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We report on a compact and cost-effective integrated label-free biosensor configuration which is based on the refractive index sensitivity of the localized surface plasmon resonance (LSPR) of gold nanostructures. Aiming for compactification and miniaturization of the sensor, arrays of nanodiscs were fabricated on the planar surface of a gradient index (GRIN) lens, which acts as a substrate as well as an imaging objective for the light scattered by the gold structures. Integration of the lens into a microfluidic flow cell enabled the controlled exchange of liquid media at the sensor surface. The light scattered by the nanostructures was investigated spatially and spectrally resolved making use of the imaging properties of the GRIN lens. Dynamic spectral analysis during refractive index changes was conducted, revealing high sensitivities of up to 372 nm per refractive index unit for the shift of the LSPR. Biosensing capabilities were demonstrated by the detection of binding of an analyte by means of a testosterone-immunoassay.

The efficiency and safety of neuronal stimulation with implants strongly depend on the electrode material. Microelectrodes composed of iridium oxide are becoming increasingly important as they exhibit excellent charge injection capacity (CIC) as well as charge storage capacity (CSC). We present the development of a robust process for the fabrication of sputtered iridium oxide films (SIROF). This process has been used for the "RETINA IMPLANT Alpha AMS" for several years of subretinal stimulation. In this paper, we describe the full experimental investigation of the electrode material. The electrochemical and morphological properties were investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), voltage transient measurements, and focused ion beam-scanning electron microscopy (FIB-SEM). The implementation on the CMOS chip of the retinal prosthesis is presented. The deposition process window was investigated extensively. Major changes in process parameters lead to a difference in impedance of only 10% of the mean. Accelerated aging tests revealed a long-term stability of the electrodes of at least 10 years under conditions of use. The SIROF electrodes (diameter 30 µm) show low impedance (15.9 kΩ), excellent CSC (50.9 mC/cm 2), and high CIC (4.2 mC/cm 2). In summary, the robustness of the presented deposition process and the large process window enable the integration of high-quality SIROF microelectrodes in active implants and thus long-term stability in a wide range of safe electrical stimulation.

Two-dimensional materials can be combined by placing individual layers on top of each other, so that they are bound only by their van der Waals interaction. The sequence of layers can be chosen arbitrarily, enabling an essentially atomic-level control of the material and thereby a wide choice of properties along one dimension. However, simultaneous control over the structure in the in-plane directions is so far still rather limited. Here, we combine spatially controlled modifications of 2D materials, using focused electron irradiation or electron beam induced etching, with the layer-by-layer assembly of van der Waals heterostructures. The presented assembly process makes it possible to structure each layer with an arbitrary pattern prior to the assembly into the heterostructure. Moreover, it enables a stacking of the layers with accurate lateral alignment, with an accuracy of currently 10 nm, under observation in an electron microscope. Together, this enables the fabrication of almost arbitrary 3D structures with highest spatial resolution.