Emergent Functional Properties of Neuronal Networks with Controlled Topology

The interplay between anatomical connectivity and dynamics in neural networks plays a key role in the functional properties of the brain and in the associated connectivity changes induced by neural diseases. However, a detailed experimental investigation of this interplay at both cellular and population scales in the living brain is limited by accessibility. Alternatively, to investigate the basic operational principles with morphological, electrophysiological and computational methods, the activity emerging from large in vitro networks of primary neurons organized with imposed topologies can be studied. Here, we validated the use of a new bio-printing approach, which effectively maintains the topology of hippocampal cultures in vitro and investigated, by patch-clamp and MEA electrophysiology, the emerging functional properties of these grid-confined networks. In spite of differences in the organization of physical connectivity, our bio-patterned grid networks retained the key properties of synaptic transmission, short-term plasticity and overall network activity with respect to random networks. Interestingly, the imposed grid topology resulted in a reinforcement of functional connections along orthogonal directions, shorter connectivity links and a greatly increased spiking probability in response to focal stimulation. These results clearly demonstrate that reliable functional studies can nowadays be performed on large neuronal networks in the presence of sustained changes in the physical network connectivity

ABSOLUTE FLUORESCENCE CROSS-SECTIONS AND QUANTUM YIELDS IN NO2NO_{2}

Author Institution:In this work we have measured fluorescence cross-section and quantum yields in the laser induced fluorescence of $NO_{2}$. A low pressure sample of $NO_{2}$ (typically 5 to 50 $\mu$) was excited by either the second harmonic of a Nd: YAG laser (532.1 nm. 0.35 nm bandwidth) or a dye laser operating in the 430-450 nm range (approx. .003 nm bandwidth). Fluorescence was observed spectrally resolved by a monochromator and time resolved by a boxcar integrator. Time resolution allowed measurement from collision-free through collisional-quenching regimes. Relatives calibration of the detection system was performed using a standard lamp Raman scattering from $N_{2}$ and $O_{2}$ served as absolute intensity standards so that absolute cross-sections for scattering into a fixed fluorescence band width were obtained in both the collision-free and collision-dominated regimes. Absolute fluorescence cross-sections have thus been measured into the 000 through 002 vibrational band of the fluorescence spectrum. Quantum yields into fixed fluorescence band-widths have been determined from these data and measured absorption cross-sections. In addition the time evolution of the fluorescence and dependence upon self-quenching and quenching in $N_{2}$ and $O_{2}$ have been explored

A Surface Plasmon Resonance Investigation of the Selective Interaction of Organic Vapors with Cavitands

A class of supramolecules, called cavitands, that have been shown to exhibit discotic phases depending on the structure, are shown to have potential for sensing applications. Certain cavitands (macrocyclic compounds based on resorcinarenes) display selectivity of interactions with organic vapors. We use Surface Plasmon Resonance (SPR) to demonstrate this principle. The two cavitands chosen for this study, had both a different size and shape of the preorganized cavity and were exposed to a variety of aromatic and chlorinated hydrocarbons. QxCav-1 (cavitand) was found to have a marked preference for the aromatic compounds; with the sequence of selectivity, determined by SPR to be nitrobenzene > toluene > benzene. MeCav-2 (cavitand) on the other hand, showed higher selectivity to dichloromethane with respect to aromatic vapors at room temperature. Cavitands therefore represent attractive sensing materials, with potential for application in devices using optical transduction schemes based on a refractive index change

Optical Sensing of the Selective Interaction of Aromatic Vapors with Cavitands

Cavitands represent an important class of synthetic molecular receptors with significant potential for chemical recognition. We use surface plasmon resonance (SPR) to demonstrate this fact using several organic vapors (aromatic and non-aromatic analytes) and three cavitands. The three cavitands (abbreviated QxCav-1, MeCav-2, and PzCav-3) chosen for this study, had a different size and shape of the pre-organized cavity. QxCav-1 was found to have a marked preference for the aromatic compounds while MeCav-2 showed an insignificant response towards these analytes and PzCav-3 showed intermediate preference for some of these analytes. The recognition pattern reveals the importance of the cavity size for interaction and confinement of the analytes. Based on the results, it is expected that cavitands will have great potential for application in chemical sensing devices using optical transduction schemes such as SPR

Fabrication of patterned DNA surfaces.

Two photolithographic methods are described for the formation of patterned single or multiple DNA species on SiO2 substrates. In the first approach, substrates are treated with a photochemically labile organosilane monolayer film. Irradiation of these surfaces with patterned deep UV (193 nm) light results in patterned chemically reactive groups which are then reacted with heterobifunctional crosslinking molecules. Covalent attachment of modified synthetic DNA oligomers to the crosslinker results in stable DNA patterns. Alternatively, a photoresist is spin-coated over a silane film which had been previously modified with the heterobifunctional crosslinker. Upon patterned irradiation and subsequent development, the underlying crosslinker-modified layer is revealed, and is then reacted with a chemically modified DNA. Feature dimensions to 1 micron are observed when a single fluorescent DNA is attached to the surface. By performing sequential exposures, we have successfully immobilized two distinguishable DNA oligomers on a single surface. Synthetic DNA immobilized in this manner retains the ability to hybridize to its complementary strand, suggesting that these approaches may find utility in the development of miniaturized DNA-based biosensors