Properties Of Single-walled Carbon Nanotubes Research Articles

Molecular Dynamics Simulations of Effects of Geometric Parameters and Temperature on Mechanical Properties of Single-Walled Carbon Nanotubes

Carbon nanotubes (CNTs) are considered an advanced form of carbon. They have superior characteristics in terms of mechanical and thermal properties compared to other available fibers and can be used in various applications, such as supercapacitors, sensors, and artificial muscles. The properties of single-walled carbon nanotubes (SWNTs) are significantly affected by geometric parameters such as chirality and aspect ratio, and testing conditions such as temperature and strain rate. In this study, the effects of geometric parameters and temperature on the mechanical properties of SWNTs were studied by molecular dynamics (MD) simulations using the Large-scaled Atomic/Molecular Massively Parallel Simulator (LAMMPS). Based on the second-generation reactive empirical bond order (REBO) potential, SWNTs of different diameters were tested in tension and compression under different strain rates and temperatures to understand their effects on the mechanical behavior of SWNTs. It was observed that the Young’s modulus and the tensile strength decreases with increasing SWNT tube diameter. As the chiral angle increases, the tensile strength increases, while the Young’s modulus decreases. The simulations were repeated at different temperatures of 300 K, 900 K, 1500 K, 2100 K and different strain rates of 1 × 10−3/ps, 0.75 × 10−3/ps, 0.5 × 10−3/ps, and 0.25 × 10−3/ps to investigate the effects of temperature and strain rate, respectively. The results show that the ultimate tensile strength of SWNTs increases with increasing strain rate. It is also seen that when SWNTs were stretched at higher temperatures, they failed at lower stresses and strains. The compressive behavior results indicate that SWNTs tend to buckle under lower stresses and strains than those under tensile stress. The simulation results were validated by and consistent with previous studies. The presented approach can be applied to investigate the properties of other advanced materials.

Novel synthesis of thermoresponsive single-walled carbon nanotubes/poly(N-isopropylacrylamide) hybrids

Poly(N-isopropylacrylamide) (PNIPAM) is one of the most well studied thermoresponsive polymers and its microgels undergo a reversible volume phase transition (VPT) at temperatures close to that of the human body. Coupling this property with the unique optical properties of single-walled carbon nanotubes (SWCNT) in the near infrared (NIR) leads to interesting nanohybrids that could be used as multi-responsive sensors/actuators for biological applications.We show the synthesis of thermoresponsive SWCNT/PNIPAM hybrids using two different non-covalent strategies, preserving the nanotube optical properties such as fluorescence. The first strategy involves the dispersion of the SWCNT in water with sodium dodecyl sulfate (SDS), and subsequent in situ synthesis of PNIPAM microgels inside the SDS coatings around the nanotubes. The second strategy starts with modifying the nanotubes with a pyrene derivative, which in turn is used as the starting point for the in situ polymerization of the PNIPAM microgels, thus ensuring that the polymer grows around the nanotubes. In both cases, we obtain hybrids showing a phase transition at temperatures close to that of the human body, with the absorption and fluorescence spectra of the hybrids in the NIR changing in response to the changing dielectric environment. These systems could be used as actuators/sensors in biological systems.

Structural, Electrical, and Optical Properties of Single-Walled Carbon Nanotubes Synthesized through Floating Catalyst Chemical Vapor Deposition.

Single-walled carbon nanotube (SWCNT) thin films were synthesized by using a floating catalyst chemical vapor deposition (FCCVD) method with a low flow rate (200 sccm) of mixed gases (Ar and H2). SWCNT thin films with different thicknesses can be prepared by controlling the collection time of the SWCNTs on membrane filters. Transmission electron microscopy (TEM) showed that the SWCNTs formed bundles and that they had an average diameter of 1.46 nm. The Raman spectra of the SWCNT films suggested that the synthesized SWCNTs were very well crystallized. Although the electrical properties of SWCNTs have been widely studied so far, the Hall effect of SWCNTs has not been fully studied to explore the electrical characteristics of SWCNT thin films. In this research, Hall effect measurements have been performed to investigate the important electrical characteristics of SWCNTs, such as their carrier mobility, carrier density, Hall coefficient, conductivity, and sheet resistance. The samples with transmittance between 95 and 43% showed a high carrier density of 1021-1023 cm-3. The SWCNTs were also treated using Brønsted acids (HCl, HNO3, H2SO4) to enhance their electrical properties. After the acid treatments, the samples maintained their p-type nature. The carrier mobility and conductivity increased, and the sheet resistance decreased for all treated samples. The highest mobility of 1.5 cm2/Vs was obtained with the sulfuric acid treatment at 80 °C, while the highest conductivity (30,720 S/m) and lowest sheet resistance (43 ohm/square) were achieved with the nitric acid treatment at room temperature. Different functional groups were identified in our synthesized SWCNTs before and after the acid treatments using Fourier-Transform Infrared Spectroscopy (FTIR).

Shielding Effects Provide a Dominant Mechanism in J-Aggregation-Induced Photoluminescence Enhancement of Carbon Nanotubes.

The unique photophysical properties of single-walled carbon nanotubes (SWCNTs) exhibit great potential for bioimaging applications. This led to extensive exploration of photosensitization methods to improve their faint shortwave infrared (SWIR) photoluminescence. Here, we report the mechanisms of SWCNT-assisted J-aggregation of cyanine dyes and the associated photoluminescence enhancement of SWCNTs in the SWIR spectral region. Surprisingly, we found that excitation energy transfer between the cyanine dyes and SWCNTs makes a negligible contribution to the overall photoluminescence enhancement. Instead, the shielding of SWCNTs from the surrounding water molecules through hydrogen bond-assisted macromolecular reorganization of ionic surfactants triggered by counterions and the physisorption of the dye molecules on the side walls of SWCNTs play a primary role in the photoluminescence enhancement of SWCNTs. We observed 2 orders of magnitude photoluminescence enhancement of SWCNTs by optimizing these factors. Our findings suggest that the proper shielding of SWCNTs is the critical factor for their photoluminescence enhancement, which has important implications for their application as imaging agents in biological settings.

Enhancing thermoelectric performance of single-walled carbon nanotube films by poly(styrene sulfonate acid) dispersing and sequential base treatment

Despite single-walled carbon nanotubes (SWCNTs) have attracted great interest for thermoelectric (TE) conversion, the strong van der Waals forces between SWCNTs cause them to aggregate into bundles with poor dispersibility, which dramatically deteriorates the charge carrier transport, and thereby induces low electrical conductivity and TE power factor. Herein, we report a facile and efficient approach to enhance TE performance of SWCNTs via the addition of poly(styrene sulfonic acid) (PSSH) and sequential base treatment. PSSH is served as a dispersant and dopant to improve the dispersibility of SWCNTs and facilitate charge carrier conduction, contributing to high electrical conductivity of 3749 ± 122 S cm−1 and power factor of 117.7 ± 3.4 μW m−1 K−2 for 20 wt% PSSH/SWCNT composite film. Further base treatment induces partial removal of insulative PSSH and de-doping effect of SWCNTs, which decreases the barriers between adjacent nanotubes junctions and modulates charge carrier transport to synergistically optimize the electrical conductivity and Seebeck coefficient. With fine-tuning base treatment temperature, the PSSH/SWCNT composite film reaches highest power factor of 160.6 ± 7.9 μW m−1 K−2, higher than pristine SWCNTs of 70.2 ± 4.4 μW m−1 K−2. This work demonstrates the feasibility of this approach to boost the TE properties of SWCNTs, exhibiting potential application for high performance renewable energy harvesting.

Functionalized single‐walled carbon nanotubes electrochemical aptasensor for human epidermal growth factor receptor 2 (HER2) breast cancer detection

AbstractIn this study, we present a novel functionalized single‐walled carbon nanotubes (SWCNTs) electrochemical aptasensor designed for the detection of HER2 breast cancer. The well‐organized SWCNTs were attained through a concentration‐based and single‐step ultrasonication‐directed assembly methodology, resulting in a well‐dispersed state and a thin, even coating on the transducer substrate. Well‐organized SWCNTs were systematically analyzed through X‐ray diffraction spectroscopy (XRD), Fourier transforms infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy and elemental mapping (TEM‐mapping) and X‐ray photoelectron spectroscopy (XPS) confirmed the superior quality and organization of the SWCNTs. Furthermore, the electrochemical sensor exhibited outstanding performance, showcasing the potential of the SWCNTs as an ideal material for such applications, including their anticancer activity against human breast cancer cells. The single‐step ultrasonication‐directed assembly approach not only enhances the electrochemical properties of SWCNT but holds promise as a potentially as versatile substrate for immobilizing enzymes, antibodies, and DNA. This versatility opens up opportunities for the creation of highly functional biosensors with broad medical applications. Overall, our findings highlight the scientific significance of SWCNTs in advancing electrochemical sensing technologies and their potential in combating breast cancer.

High figure-of-merit of single-walled carbon nanotubes films with metallic type conduction

Carbon nanotubes are promising candidates for thermoelectric power generation because of their one-dimensionality mediated high Seebeck coefficient, high electrical conductivity with added advantages of flexibility, light weight, and scalability. We report the temperature-dependent thermoelectric properties of single-walled carbon nanotube (SWCNTs) films. The SWCNTs films exhibit p-type metallic conduction with high Seebeck coefficient (∼69.5 μVK−1) and moderate electrical conductivity (∼76 Scm−1). The films exhibit low thermal conductivity (∼0.1 Wm−1 K−1) due to phonon scattering at the interjunction region. The synergetic combination of thermoelectric properties resulted in a high figure-of-merit of ∼0.11 at 305 K. A flexible thermoelectric generator based on SWCNTs films mounted on a curved hot surface exhibited an output of 17 mV and 54 μA under a small temperature gradient of 10 K. The present work provides possible avenues for developing wearable SWCNTs based thermoelectric power generation modules for harvesting body heat.

Influence of temperature and nonlinear damping on mechanical properties of single-walled carbon nanotubes

Existing experiments have demonstrated that the nonlinear terms caused by damping impact the dynamical behaviors of single-walled carbon nanotubes (SWCNTs) significantly. Although, it is still an open question to precisely describe the vibrations of SWCNTs with the combined effects, such as the scale effect, the thermal effect, and the nonlinear damping. In the present research, we proposed a new nonlocal nonlinear Euler-Bernoulli theory to model an SWCNT's mechanical properties with the combined effect of three factors. A (10,10)SWCNT was brought to demonstrate the influence of the three factors on the elastic buckling and the forced bending vibrations. The results indicate for slender SWCNTs that the combined effects have some more remarkable impacts on nonlinear mechanical behaviors than individual factors, and dramatic deviation may emerge in the vibrations once nonlinear damping terms are absent.

Modulation of Carbon Nanotube Electronic Structure by Grain Boundary Defects in RbI on Au(111).

The electronic properties of single-walled carbon nanotubes (SWCNTs) are known to be highly sensitive to environmental effects. Here, we use scanning tunneling microscopy and spectroscopy to investigate the electronic properties of SWCNTs deposited on RbI monolayer films grown on Au(111). We find that grain boundary defects in RbI monolayers cause the appearance of spatially confined localized states in the SWCNTs. Our density functional theory calculations show that grain boundary defects in RbI/Au(111) produce a stabilizing electrostatic potential caused by reduced coordination of iodine atoms at the RbI grain boundary. The presented results may offer insights into the performance of devices involving transport through SWCNTs subjected to external electrostatic disorder.

Narrow band absorption and sensing properties of single-walled carbon nanotubes at terahertz metasurface

Due to their excellent electrical and optical properties, carbon nanotubes have unique application prospects in the field of optoelectronics. In this work the vacuum self-assembly method is used to obtain an isotropic single-walled carbon nanotube film with a thickness of 2 μm by the dispersion of single-walled carbon nanotube powder through vacuum filtration; on the basis of extracting the dielectric parameters of the thin film in a range from 0.4 to 2.0 THz, a novel terahertz metasurface narrowband absorber based on single-walled carbon nanotube films is designed and prepared. This metasurface absorber is composed of square and I-shaped narrow slot resonators. The experimental and simulation results show that the proposed terahertz metasurface absorber exhibits four distinct resonance absorption peaks at 0.65, 0.85, 1.16, and 1.31 THz, respectively, achieving a perfect absorption of up to 90%. The absorption mechanism of this novel multi band terahertz metasurface is elucidated by using the theory of multiple reflection interference. By setting analytical layers with different refractive indices on the surface of metasurface device, the sensing performance of metasurface acting as refractive index sensor is studied in depth. The research results indicate that this new type of metasurface absorber has high sensitivity for refractive index sensing, providing new ideas and solutions for further developing carbon-based new terahertz metasurface absorbers.

Spatiotemporal Tracking of Near‐Infrared Fluorescent Single‐Walled Carbon Nanotubes in C. Elegans Nematodes Confined in a Microfluidics Platform

AbstractCaenorhabditis elegans (C. elegans) nematodes are a powerful model organism for diverse biological and biomedical studies, benefiting from their genetic similarities to humans, small size, and transparency. However, fluorescence imaging of C. elegans can be challenging due to the strong autofluorescence in the visible range, which obscures the signal of common fluorescent proteins or dyes. Single‐walled carbon nanotubes (SWCNTs) fluoresce in the near‐infrared (NIR) range, where there is no autofluorescence background. Herein, a platform is developed for in vivo NIR imaging of C. elegans gastrointestinal tract using biocompatible SWCNTs functionalized by single‐stranded DNA or phospholipid‐polyethylene glycol (PEG). The SWCNTs serve as fluorescent tracking probes within the worm gut, following internalization along with food intake. A microfluidic confinement device is employed to ensure an anesthetics‐free feeding environment, allowing spatiotemporal control over the SWCNTs intake imaging. Furthermore, improvements in spectral colocalization, real‐time detection of intracorporeal SWCNT dynamics, and digestive trajectory tracking are demonstrated. Owing to the unique optical properties of SWCNTs and the confinement of the worms in the microfluidics system, the proposed platform facilitates advanced in vivo imaging of C. elegans in both the visible and NIR regions, opening numerous avenues for advancing research of C. elegans and other microscopic model organisms.

Effects of copper metal organic decomposition ink on properties of single-walled carbon nanotube based flexible transparent electrodes

The effects of copper metal organic decomposition (Cu MOD) ink on the electrical and mechanical properties of SWCNT-based flexible transparent electrodes were investigated. In particular, we designed and demonstrated Cu MOD ink as bonding agents between oxidized SWCNT (Ox-SWCNT) and the polyethylene terephthalate (PET) substrate. PET substrates were surface-treated via plasma etching, and ultraviolet/ozone (UV/O3) treatment was conducted for enhancing the dispersion of SWCNTs. Subsequently, spray coating of numerous times with Ox-SWCNT dispersion and once with Cu MOD ink was applied to the PET substrates at low temperatures. In this way, a robust, flexible, and transparent Ox-SWCNT/Cu@PET composite electrode was fabricated. The as-prepared Ox-SWCNT/Cu@PET composite electrode exhibited good properties, with a sheet resistance of 483.9 Ω/sq and transmittance of 82.1%. Even after 10000 bending cycles and 100 peel-off times, the resistance was only increased by factors of 1.07 and 1.12, respectively, confirming good mechanical robustness. In addition, the electrode exhibited excellent environmental stability; its electrical resistance was only increased by a factor of 1.35 after subjected to harsh environmental conditions (85 °C, 85% relative humidity) for 48 h. These results indicate that the Ox-SWCNT/Cu@PET composite electrodes are promising for wide application as FTCEs.

Boosting CO-based synthesis of single-walled carbon nanotubes with hydrogen

Aerosol (floating catalyst) chemical vapor deposition method based on CO disproportionation (the Boudouard reaction) is one of the most promising techniques for the synthesis of single-walled carbon nanotubes (SWCNTs), especially in the form of thin films. However, despite its advantages (i.e., high quality of nanotubes, absence of double- or multi-walled nanotubes, and high controllability of the process), synthesis based on CO disproportionation fails to provide high-yield production. In this work, we examined the effect of hydrogen, admixed to the CO atmosphere as a growth promoter, on the synthesis and properties of SWCNTs. Using optical spectroscopy techniques, conductivity tests, TEM and SEM analysis, and thermodynamic calculations, we revealed hydrogen affects both catalyst activation and nanotube growth. We found a positive H2 effect in two different temperature regimes: the yield increased by a factor of ∼15 at a low temperature (880 °C), which, after doping, led to one of the lowest ratios of the equivalent sheet resistance (R90) and yield (i) and SWCNT lengthening by a factor of 2.4 leading to a 3-fold decrease in an R90 coupled with a noticeable increase in the yield at a high temperature (1000 °C) (ii). We believe the presented results are fruitful for the fundamental understanding of the mechanism for nanotube growth and practical opportunity to fine-tune the production rate of SWCNT films.

Buckling behavior of multilayer cylindrical shells composed of functionally graded nanocomposite layers under lateral pressure in thermal environments

In this study, the stability behavior of multilayer cylindrical shells made of functionally graded nanocomposite layers (FG-NCLs) subjected to the lateral pressure in thermal environments is investigated. It is postulated that nanocomposite layers forming layered cylindrical shells are made of single-walled carbon nanotube (SWCNT)-reinforced polymers that have four types of profiles based on the uniform and linear distributions of mechanical properties. The material properties of SWCNTs are assumed to be dependent on location as well as temperature and are obtained from molecular dynamics simulations. The governing equations are derived as partial differential equations within shear deformation theory (SDT) and solved in a closed form, using the Galerkin procedure, to determine the lateral critical pressure (LCP) in thermal environments. The numerical representations relate to the buckling behavior of multilayer cylindrical shells made of functionally graded nanocomposite layers under the uniform lateral pressure for different CNT patterns and temperatures within SDT and Kirchhoff-Love theory (KLT).

Nitrogen-Doped Single-Walled Carbon Nanotubes by Floating-Catalyst CVD Process

Due to the properties of single-walled carbon nanotube (SWCNT), thin film SWCNTs have been used for many versatile applications. Direct synthesis of the nanotube films with desired electronic structures without prerequisite of post treatment process then becomes one important step. Here, we present the synthesis of nitrogen-doped SWCNTs by floating-catalyst chemical vapor deposition process. With low nitrogen level incorporated into the sp2 carbon network, substitutional and pyridinic nitrogens become predominance. The electronic structure of N-doped SWCNT film could be changed into n-type doping. The localized structures of carbon and nitrogen bonding environments were also revealed by x-ray absorption spectroscopy. The formation of p-n junction was also obtained from the I-V characteristic of N-doped SWCNT heterojunction diode revealing n-type behavior of the sample.

Detection of the Inflammatory Cytokine IL-6 in Complex Human Serum Samples Via Rational Nanotube Surface Passivation Screening

In recent years, biosensors have emerged as a tool with strong potential in medical diagnostics. Single-walled carbon nanotube (SWCNT) based optical nanosensors have notably garnered interest due to the unique characteristics of their near-infrared fluorescence emission, including tissue transparency, photostability, and various chiralities with discrete absorption and fluorescence emission bands.The optoelectronic properties of SWCNT are sensitive to the surrounding environment, which makes them suitable for highly selective biosensing. Single-stranded (ss) DNA-wrapped SWCNTs have been reported as optical nanosensors for cancers and metabolic diseases. However, given the complexity of the human protein environment, non-specific interactions occur between SWCNT-based nanosensors and proteins. This inevitably leads to compromised selectivity of SWCNT-based nanosensors unless strategies for prevention are developed and employed.Non-covalent passivation of the ssDNA-SWCNT surface is reported as an excellent strategy to improve nanosensor selectivity in complex biological settings without causing irreversible changes to the optical properties of SWCNTs. Emerging studies have explored and successfully shown passivation using proteins and phospholipids. However, a systematic comparative study of passivating agents has not been done. In this work, we explore and compare the efficacy of select proteins, polymers, and surfactants as passivating agents.We, therefore, sought to evaluate various potential SWCNT surface passivation agents among broad classes of biomolecules and biomaterials. In the category of protein, Bovine serum albumin, dry-fat milk powder, and casein were selected due to their wide application to improve immunoassay selectivity. In the class of polymers, we selected 1 anionic and 2 cationic polymers, namely, polyethylene glycol, poly-ethylene imine, and poly-l-lysine. From surfactants, 2 phospholipids and 1 anionic surfactant: ammonium salt of 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(polyethylene glycol)-2000] (16:0 PE2000PEG); 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[amino(polyethylene glycol)-2000] (DSPE PEG phospholipids), and sodium dodecylbenzene sulfonate (SDBS) were selected.We analyzed the ability of all passivation agents to screen the non-specific interactions of ssDNA- SWCNTs in the presence of fetal bovine serum using fluorescence spectroscopy. The non-specific interactions between ssDNA-SWCNTs and proteins lead to a reorientation of the dipole moments and charge transfer in the corona phase around ssDNA-SWCNTs, leading to modulation in the center wavelength of the fluorescence as well as absorption peaks. We hence hypothesized that smaller changes in the center wavelength of the fluorescence peaks of passivated ssDNA-SWCNTs in presence of serum, lead to higher screening effect of the passivation agent towards non-specific interactions. We found that the most successful candidates were poly-L-lysine, polyethylene imine, dry-fat milk powder, and casein, in that order. Moreover, the ability to screen the interference was retained over a period of at least 3 hours. We further experimented with the four different mass ratios of passivating agents to ssDNA-SWCNTs and found that the mass ratio 50:1 for passivating agents: ss-DNA SWCNTs was most optimal.We confirmed the strength of passivation using absorption spectroscopy. We hypothesized that stronger surface saturation of the SWCNT-TAT6 is by a passivating agent in buffer conditions leads to a larger shift in the absorption peaks. We found that for the above successful passivation agents, the order of passivation strength followed the same trend as the screening abilities of the successful passivating agents, supporting this mechanistic hypothesis.Then, we evaluated an antibody-conjugated ssDNA-SWCNT nanosensor for the pro-inflammatory cytokine IL-6 with our successful passivation agents. We assessed the ability of the passivation agents to confer selective detection of IL-6 detection in clinical serum samples from patients with atherosclerosis and rheumatoid arthritis, both anticipated to have high IL-6 levels. Samples were compared to healthy human serum sample controls. We validated SWCNT fluorescence response with traditional immunoassays (ELISA).We expect this study to provide rational strategies to screen interferences from non-specific interactions and improve the selectivity of the SWCNT-based optical nanosensors for in vivo applications.

(Invited) Discussion on Preparation of Single-Walled Carbon Nanotubes for High-Performance Electronics

The unique structure and outstanding properties of single-walled carbon nanotubes (SWCNTs) make them top candidates for future high-performance electronics. Highly pure (>99.9999%) and dense (>125tubes/micron) SWCNTs are desired to present performance surpassing silicon-based devices and chips. Material preparation is the prerequisite of electronic applications. Selective synthesis, purification/sorting, and controlled assembling are procedures that associated with pathways to obtain SWCNT materials for high-performance electronics. However, it’s still not clear that what is the feasible strategy. More discussions and critical thinkings are in urgent need. I will try to review some of the recent developments in the field and discuss the possible directions in future study.

(Invited) Anisotropy in Complex Refractive Index Spectra of Single-Chirality-Enriched Carbon Nanotube Films

Toward macroscopic applications of exceptional optical properties of single-walled carbon nanotubes (SWCNTs), we reported in-plane complex refractive index spectra [1] of various single-chirality-enriched [2] SWCNTs films in which the SWCNTs are mostly oriented in two dimensions parallel to the film surface. However, in order to describe the anisotropic optical responses of such SWCNT films for incident light from all the directions, out-of-plane refractive index spectra are also required, in addition to the in-plane ones. We will report complete broadband complex refractive index spectra of single-chirality-enriched SWCNTs films for in-plane and out-of-plane optical responses. [1] T. Nishihara, A. Takakura, M. Shimasaki, K. Matsuda, T. Tanaka, H. Kataura, and Y. Miyauchi, Nanophotonics 11, 1011 (2022). [2] Y. Yomogida, T. Tanaka, M. Zhang, M. Yudasaka, X. Wei, and H. Kataura, Nat. Commun. 7, 12056 (2016).

(Invited) Near-Infrared Photoluminescent Nanosensors for In Vivo Pharmacology and Inflammation Monitoring

Rapid, minimally-invasive in situ detection of analytes in vivo remains a goal to study inflammatory signaling molecules and pharmacology of therapeutics. Towards this end, we are using the near-infrared photoluminescent properties of single-walled carbon nanotubes (SWCNT) to design sensors for use in live mice. The photostable, environmental-responsive, tissue-transparent emission of SWCNT is ideal for this application. Therefore, we are working toward in vivo analyte monitoring through a simple injection of hydrogel-encapsulated SWCNT sensors to localize signal to specific sites in the body. We are incorporating machine learning-based approaches coupled with molecular recognition to develop multiplexed SWCNT sensors for several inflammatory signaling proteins (cytokines) as well as chemotherapeutic agents. We are performing high-throughput near-infrared plate reader-based measurements to screen sensor responses prior to in vivo evaluation and testing with patient samples. We anticipate in vivo evaluation to lead to real-time understanding of inflammatory disease biology and drug pharmacology in the short-term, while long-term applications may include minimally-invasive and rapid clinical diagnostic development.

Stochastic Formation of Quantum Defects in Carbon Nanotubes.

Small perturbations in the structure of materials significantly affect their properties. One example is single wall carbon nanotubes (SWCNTs), which exhibit chirality-dependent near-infrared (NIR) fluorescence. They can be modified with quantum defects through the reaction with diazonium salts, and the number or distribution of these defects determines their photophysics. However, the presence of multiple chiralities in typical SWCNT samples complicates the identification of defect-related emission features. Here, we show that quantum defects do not affect aqueous two-phase extraction (ATPE) of different SWCNT chiralities into different phases, which suggests low numbers of defects. For bulk samples, the bandgap emission (E11) of monochiral (6,5)-SWCNTs decreases, and the defect-related emission feature (E11*) increases with diazonium salt concentration and represents a proxy for the defect number. The high purity of monochiral samples from ATPE allows us to image NIR fluorescence contributions (E11 = 986 nm and E11* = 1140 nm) on the single SWCNT level. Interestingly, we observe a stochastic (Poisson) distribution of quantum defects. SWCNTs have most likely one to three defects (for low to high (bulk) quantum defect densities). Additionally, we verify this number by following single reaction events that appear as discrete steps in the temporal fluorescence traces. We thereby count single reactions via NIR imaging and demonstrate that stochasticity plays a crucial role in the optical properties of SWCNTs. These results show that there can be a large discrepancy between ensemble and single particle experiments/properties of nanomaterials.