Meta-hologram-based authentication scheme employing a speckle pattern fingerprint.

A concept for an optical holographic security tag is proposed and demonstrated. When illuminated with a laser beam, the image scattered from the tag projects a Quick Response code which encodes identifying information. The image also carries pseudorandom speckle noise, from which a unique speckle pattern "fingerprint" is derived. We show numerically that the tag is unclonable without access to a secret key - the starting conditions of the design algorithm. However, given the key, it is straightforward to reproduce a tag exhibiting the expected fingerprint. Several tags have been realized, implemented as plasmonic meta-holograms, and characterized experimentally. The robustness of the tag to fabrication error and its resilience to counterfeiting are studied in detail and demonstrated experimentally.

Neuronal soma migration is determined by neurite tension.

Neuronal migration is an intricate process involving a wide range of cellular mechanisms, some of which are still largely unknown. Using specially prepared culturing substrates, we were able to explore this and other developmental processes in networks composed of cultured locust neurons, and to analyze the role of neurite tension in these processes. Time lapse investigation shows that the shape and position of the cell soma are both linked to the extent and direction of the combined tension in its neurites. In particular, for migrating neurons (over 1-2 days) with three main neurites, a force-balance between neurite tension forces was demonstrated (ΣF=0). The results presented here suggest that neuronal migration is strongly affected by tension in neurites rather than being entirely determined by the interaction between soma and substrate. The validity of these results to other in-vitro and in-vivo data is discussed.

Engineered neuronal circuits shaped and interfaced with carbon nanotube microelectrode arrays.

Standard micro-fabrication techniques which were originally developed to fabricate semi-conducting electronic devices were inadvertently found to be adequate for bio-chip fabrication suited for applications such as stimulation and recording from neurons in-vitro as well as in-vivo. However, cell adhesion to conventional micro-chips is poor and chemical treatments are needed to facilitate the interaction between the device surface and the cells. Here we present novel carbon nanotube-based electrode arrays composed of cell-alluring carbon nanotube (CNT) islands. These play a double role of anchoring neurons directly and only onto the electrode sites (with no need for chemical treatments) and facilitating high fidelity electrical interfacing-recording and stimulation. This method presents an important step towards building nano-based neurochips of precisely engineered networks. These neurochips can provide unique platform for studying the activity patterns of ordered networks as well as for testing the effects of network damage and methods of network repair.

Iron assisted growth of copper-tipped multi-walled carbon nanotubes.

Carbon nanotubes incorporating copper are highly sought after for nanoelectronic applications. Indeed, several recent studies have demonstrated the production of copper-tipped nanotubes using the chemical vapor deposition method. Here we present the growth and detailed characterization of such copper-tipped nanotubes. The nanotubes grown were of a 'bamboo-like' structure, consisting of stacked cups of graphene, and were produced by chemical vapor deposition employing iron and copper nanoparticles as a catalyst and metal source respectively. Transmission electron microscopy and electron holography analysis of the tips of these nanotubes revealed a small crystalline iron particle on the inner side of the copper tip, with the nanotube structure encapsulating the iron. This form of growth may allow the formation of similar structures with various other metal-tipped carbon nanotubes to be manufactured.

Tube-tube and tube-surface interactions in straight suspended carbon nanotube structures.

An investigation concerning the tautness of suspended carbon nanotubes (CNTs) grown using the chemical vapor deposition (CVD) method is presented. The suspended nanotubes were analyzed with both a transmission electron microscope (TEM) and a high-resolution scanning electron microscope (HR-SEM). The HR-SEM and TEM investigations revealed that the interaction between CNTs among themselves as well as with the surface on which they are grown is a primary cause for the tautness of suspended tubes. Specifically, the tube-tube and tube-surface dynamics cause adjoining tubes to create a "zipper-effect", thereby straightening and tightening them. Suspended CNTs cling to each other and to as much of the surface as possible and thus minimize their total energy, creating taut, suspended structures. This effect can be so strong so as to force wide tubes to buckle, with no other external force involved. The implications of this study include all forms of alignment processes of nanotubes using the CVD method. The results presented here provide the groundwork for the capability of fine-tuning the control of CNT network formation using substrate mechanical features.

Compact self-wiring in cultured neural networks.

We present a novel approach for patterning cultured neural networks in which a particular geometry is achieved via anchoring of cell clusters (tens of cells/each) at specific positions. In addition, compact connections among pairs of clusters occur spontaneously through a single non-adherent straight bundle composed of axons and dendrites. The anchors that stabilize the cell clusters are either poly-D-lysine, a strong adhesive substrate, or carbon nanotubes. Square, triangular and circular structures of connectivity were successfully realized. Monitoring the dynamics of the forming networks in real time revealed that the self-assembly process is mainly driven by the ability of the neuronal cell clusters to move away from each other while continuously stretching a neurite bundle in between. Using the presented technique, we achieved networks with wiring regions which are made exclusively of neuronal processes unbound to the surface. The resulted network patterns are very stable and can be maintained for as long as 11 weeks. The approach can be used to build advanced neuro-chips for bio-sensing applications (e.g. drug and toxin detection) where the structure, stability and reproducibility of the networks are of great relevance.

Transmission electron microscope imaging of single-walled carbon nanotube interactions and mechanics on nitride grids.

A method for analysing systems of isolated single-walled carbon nanotubes is of paramount importance if their structural characteristics are to be fully understood and utilized. Here we offer a simple technique for analysing such systems, with unprecedented contrast, using transmission electron microscope imaging of carbon nanotubes suspended over large holes in a silicon nitride grid. The nanotubes are grown directly on the viewing grids, using the chemical vapour deposition process, thus avoiding the use of chemicals or aggressive treatments. This method is simultaneously non-invasive, reusable, allows the analysis of multiple structures based on carbon nanotubes and is quickly implemented.