Multilayer Carbon Nanotube/Gold Nanoparticle Composites on Gallium-Based Liquid Metals for Electrochemical Biosensing

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

Chemical Analysis of the Gallium Surface in a Physiologic Buffer

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 Ga3+ 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

Multiscale Material Engineering of a Conductive Polymer and a Liquid Metal Platform for Stretchable and Biostable Human-Machine-Interface Bioelectronic Applications

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

Conductive and Robust Cellulose Hydrogel Generated by Liquid Metal for Biomedical Applications

The synthesis of cellulose hydrogels, renowned for their environmentally friendly and sustainable attributes, has gained considerable attention, especially when compared to the synthesis of polymer-based hydrogels. Here, we introduced a particle model of liquid metals into cellulose hydrogel matrices (LMCs) to provide a large surface area, facilitating the release of Ga ions. Through the release of gallium ions into the hydrogel nature, these liquid metal particles introduced additional ionic cross-linking. This enhanced cross-linking mechanism triggered a more substantial hydrogel frame, resulting in an 18-time increase in modulus and a 21-time enhancement in surface hardness compared to pristine cellulose hydrogel. In addition, the mechanical robustness of the LMC was evident as it sustained up to 80% compression and retained its structural integrity after performing 20 cycles of compression. The enhanced mechanical attributes of the LMC facilitated a unique compression-dominated contact among the liquid metal particles, thereby offering an improvement in the electrochemical properties. Also, the particles can promote the electrochemical properties due to intrinsic conductive behavior. The enhancement in the electrochemical properties allowed the LMC to be a biosensor for detecting glucose and maltose. Last, the mechanical responsiveness and enhanced electrochemical properties rendered the LMC proficient in accurately monitoring physiologic signals. This study opens up the versatile use of electrochemically conductive and robust cellulose hydrogels with the aid of liquid metal particles

Multiscale Material Engineering of a Conductive Polymer and a Liquid Metal Platform for Stretchable and Biostable Human-Machine-Interface Bioelectronic Applications

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

Multiscale Material Engineering of a Conductive Polymer and a Liquid Metal Platform for Stretchable and Biostable Human-Machine-Interface Bioelectronic Applications

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

Multiscale Material Engineering of a Conductive Polymer and a Liquid Metal Platform for Stretchable and Biostable Human-Machine-Interface Bioelectronic Applications

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

Robust Heteroepitaxial Growth of GaN Formulated on Porous TiN Buffer Layers

Gallium nitride (GaN) heteroepitaxial growth is widely studied as a semiconductor material due to its various benefits. Especially, development of a buffer layer between GaN and the substrate verifies to be an effective strategy to reduce high threading dislocation density. However, the buffer layer often impedes strong adhesion between the epilayer and foreign substrate because thermally induced residual stress often causes delamination of the epilayer during fabrication. Here, we developed a robust GaN heteroepitaxy employing a porous buffer layer formulated by hydride vapor phase epitaxy. A sufficiently low but completely coated thin Ti layer was deposited on the sapphire substrate, which led to a rough and porous TiN layer after nitridation. This porous structure enables the penetration of the GaN source into the porous structure, allowing GaN epitaxy initiation throughout the TiN layer. As a result, GaN crystal growth can fill the porous area during the GaN heteroepitaxy. Integrated visualization demonstrated that the voids were successfully removed by GaN infiltration, enabling the heteroepitaxial structure to show little deformation, confirmed by multiple indentations. Last, the void-free GaN heteroepitaxy with the porous TiN buffer layer displayed robust adhesion after delamination tests

Robust Heteroepitaxial Growth of GaN Formulated on Porous TiN Buffer Layers

Gallium nitride (GaN) heteroepitaxial growth is widely studied as a semiconductor material due to its various benefits. Especially, development of a buffer layer between GaN and the substrate verifies to be an effective strategy to reduce high threading dislocation density. However, the buffer layer often impedes strong adhesion between the epilayer and foreign substrate because thermally induced residual stress often causes delamination of the epilayer during fabrication. Here, we developed a robust GaN heteroepitaxy employing a porous buffer layer formulated by hydride vapor phase epitaxy. A sufficiently low but completely coated thin Ti layer was deposited on the sapphire substrate, which led to a rough and porous TiN layer after nitridation. This porous structure enables the penetration of the GaN source into the porous structure, allowing GaN epitaxy initiation throughout the TiN layer. As a result, GaN crystal growth can fill the porous area during the GaN heteroepitaxy. Integrated visualization demonstrated that the voids were successfully removed by GaN infiltration, enabling the heteroepitaxial structure to show little deformation, confirmed by multiple indentations. Last, the void-free GaN heteroepitaxy with the porous TiN buffer layer displayed robust adhesion after delamination tests

Multiscale Material Engineering of a Conductive Polymer and a Liquid Metal Platform for Stretchable and Biostable Human-Machine-Interface Bioelectronic Applications

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