Gallium Nitride Transistor Probes Strip Light Artifacts From Optogenetic Brain Recordings

Optogenetics has transformed neuroscience by giving researchers remote control over specific neurons with nothing more than light. But the technique has long carried an inconvenient trade-off: the same LED that fires precise pulses of light into brain tissue also floods nearby recording electrodes with electrical noise, contaminating the very neural signals scientists are trying to capture. Now, a team at Sun Yat-sen University in Guangzhou, China, has engineered a solution built on one of the most rugged materials in modern electronics, reporting an integrated probe that suppresses these optical artifacts by as much as 90 percent.

The work, published in Biomedical Microdevices, centers on a class of devices known as AlGaN/GaN heterojunction field-effect transistors, or HFETs. These transistors exploit a remarkable property of the aluminum gallium nitride and gallium nitride pair: when the two crystal layers are stacked, a two-dimensional electron gas forms spontaneously at their interface, creating an extraordinarily dense, highly mobile sheet of charge carriers. That property has made GaN-based devices famous in power electronics and radio-frequency amplifiers, but it also makes them exquisitely sensitive sensors of electrical potential, which is precisely what a neural probe needs.

Traditionally, optogenetic experiments rely on metal microelectrodes to eavesdrop on neurons while an optical fiber or LED delivers stimulation. The problem is that light striking a metal electrode, or the surrounding tissue and electrolyte, generates photoelectric artifacts: spurious voltages that can dwarf the faint millivolt-scale spikes neurons produce. These artifacts arise from photovoltaic effects at the electrode surface, photoelectrochemical reactions in the electrolyte, and light-induced currents in the recording circuitry. The result is a recording channel that goes temporarily blind every time the stimulation light turns on, obscuring the neural response the experimenter most wants to see.

The Sun Yat-sen team, led by corresponding author Baijun Zhang of the State Key Laboratory of Optoelectronic Materials and Technologies, took a different route. Instead of metal electrodes, they built their neural probe around AlGaN/GaN HFETs, which offer high sensitivity to extracellular potential changes along with the biocompatibility needed for implantable devices. The transistor architecture also brings a crucial advantage: because the sensing happens at a transistor gate rather than at a direct metal-electrolyte junction, the device can be configured in ways that metal electrodes simply cannot.

The core of the innovation lies in pairing two different flavors of transistor at the tip of the probe. The first, called the recording HFET or R-HFET, has a bare gate region exposed to the extracellular environment. It is highly sensitive to changes in potential at the electrode-tissue interface and serves as the primary channel for collecting neuronal signals. The second, the differential HFET or D-HFET, is nearly identical in structure but its gate is covered with a silicon dioxide passivation film. That insulating layer renders the D-HFET largely deaf to extracellular potentials, meaning it picks up essentially none of the neural activity.

Here is the elegant part: while the D-HFET cannot hear the neurons, it remains just as sensitive as the R-HFET to the light stimulation signal coming from the co-integrated LED photoelectrode. Both transistors sit at the probe tip, experiencing the same optical environment, the same LED pulses, and the same artifact-generating conditions. The only signal the D-HFET registers is the artifact itself. By carefully adjusting the drain-source bias of the D-HFET and then subtracting its output from the R-HFET signal, the researchers can cancel the optical artifact while preserving the genuine neuronal spikes that only the R-HFET detected.

This differential scheme is a clever inversion of a known vulnerability. AlGaN/GaN transistors are, in fact, notoriously light-sensitive: sub-bandgap photons can trap and release electrons at surface states and in the buffer layers, causing shifts in threshold voltage and persistent photoconductivity, effects that have plagued GaN photodetector and transistor designers for years. Prior work in the GaN community has documented these trap-related optical effects extensively, and passivation layers such as silicon dioxide and aluminum oxide have long been used to tame surface states. The Chinese team turned that liability into an asset, engineering a deliberately light-sensitive reference channel whose noise mirrors the noise in the recording channel.

To validate the approach, the researchers carried out simulated biological experiments in phosphate buffered saline, a standard electrolyte that mimics the ionic environment of extracellular fluid. The integrated photoelectrode probe, combining the LED stimulation element with the paired HFET recording elements, demonstrated artifact reduction of 90 percent. That level of suppression means the neuronal signal, which would otherwise be buried under a light-induced transient, can be clearly separated and read out even during active optical stimulation. For optogenetics experiments, where the most interesting neural dynamics often occur within milliseconds of a light pulse, this timing window is exactly where clean data matters most.

The significance extends beyond a single device demonstration. Integrated optogenetic probes that both stimulate and record in a single implant are the core tools of modern circuit-level neuroscience, allowing researchers to manipulate and monitor the same neuronal population in freely moving animals. Earlier efforts to combat photoelectric artifacts have included conductive shielding layers, as in double-sided sapphire optrodes, and careful materials engineering. The differential HFET approach adds a new weapon: an active, transistor-based cancellation scheme that can be tuned electrically through the drain-source bias, offering flexibility that passive shielding cannot match.

The broader GaN biosensing literature also supports the choice of platform. AlGaN/GaN high electron mobility transistor sensors have been used to detect potassium ions, cardiac troponin in physiological samples, and even SARS-CoV-2 spike proteins and virions, thanks to the sensitivity and chemical robustness of the two-dimensional electron gas. Applying the same transistor technology to neural recording, and solving its Achilles heel of optical sensitivity through differential pairing, suggests a versatile device platform that could serve multiple sensing modalities on a single probe. The work was supported by the Guangdong Basic and Applied Basic Research Foundation, the Science and Technology Plan of Guangdong Province, and joint funding from the National Natural Science Foundation of China and the Macao Science and Technology Development Fund.

Subject of Research: AlGaN/GaN heterojunction field-effect transistor neural probes that suppress optical artifacts from integrated LEDs in optogenetics

Article Title: AlGaN/GaN heterojunction field-effect transistors for suppressing optical artifacts from integrated light-emitting diodes

Article References: Cao, X., Ding, Y., Yang, X., Zhao, W., Li, X., Wen, Y., Li, Y., Huang, X., Li, Z., Weng, J., & Zhang, B. (2026). AlGaN/GaN heterojunction field-effect transistors for suppressing optical artifacts from integrated light-emitting diodes. Biomedical Microdevices, 28(4), Article 68. https://doi.org/10.1007/s10544-026-00851-9

Image Credits: AI Generated

DOI: 10.1007/s10544-026-00851-9

Keywords: optogenetics, AlGaN/GaN HFET, neural probe, optical artifacts, LED photoelectrode, differential recording, two-dimensional electron gas, biomedical microdevices, neural signal acquisition, SiO2 passivation, gallium nitride, signal-to-noise ratio