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Gallium alloy based liquid metals (LMs) have shown great promise for soft and stretchable electronics in virtue of intrinsic uidity and metallic conductivity. However, it has been a challenge by using LM to construct 3D structured circuits which are crucial for building exible electronics with high integration. Hereby, taking advantage of the solid-liquid phase transition and plastic deformation of a Ga-10In LM alloy, we propose a novel strategy to fabricate LM based exible electronic devices, in particular comprised of 3D circuits, without the need to pre-fabricate microchannels. We demonstrate applications including 3D interconnect arches for the integration of a multi-channel LED array, a 3D structured wearable sensor and a multilayer exible circuit board for monitoring of nger movement. The current work provides a facile strategy for constructing LM based exible electronics, which is of particular interest for building highly integrated electronics of hierarchical structure involving complicated 3D circuits.

Power ultrasonic vibration (20 kHz, 6 μm) was applied to assist the interaction between a liquid Al-Si alloy and solid Ti-6Al-4V substrate in air. The interaction behaviors, including breakage of the oxide film on the Ti-6Al-4V surface, chemical dissolution of solid Ti-6Al-4V, and interfacial chemical reactions, were investigated. Experimental results showed that numerous 2-20 μm diameter-sized pits formed on the Ti-6Al-4V surface. Propagation of ultrasonic waves in the liquid Al-Si alloy resulted in ultrasonic cavitation. When this cavitation occurred at or near the liquid/solid interface, many complex effects were generated at the small zones during the bubble implosion, including micro-jets, hot spots, and acoustic streaming. The breakage behavior of oxide films on the solid Ti-6Al-4V substrate, excessive chemical dissolution of solid Ti-6Al-4V into liquid Al-Si, abnormal interfacial chemical reactions at the interface, and phase transformation between the intermetallic compounds could be wholly ascribed to these ultrasonic effects. An effective bond between Al-Si and Ti-6Al-4V can be produced by ultrasonic-assisted brazing in air.

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The cavitation characteristics at filler metal/substrate interface during ultrasonic-assisted soldering were first recorded by high-speed photography in this work. Two kinds of bubbles, steady cavitation bubbles and transient cavitation bubbles were observed. Steady cavitation bubbles did not collapse within one acoustic period and could last longer than 50 acoustic periods. Transient cavitation bubbles formed and collapsed within one acoustic period. The cavitation process was divided into two stages based on the cavitation characteristics. The first violent cavitation stage was in fact the degassing process, which lasted approximately 2700 acoustic periods and was affected by the gas content trapped inside the filler metal and the stronger vibration at the initiation stage of ultrasonic-assisted soldering. The second steady cavitation stage had obvious low bubble density and accounted for the most of the soldering process. Higher cavitation densities were observed when small channel width and large ultrasonic power were used because of larger sound pressures inside the filler metal.

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The self-luminescence behavior of lanthanide MOFs (Ln-MOFs) due to the unique antenna effect is considered to be a promising electrochemiluminescence (ECL) emission for biosensors. It is more challenging for Ln-MOFs on account of the difficulty to stimulate Ln ions with the desired energy-transfer efficiency to produce stronger ECL emissions at a low potential. Here, guided by a second ligand-assisted energy-transfer strategy, we present an efficient self-enhanced luminescence mixed-ligand Eu-MOF as an ECL signal probe for an oriented antibody-decorated biosensing platform with a low detection limit and a broad detection range. Diamino terephthalic acid (NH2–H2BDC) and 1,10-phenanthroline (Phen) were selected as the first and second ligands, respectively, to form highly conjugated structures, as well as suppress the nonradiative energy transfer. Impressively, Phen precisely adjusts the energy gap between the triplet ligand and the excited state of Eu3+, realizing the self-enhancement of ECL efficiency of the Eu-MOF. The mixed ligand adjusted the molar ratio to obtain the stable and strong ECL signal at a lowered triggering potential (0.83 V). In addition, FeCo@CNT features densely active FeCo sites along with a rich hierarchy conductive carbon nanotube (CNT) network, which is efficiently a co-reaction accelerator to produce more TPA•+ radicals to accelerate the reduction process of the Eu-MOF for achieving the ECL emission amplification. FeCo@CNT with heptapeptide HWRGWVC (HWR) constructed a matrix biosensing interface that allowed the fragment antigen-binding (Fab) regions to target specific antigens and enhance the incubation efficiency. The present study has gone some way toward designing a self-enhanced luminous Eu-MOF, thus giving new fresh impetus to develop high-performance ECL emitters for biological analysis.