Probing photoresponse of aligned single-walled carbon nanotube doped ultrathin MoS2

We report a facile method to produce ultrathin molybdenum disulfide (MoS2) hybrids with polarized near-infrared (NIR) photoresponses, in which horizontally-aligned single-walled carbon nanotubes (SWNTs) are integrated with single- and few-layer MoS2 through a two-step chemical vapor deposition process. The photocurrent generation mechanisms in SWNT-MoS2 hybrids are systematically investigated through wavelength- and polarization-dependent scanning photocurrent measurements. When the incident photon energy is above the direct bandgap of MoS2, isotropic photocurrent signals are observed, which can be primarily attributed to the direct bandgap transition in MoS2. In contrast, if the incident photon energy in the NIR region is below the direct bandgap of MoS2, the maximum photocurrent response occurs when the incident light is polarized in the direction along the SWNTs, indicating that photocurrent signals mainly result from the anisotropic absorption of SWNTs. More importantly, these two-dimensional (2D) hybrid structures inherit the electrical transport properties from MoS2, displaying n-type characteristics at a zero gate voltage. These fundamental studies provide a new way to produce ultrathin MoS2 hybrids with inherited electrical properties and polarized NIR photoresponses, opening doors for engineering various 2D hybrid materials for future broadband optoelectronic applications.

Supramolecular glucose oxidase-SWNT conjugates formed by ultrasonication: effect of tube length, functionalization and processing time

BACKGROUND

Generation-3 (Gen-3) biosensors and advanced enzyme biofuel cells will benefit from direct electron transfer to oxidoreductases facilitated by single-walled carbon nanotubes (SWNTs).

METHODS

Supramolecular conjugates of SWNT-glucose oxidase (GOx-SWNT) were produced via ultrasonic processing. Using a Plackett-Burman experimental design to investigate the process of tip ultrasonication (23 kHz), conjugate formation was investigated as a function of ultrasonication times (0, 5, 60 min) and functionalized SWNTs of various tube lengths (SWNT-X-L), (X = -OH or -COOH and L = 3.0 μm, 7.5 μm).

RESULTS

Enzyme activity (KM, kcat, kcat/KM, vmax and n (the Hill parameter)) of pGOx (pristine), sGOx (sonicated) and GOx-SWNT-X-L revealed that sonication of any duration increased both KM and kcat of GOx but did not change kcat/KM. Functionalized tubes had the most dramatic effect, reducing both KM and kcat and reducing kcat/KM. UV-vis spectra over the range of 300 to 550 nm of native enzyme-bound FAD (λmax at 381 and 452 nm) or the blue-shifted solvated FAD of the denatured enzyme (λmax at 377 and 448 nm) revealed that ultrasonication up to 60 minutes had no influence on spectral characteristics of FAD but that the longer SWNTs caused some partial denaturation leading to egress of FAD. Circular dichroism spectral analysis of the 2° structure showed that sonication of any duration caused enrichment in the α-helical content at the sacrifice of the unordered sequences in GOx while the presence of SWNTs, regardless of length and/or functionality, reduced the β-sheet content of pristine GOx. Surface profiling by white light interferometry revealed that ultrasonication produced some aggregation of GOx and that GOx effectively debundled the SWNT.

CONCLUSIONS

Supramolecular conjugates formed from shorter, -OH functionalized SWNTs using longer sonication times (60 min) gave the most favored combination for forming bioactive conjugates.

Single-walled carbon nanotube-mediated small interfering RNA delivery for gastrin-releasing peptide receptor silencing in human neuroblastoma

Small interfering RNA (siRNA) has the potential to influence gene expression with a high degree of target gene specificity. However, the clinical application of siRNA therapeutics has proven to be less promising as evidenced by its poor intracellular uptake, instability in vivo, and nonspecific immune stimulations. Recently, we have demonstrated that single-walled carbon nanotube (SWNT)-mediated siRNA delivery can enhance the efficiency of siRNA-mediated gastrin-releasing peptide receptor (GRP-R) gene silencing by stabilizing siRNA while selectively targeting tumor tissues. Based on our recent findings, we introduce a novel technique to silence specific gene(s) in human neuroblastoma through SWNT-mediated siRNA delivery in vitro and in vivo.

Translocation of single-wall carbon nanotubes through solid-state nanopores

We report the translocation of individual single-wall carbon nanotubes (SWNTs) through solid-state nanopores. Single-strand DNA oligomers are used to both disperse the SWNTs in aqueous solution and to provide them with a net charge, allowing them to be driven through the nanopores by an applied electric field. The resulting temporary interruptions in the measured nanopore conductance provide quantitative information on the diameter and length of the translocated nanotubes at a single-molecule level. Furthermore, we demonstrate that the technique can be utilized to monitor bundling of SWNT in solution by using complementary nucleotides to induce tube-tube agglomeration.

High Performance In Vivo Near-IR (>1 μm) Imaging and Photothermal Cancer Therapy with Carbon Nanotubes

Short single-walled carbon nanotubes (SWNTs) functionalized by PEGylated phospholipids are biologically non-toxic and long-circulating nanomaterials with intrinsic near infrared photoluminescence (NIR PL), characteristic Raman spectra, and strong optical absorbance in the near infrared (NIR). This work demonstrates the first dual application of intravenously injected SWNTs as photoluminescent agents for in vivo tumor imaging in the 1.0-1.4 μm emission region and as NIR absorbers and heaters at 808 nm for photothermal tumor elimination at the lowest injected dose (70 μg of SWNT/mouse, equivalent to 3.6 mg/kg) and laser irradiation power (0.6 W/cm(2)) reported to date. Ex vivo resonance Raman imaging revealed the SWNT distribution within tumors at a high spatial resolution. Complete tumor elimination was achieved for large numbers of photothermally treated mice without any toxic side effects after more than six months post-treatment. Further, side-by-side experiments were carried out to compare the performance of SWNTs and gold nanorods (AuNRs) at an injected dose of 700 μg of AuNR/mouse (equivalent to 35 mg/kg) in NIR photothermal ablation of tumors in vivo. Highly effective tumor elimination with SWNTs was achieved at 10 times lower injected doses and lower irradiation powers than for AuNRs. These results suggest there are significant benefits of utilizing the intrinsic properties of biocompatible SWNTs for combined cancer imaging and therapy.

Simple, rapid, sensitive, and versatile SWNT-paper sensor for environmental toxin detection competitive with ELISA

Safety of water was for a long time and still is one of the most pressing needs for many countries and different communities. Despite the fact that there are potentially many methods to evaluate water safety, finding a simple, rapid, versatile, and inexpensive method for detection of toxins in everyday items is still a great challenge. In this study, we extend the concept of composites, impregnated porous fibrous materials, such as fabrics and papers, by single-walled carbon nanotubes (SWNTs), toward very simple but high-performance biosensors. They utilize the strong dependence of electrical conductivity through nanotubes percolation network on the width of nanotube-nanotube tunneling gap and can potentially satisfy all the requirements outlined above for the routine toxin monitoring. An antibody to the microcystin-LR (MC-LR), one of the common culprits in mass poisonings, was dispersed together with SWNTs. This dispersion was used to dip-coat the paper rendering it conductive. The change in conductivity of the paper was used to sense the MC-LR in the water rapidly and accurately. The method has the linear detection range up to 10 nmol/L and nonlinear detection up to 40 nmol/L. The limit of detection was found to be 0.6 nmol/L (0.6 ng/mL), which satisfies the strictest World Health Organization standard for MC-LR content in drinking water (1 ng/mL) and is comparable to the detection limit of the traditional ELISA method of MC-LR detection, while drastically reducing the time of analysis by more than an order of magnitude, which is one of the major hurdles in practical applications. Similar technology of sensor preparation can also be used for a variety of other rapid environmental sensors.