An advanced selective liquid-metal plating technique for stretchable biosensor applications

Abstract

This paper presents a novel stretchable pulse sensor fabricated by a selective liquid-metal plating process (SLMP), which can conveniently attach to the human skin and monitor the patient's heartbeat. The liquid metal-based stretchable pulse sensor consists of polydimethylsiloxane (PDMS) thin films and liquid metal functional circuits with electronic elements that are embedded into the PDMS substrate. In order to verify the utility of the fabrication process, various complex liquid-metal patterns are achieved by using the selective wetting behavior of the reduced liquid metal on the Cu patterns of the PDMS substrate. The smallest liquid-metal pattern is approximately 2 μm in width with a uniform surface. After verification, a transparent flowing LED light with programmed circuits is realized and exhibits stable mechanical and electrical properties under various deformations (bending, twisting and stretching). Finally, based on SLMP, a wireless pulse measurement system is developed which is composed of the liquid metal-based stretchable pulse sensor, a Bluetooth module, an Arduino development board, a laptop computer and a self-programmed visualized software program. The experimental results reveal that the portable non-invasive pulse sensor has the potential to reduce costs, simplify biomedical diagnostic procedures and help patients to improve their life in the future.

Liquid Metal–Based Soft Microfluidics

“…Directly writing [36,77,79] Injection [40] Selective plating [90,91] Magnetic field patterning [92] Electric field patterning [95] Laser patterning [68] Resolution…”

Nanofabrication for all-soft and high-density electronic devices based on liquid metal

“…This work presents a nanofabrication strategy for submicronscale, all-soft electronic devices, and transducers based on EGaIn. Figure 6 shows a comparison of resolution and film thickness of published liquid metal patterning technologies, including lithography-enabled [26][27][28][29][30][31][32] , microfluidic injection 36 , and additive 37 and subtractive 40 patterning processes and highlights the resolution and film thickness range demonstrated using the nanofabrication strategy proposed in this work. Additive direct write and injection approaches enable simple, fast, and large-area EGaIn patterning.…”

“…Being a liquid-phase conductor with a brittle oxide layer on the surface, the shape of EGaIn-filled microchannels can be easily changed in response to applied mechanical forces, with a new oxide layer being formed instantaneously on the EGaIn surface after deformation, thus making it shape reconfigurable 22 . The moldable characteristics of EGaIn have resulted in the development of a broad range of patterning methods based on lithography-enabled stamping and stencil printing [26][27][28][29][30][31][32][33] , microfluidic injection [34][35][36] , as well as additive [37][38][39] and subtractive [40][41][42][43][44][45] patterning processes. However, creating fine and uniform EGaIn thin-film patterns using current EGaIn patterning technologies remains a major technical challenge because of the high surface tension of EGaIn (γ = 624 mN m −1 ) 23 .…”

“…However, creating fine and uniform EGaIn thin-film patterns using current EGaIn patterning technologies remains a major technical challenge because of the high surface tension of EGaIn (γ = 624 mN m −1 ) 23 . Using soft lithography 28,29 or a selective wetting process 31 , the smallest EGaIn features demonstrated so far have a resolution of 2 μm with a thickness of ≈ 2 μm. Creating smaller and, especially, sub-micrometer EGaIn thin-film patterns remains challenging 22,28,29,31,39,46,47 .…”

“…Considering the size of a single biological cell, such as platelets with a diameter of 2-3 μm, mechanotransducers should be manufactured with submicronscale features and soft, biomimetic properties 1,48,49 . Existing fabrication technologies, including the transfer printing of compliant solid metal patterns [13][14][15] , nanoprinting 17,18 , direct printing of nanomaterials [19][20][21] , and EGaIn patterning [26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45] , are currently not suitable to fabricate such soft and stretchable electronic devices with submicron-scale resolution.…”