Researchers at the University of Texas, Austin, have recently developed an ultrathin, nanoelectric coating (NEC) that can be used to create multifunctional neural probes. Multifunctional probes are extremely useful for research purposes, as they allow the recording of neural activity simultaneously alongside stimulation via drug administration or light (as is the case with optogenetics). Such experiments are essential for decoding the complex network of events that occurs within the brain, yielding insight on its functionality and how certain diseases may arise or be ameliorated.

 

In the past, multifunctional probes have typically been made by 'stacking' the different components together. This stacking ultimately led to a larger probe overall that was more likely to cause increased tissue damage upon insertion. To circumvent the issues associated with traditional fabrication, Zhao et al. used a substrate-less, multilayered planar photolithography approach to create their NECs that could accommodate as many as 32 different electrodes as small as 30um wide in a variety of configurations. These different contact layouts were designed for distinct applications. For example, their NEC-a consisted of a linear array of 8 electrodes suitable for coating a micropipette which may be used for a drug delivery/recording application. Their NEC-b and NEC-c had electrodes that were spaced very closely together that could be used to discern between different neurons in a given brain region. NEC-d and NEC-e configurations had electrodes placed in 2x16 and 4x8 configurations to record information from different layers of the brain. The overall thickness of all NECs was equal to or less than 1um, and depended mainly on the thickness of their insulator layer (SU-8 photoresist). A surface tension method was used to coat the desired host probe with the NEC, where both were slowly lifted out of distilled water after alignment. The thin nature of the NECs in conjunction with the high surface tension of distilled water allowed for sufficient wrapping of the NEC around the host probe. The NECs were then thermally cured to ensure a strong, durable bond between the NEC and host probe that was shown to withstand multiple insertion/extraction cycles into hydrogel. They tested both an NEC-coated micropipette (to deliver a drug CNQX) and an NEC-coated optical fiber in live, freely behaving mice and found both to be functional and reliable in recording neural activity in response to various stimuli.

 

Zhao et al. also noted that in addition to their technique being readily accessible, it is also cost-effective and amenable to mass-production. In an era when scientific funding is becoming less reliable each day, new advances like this mean that research and progress may still be able to continue moving forward. Still too, authors highlight that their technology may have clinical applications as well. It would be interesting to see how their approach may change the design of traditional planar probes used in the clinic like ECoG arrays and strips for example. ECoG arrays typically sit on top of the brain's surface and can be used for applications such mapping out the regions of the brain during neurosurgery, or finding the region of the brain likely responsible for epileptic seizures. With the NEC's remarkably small dimensions, this technology may also be useful for the field of neuroprosthetics, an estimated $18B industry by 2028 according to Dr. Karandrea's new report for IDTechEx. For more detailed information on this topic, including applications and market forecasts, check out her report at www.idtechex.com/neuro and be on the lookout for her new report on brain machine interfaces estimated October 2017