Focus-tunable microscope for imaging small neuronal processes in freely moving animals

Miniature single-photon microscopes have been widely used to image neuronal assemblies in the brain of freely moving animals over the last decade. However, these systems have important limitations for imaging in-depth fine neuronal structures. We present a subcellular imaging single-photon device that uses an electrically tunable liquid crystal lens to enable a motion-free depth scan in the search of such structures. Our miniaturized microscope is compact (10  mm×17  mm×12  mm) and lightweight (≈1.4  g), with a fast acquisition rate (30–50 frames per second), high magnification (8.7×), and high resolution (1.4 μm) that allow imaging of calcium activity of fine neuronal processes in deep brain regions during a wide range of behavioral tasks of freely moving mice.