Yanan Chen

Mechanistic Investigations of Horseradish Peroxidase-Catalyzed Degradation of Single-Walled Carbon Nanotubes

Single-walled carbon nanotubes (SWNTs) have been investigated for a variety of applications including composite materials, electronics, and drug delivery. However, these applications may be compromised depending on the negative effects of SWNTs to living systems. While reports of toxicity induced by SWNTs vary, means to alleviate or quell these effects are in small abundance. We have reported recently the degradation of carboxylated SWNTs through enzymatic catalysis with horseradish peroxidase (HRP). In this full Article, we investigated the degradation of both carboxylated and pristine SWNTs with HRP and compared these results with chemical degradation by hemin and FeCl(3). The interaction between pristine and carboxylated SWNTs with HRP was further studied by computer modeling, and the products of the enzymatic degradation were identified. By examining these factors with both pristine and carboxylated SWNTs through a variety of techniques including atomic force microscopy (AFM), transmission electron microscopy (TEM), Raman spectroscopy, ultraviolet-visible-near-infrared (UV-vis-NIR) spectroscopy, gas chromatography-mass spectrometry (GC-MS), high-performance liquid chromatography (HPLC), and liquid chromatography-mass spectrometry (LC-MS), degradation pathways were elucidated. It was observed that pristine SWNTs demonstrate no degradation with HRP incubation but display significant degradation when incubated with either hemin or FeCl(3). Such data signify a heterolytic cleavage of H(2)O(2) with HRP as pristine nanotubes do not degrade, whereas Fenton catalysis results in the homolytic cleavage of H(2)O(2) producing free radicals that oxidize pristine SWNTs. Product analysis shows complete degradation produces CO(2) gas. Conversely, incomplete degradation results in the formation of different oxidized aromatic hydrocarbons.

Electronic Detection of Lectins Using Carbohydrate Functionalized Nanostructures: Graphene versus Carbon Nanotubes

Here we investigated the interactions between lectins and carbohydrates using field-effect transistor (FET) devices comprised of chemically converted graphene (CCG) and single-walled carbon nanotubes (SWNTs). Pyrene- and porphyrin-based glycoconjugates were functionalized noncovalently on the surface of CCG-FET and SWNT-FET devices, which were then treated with 2 μM nonspecific and specific lectins. In particular, three different lectins (PA-IL, PA-IIL, and ConA) and three carbohydrate epitopes (galactose, fucose, and mannose) were tested. The responses of 36 different devices were compared and rationalized using computer-aided models of carbon nanostructure/glycoconjugate interactions. Glycoconjugate surface coverage in addition to one-dimensional structures of SWNTs resulted in optimal lectin detection. Additionally, lectin titration data of SWNT- and CCG-based biosensors were used to calculate lectin dissociation constants (K(d)) and compare them to the values obtained from the isothermal titration microcalorimetry technique.

Carbon Nanotube Chemiresistor for Wireless pH Sensing

The ability to accurately measure real-time pH fluctuations in-vivo could be highly advantageous. Early detection and potential prevention of bacteria colonization of surgical implants can be accomplished by monitoring associated acidosis. However, conventional glass membrane or ion-selective field-effect transistor (ISFET) pH sensing technologies both require a reference electrode which may suffer from leakage of electrolytes and potential contamination. Herein, we describe a solid-state sensor based on oxidized single-walled carbon nanotubes (ox-SWNTs) functionalized with the conductive polymer poly(1-aminoanthracene) (PAA). This device had a Nernstian response over a wide pH range (2–12) and retained sensitivity over 120 days. The sensor was also attached to a passively-powered radio-frequency identification (RFID) tag which transmits pH data through simulated skin. This battery-less, reference electrode free, wirelessly transmitting sensor platform shows potential for biomedical applications as an implantable sensor, adjacent to surgical implants detecting for infection.

Carbon Nanotubes Enhance Metastatic Growth of Lung Carcinoma via Up‐Regulation of Myeloid‐Derived Suppressor Cells

Metastatic establishment and growth of Lewis lung carcinoma is promoted by single-walled carbon nanotubes (SWCNT) in C57BL6/J mice. The effect is mediated by increased local and systemic accumulation of myeloid-derived suppressor cells (MDSC), as their depletion abrogated pro-tumor activity in vivo. These data are important for the design of novel theranostics platforms with modules capable of depleting or functionally suppressing MDSC to ensure effective immunosurveillance in the tumor microenvironment.

Exploring the Chemical Sensitivity of a Carbon Nanotube/Green Tea Composite

Single-walled carbon nanotubes (SWNTs) possess unique electronic and physical properties, which make them very attractive for a wide range of applications. In particular, SWNTs and their composites have shown a great potential for chemical and biological sensing. Green tea, or more specifically its main antioxidant component, epigallocatechin gallate (EGCG), has been found to disperse SWNTs in water. However, the chemical sensitivity of this SWNT/green tea (SWNT/EGCG) composite remained unexplored. With EGCG present, this SWNT composite should have strong antioxidant properties and thus respond to reactive oxygen species (ROS). Here we report on fabrication and characterization of SWNT/EGCG thin films and the measurement of their relative conductance as a function of H(2)O(2) concentrations. We further investigated the sensing mechanism by Fourier transform infrared (FTIR) spectroscopy and field-effect transistor measurements (FET). We propose here that the response to H(2)O(2) arises from the oxidation of EGCG in the composite. These findings suggest that SWNT/green tea composite has a great potential for developing simple resistivity-based sensors.

Electronic Detection of Bacteria Using Holey Reduced Graphene Oxide

Carbon nanomaterials have been widely explored for diverse biosensing applications including bacterial detection. However, covalent functionalization of these materials can lead to the destruction of attractive electronic properties. To this end, we utilized a new graphene derivative, holey reduced graphene oxide (hRGO), functionalized with Magainin I to produce a broad-spectrum bacterial probe. Unlike related carbon nanomaterials, hRGO retains the necessary electronic properties while providing the high percentage of available oxygen moieties required for effective covalent functionalization.

Corking carbon nanotube cups with gold nanoparticles.

Nitrogen doping of carbon nanotubes during chemical vapor deposition synthesis can create unique stacked cup-shaped structures termed as nitrogen-doped carbon nanotube cups (NCNCs). These cups have semielliptical hollow cavities and elevated reactivity which could lead to various applications. In this work, by applying intense ultrasonication to the as-synthesized NCNCs, we demonstrated an effective mechanical method to isolate the individual cups with opened cavities from their stacks. The graphitic structures of the isolated cups and their inherent nitrogen functionalities were characterized by comprehensive microscopic and spectroscopic methods. In particular, we quantitatively determined the existence of amine functionalities on NCNCs and found that they were preferentially distributed at the open edges of the cups, providing localized reactive sites. Further, by thiolating the amine groups with 3-mercapto-propionic acid, we were able to effectively cork the isolated cups by gold nanoparticles with commensurate diameters. These cup-shaped carbon nanomaterials with controlled inner volumes and gold nanoparticle corks could find potential applications as nanoscale reaction containers or drug delivery vehicles.