Hyoungwon Baac

Optical measurement of neural activity using surface plasmon resonance.

We demonstrate that surface plasmon resonance (SPR) is applicable to the optical detection of neural signals. A low-noise SPR sensor was developed as a label- and artifact-free method for the extracellular recording of neural activity. The optical responses obtained from a rat sciatic nerve were highly correlated with simultaneously recorded electrical responses. Additional studies with stimulation intensity and lidocaine further confirmed that the optically measured signals originated from neural activities.

The topographical guidance of neurons cultured on holographic photo-responsive polymer

Neuronal cells to respond to submicron-scale groove structure. On the grooved structure of particular dimension, it has been reported that neuronal cells grew perpendicular to the groove direction. We used holographic photo-responsive polymer to form a submicron-scale surface relief grating structure. A sinusoidal groove pattern is built up by holographic interference of 488 nm Ar ion laser beams. The primary hippocampal neurons cultured on the surface of the polymer film grew extending their neurites in a perpendicular orientation to the groove direction. This suggests that laser holography can be used to control the neurites orientation and growth. The holographic grating and photo-responsive polymer will raise the possibility of controlling neural network formation between living cells by light.

Electrically and Optically Controllable Liquid Crystal Grating with a Patterned Surface-Command Layer

We propose a liquid crystal (LC) binary grating that can be controlled both electrically and optically in a simple scheme. The optical control scheme is obtained through the surface-induced reorientation of the LC molecules on a patterned surface-command layer by a single pump irradiation. The electrical control of the diffraction efficiency is achieved through the change in the phase retardation by the application of a bias voltage for given optically induced LC director distribution. In a coupled scheme of the optical and electrical control, the diffraction efficiency can be easily optimized.

Neural Prosthesis in the Wake of Nanotechnology : Controlled Growth of Neurons Using Surface Nanostructures

Neural prosthesis has been successfully applied to patients with motional or sensory disabilities for clinical purpose. To enhance the performance of the neural prosthetic device, the electrodes for the biosignal recording or electrical stimulation should be located in closer proximity to target neurons than they are now. Instead of revising the prior implanting surgery to improve the electrical contact of neurons, we propose a technique that can bring the neurons closer to the electrode sites. A new method is investigated that can control the direction of neural cell growth using surface nanostructures. We successfully guide the neurons to the position of the microelectrodes by providing a surface topographical cue presented by the surface nanostructure on a photoresponsive polymer material. Because the surface structure formed by laser holography is reversible and repeatable, the geometrical positioning of the neurons to microelectrodes can be adjusted by applying laser treatment during the surgery for the purpose of improving the performance of neural prosthetic device.

Extracellular Optical Recording Configuration for Neuronal Action Potential Detection by using Surface Plasmon Resonance: Preliminary Experiment

We propose an extracellular optical recording configuration for neuronal action potential detection by using surface plasmon resonance (SPR). The method does not use fluorescence dyes but still taking advantages of optical recording. As a preliminary experiment, the electrochemical SPR effect without neurons was investigated. This showed that a high resolution SPR setup (10-4~10~5 angular shift or more) is required to overcome noise and improve SPR signal. Several issues for neural signal recording are addressed to modify SPR optical configuration

One beam controllable grating in a liquid crystal cell with an azo polymer surface

Abstract We propose a novel grating in a nematic liquid crystal cell with an azo polymer surface (APS). In this system, the polarization grating inscribed on APS modulates the liquid crystal director. The grating effect can be enhanced or reduced by polarization switching of only one pump beam due to strong polarization sensitivity of azobenzene chromophores.

Optical and electro-optical control of grating efficiency in a nematic liquid crystal cell with azo polymer boundary

Abstract A novel control of the grating efficiency in a nematic liquid crystal cell with an azobenzene polymer surface is proposed. In an optical control regime, the grating effect can be controlled by alternate polarization switchings of one pump beam due to strong polarization sensitivity of azobenzene chromophores. Moreover, the grating efficiency can be easily tuned by an external ac electric field.

Optical Properties of a Chiral Liquid Crystal in a Generalized Coupled Mode Formalism

Abstract We propose a general formalism suitable for calculating the propagation of the optical normal modes through a chiral liquid crystal as one of the characteristic parameters varies. Based on the fact that the normal modes are the eigenstates of the generator of translation (the wave number operator K), the change in K is evaluated by means of a characteristic parameter such as chirality. The numerical calculations are in good agreement with the analytic results.