Molecular dynamics simulation is utilized to investigate the ionic transport of NaCl in solution through a graphene nanopore under an applied electric field. Results show the formation of concentration polarization layers in the vicinity of the graphene sheet. The nonuniformity of the ion distribution gives rise to an electric pressure which drives vortical motions in the fluid if the electric field is sufficiently strong to overcome the influence of viscosity and thermal fluctuations. The relative importance of hydrodynamic transport and thermal fluctuations in determining the pore conductivity is investigated. A second important effect that is observed is the mass transport of water through the nanopore, with an average velocity proportional to the applied voltage and independent of the pore diameter. The flux arises as a consequence of the asymmetry in the ion distribution which can be attributed to differing mobilities of the sodium and chlorine ions, and, to the polarity of water molecules. The accumulation of liquid molecules in the vicinity of the nanopore due to reorientation of the water dipoles by the local electric field is seen to result in a local increase in the liquid density. Results confirm that the electric conductance is proportional to the nanopore diameter for the parameter regimes that we simulated. The occurrence of fluid vortices is found to result in an increase in the effective electrical conductance.
Distinct magnetic nanoparticle designs can have unique spectral responses to an AC magnetic field in a technique called the magnetic spectroscopy of Brownian motion (MSB). The spectra of the particles have been measured using desktop spectrometers and in vivo measurements. If multiple particle types are present in a region of interest, the unique spectral signatures allow for the simultaneous quantification of the various particles. We demonstrate such a potential experimentally with up to three particle types. This ability to concurrently detect multiple particles will enable new biomedical applications.
This work describes an original and simple technique for protein immobilization into nanowells, fabricated using nanopatterned-array fabrication methods, while ensuring the protein retains the normal biological activity. Nanosphere-lithography was used to fabricate a nanowell array with nanowells that were 100 nm in diameter and a periodicity of 500 nm. The base of the nanowells was gold and the surrounding material was silicon dioxide. The different surface chemistries of these materials were used to attach two different self-assembled monolayers (SAM) with different affinities for the protein used here, cytochrome P450 (P450). The nanowell SAM, a methyl terminated thiol, had high affinity for the P450. The surrounding SAM, a polyethylene glycol silane, displayed very little affinity toward the P450 isozyme CYP2C9, as demonstrated by x-ray photoelectron spectroscopy and surface plasmon resonance. The regularity of the nanopatterned array was examined by scanning electron microscopy and atomic force microscopy. P450-mediated metabolism experiments of known substrates demonstrated that the nanowell bound P450 enzyme exceeded its normal activity, as compared to P450 solutions, when bound to the methyl terminated self-assembled monolayer. The nanopatterned array chips bearing P450 display long term stability and give reproducible results making them potentially useful for high throughput screening assays or as nanoelectrode arrays.
Nanowell array; Self-assembled monolayer; cytochrome P450
We report the fabrication and characterization of uniformly-sized nanopore arrays, integrated into an optical detection system for high-throughput DNA sequencing applications. Nanopore arrays were fabricated using Focused Ion Beam milling followed by TiO2 coating using Atomic Layer Deposition (ALD). The TiO2 layer decreases the initial pore diameter down to sub-10nm range, compatible with the requirements for nanopore-based sequencing using optical readout. We find that the TiO2 layers produce a lower photoluminescence background as compared with the more broadly used Al2O3 coatings. The functionality of the nanopore array was demonstrated by the simultaneous optical detection of DNA-quantum dot-conjugates, which were electro-kinetically driven through the nanopores. Our optical scheme employs Total Internal Reflection Fluorescence (TIRF) microscopy to illuminate a wide area of the TiO2-coated membrane. A highly parallel system for observing DNA capture events in a uniformly-sized 6×6 nanopore array was experimentally realized.
Controlling the size distribution of polymer-based nanoparticles is a challenging task due to their flexible core and surface structures. To accomplish such as task requires a very precise control at the molecular level. Here, we demonstrate a new approach whereby uniform-sized supramolecular nanoparticles (SNPs) can be reliably generated using a digital microfluidic droplet generator (DMDG) chip. A microfluidic environment enabled precise control over the processing parameters and, therefore, high batch-to-batch reproducibility and robust production of SNPs with a very narrow size distribution could be realized. Digitally adjusting the mixing ratios of the building blocks on the DMDG chip allowed us to rapidly scan a variety of synthesis conditions without consuming significant amounts of reagents. Nearly uniform SNPs with sizes ranging from 35 to 350 nm were obtained and characterized by transmission electron microscopy and dynamic light scattering. In addition, we could fine-tune the surface chemistry of the SNPs by incorporating an additional building block functionalized with specific ligands for targeting cells. The sizes and surface properties of these SNPs correlated strongly with their cell uptake efficiencies. This study showed a feasible microfluidic-assisted SNP production and provided a great means for preparing size-controlled SNP with desired surface ligand coverage.
Load transfer and mechanical strength of reinforced polymers are fundamental to developing advanced composites. This paper demonstrates enhanced load transfer and mechanical strength due to synergistic effects in binary mixtures of nano-carbon/polymer composites. Different compositional mixtures (always 1 wt. % total) of multi-wall carbon nanotubes (MWNTs) and single-layer graphene (SLG) were mixed in polydimethylsiloxane (PDMS), and effects on load transfer and mechanical strength were studied using Raman spectroscopy. Significant shifts in the G-bands were observed both in tension and compression for single as well binary nano-carbon counterparts in polymer composites. Small amounts of MWNT0.1 dispersed in SLG0.9/PDMS samples (subscripts represents weight percentage) reversed the sign of the Raman wavenumbers from positive to negative values demonstrating reversal of lattice stress. A wavenumber change from 10 cm−1 in compression to 10 cm−1 in tension, and an increase in elastic modulus of ~103% was observed for MWNT0.1SLG0.9/PDMS with applied uniaxial tension. Extensive scanning electron microscopy revealed the bridging of MWNT between two graphene plates in polymer composites. Mixing small amounts of MWNTs in SLG/PDMS eliminated the previously reported compressive deformation of SLG and significantly enhanced load transfer and mechanical strength of composites in tension. The orientation order of MWNT with application of uniaxial tensile strain directly affected the shift in Raman wavenumbers (2D band and G-band) and load transfer. It is observed that the cooperative behavior of binary nano-carbons in polymer composites resulted in enhanced load transfer and mechanical strength. Such binary compositions could be fundamental to developing advanced composites such as nano-carbon based mixed dimensional systems.
Epidermal Growth Factor Receptor (EGFR) is a cell surface protein overexpressed in cancerous cells. It is known to be the most common oncongene. EGFR concentration also increases in the serum of cancer patients. The detection of small changes in the concentration of EGFR can be critical for early diagnosis, resulting in better treatment and improved survival rate of cancer patients. This article reports an RNA aptamer based approach to selectively capture EGFR protein and an electrical scheme for its detection. Pairs of gold electrodes with nanometer separation were made through confluence of focused ion beam scratching and electromigration. The aptamer was hybridized to a single stranded DNA molecule, which in turn was immobilized on SiO2 surface between the gold nanoelectrodes. The selectivity of the aptamer was demonstrated by using control chips with mutated non–selective aptamer and with no aptamer. Surface functionalization was characterized by optical detection and two orders of magnitude increase in direct current (DC) was measured when selective capture of EGFR occurred. This represents an electronic biosensor for the detection of proteins of interest for medical applications.
Epidermal Growth Factor Receptor (EGFR); Focused Ion Beam (FIB) milling; electromigration; DNA; Aptamer; Break-junction
Rapid phenotype characterization and identification of cultured cells, which is needed for progress in tissue engineering and drug testing, requires an experimental technique that measures physical properties of cells with sub-micron resolution. Recently, band excitation piezoresponse force microscopy (BEPFM) has been proven useful for recognition and imaging of different types of bacteria in pure water. Here, the BEPFM method is performed for the first time in physiologically-relevant electrolyte media, such as Dulbecco’s phosphate-buffered saline (DPBS) and Dulbecco’s modified Eagle’s medium (DMEM). Distinct electromechanical responses for Micrococcus lysodeikticus (Gram-positive) and Pseudomonas fluorescens (Gram-negative) bacteria are demonstrated in DPBS. The results suggest that mechanical properties of the outer surface coating each bacterium, as well as the electrical double layer around them, are responsible for the BEPFM image formation mechanism in electrolyte media.
bacteria; electromechanical coupling; double layer; PFM; SPM
4(5)-(2-mercaptoethyl)-1H-imidazole-2-carboxamide is a molecule that has multiple hydrogen bonding sites and a short flexible linker. When tethered to a pair of electrodes, it traps target molecules in a tunnel junction. Surprisingly large recognition-tunneling signals are generated for all naturally occurring DNA bases A, C, G,T, and 5-methyl-Cytosine. Tunnel current spikes are stochastic and broadly distributed, but characteristic enough so that individual bases can be identified as a tunneling probe is scanned over DNA oligomers. Each base yields a recognizable burst of signal, the duration of which is controlled entirely by the probe speed, down to speeds of 1 nm/s, implying a maximum off-rate of 3 s-1 for the recognition complex. The same measurements yield a lower bound on the on-rate of ~1 M-1s-1. Despite the stochastic nature of the signals, an optimized multi-parameter fit allows base-calling from a single signal peak with an accuracy that can exceed 80% when a single type of nucleotide is present in the junction, meaning that recognition-tunneling is capable of true single-molecule analysis. The accuracy increases to 95% when multiple spikes in a signal cluster are analyzed.
Atomic force microscope (AFM) probe with a long and rigid needle tip was fabricated and studied for high Q factor dynamic (tapping mode) AFM imaging of samples submersed in liquid. The extended needle tip over a regular commercially-available tapping mode AFM cantilever was sufficiently long to keep the AFM cantilever from submersed in liquid, which significantly minimized the hydrodynamic damping involved in dynamic AFM imaging of samples in liquid. Dynamic AFM imaging of samples in liquid at an intrinsic Q factor of over 100 and an operation frequency of over 200 kHz was demonstrated. The method has the potential to be extended to acquire viscoelastic materials properties and provide truly gentle imaging of soft biological samples in physiological environments.
We demonstrate that a low energy focused electron beam can locally pattern graphene coated with a thin ice layer. The irradiated ice plays a crucial role in the process by providing activated species that locally remove graphene from a silicon dioxide substrate. After patterning the graphene, the ice resist is easily removed by sublimation to leave behind a clean surface with no further processing. More generally, our findings demonstrate that ice-assisted e-beam lithography can be used to pattern very thin materials deposited on substrate surfaces. The procedure is performed in situ in a modified scanning electron microscope. Desirable structures such as nanoribbons are created using the method. Defects in graphene from electrons backscattered from the bulk substrate are identified. They extend several microns from the e-beam writing location. We demonstrate that these defects can be greatly reduced and localised by using thinner substrates and/or gentle thermal annealing.
We report ultrabright, photostable, sub-25 nm nanoparticle agglomerates (suprananoparticles) assembled from a few hundred 3.3 ± 0.9 nm units, each hosting on average a single rhodamine 6G (Rh6G) dye molecule encased in a thin organosilicate cage. These individual Rh6G-doped nanoparticle (DOSNP) units consist of a hydrophobic core containing the dye and an ultrathin, conformal silicate shell modified by CO2 plasma to confer a beneficial “cage effect” as well as surface hydrophilicity. The isolation of the dye within individual DOSNP units in the final 22 ± 5 nm agglomerate avoids dimerization and related spontaneous molecular interactions that otherwise lead to self-quenching in closely co-localized fluorophores. The resulting suprananoparticles are over 200 times brighter than the free Rh6G molecules in the same volume. There is no observable dye leaching, and the labels are 20-fold more resistant to photobleaching than free Rh6G in solution. We demonstrate the attractive features of DOSNPs as labels in bioimaging applications.
High resolution and isolated scanning probe microscopy (SPM) is in demand for continued development of energy storage and conversion systems involving chemical reactions at the nanoscale as well as an improved understanding of biological systems. Carbon nanotubes (CNTs) have large aspect ratios and, if leveraged properly, can be used to develop high resolution SPM probes. Isolation of SPM probes can be achieved by deposited a dielectric film and selectively etching at the apex of the probe. In this paper the fabrication of a high resolution and isolated SPM tip is demonstrated using electron beam induced etching of a dielectric film deposited onto an SPM tip with an attached CNT at the apex.
Carbon nanotubes (CNTs) are well-known as materials for nanoelectronics and show great potential to be used as the sensing element in chemical and biological sensors. Recently, CNTs have been shown to be effective nanofluidic channels and the transport of substances through small diameter CNTs is intrinsically fast, selective, and operates at the single molecule level. It has been shown that the transport characteristics of semiconducting single-walled CNT (SWCNT) field effect transistor (FET) are sensitive to internal water wetting. We report here that the characteristics of semiconducting SWCNT FETs are also sensitive to the concentration, pH and ion type of ionic solution when the electrolytes are inside the CNT. Such sensitivity is not observed at the outside surface of a semiconducting SWCNT. This opens a new avenue for building new types of CNT sensor devices in which the SWCNT concurrently functions as a nanochannel and an electronic detector.
nanofluidics; nanopore; nanochannel; carbon nanotube; CNT FET; chemical and biosensor
In this paper, the use of magnetic nanowires for the study of cellular response to force is demonstrated. High-aspect ratio Ni rods with diameter 300 nm and lengths up to 20 μm were bound to or internalized by pulmonary artery smooth muscle cells (SMCs) cultured on arrays of flexible micropost force sensors. Forces and torques were applied to the cells by driving the nanowires with AC magnetic fields in the frequency range 0.1 – 10 Hz, and the changes in cellular contractile forces were recorded with the microposts. These local stimulations yield global force reinforcement of the cells’ traction forces, but this contractile reinforcement can be effectively suppressed upon addition of a calcium channel blocker, ruthenium red, suggesting the role of calcium channels in the mechanical response. The responsiveness of the SMCs to actuation depends on the frequency of the applied stimulation. These results show that the combination of magnetic nanoparticles and micropatterned, flexible substrates can provide new approaches to the study of cellular mechanotransduction.
Nanoscale drug delivery vehicles have been extensively studied as carriers for cancer chemotherapeutics. However the formulation of platinum chemotherapeutics in nanoparticles has been a challenge arising from their physicochemical properties. There are only few reports describing oxaliplatin nanoparticles. In this study, we derivatized the monomeric units of a polyisobutylene maleic acid copolymer with glucosamine, which chelates trans-1,2-diaminocyclohexane (DACH) platinum (II) through a novel monocarboxylato and O→Pt coordination linkage. At a specific polymer to platinum ratio, the complex self assembled into a nanoparticle, where the polymeric units act as the leaving group, releasing DACH-platinum in sustained pH-dependent manner. Sizing was done using dynamic light scatter and electron microscopy. The nanoparticles were evaluated for efficacy in vitro and in vivo. Biodistribution was quantified using inductive-coupled plasma-atomic absorption spectroscopy (ICP-AAS). The PIMA-GA-DACH-platinum nanoparticle was found to be more active than free oxaliplatin in vitro. In vivo, the nanoparticles resulted in greater tumor inhibition than oxaliplatin (equivalent to 5mg/kg platinum dose) with minimal nephrotoxicity or body weight loss. ICP-AAS revealed significant preferential tumor accumulation of platinum with reduced biodistribution to the kidney or liver following PIMA-GA-DACH-platinum nanoparticle administration as compared with free oxaliplatin. These results indicate that the rational engineering of a novel polymeric nanoparticle inspired by the bioactivation of oxaliplatin results in increased antitumor potency with reduced systemic toxicity compared with the parent cytotoxic. Rational design can emerge as an exciting strategy in the synthesis of nanomedicines for cancer chemotherapy.
Oxaliplatin; Nanoparticle; Cancer
Silica nanowire arrays were grown directly onto plain glass substrates by scalable flame spray pyrolysis of organometallic solutions (hexamethyldisiloxane or tetraethyl orthosilicate). The silicon dioxide films consisted of a network of interwoven nanowires from a few to several hundred nanometres long (depending on the process conditions) and about 20 nm in diameter, as determined by scanning electron microscopy. These films were formed rapidly (within 10–20 s) at high growth rates (ca 11–30 nm s−1) by chemical vapour deposition (surface growth) at ambient conditions on the glass substrate as determined by thermophoretic sampling of the flame aerosol and microscopy. In contrast, on high purity quartz nearly no nanowires were grown while on steel substrates porous SiO2 films were formed. Functionalization with perfluorooctyl triethoxysilane converted the nanowire surface from super-hydrophilic to hydrophobic. Additionally, their hermetic coating by thin carbon layers was demonstrated also revealing their potential as substrates for synthesis of other functional 1D composite structures. This approach is a significant step towards large scale synthesis of SiO2 nanowires facilitating their utilization in several applications.
In the recent past, remarkable advances in nanotechnology have generated nanoparticles of different shapes and sizes, which have been shown to exhibit unique properties suitable for biomedical applications such as cancer therapy and imaging. Obviously, all nanoparticles are not made equal. This becomes evident when we consider their transport behavior under blood flow in microcirculation. In this work, we evaluated the effect of critical physical characteristics such as the particle shape, size and density on a nanoparticle’s tendency to marginate towards the vessel walls in microcirculation using an in vitro model. The wall-deposition of nanoparticles was tested in a fibronectin-coated microfluidic channel at a physiologically relevant flow rate. Different classes of nanoparticles (liposome, metal particles) of different sizes (60–130 nm), densities (1–19 g/mL) and shapes (sphere, rod) displayed significantly different deposition as a result of different margination rates. The smaller-sized and the oblate-shaped particles displayed a favorable behavior as indicated by their higher margination rates. Notably, the particle density showed an even more essential role, as it was observed that the lighter particles marginated significantly more. Since nanoparticles must escape the flow in order to approach the vascular bed and subsequently extravascular components for meaningful interactions, the design of nanoparticles strongly affects their margination, a key factor for their ultimate in vivo effectiveness.
Margination; drifting; nanoparticles; microfluidic channel; tumor microcirculation; nanoparticle shape; nanoparticle size; nanoparticle density
A new form of tunable magnetic resonance imaging agent based on precisely dimensioned cylindrical magnetic nanoshells is introduced. Using top-down prepatterned substrates, the nanoshells are fabricated by exploiting what is usually regarded as a detrimental processing side-effect, namely the redeposition of material back-sputtered during ion-milling. The resulting nanostructures’ well-resolved nuclear magnetic resonance peaks attest to the nanoscale fabrication control and the general feasibility of such sputter redeposition for fabrication of a variety of self-supporting, highly monodisperse nanoscale structures.
In the native tissue, the interaction between cells and the extracellular matrix (ECM) is essential for cell migration, proliferation, differentiation, mechanical stability, and signaling. It has been shown that decellularized ECMs can be processed into injectable formulations, thereby allowing for minimally invasive delivery. Upon injection and increase in temperature, these materials self-assemble into porous gels forming a complex network of fibers with nano-scale structure. In this study we aimed to examine and tailor the material properties of a self-assembling ECM hydrogel derived from porcine myocardial tissue, which was developed as a tissue specific injectable scaffold for cardiac tissue engineering. The impact of gelation parameters on ECM hydrogels has not previously been explored. We examined how modulating pH, temperature, ionic strength, and concentration affected the nanoscale architecture, mechanical properties, and gelation kinetics. These material characteristics were assessed using scanning electron microscopy, rheometry, and spectrophotometry, respectively. Since the main component of the myocardial matrix is collagen, many similarities between the ECM hydrogel and collagen gels were observed in terms of the nanofibrous structure and modulation of properties by altering ionic strength. However, variation from collagen gels was noted for the gelation temperature along with varied times and rates of gelation. These discrepancies when compared to collagen are likely due to the presence of other ECM components in the decellularized ECM based hydrogel. These results demonstrate how the material properties of ECM hydrogels could be tailored for future in vitro and in vivo applications.
decellularization; extracellular matrix; injectable; hydrogel; biomaterial
Exogenous cell therapy aims to replace/repair diseased or dysfunctional cells and promises to revolutionize medicine by restoring tissue and organ function. To develop effective cell therapy, the location, distribution and long-term persistence of transplanted cells must be evaluated. Nanoparticle (NP) based imaging technologies have the potential to track transplanted cells non-invasively. Here we summarize the most recent advances in NP-based cell tracking with emphasis on (1) the design criteria for cell tracking NPs, (2) protocols for cell labeling, (3) a comparison of available imaging modalities and their corresponding contrast agents, (4) a summary of preclinical studies on NP-based cell tracking and finally (5) perspectives and future directions.
Stimuli-responsive materials are promising as smart materials for a range of applications. In this work, a photocrosslinkable, thermoresponsive macromer was electrospun into fibrous scaffolds containing gold nanorods (AuNRs). The resulting fibrous nanocomposites composed of poly (N-isopropylacrylamide-co-polyethylene glycol acrylate) (PNPA) and PEGylated AuNRs were crosslinked and swollen in water. AuNRs strongly absorb in the near infrared (NIR) region to generate heat and triggered the fiber thermal transition upon NIR exposure. During the thermal transition, scaffolds collapsed both macroscopically and microscopically, with individual fibers deswelling and pulling together. Exposure to a 1.1 W NIR laser decreased the diameter of swollen fibers by 34.7% from 1332 ± 193.3 to 868.9 ± 168.3 nm, and increased fiber density 116% from 209.5 ± 26.34 to 451.9 ± 23.68 fibers/mm. This transition was dependent on the incorporation of the AuNRs, and was utilized to trigger the release of encapsulated proteins from the nanocomposite fiber mats. The expulsion of water from fibers upon NIR exposure caused the release rate of incorporated protein to increase great than 10-fold, from 0.038 ± 0.052 without external stimulus to 0.462 ± 0.227 μg protein/mg polymer/min with NIR exposure. These results suggest that light-responsive fibrous nanocomposites can be utilized in applications such as drug delivery.
As applications of nanoparticles in medical imaging and biomedicine rapidly expand, the interactions of nanoparticles with living cells have become an area of active interest. For example, intracellular trafficking of nanoparticles – an important part of cell-nanoparticle interaction, has been well studied using plasmonic nanoparticles and optical or optics-based techniques due to the change in optical properties of the nanoparticle aggregates. However, magnetic nanoparticles, despite their wide range of clinical applications, do not exhibit plasmonic-resonant properties and therefore their intracellular aggregation cannot be detected by optics-based imaging techniques. In this study, we investigated the feasibility of a novel imaging technique – pulsed magneto-motive ultrasound (pMMUS), to identify intracellular trafficking of endocytosed magnetic nanoparticles. In pulsed magneto-motive ultrasound imaging a focused, high intensity, pulsed magnetic field is used to excite the cells labeled with magnetic nanoparticles, and ultrasound imaging is then used to monitor the mechanical response of the tissue. We demonstrated previously that clusters of magnetic nanoparticles amplify the pMMUS signal in comparison to signal from individual nanoparticles. Here we further demonstrate that pMMUS imaging can identify interaction between magnetic nanoparticles and living cells, i.e. intracellular aggregation of nanoparticles within the cells. The results of our study suggest that pMMUS imaging can not only detect the presence of magnetic nanoparticles but also provides information about their intracellular trafficking non-invasively and in real-time.
Pulsed magneto-motive ultrasound imaging; superparamagnetic iron-oxide nanoparticles; macrophage; endocytosis; intracellular trafficking
Gold nanoshells have been intensively investigated and applied to various biomedical fields because of their flexible optical tunability and biological compatibility. They hold great potential to serve as luminescent contrast agents excitable with near infrared (NIR) lasers. In this paper, we describe the development of nanoshells with a peak of plasmon resonance at 800 nm and their subsequent use for in vivo blood vessel imaging using two-photon excitation microscopy at an excitation wavelength of 750 nm. We were able to image single nanoshell particles in blood vessels and generate optical contrast for blood vessel structure using luminescent signals. These results confirm the feasibility of engineering nanoshells with controlled optical properties for single-particle-based in vivo imaging.
Gold nanoshells; Luminescent; Two-photon Excitation Microscopy