Polymer-Functionalized Carbon Nanotube Sensors for Volatile Organic Compound Signal Exchange and Bioinspired Molecular Communication.

We proposed to use a miniature single-walled carbon nanotube (SWNT) sensor, fabricated by alternating current dielectrophoresis, to detect dissociated and oxidized sulfur hexafluoride (SF6) gas species generated by partial discharge (PD) activity in a concealed chamber such as gas-insulated switchgear (GIS). The SWNT sensor did not react with pure SF6 gas but sensitively responded to the dissociated and oxidized SF6 species. Also, the SWNT sensor could be regenerated by purging with fresh air since the transduction was based on the physisorption of analytes. Therefore, the SWNT sensor is a promising device for the detection of the dissociated and oxidized SF6 species and for the monitoring of the PD activity inside GIS.

Nine deoxyribonucleic acid (DNA) sequences were used to functionalize single-walled carbon nanotube (SWNT) sensors to detect the trace amount of methanol, acetone, and HCl in vapor. DNA 24 Ma (24 randomly arranged nitrogenous bases with one amine at each end of it) decorated SWNT sensor and DNA 24 A (only adenine (A) base with a length of 24) decorated SWNT sensor have demonstrated the largest sensing responses towards acetone and HCl, respectively. On the other hand, for the DNA GT decorated SWNT sensors with different sequence lengths, the optimum DNA sequence length for acetone and HCl sensing is 32 and 8, separately. The detection of methanol, acetone, and HCl have identified that DNA functionalized SWNT sensors exhibit great selectivity, sensitivity, and repeatability with an accuracy of more than 90%. Further, a sensor array composed of SWNT functionalized with various DNA sequences was utilized to identify acetone and HCl through pattern recognition. The sensor array is a combination of four different DNA functionalized SWNT sensors and two bare SWNT sensors (work as reference). This wireless sensing system has enabled real-time gas monitoring and air quality assurance for safety and security.

Conducting polymer coated single-walled carbon nanotube gas sensors for the detection of volatile organic compounds.

Computer simulation of the interaction of diatomic A2 molecules (A = C, Si, N, P, O, S) with a super-small single-walled carbon nanotube (SWCNT) sensor was performed. The nonlocal density functional B3LYP / 3-21G (ORCA package) was used to study the supratomical nanosystem. For all molecules, it has been shown that the most preferable orientation of their axis is perpendicular to the outer surface of the SWCNT. Significant differences were found in the adsorption of molecules of group IV a (C, Si), group V a (N, P) and group VI a (O, S) of the periodic table of elements. The calculation showed that the chemisorption of the molecules C2 and Si is characterized by binding energies of 2.91 eV, 1.51 eV and equilibrium distances from the SWCNT surface of 1.39 A and 2.91 A, respectively. For a C2 molecule, a covalent bond with a pair of carbon atoms is preferred, while for a Si2 molecule, a covalent bond with one of the carbon atoms is more stable. In turn, for the N2, P2, O2, S2 molecules, it is preferable to be located in the center of carbon sextet at a distance from the surface of the SWCNT: 3.00 A, 3.17 A, 2.66 A, 2.96 A with binding energy: 0.15 eV, 0.27 eV, 0.39 eV, 0.52 eV, respectively.

Tailoring selectivity of sprayed carbon nanotube sensors (CNT) towards volatile organic compounds (VOC) with surfactants

MicroRNAs (miRNAs) are single-stranded non-coding short ribonucleic acid sequences that take part in many cellular and biological processes. Recent studies have shown that altered expression of miRNAs is involved in pathological processes, and they can thus be considered biomarkers for the early detection of various diseases. Here, we demonstrate a selection and elimination process of fluorescent single-walled carbon nanotube (SWCNT) sensors for miRNA biomarkers based on RNA-DNA hybridization with a complementary DNA recognition unit bound to the SWCNT surface. We use known miRNA biomarkers for acute myocardial infarction (AMI), commonly known as a heart attack, as a case study. We have selected five possible miRNA biomarkers which are selective and specific to AMI and tested DNA-SWCNT sensor candidates with the target DNA and RNA sequences in different environments. Out of these five miRNA sensors, three could recognize the complementary DNA or RNA sequence in a buffer, showing fluorescence modulation of the SWCNT in response to the target sequence. Out of the three working sensors in buffer, only one could function in serum and was selected for further testing. The chosen sensor, SWCNT-miDNA208a, showed high specificity and selectivity toward the target sequence, with better performance in serum compared to a buffer environment. The SWCNT sensor selection pipeline highlights the importance of testing sensor candidates in the appropriate environment and can be extended to other libraries of biomarkers.

Theoretical exploration of VOCs removal mechanism by carbon nanotubes through persulfate-based advanced oxidation processes: Adsorption and catalytic oxidation

Fluorescent sensors are frequently not used for in vivo research due to photobleaching and difficulty in signal detection. Single walled carbon nanotubes (SWNT) circumvent these issues with near infrared fluorescent emission and long term stability; yet detection of carbon nanotube sensors has never before been performed in large animal models. The ability to place and read SWNT sensors in vivo for a large animal requires specialized instrumentation and research facilities. By teaming up with large animal veterinarians and meat scientists, our lab was able to surgically place, monitor, and recover SWNT sensors from 14 sheep. We examined various SWNT platforms, implantation locations, and detection methods to determine a strategy for frequent, consistent detection of SWNT sensors that serve as an indicator of animal stress and overall health.

Fluorescent sensors are frequently not used for in vivo research due to photobleaching and difficulty in signal detection. Single walled carbon nanotubes (SWNT) circumvent these issues with near infrared fluorescent emission and long term stability; yet detection of carbon nanotube sensors has never before been performed in large animal models. The ability to place and read SWNT sensors in vivo for a large animal requires specialized instrumentation and research facilities. By teaming up with large animal veterinarians and meat scientists, our lab was able to surgically place, monitor, and recover SWNT sensors from 14 sheep. We examined various SWNT platforms, implantation locations, and detection methods to determine a strategy for frequent, consistent detection of SWNT sensors that serve as an indicator of animal stress and overall health.

Single-walled carbon nanotubes (SWNTs) with their unique electrical properties and large surface area are remarkable materials for detecting low concentration of toxic and hazardous chemicals (both from the gaseous and liquid phases). Ionic adsorbates in water will attach on to SWNTs and drastically alter their electrical properties. Several SWNTs based pH and chemical sensors have been demonstrated. However, most of them require external components to test and analyze the response of SWNTs to ions inside the liquid samples. Here, we report a water quality monitoring sensor composed of SWNTs integrated inside microfluidic channels and on-chip testing components with a wireless transmission board. To detect multiple analytes in water requires the functionalization of SWNTs with different chemistries. In addition, microfluidic channels are used to guide liquid samples to individual nanotube sensors in an efficient manner. Furthermore, the microfluidic system enables sample mixing and separation before testing. To realize the nanosensors, first microelectrodes were fabricated on an oxidized silicon substrate. Next, PDMS micro channels were fabricated and bonded on the substrate. These channels can be incorporated with a microfluidic system which can be designed to manipulate different analytes for specific molecule detection. Low temperature, solution based Dielectrophoretic (DEP) assembly was conducted inside this microfluidic system which successfully bridged SWNTs between the microelectrodes. The SWNTs sensors were next characterized with different pH buffer solutions. The resistance of SWNTs had a linearly increase as the pH values ranged from 5 to 8. The nanosensor incorporated within the microfluidic system is a versatile platform and can be utilized to detect numerous water pollutants, including toxic organics and microorganisms down to low concentrations. On-chip processing and wireless transmission enables the realization of a full autonomous system for real time monitoring of water quality.

Single walled carbon nanotubes (SWNT) that are well aligned have a broad range of applications, including solar cells, sensors, transistors, and optoelectronic devices. Alignment of SWNT is typically performed either during SWNT fabrication or out of post-processed SWNT solutions through vacuum filtration, spin-coating, electromagnetic fields, surfactant-aided microfluidic alignment techniques or concentration-dependent shear alignment. Alignment of SWNT during fabrication requires a lot of time and money and precludes the ability to wrap the SWNT with DNA, which is what creates the SWNT’s sensing capabilities. Unfortunately, most of these techniques have not been widely adopted since it is labor-intensive, difficult to reproduce or hard to scale up. We developed a scalable method to align DNA wrapped SWNT through heat activation without altering the SWNT’s wrapping and sensing capabilities. This research will pave the way for the development of both research and industrial scale aligned SWNT from aqueous solutions for next-generation of SWNT based optical sensors.

Beyond the Usual Suspects

Nanoparticle-based optical sensors are capable of highly sensitive and selective chemical interactions and can form the basis of molecular recognition for various classes of analytes. However, their incorporation into standardized in vitro assays has been limited by their incompatibility with packaging or form factors necessary for specific applications. Here, we have developed a technique for immobilizing nIR-fluorescent single-walled carbon nanotube (SWCNT) sensors on seven different types of paper substrates including nitrocellulose, nylon, poly(vinylidene fluoride), and cellulose. Sensors remain functional upon immobilization and exhibit nIR fluorescence in nonaqueous solvent systems. We then extend this system to the Corona Phase Molecular Recognition (CoPhMoRe) approach of synthetic molecular recognition by screening ssDNA-wrapped SWCNTs with different sequences against a panel of fat-soluble vitamins in canola oil, identifying a sensor which responds to β-carotene with a dissociation constant of 2.2 μM. Moreover, we pattern hydrophobic regions onto nitrocellulose using the wax printing method and form one-dimensional sensor barcodes for rapid multiplexing. Using a sensor array of select ssDNA wrappings, we are able to distinguish between Cu(II), Cd(II), Hg(II), and Pb(II) at a concentration of 100 μM. Finally, we demonstrate that immobilized sensors remain fluorescent and responsive for nearly 60 days when stability is addressed. This work represents a significant step toward the deployment of fluorescent nanoparticle sensors for point-of-use applications.

Nitric oxide (NO) is an important biological signaling factor, but due to its fast degradation rate quantification is difficult. Single walled carbon nanotube sensors for NO are unique in their ability to quantify NO concentrations in vitro over extended time periods without genetically altering the cells of interest. Since nanotubes are so small they are readily taken up by cells. To investigate just the extracellular concentration of nitric oxide, avoiding detection of the intracellular concentration, we developed a system to look at extracellular nitric oxide concentrations for in vitro samples. This new system allows for seeding adherent cells in desired patterns without altering the nanotube sensors, therefore allowing spatial and temporal detection of NO in regions between cell islands or associated with multiple cell types. The system is robust enough to allow for other nanotube sensors to be used with alternate cell types, creating a technique to quantify multiple analytes that are excreted from cells in a temporal and spatial fashion.

In this work, we report on the integration of Hollow-core Optical Fibers (HOF) and Single Walled Carbon NanoTubes (SWCNTs) in order to obtain new functionalized devices by means of the modification of the photonic bandgap (PBG) characterizing the HOF itself. The samples were obtained by coating and partially filling by SWCNTs the termination of HOFs. The infiltration of SWCNTs inside the HOF holes has been accomplished by means of the Langmuir-Blodgett technique. Far field transmission characterizations have been carried out at 1550nm in order to study the influence of the carbon nanotubes within the HOF holes on the HOF PBG. Finally, in light of the sensing features of the SWCNTs, the realized samples have been employed as opto-chemical sensors for volatile organic compounds (VOCs) detection and their sensing capability has been proved by their exposure to VOCs traces. Experimental results demonstrate the success of the SWCNTs partial filling within the HOF holes, the influence of the deposition parameters on the HOF PBG and sensing performances as well as the sensor capability to perform VOCs detection with a good sensitivity and fast response times.