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.

Stimulating neuron cells with light is an exciting new technology that is revolutionizing the neurosciences. To date, due to the optical complexity that is involved, photostimulation has only been achieved at a single site using high power light sources. Here we present a GaN based micro-light emitting diode (LED) array that can open the way to multi-site photostimulation of neuron cells. The device is a two-dimensional array of micrometre size LED emitters. Each emitter has the required wavelength, optical power and modulation bandwidth to trigger almost any photosensitizer and is individually addressable. We demonstrate micrometre resolution photoactivation of a caged fluorophore and photostimulation of sensitized living neuron cells. In addition, a complete system that combines the micro-LED array with multi-site electrophysiological recording based on microelectrode array technology and/or fluorescence imaging is presented.

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Lensless on-chip imaging is a promising technique to count and monitor cells and micro-objects in liquid sample. In this paper we apply this technique to the observation of µL sample containing bacteria evaporated onto a microscope slide. Compared with previously reported techniques, a large improvement in signal to noise ratio is obtained due to the presence of a few μm thick wetting film creating a micro-lens on top of each bacteria. In these conditions, standard CMOS sensor are able to detect micro-objects as small as few μm, e.g. E.coli and Bacillus subtilis bacteria and 1 μm polymer beads with a large signal to noise ratio of 45 ± 10. An overall detection efficiency of 85 ± 7% and a co-localization error of σ1D = 1.1μm compared with reference fluorescence microscopy images are achieved. This novel technique will be used as a pre-positioning tool prior to other optical identification methods, e.g. Raman spectroscopy.

We describe an optical sectioning microscopy system with no moving parts based on a micro-structured stripe-array light emitting diode (LED). By projecting arbitrary line or grid patterns onto the object, we are able to implement a variety of optical sectioning microscopy techniques such as grid-projection structured illumination and line scanning confocal microscopy, switching from one imaging technique to another without modifying the microscope setup. The micro-structured LED and driver are detailed and depth discrimination capabilities are measured and calculated.

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Flip-chip InGaN micro-pixellated LED arrays with high pixel density and improved device performance are presented. The devices, with 64 × 64 elements, each of which have a 20 µm emission aperture on a 50 µm pitch, are fabricated with a matrix-addressable scheme at blue (470 nm) and UV (370 nm) wavelengths, respectively. These devices are then flip-chip bonded onto silicon mounts. Good emission uniformity across the LED array is demonstrated, which can be attributed to the introduced n-metal tracks adjacent to each n-GaN mesa and the p-contact lines running across parallel columns. More importantly, with a flip-chip configuration, the optical power output and the current-handling capability of these new devices are substantially enhanced, due to the improved heat dissipation capability and the increased light extraction efficiency. For instance, each pixel in the flip-chip blue (respectively UV) LED arrays can provide a maximum power density 43 W cm−2 (respectively 6.5 W cm−2) at an extremely high current density up to 4000 A cm−2 before breakdown. These flip-chip devices are then combined with a computer-programmable driver circuit interface to produce high-quality micro-scale displays. Other promising applications of these LEDs, such as colour conversion with quantum dots, are also demonstrated.

Here, we demonstrate the use of a micro light emitting diode (LED) array as a powerful tool for complex spatiotemporal control of photosensitized neurons. The array can generate arbitrary, 2-D, excitation patterns with millisecond and micrometer resolution. In particular, we describe an active matrix control address system to allow simultaneous control of 256 individual micro LEDs. We present the system optically integrated into a microscope environment and patch clamp electrophysiology. The results show that the emitters have sufficient radiance at the required wavelength to stimulate neurons expressing channelrhodopsin-2 (ChR2).