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Fluorescence Lifetime Imaging Microscopy (FLIM) is a powerful technique that is increasingly being used in the life sciences during the past decades. However, a broader application of FLIM requires more cost-effective and user-friendly solutions. We demonstrate the use of a simple CCD/CMOS lock-in imager for fluorescence lifetime detection. The SwissRanger SR-2 time-of-flight detector, originally developed for 3D vision, embeds all the functionalities required for FLIM in a compact system. The further development of this technology and its combination with light-emitting-and laser diodes could drive a wider spreading of thuse of FLIM including high-throughput applications.

Fluorescence lifetime imaging microscopy (FLIM) allows the investigation of the physicochemical environment of fluorochromes and protein-protein interaction mapping by Forster resonance energy transfer (FRET) in living cells. However, simpler and cheaper solutions are required before this powerful analytical technique finds a broader application in the life sciences. Wide-field frequency-domain FLIM represents a solution whose application is currently limited by the need for multichannel-plate image intensifiers. We recently showed the feasibility of using a charge-coupled device/complementory metal-oxide semiconductor (CCD/CMOS) hybrid lock-in imager, originally developed for 3-D vision, as an add-on device for lifetime measurements on existing wide-field microscopes. In the present work, the performance of the setup is validated by comparison with well-established wide-field frequency-domain FLIM measurements. Furthermore, we combine the lock-in imager with solid-state light sources. This results in a simple, inexpensive, and compact FLIM system, operating at a video rate and capable of single-shot acquisition by virtue of the unique parallel retrieval of two phase-dependent images. This novel FLIM setup is used for cellular and FRET imaging, and for high-throughput and fast imaging applications. The all-solid-state design bridges the technological gap that limits the use of FLIM in areas such as drug discovery and medical diagnostics.

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The time-of-flight (TOF) principle is a well known technology to acquire a scene in all three dimensions. The advantages of the knowledge of the third dimension are obvious for many kinds of applications. The distance information within the scene renders automatic information-processing systems more robust and much less complex or even enables completely new solutions. A solid-state image sensor containing 124 × 160 pixels and the corresponding 3D-camera, the so-called SwissRanger camera has already been presented in detail 1 . It has been shown that the SwissRanger camera achieves depth resolutions in the sub-centimeter range, corresponding to a measured time resolution of a few tens of picoseconds with respect to the speed of light (c ≈ 3 · 10 8 m s −1 ).However, one main drawback of these so-called lock-in TOF pixels is their limited capacity to handle background illumination. Keeping in mind that in outdoor applications the optical power on the sensor originating from background illumination such as sunlight may be up to a few 100 times higher than the power of the modulated illumination, the sensor requires new pixel structures eliminating or at least reducing the currently experienced restrictions in terms of background illumination. Based on a custom 0.6µm CMOS/CCD technology, a new pixel architecture suppressing background illumination and/or improving the ratio of modulated signal to background signal at the pixel-output level was developed and will be presented in this paper. The theoretical principle of operation and the expected performance measures are described. Furthermore, test results obtained in a laboratory setup are published. The sensor structure is characterized in a high background-light environment. This in-depth evaluation leads to a comparison of the background suppression approach with the traditional pixel structure in order to highlight the benefits of the new approach.