Polyacrylamide hydrogels were prepared with variable stiffness within a range of effective surface Young's 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 (b-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 b-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.

As nanoelectronic device design pushes towards ever smaller feature sizes, there is an increasing need for new lithographic patterning techniques and resists. A new class of fullerene-based molecular resists are being developed to meet this need, taking advantage of a smaller molecular size to achieve higher resolution pattern definition for electron beam lithography (EBL) than conventional resists such as PMMA allow [1]. Recent EBL investigations with fullerene resists have demonstrated high resolution patterning, with a high sensitivity and low line edge roughness [2]. Furthermore, the resists exhibit high etch resistance, which is desirable for subsequent pattern transfer. Helium ion beam lithography (HIBL), an emerging technique that uses a sub-nanometer focused beam of helium ions generated in the helium ion microscope (HIM) to expose resist, promises to drive nano-patterning beyond the capabilities of conventional EBL [3,4]. Here we present the latest results from an investigation into HIBL with a novel fullerene-derivative molecular resist.A fullerene derivative dissolved in anisole (HM-01, Irresistible Materials Ltd.) was spin-coated onto silicon wafers to a thickness of approximately 15 nm. Following a pre-exposure bake, the samples were exposed in a helium ion microscope (HIM, Zeiss Orion Plus) to a 30 keV focused helium ion beam. The samples were then developed in cyclohexanone to produce various negative tone patterns which were characterised using atomic force microscopy (AFM) and HIM.To determine the limits of HIBL pattern definition in HM-01 resist, arrays of single pixel lines with pitches ranging from 44 nm to 10 nm were exposed over a range of doses from 0.005 to 0.1 nC/cm. Examples of HIM secondary electron images of the resulting patterns are presented in Figure 1 and individual lines are still resolvable with a 12 nm pitch (Figure 1 f)). The optimum dose for single pixel line arrays with pitches down to 14.5 nm was determined to be 0.06 nC/cm (Figure 1 b) and e)). The optimum dose was found to reduce for pitches below this range, possibly due to proximity effects, which, whilst significantly smaller than in conventional EBL, do become noticeable at these very small length scales. Continuous and well defined lines with a 17 nm pitch and a 0.5 mark-space ratio (line width of ~ 8.5 nm) were achieved as shown in the HIM image and corresponding contrast line profile in Figure 2. This is comparable to the best achievable with state-of-the-art EBL, despite being carried out using a tool not optimized for lithography. Area exposure of HM-01 resist using HIBL was also investigated: AFM characterisation on large area exposures resulted in the dose response curve shown in Figure 3, confirming negative tone behaviour with a sensitivity (50% of final full exposed thickness) of ~40 µC/cm 2 .Further process optimization and pattern transfer development are currently underway with the aim of providing a full assessment of the capabilities and limitations of HIBL in combination with molecular resists for nex...

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.