Wearable Sensors Based on Solid-Phase Molecular Self-Assembly: Moisture-Strain Dual Responsiveness Facilitated Extremely High and Damage-Resistant Sensitivity

Abstract

Wearable sensing technologies have gained increasing interest in biomedical fields because they are convenient and could efficiently monitor health conditions by detecting various physiological signals in real time. However, common film sensors often neglect body moisture and enhance the sensitivity by enhancing the conductive dopants and self-healing ability. We report in this work a supramolecular film sensor based on solid-phase molecular self-assembly (SPMSA), which smartly utilizes the body moisture to enhance the sensitivity for human-machine interaction. The carbon nanotube (CNT)-doped SPMSA film is able to capture environmental moisture quickly. Upon contact to human skin, the moisture not only promotes the junction between CNTs but also contributes to the conductivity. As a result, the sensitivity can be enhanced 4 times. In this way, we are able to obtain the highest sensitivity of 700% with the lowest CNT doping rate of 0.5%. Furthermore, the current sensor displays damage-inert sensing performance. In the presence of a hole of up to 50% of the film area, the sensitivity remains unaffected due to the decreases in the absolute conductivity of the film sensor before and after a trigger to the same extent. In this way, we have developed a new principle in the design of a film sensor for human-machine interaction, which releases the sensor from focus on promoting conductivity and self-healing materials.

Physical Insight into the Conditions Required in the Solid-Phase Molecular Self-Assembly of SDS Revealed by Coarse-Grained Molecular Dynamics Simulation

“…Recently, Yan et al found that molecules in the precipitates formed with the aqueous mixture of ionic surfactant and oppositely charged polyelectrolyte may undergo self-assembly to form large-area self-supporting films under pressure in the presence of a tiny amount of water. − The driving forces for the multiscale self-assembly process are mainly the hydrophobic interaction between surfactant molecules. The electrostatic interaction between the polyelectrolyte chain and surfactant molecules is to endow the film with the self-supporting ability through the cross-linking of nanodomains formed by surfactants.…”

“…However, so far most molecular self-assemblies are obtained in the form of solution-based colloidal dispersions. − This solution-based molecular self-assembly is hard to work with when bulk macroscopic materials are required . To tackle this problem, we recently developed a strategy of solid-phase molecular self-assembly (SPMSA), − with which supramolecular films can be obtained at large scales . This not only allows the preparation of noncolloidal form self-supporting macroscopic molecular self-assembled materials but also makes it possible to achieve diversified functions. − ,, …”

“…To tackle this problem, we recently developed a strategy of solid-phase molecular self-assembly (SPMSA), − with which supramolecular films can be obtained at large scales . This not only allows the preparation of noncolloidal form self-supporting macroscopic molecular self-assembled materials but also makes it possible to achieve diversified functions. − ,, …”

“…It was previously found that nanoscaled preassembled structure, pressure, and a small amount of water are the necessary factors for the SPMSA. − To gain more physical insights into the mechanism of the SPMSA across multiple time and space scales, in this study, we employ molecular dynamics (MD) simulations in combination with the experiment to reveal the micropictures obtained during the complicated self-assembly process. According to the time and space scale, MD simulation can be divided into quantum MD simulation (QM), all-atom (AA) MD simulation, and coarse-grained (CG) MD simulation.…”

“…13 This not only allows the preparation of noncolloidal form self-supporting macroscopic molecular self-assembled materials but also makes it possible to achieve diversified functions. [12][13][14]16,17 It was previously found that nanoscaled preassembled structure, pressure, and a small amount of water are the necessary factors for the SPMSA. 12−18 To gain more physical insights into the mechanism of the SPMSA across multiple time and space scales, in this study, we employ molecular dynamics (MD) simulations in combination with the experiment to reveal the micropictures obtained during the complicated self-assembly process.…”