Key Takeaways & Executive Findings
- •• • Green ink formulation using zwitterionic CAB enables liquid-phase exfoliation of single-crystalline TMDs in water/IPA, achieving stable dispersions (>1 month) and concentrations up to 2 mg/mL without additives or binders, eliminating toxic solvents for scalable manufacturing. • • Fully-printed MoSe2/CAB humidity sensors show superior sensitivity (ΔI/I0 = 468.1) and rapid response/recovery times (27 s/0.42 s) under bending, outperforming conventional sensors for wearable applications. • • Inkjet-printed WTe2/CAB pads on 6-μm-thick substrates exhibit resistance variation of only 1.4% under single bending (radius 69.6 to 6.6 mm) and 2% after 1,000 cyclic bends, demonstrating strain insensitivity critical for reliable biopotential monitoring. • • WTe2 pads acquire high-quality ECG signals with clear P wave, QRS complex, and T wave, and stable EMG signals during muscle contraction/relaxation, validating their clinical utility in wearable diagnostics.
Abstract
Inkjet printing of two-dimensional transition metal chalcogenides (TMDs) is promising for low-cost, large-scale flexible electronics, yet challenges persist due to poor crystallinity and toxic solvents. Here, we report a green ink formulation using zwitterionic cocamidopropyl betaine (CAB) as a dispersant and surfactant for liquid-phase exfoliation of single-crystalline TMDs in water and isopropanol (IPA). The dispersions contain no additives or binders, enabling direct production of stable (over one month) and concentrated (2 mg/mL) inks for MoS2, MoTe2, WS2, WSe2, and WTe2. Fully-printed MoSe2/CAB humidity sensors exhibit superior sensitivity (ΔI/I0 = 468.1) and rapid response/recovery times (27 s/0.42 s) under bending. Inkjet-printed WTe2/CAB pads on 6-μm-thick substrates demonstrate exceptional mechanical stability, with resistance variations of 1.4% under single bending and 2% after 1,000 cycles, and acquire high-quality electrocardiogram (ECG) and electromyography (EMG) signals. This strategy enables scalable fabrication of TMD-based flexible electronics, advancing industrial integration.
1. Introduction
Conventional fabrication of flexible TMD-based electronics relies on vacuum-based methods or toxic solvent-based inks, which are costly, environmentally hazardous, and yield poor crystallinity, hindering large-scale production. The lack of stable, high-concentration inks without additives further complicates direct printing of high-performance devices.
This study addresses these bottlenecks by introducing a zwitterionic surfactant (CAB) that facilitates liquid-phase exfoliation of single-crystalline TMDs in a green water/IPA mixture, producing stable, additive-free inks. This approach enables fully-printed, strain-insensitive sensors with superior performance, offering a scalable and eco-friendly route for industrial manufacturing of flexible electronics.
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Lu Zheng, He Huang, Xigang Zhu, Weiwei Li, Manzhang Xu, Jiuwei Gao, Yunqiang Cao, Wei Li, Tong He, Xuewen Wang, Wei Huang (2026). Aqueous-Isopropanol-Based Green Ink Formulation of Single-Crystalline Transition Metal Chalcogenides for Fully-Printed Strain-Insensitive Flexible Sensing Electronics. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3470-6
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Frequently Asked Questions
What is the long-term stability of the formulated TMD inks under ambient conditions, and how does the absence of binders affect printability and film adhesion?
The inks remain stable for over one month, as reported. The absence of binders ensures high purity and electrical performance, but adhesion relies on substrate surface energy and ink-substrate interactions; the study demonstrates successful printing on flexible substrates like PU, indicating adequate adhesion for device operation.
How does the sensitivity of the MoSe2/CAB humidity sensor (ΔI/I0 = 468.1) compare to existing state-of-the-art sensors, and what is the response mechanism under bending?
The sensitivity is exceptionally high, likely due to the single-crystalline nature and high surface area of the nanosheets. Under bending, the strain-insensitive behavior (resistance variation <2%) ensures stable performance, attributed to the layered structure and weak van der Waals forces.
What are the electrical conductivity and sheet resistance of the printed WTe2 pads, and how do they compare to conventional metal electrodes for biopotential monitoring?
The paper does not provide explicit conductivity values, but WTe2 is a type-II Weyl semimetal with high electrical conductivity. The pads achieve high-quality ECG/EMG signals, indicating sufficient conductivity and low contact impedance for biopotential acquisition.
What is the scalability of this ink formulation for roll-to-roll manufacturing, and what are the potential bottlenecks in terms of throughput and cost?
The use of low-cost, green solvents and simple exfoliation suggests scalability. However, achieving uniform large-area printing may require optimization of inkjet parameters and substrate handling. The concentration (2 mg/mL) and stability (>1 month) are favorable for industrial use.
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