Microscopic imaging and photo-stimulation using micro-structured light emitting diodes

Imperial Users onl

A Method for the Determination of Bi-substrate Kinetic Coefficients: the Example of the β-D-glucose-NAD-GDH Enzymatic Reaction

Abstract: Colorimetric detection of glucose in sample liquids such as human plasma is made by using enzymatic reactions. Either glucose oxidase (GOX) or glucose dehydrogenase (GDH) can be used to convert glucose. In the multi reactional scheme, the first enzymatic reaction is determinant. We focused here on the study of the enzyme GDH together with the enzymatic cofactor NAD (nicotinamide adenine dinucleotide). This reaction falls in the category of ternary enzymatic reactions. Such reactions depend on four parameters. A method to determine these four parameters is presented in this work, based on a comparison between a series of experiments and the theory. The best values of the parameters are indicated

Laser line illumination scheme allowing the reduction of background signal and the correction of absorption heterogeneities effects for fluorescence reflectance imaging

International audienceIntraoperative fluorescence imaging in reflectance geometry is an attractive imaging modality as it allows to noninvasively monitor the fluorescence targeted tumors located below the tissue surface. Some drawbacks of this technique are the background fluorescence decreasing the contrast and absorption heterogeneities leading to misinterpretations concerning fluorescence concentrations. We propose a correction technique based on a laser line scanning illumination scheme. We scan the medium with the laser line and acquire at each position of the line both fluorescence and excitation images. We then use the finding that there is a relationship between the excitation intensity profile and the background fluorescence one to predict the amount of signal to subtract to the fluorescence images to get a better contrast. As the light absorption information is contained both in fluorescence and excitation images, this method also permits us to correct the effects of absorption heterogeneities. This technique has been validated on simulations and experimentally. Fluorescent inclusions are observed in several configurations at depths ranging from 1 mm to 1 cm. Results obtained with this technique are compared to those obtained with a classical wide-field detection scheme for the contrast enhancement and to the fluorescence by excitation ratio approach for the absorption correction

Laser line scanning for fluorescence reflectance imaging: a phantom study and in vivo validation of the enhancement of contrast and resolution

International audienceIntraoperative fluorescence imaging in reflectance geometry is an attractive imaging modality to non-invasively monitor fluorescence-targeted tumors. In some situations, this kind of imaging suffers from poor res-olution due to the diffusive nature of photons in tissue. The objective of the proposed technique is to tackle this limitation. It relies on the scanning of the medium with a laser line illumination and the acquisition of images at each position of excitation. The detection scheme proposed takes advantage of the stack of images acquired to enhance the resolution and the contrast of the final image. The experimental protocol is described to fully under-stand why we overpass the classical limits and validate the scheme on tissue-like phantoms and in vivo with a preliminary testing. The results are compared with those obtained with a classical wide-field illumination. pub-lished online Oct. 1, 2014

A Method for the Determination of Bi-substrate Kinetic Coefficients: the Example of the b-D-glucose- NAD-GDH Enzymatic Reaction

Colorimetric detection of glucose in sample liquids such as human plasma is made by using enzymatic reactions. Either glucose oxidase (GOX) or glucose dehydrogenase (GDH) can be used to convert glucose. In the multi reactional scheme, the first enzymatic reaction is determinant. We focused here on the study of the enzyme GDH together with the enzymatic cofactor NAD (nicotinamide adenine dinucleotide). This reaction falls in the category of ternary enzymatic reactions. Such reactions depend on four parameters. A method to determine these four parameters is presented in this work, based on a comparison between a series of experiments and the theory. The best values of the parameters are indicated

Diffuse reflectance spectroscopy: a clinical study of tuberculin skin tests reading

International audienceDiffuse reflectance spectroscopy is a technique widely used to determine optical properties of tissues: scattering and absorption coefficients. In this study, we present the development of a low-cost optical instrument usable in a clinical environment based upon the spatially resolved diffuse reflectance spectroscopy approach. This instrument has been used in a clinical study to support the diagnosis of tuberculosis. The idea is to establish a new scanning method for an early detection of inflammation due to a reagent injection, before the onset of visual signs. Results comparing the instrumental and classical clinical readings are presented

Depth-enhanced fluorescence imaging using masked detection of structured illumination

International audienceThere is a growing interest in imaging fluorescence contrast at depth within living tissues over wide fields of view and in real time. Most methods used to date to improve depth detection of fluorescence information involve acquisition of multiple images, postprocessing of the data using a light propagation model, and are capable of providing either depth-sectioned or tomographic fluorescence information. We introduce a method, termed masked detection of structured illumination, that allows the enhancement of fluorescence imaging at depth without postprocessing. This method relies on the scanning of a collimated beam onto a turbid medium and the physical masking of the point spread function on the detection arm before acquisition on a CCD camera. By preferentially collecting diffuse photons at a chosen source-detector range, this method enhances fluorescence information at depth and has the potential to form images without postprocessing and in real time

Multi-site optical excitation using ChR2 and micro-LED array

Studying neuronal processes such as synaptic summation, dendritic physiology and neural network dynamics requires complex spatiotemporal control over neuronal activities. The recent development of neural photosensitization tools, such as channelrhodopsin-2 (ChR2), offers new opportunities for non-invasive, flexible and cell-specific neuronal stimulation. Previously, complex spatiotemporal control of photosensitized neurons has been limited by the lack of appropriate optical devices which can provide 2D stimulation with sufficient irradiance. Here we present a simple and powerful solution that is based on an array of high-power micro light-emitting diodes (micro-LEDs) that can generate arbitrary optical excitation patterns on a neuronal sample with micrometre and millisecond resolution. We first describe the design and fabrication of the system and characterize its capabilities. We then demonstrate its capacity to elicit precise electrophysiological responses in cultured and slice neurons expressing ChR2