Ejaz Huq

Label-free sub-picomolar protein detection with field-effect transistors

Proteins mediate the bulk of biological activity and are powerfully assayed in the diagnosis of diseases. Protein detection relies largely on antibodies, which have significant technical limitations especially when immobilized on two-dimensional surfaces. Here, we report the integration of peptide aptamers with extended gate metal-oxide-semiconductor field-effect transistors (MOSFETs) to achieve label-free sub-picomolar target protein detection. Specifically, peptide aptamers that recognize highly related protein partners of the cyclin-dependent kinase (CDK) family are immobilized on the transistor gate to enable human CDK2 to be detected at 100 fM or 5 pg/mL, well within the clinically relevant range. The target specificity, ease of fabrication, and scalability of these FET arrays further demonstrate the potential application of the multiplexable field effect format to protein sensing.

Substrate induced differentiation of human mesenchymal stem cells on hydrogels with modified surface chemistry and controlled modulus

Polyacrylamide hydrogels were prepared with variable stiffness within a range of effective surface Youngs modulus values from 5.5 kPa to 152 kPa measured in the hydrated state using atomic force microscopy (AFM). The gel surface was modified with either collagen or plasma polymer coatings containing amino, carboxyl or phosphate moieties. Analysis of the surface chemistry using X-ray photoelectron spectroscopy and AFM indentation showed that the coated gels present very different surface chemistries while maintaining the range of stiffness. The density of human mesenchymal stem cells (hMSC) adhered to the materials was found to depend on the surface chemistry, with the highest cell densities achieved for collagen coated gels. The spread of each cell was shown to be greater for the stiffer surfaces independent of surface chemistry. To assess the differentiation of the hMSCs, antibody staining was carried out using markers for osteogenic (Runx2), myogenic (MyoD1) and neurogenic (β-III tubulin) cell types which revealed a dependence of marker protein expression upon both surface stiffness and chemistry. The expression of the osteogenic Runx2 marker was maximal for cells cultured on gels of 41 kPa stiffness when modified with the phosphate plasma polymer. Myogenic MyoD1 expression was maximal on the carboxyl coated gels of intermediate stiffness (10 kPa to 17 kPa). Neurogenic differentiation indicated by β-III tubulin expression was seen to be greatest on the carboxyl surfaces and for the lowest surface stiffness substrates. Using soluble factors in the medium to induce osteogenic behaviour resulted in the formation of bone nodules and matrix calcification for gel stiffness values higher than 10 kPa, especially on amino-functionalized coatings but not for collagen coated gels. The results indicate that control over differentiation fate of hMSCs can be exerted using not only surface stiffness, a result previously widely reported, but also surface chemistry working in tandem with the influence of compliance. This has great significance in developing stem cell therapies when synthetic surfaces are used as scaffolds, delivery vehicles or culture ware.

Microtextured surfaces for deep-brain stimulation electrodes: a biologically inspired design to reduce lead migration.

OBJECTIVE Hardware-related complications of deep brain stimulation (DBS) surgery have been reported with adverse effects in postoperative electrode migration. We report that the addition of microtextured features to the surface of a DBS-like probe can minimize the extent of electrode migration in ex vivo porcine brain. METHODS A DBS lead and microtextured strips, mounted with a fiberoptic displacement sensor, were embedded 15-mm deep inside a cadaveric porcine brain through holes on the skull. The local displacement of brain tissue surrounding each strip was detected along the direction of insertion by the optical sensor while the porcine head simulated brain shift during rotation between supine and upright postures. RESULTS The triangular toothed strip with protruding height of 250 μm enabled a better grip of the surrounding brain tissue than standard DBS lead, minimizing local brain displacement to 77 μm versus 326 μm respectively, when the porcine head was shifted from the supine to the upright position as the result of gravity. In addition, brain tissue damage resulting from the removal of toothed strips exhibited less-extensive tissue disruption, attributable to the microtextured surface. CONCLUSIONS These preliminary results show that microtextured strips embedded into cadaveric porcine brain produce an anchoring effect on local tissue during brain shift, suggesting a way to reduce DBS lead migration without additional tissue damage beyond the strip geometry.

APPLICATIONS OF NANOIMPRINT LITHOGRAPHY FOR BIOCHEMICAL AND NANOPHOTONIC STRUCTURES USING SU-8

Nanoimprint lithography (NIL) technology has aroused great interests in both academia and industry due to its high resolution, low-cost, and high-volume nanopatterning capability. And as an expoxy resin-based negative amplified photoresist, SU-8 is an ideal candidate for NIL because of its low-glass-transition temperature, low-volume shrinkage coefficient, and good optical properties. In this reviewing paper, we highlight the major technical achievements in NIL on epoxy resin and its applications for bio- and nanophotonic structures. NIL was also applied for the duplication of imprint templates, originally fabricated by e-beam lithography (EBL) followed by reactive ion etch (RIE), using a SU-8/SiO2/PMMA tri-layer technique. And nanoimprint properties were systematically investigated for optimization. The developed nanoimprint process for different applications indicates promising industrial potentials in the next generation lithography resolution.

Surface stiffness modification by e-beam irradiation for stem cell growth controla)

This article reports a novel method to effectively modify the surface stiffness for the differentiation of stem cell growth. To achieve large range of surface hardness, focused electron beam is first employed to radiate hydrogen silsesquioxane (HSQ) film. With different degrees of curing caused by certain e-beam exposure, the HSQ demonstrates various Young’s modulus from 0.5 to 2 GPa, measured by an atomic force microscope. Fourier transform infrared spectra were used to investigate the origin of the stiffness change, which is due to the e-beam irradiation induced network formation inside HSQ. The novel technique possesses a number of advantages such as precision control of stiffness in a broad matrix with high spatial resolution. It also offers a good opportunity to define the geometry shape with a constant stiffness in nanometer scale.

Potentiometric detection of protein interactions with peptide aptamers

Label-free electrical detection of protein interactions has been achieved by direct measurement of variations in open circuit potential using an accurate differential voltage measurement as well as field-effect transistors. Our model system involves a panel of peptide aptamers that recognise specific protein partners of the cyclin-dependent kinase family, which are relevant to cancer research applications.

Surface microstructuring of biocompatible bone analogue material HAPEX using LIGA technique and embossing

HAPEX is an artificial bone analogue composite based on hydroxyapatite and polyethylene, which can be applied for growth of bone cells. Due to its biocompatibility and favourable mechanical properties, HAPEX is used for orthopaedic implants like tympanic (middle ear) bones. The morphology of HAPEX surfaces is of high interest and it is believed that surface structuring on a micron scale might improve the growth conditions for bone cells. A new and simple approach for the microstructuring of HAPEX surfaces has been investigated using LIGA technique. LIGA is a combination of several processes, in particular lithography, electroplating and forming/moulding. For HAPEX surface structuring, arrays of dots, grids and lines with typical lateral dimension ranging from 5 μm to 50 μm were created on a chromium photomask and the patterns were transferred into thick SU-8 photoresist (structure height > 10 μm) by UV lithography. Subsequently, the SU-8 structures served as moulds for electroplating nickel on Si wafers and nickel substrates. The final nickel microstructures were used as embossing master for the HAPEX material. Embossing was carried out using a conventional press (> 500 hPa) with the facility to heat the master and the HAPEX. The temperature ranged from ambient to a few degrees above glass transition temperature (Tg) of HAPEX. The paper will include details of the fabrication process and process tolerances in lateral and vertical directions. Data obtained are correlated to the temperature used during embossing.

Dataset for Helium Ion Beam Lithography on Fullerene Molecular Resists for Sub-10 nm Patterning

Dataset supporting: Shi, Xiaoqing et al (2016) Helium ion beam lithography on fullerene molecular resists for sub-10 nm patterning. Microelectronic Engineering.Helium ion beam lithography (HIBL) is an emerging technique that uses a sub-nanometre focused beam of helium ions generated in the helium ion microscope to expose resist. It benefits from high resolution, high sensitivity and a low proximity effect. Here we present an investigation into HIBL on a novel, negative tone fullerene-derivative molecular resist. Analysis of large area exposures reveals a sensitivity of ~40 ?C/cm2 with a 30 keV helium beam which is almost three orders of magnitude higher than the sensitivity of this resist to a 30 keV electron beam. Sparse line features with line widths of 7.3 nm are achieved on the ~10 nm thick resist. The fabrication of 8.5 half-pitched lines with good feature separation and 6 nm half-pitched lines with inferior but still resolvable separation are also shown in this study. Thus, sub-10 nm patterning with small proximity effect is demonstrated using HIBL using standard processing conditions, establishing its potential as an alternative to EBL for rapid prototyping of beyond CMOS devices.Funded by Single Nanometer Manufacturing for beyond CMOS devices (SNM, 318804), 2013 to 2016.

Highly ordered growth of ZnO nanostructures by combination of nanoimprint lithography and hydrothermal method

By combining nanoimprint lithography and traditional hydrothermal growth method of ZnO nanorods, vertical and well patterned ZnO nanostructures were successfully fabricated. The imprinted SU-8 resist deep trenches above the ZnO seed layer prohibit the lateral growth of ZnO nanorods. Various patterned vertical ZnO nanostructures like nanorods and nanowalls can be obtained. The improvement of photoluminescence property of ZnO nanorods was observed after removing the SU-8 resist from the substrate by O2 reactive ion etching (RIE).

Trilayer nanoimprint fabrication and simulation of the silicon nanowire sensor for gas detection

In this work, we demonstrate a novel SU8/SiO2 /PMMA trilayer nanoimprint technique to fabricate the silicon nanowire (SiNW) sensor used for gas detection. The SiNW sensor fabricated in our experiment is based on the silicon on insulator (SOI) substrate which is doped by boron with a dopant concentration of 8×1017cm−3. Two nanowire sensors with different linewidths as well as a thin-film plane device were fabricated for comparison. The fabricated devices were then used for detecting 250ppm NO2 and 250ppm NH3. The results show a large enhanced sensitivity especially for the narrower device. Finally, a computer simulation work was done to qualitatively explain our experimental results.