicity and pro-inflammatory response. Thus, a better understanding of the cytotoxicity mechanisms, the cellular interactions and the effects that these materials have on cell survival and on biological membranes is an important first step for an appropriate assessment of their biocompatibility. In this study we show how bovine serum albumin (BSA) is able to generate homogeneous and stable dispersions of SWCNTs (BSA-CNTs), suggesting their possible use in the biomedical field. On the other hand, this study wishes to shed more light on the impact and the interactions of protein-stabilized SWCNTs with two different cell types exploiting multidisciplinary techniques. We show that BSA-CNTs are efficiently taken up by cells. We also attempt to describe the effect that the interaction with cells has on the dielectric characteristics of the plasma membrane and ion flux using electrorotation. We then focus on the BSA-CNTs' acute toxicity using different cellular models. The novel aspect of this work is the evaluation of the membrane alterations that have been poorly investigated to date.

Developing Xenopus embryos recover by compacting and expelling single wall carbon nanotubes

Single wall carbon nanotubes are high aspect ratio nanomaterials being developed for use in materials, technological and biological applications due to their high mechanical stiffness, optical properties and chemical inertness. Because of their prevalence, it is inevitable that biological systems will be exposed to nanotubes, yet studies of the effects of nanotubes on developing embryos have been inconclusive and are lacking for single wall carbon nanotubes exposed to the widely studied model organism Xenopus laevis (African clawed frog). Microinjection of experimental substances into the Xenopus embryo is a standard technique for toxicology studies and cellular lineage tracing. Here we report the surprising finding that superficial (12.5 ± 7.5 µm below the membrane) microinjection of nanotubes dispersed with Pluronic F127 into one- to two-cell Xenopus embryos resulted in the formation and expulsion of compacted, nanotube-filled, punctate masses, at the blastula to mid-gastrula developmental stages, which we call "boluses." Such expulsion of microinjected materials by Xenopus embryos has not been reported before and is dramatically different from the typical distribution of the materials throughout the progeny of the microinjected cells. Previous studies of microinjections of nanomaterials such as nanodiamonds, quantum dots or spherical nanoparticles report that nanomaterials often induce toxicity and remain localized within the embryos. In contrast, our results demonstrate an active recovery pathway for embryos after exposure to Pluronic F127-coated nanotubes, which we speculate is due to a combined effect of the membrane activity of the dispersing agent, Pluronic F127, and the large aspect ratio of nanotubes.

Distribution of single wall carbon nanotubes in the Xenopus laevis embryo after microinjection

Single wall carbon nanotubes (SWCNTs) are advanced materials with the potential for a myriad of diverse applications, including biological technologies and large-scale usage with the potential for environmental impacts. SWCNTs have been exposed to developing organisms to determine their effects on embryogenesis, and results have been inconsistent arising, in part, from differing material quality, dispersion status, material size, impurity from catalysts and stability. For this study, we utilized highly purified SWCNT samples with short, uniform lengths (145 ± 17 nm) well dispersed in solution. To test high exposure doses, we microinjected > 500 µg ml(-1) SWCNT concentrations into the well-established embryogenesis model, Xenopus laevis, and determined embryo compatibility and subcellular localization during development. SWCNTs localized within cellular progeny of the microinjected cells, but were heterogeneously distributed throughout the target-injected tissue. Co-registering unique Raman spectral intensity of SWCNTs with images of fluorescently labeled subcellular compartments demonstrated that even at regions of highest SWCNT concentration, there were no gross alterations to subcellular microstructures, including filamentous actin, endoplasmic reticulum and vesicles. Furthermore, SWCNTs did not aggregate and localized to the perinuclear subcellular region. Combined, these results suggest that purified and dispersed SWCNTs are not toxic to X. laevis animal cap ectoderm and may be suitable candidate materials for biological applications.

Lysine-functionalized nanodiamonds as gene carriers: development of stable colloidal dispersion for in vitro cellular uptake studies and siRNA delivery application

PURPOSE

Nanodiamonds (NDs) are emerging as an attractive tool for gene therapeutics. To reach their full potential for biological application, NDs should maintain their colloidal stability in biological milieu. This study describes the behavior of lysine-functionalized ND (lys-ND) in various dispersion media, with an aim to limit aggregation and improve the colloidal stability of ND-gene complexes called diamoplexes. Furthermore, cellular and macromolecular interactions of lys-NDs are also analyzed in vitro to establish the understanding of ND-mediated gene transfer in cells.

METHODS

lys-NDs were synthesized earlier through covalent conjugation of lysine amino acid to carboxylated NDs surface generated through re-oxidation in strong oxidizing acids. In this study, dispersions of lys-NDs were prepared in various media, and the degree of sedimentation was monitored for 72 hours. Particle size distributions and zeta potential measurements were performed for a period of 25 days to characterize the physicochemical stability of lys-NDs in the medium. The interaction profile of lys-NDs with fetal bovine serum showed formation of a protein corona, which was evaluated by size and charge distribution measurements. Uptake of lys-NDs in cervical cancer cells was analyzed by scanning transmission X-ray microscopy, flow cytometry, and confocal microscopy. Cellular uptake of diamoplexes (complex of lys-NDs with small interfering RNA) was also analyzed using flow cytometry.

RESULTS

Aqueous dispersion of lys-NDs showed minimum sedimentation and remained stable over a period of 25 days. Size distributions showed good stability, remaining under 100 nm throughout the testing period. A positive zeta potential of >+20 mV indicated a preservation of surface charges. Size distribution and zeta potential changed for lys-NDs after incubation with blood serum, suggesting an interaction with biomolecules, mainly proteins, and a possible formation of a protein corona. Cellular internalization of lys-NDs was confirmed by various techniques such as confocal microscopy, soft X-ray spectroscopy, and flow cytometry.

CONCLUSION

This study establishes that dispersion of lys-NDs in aqueous medium maintains long-term stability and also provides evidence that lysine functionalization enables NDs to interact effectively with the biological system to be used for RNAi therapeutics.

Delivering Single-Walled Carbon Nanotubes to the Nucleus Using Engineered Nuclear Protein Domains

Single-walled carbon nanotubes (SWCNTs) have great potential for cell-based therapies due to their unique intrinsic optical and physical characteristics. Consequently, broad classes of dispersants have been identified that individually suspend SWCNTs in water and cell media in addition to reducing nanotube toxicity to cells. Unambiguous control and verification of the localization and distribution of SWCNTs within cells, particularly to the nucleus, is needed to advance subcellular technologies utilizing nanotubes. Here we report delivery of SWCNTs to the nucleus by noncovalently attaching the tail domain of the nuclear protein lamin B1 (LB1), which we engineer from the full-length LMNB1 cDNA. More than half of this low molecular weight globular protein is intrinsically disordered but has an immunoglobulin-fold composed of a central hydrophobic core, which is highly suitable for associating with SWCNTs, stably suspending SWCNTs in water and cell media. In addition, LB1 has an exposed nuclear localization sequence to promote active nuclear import of SWCNTs. These SWCNTs-LB1 dispersions in water and cell media display near-infrared (NIR) absorption spectra with sharp van Hove peaks and an NIR fluorescence spectra, suggesting that LB1 individually disperses nanotubes. The dispersing capability of SWCNTs by LB1 is similar to that by albumin proteins. The SWCNTs-LB1 dispersions with concentrations ≥150 μg/mL (≥30 μg/mL) in water (cell media) remain stable for ≥75 days (≥3 days) at 4 °C (37 °C). Further, molecular dynamics modeling of association of LB1 with SWCNTs reveal that the exposure of the nuclear localization sequence is independent of LB1 binding conformation. Measurements from confocal Raman spectroscopy and microscopy, NIR fluorescence imaging of SWCNTs, and fluorescence lifetime imaging microscopy show that millions of these SWCNTs-LB1 complexes enter HeLa cells, localize to the nucleus of cells, and interact with DNA. We postulate that the modification of native cellular proteins as noncovalent dispersing agents to provide specific transport will open new possibilities to utilize both SWCNT and protein properties for multifunctional subcellular targeting applications. Specifically, nuclear targeting could allow delivery of anticancer therapies, genetic treatments, or DNA to the nucleus.

Effects of multiwalled carbon nanotube surface modification and purification on bovine serum albumin binding and biological responses

The potential diagnostic and therapeutic applications such as drug delivery of multi-walled carbon nanotubes (MWCNTs) are being increasingly explored due to their unique mechanical, chemical and biological properties. Carboxylation of MWCNTs has been widely used to improve the solubility in aqueous systems, and for further functionalization with biologically active moieties. Purity of carboxylated MWCNTs is of great importance in nanomedicine. An important consideration is that oxidation debris is generated during the process of carboxylation, which can be removed by base washing. We hypothesized that surface modification as well as further purification by debris removal may alter physicochemical properties of MWCNTs and their ability to bind proteins. In this study, we utilized pristine MWCNT carboxylated MWCNTs (F-MWCNTs) and base-washed carboxylated MWCNTs (BW-F-MWCNTs) to examine formation of a bovine serum albumin (BSA) protein corona and impact on biological responses. We found that carboxylation increased the capability of F-MWCNTs to bind BSA, and base washing further increased this binding by 41% implying that purification of F-MWCNTs is an important consideration in biological applications. The BSA protein corona decreased the hydrodynamic size of MWCNTs by nearly 50% because the coating improved colloidal behavior. The effect was significantly less pronounced for F-MWCNTs and BW-F-MWCNTs because they were highly dispersible to begin with. Functionalization increased cellular uptake by both rat aortic endothelial cells (RAEC) and macrophage-like murine cells (RAW264.7), while base washing showed results similar to the functionalized analog. Interestingly, BSA binding downregulated mRNA levels of interleukin-6 (IL-6) and heme oxygenase 1 (Hmox1) in RAEC cells but upregulated the expression of IL-6 and Hmox1 in RAW264.7 cells, indicating the dependence of cell types in biological responses to MWCNTs. Overall, our study demonstrated that surface modification as well as further purification impacted the interaction of MWCNTs with proteins and subsequent cellular responses. Interestingly, while the corona associated with the F-MWCNTs and BW-F-MWCNTs were significantly different, their respective cellular uptake and biological responses were similar. This implied that surface functionalization played a more important role than surface corona.

Enhanced intracellular delivery of small molecules and drugs via non-covalent ternary dispersions of single-wall carbon nanotubes

Non-covalent dispersions of carbon nanotubes using albumin proteins pre-loaded with hydrophobic molecules increase intracellular delivery and promote cell-mediated release of small molecules and drugs for therapy.

A review on protein functionalized carbon nanotubes

Carbon nanotubes (CNTs) have been widely recognized and used for controlled drug delivery and in various other fields due to their unique properties and distinct advantages. Both single-walled carbon nanotubes (SWCNTs) and multiwalled (MWCNTs) carbon nanotubes are used and/or studied for potential applications in medical, energy, textile, composite, and other areas. Since CNTs are chemically inert and are insoluble in water or other organic solvents, they are functionalized or modified to carry payloads or interact with biological molecules. CNTs have been preferably functionalized with proteins because CNTs are predominantly used for medical applications such as delivery of drugs, DNA and genes, and also for biosensing. Extensive studies have been conducted to understand the interactions, cytotoxicity, and potential applications of protein functionalized CNTs but contradicting results have been published on the cytotoxicity of the functionalized CNTs. This paper provides a brief review of CNTs functionalized with proteins, methods used to functionalize the CNTs, and their potential applications.

Photosensitizer-Conjugated Albumin-Polypyrrole Nanoparticles for Imaging-Guided In Vivo Photodynamic/Photothermal Therapy

Conjugated polymers with strong absorbance in the near-infrared (NIR) region have been widely explored as photothermal therapy agents due to their excellent photostability and high photothermal conversion efficiency. Herein, polypyrrole (PPy) nanoparticles are fabricated by using bovine serum albumin (BSA) as the stabilizing agent, which if preconjugated with photosensitizer chlorin e6 (Ce6) could offer additional functionalities in both imaging and therapy. The obtained PPy@BSA-Ce6 nanoparticles exhibit little dark toxicity to cells, and are able to trigger both photodynamic therapy (PDT) and photothermal therapy (PTT). As a fluorescent molecule that in the meantime could form chelate complex with Gd(3+), Ce6 in PPy@BSA-Ce6 nanoparticles after being labeled with Gd(3+) enables dual-modal fluorescence and magnetic resonance (MR) imaging, which illustrate strong tumor uptake of those nanoparticles after intravenous injection into tumor-bearing mice. In vivo combined PDT and PTT treatment is then carried out after systemic administration of PPy@BSA-Ce6, achieving a remarkably improved synergistic therapeutic effect compared to PDT or PTT alone. Hence, a rather simple one-step approach to fabricate multifunctional nanoparticles based on conjugated polymers, which appear to be promising in cancer imaging and combination therapy, is presented.

Raman microscopy for cellular investigations--From single cell imaging to drug carrier uptake visualization

Progress in advanced therapeutic concepts requires the development of appropriate carrier systems for intracellular drug delivery. Consequently, analysis of interaction between carriers, drugs and cells as well as their uptake and intracellular fate is a current focus of research interest. In this context, Raman spectroscopy recently became an emerging analytical technique, due to its non-destructive, chemically selective and label-free working principle. In this review, we briefly present the state-of-the-art technologies for cell visualization and drug internalization. Against this background, Raman microscopy is introduced as a versatile analytical technique. An overview of various Raman spectroscopy investigations in this field is given including interactions of cells with drug molecules, carrier systems and other nanomaterials. Further, Raman instrumentations and sample preparation methods are discussed. Finally, as the analytical limit is not reached yet, a future perspective for Raman microscopy in pharmaceutical and biomedical research on the single cell level is given.