Implantable photonic neural probes for light-sheet fluorescence brain imaging

Abstract

<b>Significance:</b> Light-sheet fluorescence microscopy (LSFM) is a powerful technique for high-speed volumetric functional imaging. However, in typical light-sheet microscopes, the illumination and collection optics impose significant constraints upon the imaging of non-transparent brain tissues. We demonstrate that these constraints can be surmounted using a new class of implantable photonic neural probes. <b>Aim:</b> Mass manufacturable, silicon-based light-sheet photonic neural probes can generate planar patterned illumination at arbitrary depths in brain tissues without any additional micro-optic components. <b>Approach:</b> We develop implantable photonic neural probes that generate light sheets in tissue. The probes were fabricated in a photonics foundry on 200-mm-diameter silicon wafers. The light sheets were characterized in fluorescein and in free space. The probe-enabled imaging approach was tested in fixed, <i>in vitro</i>, and <i>in vivo</i> mouse brain tissues. Imaging tests were also performed using fluorescent beads suspended in agarose. <b>Results:</b> The probes had 5 to 10 addressable sheets and average sheet thicknesses <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mo><</mml:mo> <mml:mn>16</mml:mn> <mml:mtext> </mml:mtext> <mml:mi>μ</mml:mi> <mml:mi>m</mml:mi></mml:mrow> </mml:math> for propagation distances up to <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mn>300</mml:mn> <mml:mtext> </mml:mtext> <mml:mi>μ</mml:mi> <mml:mi>m</mml:mi></mml:mrow> </mml:math> in free space. Imaging areas were as large as <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mo>≈</mml:mo> <mml:mn>240</mml:mn> <mml:mtext> </mml:mtext> <mml:mi>μ</mml:mi> <mml:mi>m</mml:mi> <mml:mo>×</mml:mo> <mml:mn>490</mml:mn> <mml:mtext> </mml:mtext> <mml:mi>μ</mml:mi> <mml:mi>m</mml:mi></mml:mrow> </mml:math> in brain tissue. Image contrast was enhanced relative to epifluorescence microscopy. <b>Conclusions:</b> The neural probes can lead to new variants of LSFM for deep brain imaging and experiments in freely moving animals.