Suspended Single-walled Carbon Nanotubes Research Articles

Ratiometric Normalization of Near-Infrared Fluorescence in Defect-Engineered Single-Walled Carbon Nanotubes for Cholesterol Detection.

Ratiometric probing of analytes presents a substantial advancement in molecular recognition, offering self-calibrating signals that enhance the measurement accuracy and reliability. We present a dual-emitting probe based on (6,5) chirality-enriched single-walled carbon nanotubes (SWCNTs) with oxygen defects for cholesterol (Chol) detection using ratiometric fluorescence readouts. The interaction with Chol induced significant intensity variations in the E11 and E11* emission peaks of oxygen defect-induced SWCNTs, giving rise to ratiometric fluorescence changes. The sensitivity of these probes toward Chol in water and serum was 0.28 ± 0.01 and 0.72 ± 0.05 μM, respectively, which is comparable to that of common gold standards for cholesterol detection used in clinical samples. By utilizing ratiometric readouts, our approach enhanced selectivity over numerous competing analytes, including amino acids, sugars, cations, anions, proteins, steroid hormones, surfactants, and phospholipids. Mechanistic investigations revealed that Chol detection by defect-integrated SWCNTs was facilitated by Chol incorporation within micelles formed by sodium cholate, the surfactant dispersant used for the SWCNT suspension. Oxygen defects played a crucial role by directly interacting with Chol. This strategy employing defect-integrated dual-peak NIR-emitting SWCNTs as sensors for Chol in aqueous and serum environments not only enables background-free detection of biologically relevant analytes but also advances biosensing using SWCNTs through tailored surface functionalization and advanced read-out concepts.

Size Matters in Conjugated Polymer Chirality-Selective SWCNT Extraction.

Carbon-based nanomaterials have catalyzed breakthroughs across various scientific and engineering disciplines. The key to unlocking a new generation of tailor-made nanomaterials based on single-walled carbon nanotubes (SWCNTs) lies in the precise sorting of raw material into individual chiralities, each possessing unique properties. This can be achieved using conjugated polymer extraction (CPE), but to a very limited extent since the process generates only a few chirality-enriched suspensions. Therefore, it is imperative to comprehend the mechanism of the wrapping of SWCNTs by polymers to unleash CPE's full potential. However, the lack of a diverse palette of chirality-selective polymers with varying macromolecular parameters has hindered a comprehensive understanding of how the nature of the polymer affects the performance and selectivity of SWCNT isolation. To address this gap, multiple batches of such polymers are synthesized to elucidate the impact of molecular weight and dispersity on the purity and concentrations of the generated SWCNT suspensions. The obtained results explain the inconsistent outcomes reported in the literature, greatly improving the application potential of this promising SWCNT sorting approach. Concomitantly, the discovered significant influence of the macromolecular characteristics of conjugated polymers on the SWCNT isolation efficacy sheds considerable insight into the unresolved mechanism of this sorting technique.

Heat transfer analysis of single-walled carbon nanotubes in Ellis's fluid model: Comparative study of uniform and non-uniform channels

BackgroundThe essential features of nanoparticles in nanofluids play a vital role in nanotechnology. The nanosized particles of carbon are known as carbon nanotubes (CNTs). The properties of CNT like thermal and electrical conductivity, lightweight, flexibility, and mechanical strength support its applications in the medical field i.e., diagnostic and therapeutic agents (drugs, antibodies, biosensors, vaccines etc.). These are not only excellent vehicles for drug delivery and gene therapies but also useful in biosensor diagnostic, enantiomer separation of chiral drugs, tissue regeneration, extraction, and analysis of pollutants and drugs. ObjectiveThe focus of this research work is to open the essential features of peristaltic transport of Ellis nanofluid through uniform and non-uniform channels with suspension of single-walled carbon nanotubes (SWCNT). The consideration of blood flow with SWCNT under the effects of heat generation and electroosmosis is one of the key factors of this investigation. MethodThe complexity of the system is reduced with the implementation of the concepts of longer wavelength and lower Reynolds number. The governing two-dimensional equations are simplified by introducing dimensionless variables and parameters. The mathematical tool “MATHEMATICA 13.3” is used to compute the exact solution and graphical demonstration of velocity, temperature, heat transfer rate, and streamlines. Computational resultsIt is noticed that velocity, temperature, and heat transfer rate are prominent in non-uniform channels as compared to uniform channels. Similarly, the size and number of boluses during the trapping phenomenon increase or decrease quickly in non-uniform channels. The volumetric addition of SWCNT diminishes the velocity and temperature while the heat transfer rate is enhanced in both channels but in the nonuniform channel effects are more prominent. ApplicationsThis study explores the applications of SWCNT in medical fields like angiography, angioplasty, and cancer therapy. NoveltyThe present study is new and has never been addressed before.

Enhanced Thermal Conductivity of Single-Walled Carbon Nanotube with Axial Tensile Strain Enabled by Boron Nitride Nanotube Anchoring.

Thermal conductivity measurements are conducted by optothermal Raman technique before and after the introduction of an axial tensile strain in a suspended single-walled carbon nanotube (SWCNT) through end-anchoring by boron nitride nanotubes (BNNTs). Surprisingly, the axial tensile strain (<0.4 %) in SWCNT results in a considerable enhancement of its thermal conductivity, and the larger the strain, the higher the enhancement. Furthermore, the thermal conductivity reduction with temperature is much alleviated for the strained nanotube compared to previously reported unstrained cases. The thermal conductivity of SWCNT increases with its length is also observed.

The linear and non-linear study of effect of rotation and internal heat source/sink on Bénard convection

The primary objective of this study is to investigate non-linear Bénard convection in a single-walled carbon nanotube suspension saturated in a rotating porous medium with an internal heat sink/source. The modified Buongiorno model is utilized to formulate the governing equations for the flow. Both linear and weak non-linear stability analyses are conducted in this investigation. The linear stability analysis employs the truncated Fourier series transformation, while the weakly non-linear stability analysis utilizes the Lorenz model, assuming weak thermophoresis, porous friction, and small-scale convective motion. The cubic Ginzburg–Landau equation is formulated and subsequently solved to derive the expression for the amplitude. The influence of various parameters, such as the Taylor number, heat sink/source parameter, and viscosity parameter, is discussed in relation to the threshold criteria of convection, as well as heat and mass transport rates. Based on the linear stability analysis, it is determined that the introduction of a rotating frame of reference delays the initiation of convection, whereas the energy supplied to the system accelerates the onset of convection. The heat transfer rate increases by when the nanofluidic system is placed in the rotating frame of reference under the presence of an internal heat source.

Influence of Single-Wall Carbon Nanotube Suspension on the Mechanical Properties of Polymeric Films and Electrospun Scaffolds.

Carbon nanotubes (CNTs) are used in applications ranging from electrical engineering to medical device manufacturing. It is well known that the addition of nanotubes can influence the mechanical properties of various industrial materials, including plastics. Electrospinning is a popular method for fabricating nanomaterials, widely suggested for polymer scaffold manufacturing. In this study, we aimed to describe the influence of single-walled carbon nanotube (SWCNT) suspensions on polymeric poured films and electrospun scaffolds and to investigate their structural and mechanical properties obtained from various compositions. To obtain films and electrospun scaffolds of 8 mm diameter, we used poly-ε-caprolactone (PCL) and poly(cyclohexene carbonate) (PCHC) solutions containing several mass fractions of SWCNT. The samples were characterized using tensile tests, atomic force and scanning electronic microscopy (AFM and SEM). All the studied SWCNT concentrations were shown to decrease the extensibility and strength of electrospun scaffolds, so SWCNT use was considered unsuitable for this technique. The 0.01% mass fraction of SWCNT in PCL films increased the polymer strength, while fractions of 0.03% and more significantly decreased the polymer strength and extensibility compared to the undoped polymer. The PHCH polymeric films showed a similar behavior with an extremum at 0.02% concentration for strength at break.

Highly Efficient Electrocatalytic Hydrogen Production over Carbon Nanotubes Loaded with Platinum Nanoparticles Using Solution Processing

AbstractProton exchange membrane (PEM) electrolyzers are used for hydrogen (H2) production by water electrolysis. The commercial cathodic electrocatalyst for this process is typically mechanically mixed platinum on carbon (Pt/C). However, aggregation of the platinum (Pt) makes high loading of the catalyst difficult. Therefore, a method for the homogeneous combination of Pt and carbon materials is required. Herein, the first example of a highly efficient single‐walled carbon nanotube (SWCNT) cathodic H2‐production electrocatalyst that is loaded with platinum nanoparticles (PtNPs) using a newly developed suspension method is reported. Combining SWCNTs lapped with a water‐soluble, thiol‐functionalized polymer with PtNPs in water yields a PtNP‐conjugated SWCNT suspension. The electrocatalyst exhibits a low overpotential of 47 mV at a current density of 10 mA cm−2 toward H2 evolution in 0.5 m sulfuric acid. A PEM electrolyzer fabricated using the optimally prepared electrocatalyst with the low loading of 15 µgPt cm−2 shows a high mass activity of 27 200 A gPt−1, which is 80 times that of Pt/C with a loading amount of 2.8 mgPt cm−2 (324 A gPt−1). In addition, the PEM electrolyzer produces H2 at a Faradaic efficiency of 97% and operates stably for 150 h at 100 mA cm−2.

Hybridization of papain molecules and DNA-wrapped single-walled carbon nanotubes evaluated by atomic force microscopy in fluids

Although various conjugates of single-walled carbon nanotubes (SWNTs) and biomolecules, such as nanobiosensors and nanobiodevices, have been reported, the conjugation of papain and SWNTs have not been reported because of the formation of unexpected aggregates. In this study, atomic force microscopy (AFM) in liquid was used to investigate the interactions between papain and DNA-wrapped SWNTs (DNA–SWNTs) at two different pH values (pH 3.0 and 10.5). The direct AFM observation of the mixture of papain and DNA–SWNTs confirmed the aggregation of papain molecules with DNA–SWNTs in the buffer solutions. The numerous and non-uniform adsorption of papain molecules onto DNA–SWNTs was more pronounced at pH 3.0 than that at pH 10.5. Furthermore, thick conjugates appeared when papain and DNA–SWNTs were simultaneously mixed. The near-infrared photoluminescence spectra of the SWNTs drastically changed when the papain molecules were injected into the DNA–SWNT suspension at pH 3.0. Thus, the regulation of electrostatic interactions is a key aspect in preparing optimal conjugates of papain and DNA–SWNTs. Furthermore, although previous papers reported AFM images of dried samples, this study demonstrates the potential of AFM in liquid in evaluating individual bioconjugates of SWNTs.

STUDY OF HEAT TRANSFER IN ANISOTROPIC POROUS ENCLOSURES SATURATED WITH CASSON NANOFLUID

The present study aims at discussing the onset of convection and heat transfer rate in a Casson nanofluid saturated in anisotropic porous enclosures of three types: shallow, square, and tall. The effects of Brownian motion and thermophoresis are included in the model. Normal modes are used to obtain the expression of stationary thermal Rayleigh number. Further, nonlinear stability analysis is performed using the truncated Fourier series expansion. The Nusselt number is calculated from the Lorentz model. The effects of pertinent flow governing parameters such as Casson parameter, thermal anisotropic parameter, mechanical anisotropic parameter, and nanoparticle concentration Rayleigh number are shown graphically on the onset of convection, Nusselt number, streamlines, isotherms, and isohalines. It is observed that shallow enclosure allows quick heat transfer by setting the convection earlier. Furthermore, it is concluded that the use of Casson-based single-walled carbon nanotube suspension (SWCNTS) enhances heat transportation and strengthens the magnitude of streamlines.

Attachment of DNA-Wrapped Single-Walled Carbon Nanotubes (SWNTs) for a Micron-Sized Biosensor.

We fabricated a micron-sized biodevice based on the near-infrared photoluminescence (PL) response of single-walled carbon nanotubes (SWNTs). Various biosensors using the unique optical responses of SWNTs have been proposed by many research groups. Most of these employed either colloidal suspensions of dispersed SWNTs or SWNT films on flat surfaces, such as electrodes. In this study, we attached DNA-wrapped SWNTs (DNA-SWNTs) to frustule (micron-sized nanoporous biosilica) surfaces, which were purified from cultured isolated diatoms. After the injection of an oxidant and a reductant, the SWNTs on the frustules showed prominent PL responses. This suggests that the biodevice functions as a micron-sized redox sensor. Frustules can be easily suspended in aqueous solutions because of their porous structures and can easily be collected as pellets by low-speed centrifugation. Thus, the removal of unbound SWNTs and the recovery of the fabricated DNA-SWNT frustules for reuse were achieved by gentle centrifugation. Our proposal for micron-sized SWNT biodevices would be helpful for various biological applications.

Compositional Analysis of ssDNA-Coated Single-Wall Carbon Nanotubes through UV Absorption Spectroscopy.

Aqueous suspensions of single-wall carbon nanotubes (SWCNTs) coated by ssDNA are analyzed using UV absorption and total carbon measurements. The results give absolute average concentrations of both components in samples without free ssDNA. From those values, the average mid-UV SWCNT absorptivity is deduced for three different batches of relatively small diameter nanotubes: two HiPco and one CoMoCAT. The absorptivity values enable the use of simple spectrophotometry to measure absolute concentrations of similar SWCNT samples in aqueous SDS. The results also quantify the mass ratio of ssDNA to SWCNT, defining the average number of nanotube carbon atoms suspended by one ssDNA strand of T15GT15 or T30G. Comparing this experimental parameter with results from replica exchange molecular dynamics simulations of one ssDNA strand freely adsorbed on a (6,5) segment shows close agreement between the computed number of SWCNT atoms covered per strand and the measured number of SWCNT atoms suspended per strand.

Nanostructured label–free electrochemical immunosensor for detection of a Parkinson's disease biomarker

Aggregation of α-synuclein has been recognized as a critical event in the pathogenesis of Parkinson's disease whose prevalence is increasing with great socio-economic challenges for future generations. Here, we developed a sensitive and specific electrochemical immunosensor for the detection and quantification of this biomarker, based on the voltammetric study of a redox indicator signal, which decreases upon the analyte recognition by the antibody due to the electronic resistance increase. The proposed immunosensor is based on a screen-printed carbon electrode modified in a layer-by-layer approach, which through extensive characterization led to the successful nanostructuration of the transducer, through the drop-cast of 3.0 μL of a 0.1 mg mL−1 single-walled carbon nanotubes suspension followed by electrodeposition of gold nanoparticles in a 3 mM HAuCl4 solution under a −0.2 V potential for 150 s. Monoclonal antibodies were immobilized on the gold nanoparticles surface through chemical modification at an optimal concentration of 200 μg mL−1. Using the proposed immunosensor, α-synuclein was detected in the range of 0.01–10 ng mL−1 with a 4.1 and 12.6 pg mL−1 limits of detection and quantification, respectively. Recovery values of 96.7, 106.2 and 102.9% were attained for the tested concentrations spiked in fetal bovine serum while also presenting excellent specificity and stability throughout one month. The nanostructured immunosensor provided a great interface for electronic transduction and biological recognition events, which enabled fast, sensitive and specific detection of α-synuclein while being based on a simple and inexpensive technology requiring small sample volumes, crucial characteristics for application in point-of-care testing.

Distinguishing Antioxidant Molecules with Near-Infrared Photoluminescence of DNA-Wrapped Single-Walled Carbon Nanotubes.

In this study, two biomolecule solutions were distinguished using the capacity difference in the near-infrared photoluminescence (PL) of single-walled carbon nanotubes (SWNTs). Biosensing techniques using sensitive responses of SWNTs have been intensively studied. When a small amount of an oxidant or reductant solution was injected into the SWNT suspensions, the PL intensity of the SWNTs is significantly changed. However, distinguishing between different molecules remains challenging. In this study, we comparably injected saponin and banana solutions, which are known antioxidant chemicals, into an SWNT suspension. The SWNTs were solubilized by wrapping them with DNA molecules. The results show that 69.1 and 155.2% increases of PL intensities of SWNTs were observed after injection of 20 and 59 μg/mL saponin solutions, respectively. Subsequently, the increase in PL was saturated. With the banana solution, 18.1 and 175.4% increases in PL intensities were observed with 20 and 59 μg/mL banana solutions, respectively. Based on these results, the two antioxidant molecules could be distinguished based on the different PL responses of the SWNTs. In addition, the much higher saturated PL intensities observed with the banana solution suggests that the banana solution increased the capacity of the PL increase for the same SWNT suspension. These results provide helpful information for establishing biosensing applications of SWNTs, particularly for distinguishing chemicals.

Thermal outcomes for blood-based carbon nanotubes (SWCNT and MWCNTs) with Newtonian heating by using new Prabhakar fractional derivative simulations

The mixed convection flow of carbon nanotubes due to porous vertical plate has been presented via fractional simulations. The single and multi-wall carbon nanotubes are used to observe the thermal aspect of hybrid nanofluid model. The blood is treated as base material. The shear thinning and thickening aspect of blood are predicted by using the Casson fluid model. The comparative thermal observations of blood base fluid with multi-wall carbon nanotubes (MWCNTs) and single-wall carbon nanotubes (SWCNTs) are reported. The Prabhakar fractional derivative simulations are performed to analyze the physical pattern of problem. The Laplace transformations are implemented to the integrating task. It is noticed that fractional parameter reduces the velocity profile for both MWCNTs and SWCNTs suspension. With increment in volume fraction and fractional parameters reduces the thermal profile effectively.

Guanine-Specific Chemical Reaction Reveals ssDNA Interactions on Carbon Nanotube Surfaces.

Understanding the conformations of physisorbed single-stranded DNA (ssDNA) oligos on single-wall carbon nanotube (SWCNT) surfaces is important for advancing basic nanoscience and for developing applications in biomedicine and quantum information processing. Here we report evidence that the ssDNA strands are partly desorbed from the nanotube surface under common conditions. SWCNT suspensions were prepared in eight ssDNA oligos, each containing 1 guanine and 30 thymine bases but differing in the position of the guanine within the strand. Singlet oxygen exposure then covalently functionalized the guanine to the SWCNT surface, red-shifting the nanotube fluorescence by an amount reflecting the guanine spatial density at the surface. Spectral shifts were greatest for central guanine positions and smallest for end positions. In conjunction with steered molecular dynamics simulations, the results suggest that steric interference between neighboring ssDNA strands on an individual nanotube causes significant dislocation or desorption of the strand ends while central regions remain better wrapped around the nanotube. This effect decreases with decreasing concentrations of free ssDNA.

A Micro Broadband Photodetector Based on Single Wall Carbon Nanotubes-Graphene Heterojunction

A room-temperature broadband (visible to near infrared spectrum) photodetector based on single wall carbon nanotubes (SWCNTs) and graphene heterojunction was fabricated in this work, by drop-casting the SWCNTs suspension onto the graphene field-effect transistor with the buried-gate electrode. A high photoresponsivity of 109 A/W and a fast photoresponse speed of 2.9 ms were obtained within the visible region based on the photogating effect. This high gain mechanism leads to a high photoconductive gain (9.1 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> ). In addition, the photodetector exhibits a photoresponsivity of 51.5 A/W at 940 nm, indicating a wide spectrum detection capability. Moreover, a higher photoresponsivity can be obtained by tuning the source-drain and gate bias voltages. This approach provides an easy and feasible way to achieve broadband heterojunction photodetectors with high-performance.

Rheological Analysis of Suspended Single-Walled Carbon Nanotubes in a Walters' B fluid

Objective: In this paper, we present a rheological analysis of suspended single-walled Carbon nanotubes in a Walters' B fluid. Methods: We assume that the viscosity varies exponentially as a function of the temperature use the Reynolds model of viscosity for the study. A variable thermal conductivity is also assumed along with buoyancy, magnetic field, viscous dissipation and a convective boundary condition. The system of nonlinear coupled equations is solved using the spectral local linearization method. Results: Our solutions are validated using through comparison with previously published results for a given set of conditions. Conclusion: The study finds that good agreement is achieved.

Stable Near-Infrared Photoluminescence of Single-Walled Carbon Nanotubes Dispersed Using a Coconut-Based Natural Detergent.

We prepared single-walled carbon nanotube (SWNT) suspensions in phosphate buffer solutions containing 1% of a coconut-based natural detergent (COCO) or 1% of sodium dodecyl sulfate (SDS). The suspensions exhibited strong photoluminescence (PL) in the near-infrared region, suggesting that the SWNTs, such as those with (9, 4) and (7, 6) chiralities, were monodispersed. Upon diluting the suspensions with a detergent-free phosphate buffer solution, the PL intensity of the SDS-containing SWNT suspension was significantly lower than that of the COCO-containing SWNT suspension. The COCO-containing SWNT suspension was more stable than the SDS-containing SWNT suspension. The SWNT concentration of the suspensions prepared via bath-type sonication was lower than that of the suspensions prepared via probe-type sonication. However, near-infrared (NIR) PL intensity of the SWNT suspensions prepared via bath-type sonication was much higher than that of the SWNT suspensions prepared via probe-type sonication regardless of the detergent. This suggested that the fraction of monodispersed SWNTs of the suspensions prepared via bath-type sonication was larger than that of the suspensions prepared via probe-type sonication, although the SWNT concentration was low. Our results indicated that COCO favored the fabrication of SWNT suspensions with stable and strong NIR PL, which are useful for various biological applications.

Indentation behavior of suspended single-walled carbon nanotube films

Suspended thin film carbon nanotubes with suitable mechanical strength are in high demand for applications such as sensors, particle filters, or thermoacoustic speakers. However, researchers working on the production and development of applications for thin films have found difficulty in evaluating their mechanical strength. This research shows the nano-indentation behavior of thin (<26 nm thickness) single-walled carbon nanotube suspended films, to evaluate their mechanical strength. Indentation tests, scanning electron microscopy, and Raman, infrared, reflection spectroscopy showed that the high crystallinity of carbon nanotubes and film thickness uniformity are important for achieving high mechanical strength.

(Invited) Different Pathways of Fluorescent SWCNT Modifications with Aromatic Reactants

Modification of electronic and chemical properties of single-wall carbon nanotubes (SWCNTs) by covalent side-wall functionalization can produce a stable material with purposely-enhanced electronic and optical properties. In the report we describe a new type of reactions between simple aromatic compounds and SWCNTs, creating different fluorescent trapping states in SWCNTs. The photoreactions take place in aqueous suspensions of SWCNTs with small addition of soluble or even very-slightly soluble organic aromatic compounds excited by UV light. The reaction rates depend on the aromatic compound structure and proportional to its concentration, and in some cases, as with aniline or iodoaniline, new strong and well-resolved spectral sidebands appear within one minute. Total SWCNT photoluminescence intensity can increase, and the increase was in some cases by a factor of 5 as compare to original species. The shifted emission bands and the trapping nature of them, when the main part of the nanotube is performing as an absorbing antenna delivering excitation energy to the modified sites, may be interesting for a variety of optical and electronic applications.Most notably, in most cases of these photochemical reactions, the shifted emission spectra from modified SWCNTs become different, displaying never observed previously structure upon removal of molecular oxygen from the solution. For instance, treatment with normal dissolved oxygen gives a rise to a new emission band red-shifted for (6,5) SWCNTs by 160 meV from the pristine position, which is similar to many previously studied reactions starting with oxygen doping. Corresponding results will appear for other species as well. However, if the molecular oxygen is removed from the suspension by degassing or gas substitution, same UV treatments will lead to two different emission bands red-shifted by 140 and 270 meV, one less shifted and one more shifted, thus indicating different chemical products of the reactions. These new bands grow with different rate under UV illumination. Variance spectroscopy of such samples shows the presence of individual “multicolor” nanotubes with three distinct emission bands, one original/unmodified plus two shifted. The reaction demonstrates new possibilities for creation different trapping states on individual nanotubes, and opens new options for tuning electronic and optical properties of nanotubes for possible applications.