No abstract

We report on the optical and electrical performances of periodic photonic nanostructures, prepared by nanoimprint lithography (NIL) and two different etching routes, plasma, and wet chemical etching. Optically, these periodic nanostructures offer a lower integrated reflectance compared with the industrial state-of-the-art random pyramid texturing. However, electrically, they are known to be more challenging for solar cell integration. We propose the use of wet chemical etching for fabricating inverted nanopyramids as a way to minimize the surface recombination velocities and maintain a conventional cell integration flow. In contrast to the broadly used plasma etching for nanopatterning, the wet chemically etched nanopatterning results in low surface recombination velocities, comparable with the state-of-the-art random pyramid texturing. Applied to 40-μm thick epitaxially grown crystalline silicon foils bonded to a glass carrier superstrate, the periodic-inverted nanopyramids show carrier lifetimes comparable with the non-textured reference foils (τ eff = 250 μs). We estimate a maximum effective surface recombination velocity of~8 cm/s at the patterned surface, which is comparable with the state-of-the-art values for crystalline silicon solar cells.

In recent years, the development of portable platforms for performing fast and point-of-care analyses has drawn considerable attention for their wide variety of applications in life science. In this framework, tools combining magnetoresistive biosensors with magnetic markers have been widely studied in order to detect concentrations of specific molecules, demonstrating high sensitivity and ease of integration with conventional electronics. In this work, first, we develop a protocol for efficient hybridization of natural DNA; then, we show the detection of hybridization events involving natural DNA, namely genomic DNA extracted from the pathogenic bacterium Listeria monocytogenes, via a compact magnetic tunneling junction (MTJ)-based biosensing apparatus. The platform comprises dedicated portable electronic and microfluidic setups, enabling point-of-care biological assays. A sensitivity below the nM range is demonstrated. This work constitutes a step forward towards the development of portable lab-on-chip platforms, for the multiplexed detection of pathogenic health threats in food and food processing environment

Abstract:The fine control of the exchange coupling strength and blocking temperature ofexchange bias systems is an important requirement for the development of magnetoresistive sensors with two pinned electrodes. In this paper, we successfully tune these parameters in top-and bottom-pinned systems, comprising 5 nm thick Co 40 Fe 40 B 20 and 6.5 nm thick Ir 22 Mn 78 films. By inserting Ru impurities at different concentrations in the Ir 22 Mn 78 layer, blocking temperatures ranging from 220˝C to 100˝C and exchange bias fields from 200 Oe to 60 Oe are obtained. This method is then applied to the fabrication of sensors based on magnetic tunneling junctions consisting of a pinned synthetic antiferromagnet reference layer and a top-pinned sensing layer. This work paves the way towards the development of new sensors with finely tuned magnetic anisotropies.

Magnetoencephalography has been established nowadays as a crucial in vivo technique for clinical and diagnostic applications due to its unprecedented spatial and temporal resolution and its non-invasive methods. However, the innate nature of the biomagnetic signals derived from active biological tissue is still largely unknown. One alternative possibility for in vitro analysis is the use of magnetic sensor arrays based on Magnetoresistance. However, these sensors have never been used to perform long-term in vitro studies mainly due to critical biocompatibility issues with neurons in culture. In this study, we present the first biomagnetic chip based on magnetic tunnel junction (MTJ) technology for cell culture studies and show the biocompatibility of these sensors. We obtained a full biocompatibility of the system through the planarization of the sensors and the use of a three-layer capping of SiO2/Si3N4/SiO2. We grew primary neurons up to 20 days on the top of our devices and obtained proper functionality and viability of the overlying neuronal networks. At the same time, MTJ sensors kept their performances unchanged for several weeks in contact with neurons and neuronal medium. These results pave the way to the development of high performing biomagnetic sensing technology for the electrophysiology of in vitro systems, in analogy with Multi Electrode Arrays.

High-performing hybridization platforms fabricated by reactive microcontact printing of DNA probes are presented. Multishaped PDMS molds are used to covalently bind oligonucleotides over a functional copolymer (DMA-NAS-MAPS) surface. Printed structures with minimum width of about 1.5 μm, spaced by 10 μm, are demonstrated, with edge corrugation lower than 300 nm. The quantification of the immobilized surface probes via fluorescence imaging gives a remarkable concentration of 3.3 × 10(3) oligonucleotides/μm(2), almost totally active when used as probes in DNA-DNA hybridization assays. Indeed, fluorescence and atomic force microscopy show a 95% efficiency in target binding and uniform DNA hybridization over printed areas.

Magnetic cell manipulation utilizing magnetic particles and diamagnetic collagen fibers J. Appl. Phys. 99, 08R906 (2006); 10.1063/1.2175957Superconducting quantum interference device-based magnetic nanoparticle relaxation measurement as a novel tool for the binding specific detection of biological binding reactions (abstract)

A promising strategy to get deeper insight on brain functionalities relies on the investigation of neural activities at the cellular and sub-cellular level. In this framework, methods for recording neuron electrical activity have gained interest over the years. Main technological challenges are associated to finding highly sensitive detection schemes, providing considerable spatial and temporal resolution. Moreover, the possibility to perform non-invasive assays would constitute a noteworthy benefit. In this work, we present a magnetoresistive platform for the detection of the action potential propagation in neural cells. Such platform allows, in perspective, the in vitro recording of neural signals arising from single neurons, neural networks and brain slices.