Miniaturized fiber-coupled confocal fluorescence microscope with an electrowetting variable focus lens using no moving parts

Abstract

We report a miniature, lightweight fiber-coupled confocal fluorescence microscope that incorporates an electrowetting variable focus lens to provide axial scanning for full three-dimensional (3D) imaging. Lateral scanning is accomplished by coupling our device to a laser-scanning confocal microscope through a coherent imaging fiber-bundle. The optical components of the device are combined in a custom 3D-printed adapter with an assembled weight of <2 g that can be mounted onto the head of a mouse. Confocal sectioning provides an axial resolution of ~12 µm and an axial scan range of ~80 µm. The lateral field-of-view is 300 µm, and the lateral resolution is 1.8 µm. We determined these parameters by imaging fixed sections of mouse neuronal tissue labeled with green fluorescent protein (GFP) and fluorescent bead samples in agarose gel. To demonstrate viability for imaging intact tissue, we resolved multiple optical sections of ex vivo mouse olfactory nerve fibers expressing yellow fluorescent protein (YFP).

Compact diode laser source for multiphoton biological imaging

“…The laser design can be extended to other wavelengths to excite other fluorescent molecules or implement three-photon excitation. Combined with miniaturized microscope components [36], we anticipate compact, portable, and efficient pulsed laser sources will revolutionize in vivo multiphoton fluorescence imaging.…”

The real-time technicolour living brain

“…And they can change the lens' shape and focal plane by altering the electrical field. Restrepo's team has used this lens in combination with a confocal microscope and a fibreoptic system to image brain slices 6 , and now plan to attach the device to a mouse's head.…”

Converting lateral scanning into axial focusing to speed up 3D microscopy

“…The former is typically achieved either by tunable acoustic gradient index of refraction lenses 3,4 , electro-tunable lenses (ETL) 5 or deformable mirrors 6 and the latter by moving a mirror axially in a remote image space. Advances in ETL design have led to hundreds of kHz axial scan rates in resonantly operated devices 5,7,8 . However, all ETL designs so far approximate only a quadratic phase function for defocus, which cannot account for the higher order spherical aberrations that need to be addressed in order to maintain a diffraction-limited focus.…”