Tao Kong

The promotion of neurite sprouting and outgrowth of mouse hippocampal cells in culture by graphene substrates.

Graphene has been demonstrated in many biomedical applications and its potentials for neural interfacing. Emerging concerns on graphene, as a biomedical material, are its biocompatibility and how biologically targeted tissue/cells respond to it. Relatively few studies attempted to address the interactions of graphene or its derivatives with the tissues/cells, while very few reports on neural system. In this study, we tried to explore how neurites, one of the key structures for neural functions, are affected by graphene during the development until maturation in a mouse hippocampal culture model. The results reveal that graphene substrates exhibited excellent biocompatibility, as cell viability and morphology were not affected. Meanwhile, neurite numbers and average neurite length on graphene were significantly enhanced during 2-7 days after cell seeding compared with tissue culture polystyrene (TCPS) substrates. Especially on Day 2 of the neural development period, graphene substrates efficiently promoted neurite sprouting and outgrowth to the maximal extent. Additionally, expression of growth-associate protein-43 (GAP-43) was examined in both graphene and TCPS groups. Western blot analysis showed that GAP-43 expression was greatly enhanced in graphene group compared to TCPS group, which might result in the boost of neurite sprouting and outgrowth. This study suggests the potential of graphene as a material for neural interfacing and provides insight into the future biomedical applications of graphene.

Enhancement of Radiation Cytotoxicity in Breast‐Cancer Cells by Localized Attachment of Gold Nanoparticles

Gold nanoparticles (GNPs) and modified GNPs having two kinds of functional molecules, cysteamine (AET) and thioglucose (Glu), are synthesized. Cell uptake and radiation cytotoxicity enhancement in a breast-cancer cell line (MCF-7) versus a nonmalignant breast-cell line (MCF-10A) are studied. Transmission electron microscopy (TEM) results show that cancer cells take up functional Glu-GNPs significantly more than naked GNPs. The TEM results also indicate that AET-capped GNPs are mostly bound to the MCF-7 cell membrane, while Glu-GNPs enter the cells and are distributed in the cytoplasm. After MCF-7 cell uptake of Glu-GNPs, or binding of AET-GNPs, the in vitro cytotoxicity effects are observed at 24, 48, and 72 hours. The results show that these functional GNPs have little or no toxicity to these cells. To validate the enhanced killing effect on cancer cells, various forms of radiation are applied such as 200 kVp X-rays and gamma-rays, to the cells, both with and without functional GNPs. By comparison with irradiation alone, the results show that GNPs significantly enhance cancer killing.

Surface functionalization of zinc oxide by carboxyalkylphosphonic acid self-assembled monolayers.

Two carboxyalkylphosphonic acids (HOOC(CH(2))(n)P(O)(OH)(2), n = 2 for 3-PPA and n = 9 for 10-PDA) have been deposited onto 1D zinc oxide (ZnO) nanowires and bare ZnO wafers to form stable self-assembled monolayers (SAMs). The samples were systematically characterized using wettability, atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS). 3-PPA was bound to the ZnO surfaces mainly through the CO(2)H headgroup, and 10-PDA formed self-assembled monolayers on the nanoscaled ZnO surface through the PO(3)H(2) headgroups. To verify the potential utilization of the functionalized surfaces in the construction of biosensors or bioelectronics, IgG (immunoglobulin G) protein immobilization through SAM bridging was demonstrated. This work expands the application of phosphonic acid-based surface functionalization on sensing and optoelectronic devices.

Enhanced nonenzymatic hydrogen peroxide sensing with reduced graphene oxide/ferroferric oxide nanocomposites.

A nonenzymatic hydrogen peroxide (H(2)O(2)) sensor was fabricated using the reduced graphene oxide (RGO) and ferroferric oxide (Fe(3)O(4)) nanocomposites as the sensing material. The nanocomposites were synthesized by coprecipitation method and characterized by high-resolution transmission electron microscopy and X-ray diffraction. Results showed that the RGO sheet was evenly decorated by the well-crystallized Fe(3)O(4) nanoparticles. The nanocomposites showed enhanced catalytic ability to the reduction of hydrogen peroxide compared with the RGO, Fe(3)O(4) nanoparticles alone and the mixture materials. The sensor has a quite wide linear range from 0.1mM to 6mM (R(2)=0.990) with less than 5s response time. Moreover, its detection limit is 3.2 μM (S/N=3). The anti-interference ability, long-term stability and potential application in real samples of the sensor is also assessed. This work expands the application of the graphene-based nanomaterials in the sensor areas.

CMOS-compatible, label-free silicon-nanowire biosensors to detect cardiac troponin I for acute myocardial infarction diagnosis

A label-free biosensor for electrical detection of cardiac troponin I (cTnI), a highly sensitive and selective biomarker of acute myocardial infarction (AMI), is demonstrated using silicon nanowire (SiNW) based field-effect transistors (FETs). The FET devices were fabricated by a complementary metal oxide semiconductor (CMOS) compatible top-down approach to define the SiNW followed by tetramethylammonium hydroxide (TMAH) wet etching. Electrical characterizations of the SiNW FET revealed an ambipolar conduction characteristic with an on/off ratio of 10(5)-10(6). CTnI monoclonal antibodies were then covalently immobilized on the SiNW surfaces. By integrating with a homemade biosensor measurement system, the biosensor exhibited rapid and sensitive response to cTnI proteins. The current response showed a nature of logarithm relationship against the cTnI concentration from 46 ng/mL down to 0.092 ng/mL. Moreover, an anti-interference capability of the fabricated biosensor was also assessed. By utilizing the top-down fabrication method, this work provides an efficient way for the cTnI proteins detection with an enormous potential of mass-production, which definitely facilitate the practical applications.

The Effects of Topographical Patterns and Sizes on Neural Stem Cell Behavior

Engineered topographical manipulation, a paralleling approach with conventional biochemical cues, has recently attracted the growing interests in utilizations to control stem cell fate. In this study, effects of topological parameters, pattern and size are emphasized on the proliferation and differentiation of adult neural stem cells (ANSCs). We fabricate micro-scale topographical Si wafers with two different feature sizes. These topographical patterns present linear micro-pattern (LMP), circular micro-pattern (CMP) and dot micro-pattern (DMP). The results show that the three topography substrates are suitable for ANSC growth, while they all depress ANSC proliferation when compared to non-patterned substrates (control). Meanwhile, LMP and CMP with two feature sizes can both significantly enhance ANSC differentiation to neurons compared to control. The smaller the feature size is, the better upregulation applies to ANSC for the differentiated neurons. The underlying mechanisms of topography-enhanced neuronal differentiation are further revealed by directing suppression of mitogen-activated protein kinase/extracellular signaling-regulated kinase (MAPK/Erk) signaling pathway in ANSC using U0126, known to inhibit the activation of Erk. The statistical results suggest MAPK/Erk pathway is partially involved in topography-induced differentiation. These observations provide a better understanding on the different roles of topographical cues on stem cell behavior, especially on the selective differentiation, and facilitate to advance the field of stem cell therapy.

Label-Free MicroRNA Detection Based on Fluorescence Quenching of Gold Nanoparticles with a Competitive Hybridization.

MicroRNAs (miRNAs), critical biomarkers of acute and chronic diseases, play key regulatory roles in many biological processes. As a result, there is great demand for robust assay platforms to enable an accurate and efficient detection of low-level miRNAs in complex biological samples. In this work, a label-free and Au nanoparticles (NPs) quenching-based competition assay system was developed. In the designed system, Au NPs with diameter sizes of 10 and 20 nm displayed fluorescence quenching efficiencies of 84% and 82% for Cy3 dye on slide surface, whereas the quenching efficiency of commercial BHQ2 quencher was roughly 50%. Assay conditions were optimized for miRNA-205 detection. A limit of detection of 3.8 pM and a detection range covering from 3.8 pM to 10 nM were achieved. Furthermore, the proposed system was capable of specifically discriminating miRNAs with slight variations in their nucleotide sequence and was also qualified for assessing miRNA levels in human serum. Our strategy has the potential to provide new perspectives in profiling the pattern of miRNA expression and biomedical utilizations.

Iron nanoparticles decoration onto three-dimensional graphene for rapid and efficient degradation of azo dye.

Porous three-dimensional graphene (3DG) prepared by chemical vapor deposition, was utilized as a matrix to support nanoscale zero-valent iron (nZVI) particles. The strategies to manipulate the morphology, distribution and size of nZVI particles on the 3DG support were demonstrated. The immobilized nZVI particles with a size of 100 nm and dense deposition were achieved. A 94.5% of orange IV azo dye was removed in 60 min using nZVI particles immobilized 3DG (3DG-Fe), whereas only 70.9% was removed by free Fe nanoparticles in aqueous solution. Meanwhile, a reaction rate with orange IV of 3DG-Fe was approximately 5-fold faster than that of free Fe nanoparticles. The effects of 3DG-Fe dosage, dye concentration, reaction pH and temperature on dye degradation were also addressed. Those results imply that both lowering pH and increasing temperature led to higher reaction efficiency and rate. The kinetic data reveal that the degradation process of orange IV dye, modeled by the pseudo-first-order kinetics, might involve adsorption and redox reaction with an activation energy of 39.2 kJ/mol.

Tuning surface wettability of In(x)Ga(1-x)N nanotip arrays by phosphonic acid modification and photoillumination.

We report a facile route to reversibly tune surface wettability of In(x)Ga((1-x))N (InGaN) nanotip arrays by octylphosphonic acid (OPA) modification and ultraviolet-visible (UV-vis) light illuminations. Well-aligned InGaN nanotip arrays were grown by chemical vapor deposition (CVD). OPA was covalently attached to the InGaN nanotip surface, which was initially oxidized in Piranha solution. Because of the high surface energy of polar groups, OPA-coated InGaN nanotip arrays demonstrated superhydrophobic properties (contact angle of 154°). Transitions between superhydrophobicity and hydrophilicity were obtained through OPA adsorption and UV-vis light illumination. The InGaN nanotip surface chemistry was further characterized by X-ray photoelectron spectroscopy (XPS), which suggested a scission mechanism at P-C and MO-P (M = In and Ga) bonds of bound OPA molecules. Meanwhile, no significant surface degradation was observed after the OPA modification and phototreatments.

Noise spectroscopy as an equilibrium analysis tool for highly sensitive electrical biosensing

We demonstrate an approach for highly sensitive bio-detection based on silicon nanowire field-effect transistors by employing low frequency noise spectroscopy analysis. The inverse of noise amplitude of the device exhibits an enhanced gate coupling effect in strong inversion regime when measured in buffer solution than that in air. The approach was further validated by the detection of cardiac troponin I of 0.23 ng/ml in fetal bovine serum, in which 2 orders of change in noise amplitude was characterized. The selectivity of the proposed approach was also assessed by the addition of 10 μg/ml bovine serum albumin solution.