Gallium-based liquid metals have emerged as an important class of materials for bioelectronic and biosensor devices due to their low mechanical properties and fluidic behavior. However, liquid metals are susceptible to oxidation and corrosion, causing instability and limited electrochemical properties under physiological environments. The limited biostability and electrochemical properties hinder the use of liquid metals for potential biosensing applications.Here we developed a nanomaterial electrochemical deposition method to prevent the oxidation process, improve the biostability, and enhance the electrochemical properties of liquid metals in the physiological buffer. A carbon nanotube composite was designed to be deposited by a cathodic reaction on a gallium surface to prevent oxidation during the deposition. Then gold nanoparticles were functionalized onto the carbon nanocomposite to enhance the electrochemical properties further. The nanocomposite multilayer on the liquid metals provided excellent biostability and substrate adhesion confirmed by a long-term aging test in physiological buffer and repeated bending. We conducted dopamine sensing to confirm the enhanced electrochemical performance of the nanocomposite multilayer on the liquid metal. The liquid metal-based biosensor demonstrated a sensitivity of 0.236 ± 0.013 μA/μM and LOD of 23.2 nM that are competitive with current electrochemical tools used for in vivo dopamine sensing. Also, the nanocomposite structure displayed good dopamine detection selectivity under a plethora of metabolic byproducts. Lastly, a fast-scan cyclic voltammetry (FSCV) test was performed to demonstrate the fast responsiveness and high sensitivity of this liquid metal biosensing platform. Overall, this study systematically evaluated the electrochemical deposition conditions of nanomaterials on gallium alloys. This study also developed a method to enable a biostable and high-performance electrochemical sensing capability of liquid metals and opens up opportunities for potential biosensing applications of liquid metal devices in the future.

Gallium (Ga)-based liquid metal materials have emerged as a promising material platform for soft bioelectronics. Unfortunately, Ga has limited biostability and electrochemical performance under physiological conditions, which can hinder the implementation of its use in bioelectronic devices. Here, an effective conductive polymer deposition strategy on the liquid metal surface to improve the biostability and electrochemical performance of Ga-based liquid metals for use under physiological conditions is demonstrated. The conductive polymer [poly(3,4-ethylene dioxythiophene):tetrafluoroborate]-modified liquid metal surface significantly outperforms the liquid metal.based electrode in mechanical, biological, and electrochemical studies. In vivo action potential recordings in behaving nonhuman primate and invertebrate models demonstrate the feasibility of using liquid metal electrodes for high-performance neural recording applications. This is the first demonstration of single-unit neural recording using Ga-based liquid metal bioelectronic devices to date. The results determine that the electrochemical deposition of conductive polymer over liquid metal can improve the material properties of liquid metal electrodes for use under physiological conditions and open numerous design opportunities for next-generation liquid metal-based bioelectronics.

Gallium and its alloys have been regarded as one of the promising materials for flexible bioelectronics due to their liquid-like mechanical properties, excellent electrical property, and low toxicity. Although many studies have fabricated bioelectronics from gallium-based liquid metals, gallium surface chemistry in physiologic conditions is rarely investigated. Here, we investigated the chemical change of the gallium surface in a physiologic buffer at 37 °C over 45 days. The gallium ion concentration and pH measurement indicated that the oxidation and corrosion progressed more rapidly in the physiological buffer than in air. Also, the release of gallium ions and protons followed a square root of time growth. Various spectroscopic techniques were used to measure the chemical composition change on the gallium surface. The FT-IR study indicated that the GaOOH-rich gallium surface produced Ga 3+ and OH − ions. The XPS study indicated the oxide layer formation within 5 days, and then the contamination layer was deposited over time, which includes different ions and organic materials derived from the physiologic buffer. This study provides a detailed chemical analysis of the gallium surface in a physiological buffer. These fundamental studies would be a cornerstone for understanding the complex interaction between the gallium surface and the biological environment.

Liquid-metal-based stretchable bioelectronics can conform to the dynamic movements of tissues and enable human-interactive biosensors to monitor various physiologic parameters. However, the fluidic nature, surface oxidation, and low biostability of the liquid metals have limited the long-term use of bioelectronics. Here we have developed a rationally designed material engineering approach to overcome these challenges in liquid metal bioelectronics. To our knowledge, this is the first demonstration of stretchable, leak-free, and highly conductive gallium-based bioelectronic devices with exceptional biostability and electrochemical properties. We first utilized unique gallium oxide properties to create 3D microscale wrinkled structures on the gallium surface. Then, gold nanoparticles and biostable poly(3,4-ethylenedioxythiophene) were successively deposited on the wrinkled liquid metal surface. We demonstrated this multilayer encapsulation material could conform to the stretching deformation and showed excellent environmental stabilities while maintaining high electrical properties. Electromyographic measurements were used to evaluate the bioelectrical performance of the stretchable electronics, and the results demonstrated the encapsulated liquid metal device could outperform bare liquid metal devices. Finally, a sensory feedback study demonstrated our liquid metal bioelectronic device could record precise physiologic signals to control robots for mimicking dexterous hand gestures. This study opens the possibility of chronic liquid-metal-based stretchable bioelectronics.