Ruigong Su

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.

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.

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.

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.

Reactant-governing growth direction of indium nitride nanowires

Hexagonal wurtzite InN nanowires are grown via a vapor-liquid-solid (VLS) mechanism with an Au catalyst. Microstructure characterizations of a large number of nanowires demonstrate that the growth direction of InN nanowires is governed by variable NH(3) flux. InN nanowires at a NH(3) flux of 10 standard cubic centimeters per minute (sccm) grow preferentially in a hexagonal close-packed (hcp) <1010> direction, while those at 100 sccm NH(3) flux favor the hcp <0001> direction. A free energy minimization model is proposed to interpret this phenomenon. The first-principles calculations reveal that the <1010> oriented nucleus has the lowest energy at the lower NH(3) flux. In contrast, when NH(3) flux is high, the <0001> oriented nucleus has the lowest energy.