Multi-Fiber Optrode Development

August 12, 2014



Optogenetics has been one of the most exciting fields in neuroscience with tremendous efforts undertaken to advance the techniques and tools. NeuroNexus adapted early to provide researchers with innovative optogenetics products, exemplified by the industry leading Optoelectrode product line. NeuroNexus Optoelectrodes have been continuously evolving products, starting from the very first Optoelectrodes that featured basic LC connectors with limited packaging options. Since then we have used extensive design insight as well as refinement of optics to fine-tune and further develop the Optoelectrode, resulting in the NeuroNexus Coupler (NNc) and supporting accessories such as patch-cords and implantable fibers. The NeuroNexus Optoelectrode has become the standard research tool for simultaneous optical stimulation and neural recordings. We continue to research new areas to provide critical value to our Optogenetics customers and are excited to share the addition of two new in-house capabilities: (1) introduction of etched smaller diameter fibers and (2) robust, high-fiber count packaging.

QuadOptrode Pix

Left: Dual-fiber Optrode; Middle: Quad-fiber Optrode, with lasers attached;
Right: Close-up of Quad-fiber Optrode microelectrode array

Etched, Smaller Diameter Fibers

NeuroNexus has historically provided Optoelectrodes with our standard fiber with the following specification: 105 µm core, 125 µm cladding, 0.22 NA. We have since then introduced the 0.66 NA fiber to provide a solution to customers requiring higher numerical aperture. Our next development project for our fibers was to provide a smaller diameter fiber Optoelectrode. Smaller diameter fibers would theoretically attach better to our 15 µm thin microelectrode arrays as the flexibility of smaller diameter fibers provide better mechanical matching with the narrow shanks. We also expected insertion to improve with less dimpling. Lastly, tissue damage would decrease significantly as the cross-sectional area of the fiber would decrease.

With input from Dr. Kenji Mizuseki from Allen Institute for Brain Science, we pursued the approach of HF (hydrogen fluoride) etching the 50 µm core, 125 µm cladding fiber to reduce the cladding diameter. By immersing the fiber for a calculated period, we were able to successfully predict and accomplish desired cladding diameter resulting in 50 µm core, ~65 µm cladding fibers. This decrease of cladding diameter leads to a reduction in cross-sectional area of approximately 73%! We are very excited that our approach yields repeatable results that provide improved tissue interface for our Optoelectrodes.


Above: HF-etched optical fiber, shown on a SEM.
The OD has been reduced to ≈ 62.5 µm, with the core remaining at 50 µm.

Robust, High-Count Fiber Optoelectrodes

Optoelectrodes featuring multiple fibers have been popularly requested by our customers, with one-fiber-per-shank mounting on the Buzsaki design microelectrode arrays being of particular interest. While lab-built, multi-fiber optrodes have been used in several research studies, combining many fiber terminations into a minimal, robust package has been a large hurdle for commercial multi-fiber Opeoelctrode development. Our standard fibers pose additional challenges:

  1. Size and mechanical stiffness of our standard fibers pose assembly difficulties
  2. The increase in cross-sectional area with each additional fiber leads to significant tissue damage and higher risk of insertion failure

With the development of our etched fibers, the two above concerns are significantly dissipated. We were also able to solve the packaging problem by utilizing our new, precise 3D printer to design and fabricate connectors that can house many ferrule terminations without adding significant bulk to the probe package. Thus yielding a robust probe package that allows many fibers to be mounted on one Optoelectrode.

Learn more about multi-fiber optoelectrodes here.