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We report artificial nanopores in the form of quartz nanopipettes with ca. 10 nm orifices functionalized with molecular recognition elements termed aptamers that reversibly recognize serotonin with high specificity and selectivity. Nanoscale confinement of ion fluxes, analyte-specific aptamer conformational changes, and related surface charge variations enable serotonin sensing. We demonstrate detection of physiologically relevant serotonin amounts in complex environments such as neurobasal media in which neurons are cultured in vitro. In addition to sensing in physiologically relevant matrices with high sensitivity (picomolar detection limits), we interrogate the detection mechanism via complementary techniques such as quartz crystal microbalance with dissipation monitoring and electrochemical impedance spectroscopy. Moreover, we provide a novel theoretical model for structureswitching aptamer-modified nanopipette systems that supports experimental findings. Validation of specific and selective smallmolecule detection in parallel with mechanistic investigations, demonstrates the potential of conformationally changing aptamermodified nanopipettes as rapid, label-free, and translatable nanotools for diverse biological systems.

Label-free biosensors enable the monitoring of biomolecular interactions in real-time, which is key to the analysis of the binding characteristics of biomolecules. While refractometric optical biosensors such as SPR [Surface Plasmon Resonance] are sensitive and well-established, they are susceptible to any change of the refractive index in the sensing volume caused by minute variations in composition of the sample buffer, temperature drifts and most importantly nonspecific binding to the sensor surface. Refractometric biosensors require reference channels as well as temperature stabilisation and their applicability in complex fluids such as blood is limited by nonspecific bindings. Focal molography does not measure the refractive index of the entire sensing volume but detects the diffracted light from a coherent assembly of analyte molecules. Thus, it does not suffer from the limitations of refractometric sensors since they stem from non-coherent processes and therefore do not add to the coherent molographic signal. The coherent assembly is generated by selective binding of the analyte molecules to a synthetic binding pattern -the mologram. Focal Molography has been introduced theoretically [C. Fattinger, Phys. Rev. X 4, 031024 (2014)] and verified experimentally Nat. Nanotechnol. 12, 1089 (2017)] in previous papers. However, further understanding of the underlying physics and a diffraction-limited readout is needed to unveil its full potential. This paper introduces refined theoretical models which can accurately quantify the amount of biological matter bound to the mologram from the diffracted intensity. In addition, it presents measurements of diffraction-limited molographic foci i.e. Airy discs. These improvements enabled us to demonstrate a resolution in real-time binding experiments comparable to the best SPR sensors, without the need of temperature stabilisation or drift correction and to detect low molecular weight compounds labelfree in an endpoint format. The presented experiments exemplify the robustness and sensitivity of the diffractometric sensor principle.

Thin networks of high aspect ratio conductive nanowires can combine high electrical conductivity with excellent optical transparency, which has led to a widespread use of nanowires in transparent electrodes, transistors, sensors, and flexible and stretchable conductors. Although the material and application aspects of conductive nanowire films have been thoroughly explored, there is still no model which can relate fundamental physical quantities, like wire resistance, contact resistance and nanowire density, to the sheet resistance of the film. Here we derive an analytical model for the electrical conduction within nanowire networks based on an analysis of the parallel resistor network.The model captures the transport characteristics and fits a wide range of experimental data, allowing for the determination of physical parameters and performance limiting factors, in sharp contrast to the commonly employed percolation theory. The model

We introduce a photolithography process compatible with soft and rigid substrates, enabling the fabrication of complex 3D interconnected patterns of silver nanowire (AgNW) networks embedded in polydimethylsiloxane (PDMS). Dimensions of the AgNW micropatterns are controlled within the film plane by photolithography, whereas thickness is controlled via a novel and uniform deposition technique using centrifugation. We report the first systematic characterization of the electromechanical properties of such microelectrodes with finest stretchable feature of 15 μm. We observe a geometry-dependent behavior of the gauge factor not only by changing the thickness of the microelectrodes, as it has been commonly reported so far, but also by varying their lateral dimensions. The presented nanocomposites exhibited sheet resistances down to 0.6 Ω/sq, gauge factors ranging from 0.01 to 100, and stretchability above 50% uniaxial strain. This versatile process allows for the production of highly sensitive strain sensors and robust high-density stretchable conductors on a wafer scale with direct implications in mass production of stretchable electronic devices.

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