Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

  • Article
  • Published:

A wearable pH sensor with high sensitivity based on a flexible charge-coupled device

Nature Electronics volume 1, pages 596–603 (2018)Cite this article

Subjects

Abstract

Flexible chemical sensors could be used to create wearable devices that continuously monitor a variety of health conditions through the analysis of a person’s sweat. Current wearable pH sensors for sweat monitoring have a limited pH detection sensitivity at room temperature of about 59 millivolts per pH unit, which is determined by the Nernst equation. Here we show that a sensitive pH sensor can be created using a flexible charge-coupled device (CCD) and integrated with a temperature sensor. Our CCD-based pH sensor can, through accumulation cycles of electron charge transfer, achieve a sensitivity of around 240 millivolts per pH unit, which is roughly four times larger than the Nernst theoretical limit. Furthermore, the integrated flexible temperature sensor can be simultaneously used to compensate for the temperature dependence of the pH detection and to monitor skin temperature. As a proof of concept, we demonstrate that our CCD-based chemical sensor can be used to monitor the sweat pH and skin temperature of a person in real time.

This is a preview of subscription content, access via your institution

Access options

Buy this article

  • Purchase on Springer Link
  • Instant access to full article PDF
Buy now

Prices may be subject to local taxes which are calculated during checkout

Fig. 1: CCD-based flexible device.
Fig. 2: Fundamental operation mechanism and electrical characteristics of the CCD-based sensor.
Fig. 3: Fundamental CCD-based flexible pH sensor characteristics.
Fig. 4: Flexible temperature sensor fabricated by a solution-based process.
Fig. 5: Real-time pH monitoring.

Similar content being viewed by others

Data availability

The data that support the finding of this study are available from the corresponding author upon reasonable request.

References

  1. Cao, Q. et al. Medium-scale carbon nanotube thin-film integrated circuits on flexible plastic substrates. Nature 454, 495–500 (2008).

    Article  Google Scholar 

  2. Kim, D. H. et al. Materials for multifunctional balloon catheters with capabilities in cardiac electrophysiological mapping and ablation therapy. Nat. Mater. 10, 316–323 (2011).

    Article  Google Scholar 

  3. Someya, T. et al. Conformable, flexible, large-area networks of pressure and thermal sensors with organic transistor active matrixes. Proc. Natl Acad. Sci. USA 102, 12321–12325 (2005).

    Article  Google Scholar 

  4. Wang, S. et al. Skin electronics from scalable fabrication of an intrinsically stretchable transistor array. Nature 555, 83–88 (2018).

    Article  Google Scholar 

  5. Takei, K. et al. Nanowire active-matrix circuitry for low-voltage macroscale artificial skin. Nat. Mater. 9, 821–826 (2010).

    Article  Google Scholar 

  6. Chen, H., Cao, Y., Zhang, J. & Zhou, C. Large-scale complementary macroelectronics using hybrid integration of carbon nanotubes and IGZO thin-film transistors. Nat. Commun. 5, 4097 (2014).

    Article  Google Scholar 

  7. Honda, W. et al. High-performance, mechanically flexible, and vertically integrated 3D carbon nanotube and InGaZnO complementary circuits with a temperature sensor. Adv. Mater. 27, 4674–4680 (2015).

    Article  Google Scholar 

  8. Choi, S., Lee, H., Ghaffari, R., Hyeon, T. & Kim, D. H. Recent advances in flexible and stretchable bio-electronic devices integrated with nanomaterials. Adv. Mater. 28, 4203–4218 (2016).

    Article  Google Scholar 

  9. Chortos, A., Liu, J. & Bao, Z. Pursuing prosthetic electronic skin. Nat. Mater. 15, 937–950 (2016).

    Article  Google Scholar 

  10. Gao, W. et al. Fully integrated wearable sensor arrays for multiplexed in situ perspiration analysis. Nature 529, 509–514 (2016).

    Article  Google Scholar 

  11. Kim, D. H. et al. Epidermal electronics. Science 333, 838–843 (2011).

    Article  Google Scholar 

  12. Lee, H. et al. A graphene-based electrochemical device with thermoresponsive microneedles for diabetes monitoring and therapy. Nat. Nanotech. 11, 566–572 (2016).

    Article  Google Scholar 

  13. Lee, H. et al. Wearable/disposable sweat-based glucose monitoring device with multistage transdermal drug delivery module. Sci. Adv. 3, e1601314 (2017).

    Article  Google Scholar 

  14. Park, J., Kim, M., Lee, Y., Lee, H. S. & Ko, H. Fingertip skin-inspired microstructured ferroelectric skins discriminate static/dynamic pressure and temperature stimuli. Sci. Adv. 1, e1500661 (2015).

    Article  Google Scholar 

  15. Yamamoto, Y. et al. Printed multifunctional flexible device with an integrated motion sensor for health care monitoring. Sci. Adv. 2, e1601473 (2016).

    Article  Google Scholar 

  16. Sekitani, T. et al. A rubberlike stretchable active matrix using elastic conductors. Science 321, 1468–1472 (2008).

    Article  Google Scholar 

  17. Honda, W., Arie, T., Akita, S. & Takei, K. Printable and foldable electrodes based on a carbon nanotube-polymer composite. Phys. Status Solidi A 211, 2631–2634 (2014).

    Article  Google Scholar 

  18. Kim, J. et al. Battery-free, stretchable optoelectronic systems for wireless optical characterization of the skin. Sci. Adv. 2, e1600418 (2016).

    Article  Google Scholar 

  19. Cheng, Q. et al. Folding paper-based lithium-ion batteries for higher areal energy densities. Nano. Lett. 13, 4969–4974 (2013).

    Article  Google Scholar 

  20. Hu, L. et al. Highly conductive paper for energy-storage devices. Proc. Natl Acad. Sci. USA 106, 21490–21494 (2009).

    Article  Google Scholar 

  21. Bariya, M., Nyein, H. Y. Y. & Javey, A. Wearable sweat sensors. Nat. Electron. 1, 160–171 (2018).

    Article  Google Scholar 

  22. Takei, K., Honda, W., Harada, S., Arie, T. & Akita, S. Toward flexible and wearable human-interactive health-monitoring devices. Adv. Healthcare Mater. 4, 487–500 (2015).

    Article  Google Scholar 

  23. Sawada, K., Shimada, T., Ohshina, T., Takao, H. & Ishida, M. Highly sensitive ion sensors using charge transfer technique. Sens. Actuat. B 98, 69–72 (2004).

    Article  Google Scholar 

  24. Hizawa, T., Sawada, K., Takao, H. & Ishida, M. Fabrication of a two-dimensional pH image sensor using a charge transfer technique. Sens. Actuat. B 117, 509–515 (2006).

    Article  Google Scholar 

  25. Gao, W. et al. Wearable microsensor array for multiplexed heavy metal monitoring of body fluids. ACS Sens. 1, 866–874 (2016).

    Article  Google Scholar 

  26. Nakata, S., Arie, T., Akita, S. & Takei, K. Wearable, flexible, and multifunctional healthcare device with an ISFET chemical sensor for simultaneous sweat pH and skin temperature monitoring. ACS Sens. 2, 443–448 (2017).

    Article  Google Scholar 

  27. Bandodkar, A. J., Jeerapan, I. & Wang, J. Wearable chemical sensors: present challenges and future prospects. ACS Sens. 1, 464–482 (2016).

    Article  Google Scholar 

  28. Imani, S. et al. A wearable chemical-electrophysiological hybrid biosensing system for real-time health and fitness monitoring. Nat. Commun. 7, 11650 (2016).

    Article  Google Scholar 

  29. Akiyama, T., Ujihira, Y., Okabe, Y., Sugano, T. & Niki, E. Ion-sensitive field-effect transistors with inorganic gate oxide for pH sensing. IEEE Trans. Elect. Devices 29, 1936–1941 (1982).

    Article  Google Scholar 

  30. Bousse, L. & Bergveld, P. The role of buried OH sites in the response mechanism of inorganic-gate pH-sensitive ISFETs. Sens. Actuat. 6, 65–78 (1984).

    Article  Google Scholar 

  31. Nyein, H. Y. et al. A wearable electrochemical platform for noninvasive simultaneous monitoring of Ca2+ and pH. ACS Nano. 10, 7216–7224 (2016).

    Article  Google Scholar 

  32. Lee, D. & Cui, T. Low-cost, transparent, and flexible single-walled carbon nanotube nanocomposite based ion-sensitive field-effect transistors for pH/glucose sensing. Biosens. Bioelectron. 25, 2259–2264 (2010).

    Article  Google Scholar 

  33. Yan, C., Wang, J. & Lee, P. S. Stretchable graphene thermistor with tunable thermal index. ACS Nano. 9, 2130–2137 (2015).

    Article  Google Scholar 

  34. Martin, A. et al. Epidermal microfluidic electrochemical detection system: enhanced sweat sampling and metabolite detection. ACS Sens. 2, 1860–1868 (2017).

    Article  Google Scholar 

  35. Lee, Y. K. et al. Kinetics and chemistry of hydrolysis of ultrathin, thermally grown layers of silicon oxide as biofluid barriers in flexible electronic systems. ACS Appl. Mater. Interf. 9, 42633–42638 (2017).

    Article  Google Scholar 

Download references

Acknowledgements

This work was partially supported by a JSPS KAKENHI grant (17H04926), a JST PRESTO grant (JPMJPR17J5) and the TEPCO Memorial Foundation.

Author information

Author notes

  1. These authors contributed equally: Shogo Nakata, Mao Shiomi.

Authors and Affiliations

  1. Department of Physics and Electronics, Osaka Prefecture University, Sakai, Osaka, Japan

    Shogo Nakata, Mao Shiomi, Yusuke Fujita, Takayuki Arie, Seiji Akita & Kuniharu Takei

  2. JST PRESTO, Kawaguchi, Saitama, Japan

    Kuniharu Takei

Authors
  1. Shogo Nakata
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. Mao Shiomi
    View author publications

    You can also search for this author in PubMed Google Scholar

  3. Yusuke Fujita
    View author publications

    You can also search for this author in PubMed Google Scholar

  4. Takayuki Arie
    View author publications

    You can also search for this author in PubMed Google Scholar

  5. Seiji Akita
    View author publications

    You can also search for this author in PubMed Google Scholar

  6. Kuniharu Takei
    View author publications

    You can also search for this author in PubMed Google Scholar

Contributions

S.N. and K.T. conceived the idea and designed the experiments. S.N., M.S., Y.F. and K.T. carried out the device fabrication and characterization. All authors contributed to analysing the data. K.T. wrote the paper and all authors provided feedback.

Corresponding author

Correspondence to Kuniharu Takei.

Ethics declarations

Competing interests

The authors declare no competing interests.

Additional information

Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Supplementary information

Supplementary Information

Supplementary Figures 1–12

Reporting Summary

Rights and permissions

Reprints and permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Nakata, S., Shiomi, M., Fujita, Y. et al. A wearable pH sensor with high sensitivity based on a flexible charge-coupled device. Nat Electron 1, 596–603 (2018). https://doi.org/10.1038/s41928-018-0162-5

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1038/s41928-018-0162-5

This article is cited by

Search

Advanced search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing