SummaryDuring development, cells undergo dramatic changes in their morphology. By affecting contact geometry, these morphological changes could influence cellular communication. However, it has remained unclear whether and how signaling depends on contact geometry. This question is particularly relevant for Notch signaling, which coordinates neighboring cell fates through direct cell-cell signaling. Using micropatterning with a receptor trans-endocytosis assay, we show that signaling between pairs of cells correlates with their contact area. This relationship extends across contact diameters ranging from microns to tens of microns. Mathematical modeling predicts that dependence of signaling on contact area can bias cellular differentiation in Notch-mediated lateral inhibition processes, such that smaller cells are more likely to differentiate into signal-producing cells. Consistent with this prediction, analysis of developing chick inner ear revealed that ligand-producing hair cell precursors have smaller apical footprints than non-hair cells. Together, these results highlight the influence of cell morphology on fate determination processes.

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We combine Kelvin probe force microscopy and current-voltage measurements in order to characterize silicon-on-insulator bioFETs. The measurements were conducted on monolayer of (3-aminopropyl)-trimethoxysilane, which was deposited on ozone activated silicon oxide surface covering the transistor channel. The work function of the modified surface decreased by more than 2eV, and the threshold voltage measured on the same devices showed a very large increase (∼10V) following the chemical modification. A detailed analysis enables us to distinguish between electron affinity and field effects in such devices, and in molecular gated transistors in general.

The utilization of field-effect transistor (FET) devices in biosensing applications have been extensively studied in recent years. Qualitative and quantitative understanding of the contribution of the organic layers constructed on the device gate, and the electrolyte media, on the behavior of the device is thus crucial. In this work we analyze the contribution of different organic layers on the pH sensitivity, threshold voltage, and gain of a silicon-on-insulator based FET device. We further monitor how these properties change as function of the electrolyte screening length. Our results show that in addition to electrostatic effects, changes in the amphoteric nature of the surface also affect the device threshold voltage. These effects were found to be additive for the first (3-aminopropyl)trimethoxysilane linker layer and second biotin receptor layer. For the top streptavidin protein layer, these two effects cancel each other. The number and nature of amphoteric groups on the surface, which changes upon the formation of the layers, was shown also to affect the pH sensitivity of the device. The pH sensitivity reduces with the construction of the first two layers. However, after the formation of the streptavidin protein layer, the protein's multiple charged side chains induce an increase in the sensitivity at low ionic strengths. Furthermore, the organic layers were found to influence the device gain due to their dielectric properties, reducing the gain with the successive construction of each layer. These results demonstrate the multilevel influence of organic layers on the behavior of the FET devices.

In order to understand the mechanism of biosensing of field-effect-based biosensors and optimize their performance, the effect of each of its molecular building blocks must be understood. In this work the effect of the self-assembled linker molecules on the top of a biofield-effect transistor was studied in detail. We have combined Kelvin probe force microscopy, current-voltage measurements, and device simulations in order to trace the mechanism of silicon-on-insulator biological field-effect transistors. The measurements were conducted on the widely used linker molecules (3-aminopropyl)trimethoxysilane (APTMS) and (11-aminoundecyl)triethoxysilane (AUTES), which were self-assembled on an ozone-activated silicon oxide surface covering the transistor channel. The work function of the modified silicon oxide decreased by more then 1.5 eV, while the transistor threshold voltage increased by about 30 V following the self-assembly. A detailed analysis indicates that these changes are due to negative-induced charges on the top dielectric layer, and an effective dipole due to the polar monolayer. The results were compared with metal gated transistors fabricated on the same die, and a factor converting the molecular charge to the metal gate voltage was extracted.