Self-Powered, Low-Cost Respiration Monitoring in Real-Time

Recent years have seen a lot of interest in developing portable, high-performance, and low-cost humidity sensors for respiratory monitoring. In a paper published in the journal Nano Energy, carbon nanodots (CDs) have been used to produce humidity sensors that have great sensitivity (5318%) at 94% relative humidity (RH) and exceptional long-term stability in the 11-94 percent RH range.

Self-Powered, Low-Cost Respiration Monitoring in Real-Time​​​​​​​

​​​​​​​Study: Carbon nanodot-based humidity sensor for self-powered respiratory monitoring. Image Credit: Crystal Eye Studio/

Research on Respiratory Monitoring

One of the most essential physiological indicators for human health care is respiratory monitoring, which can reveal crucial health data and identify potential health risks. However, the limitations of the available respiratory monitoring technology are due to its dependence on external power sources, high price, intricate design and low portability.

Therefore, it is highly desirable to develop a self-powered, economic, and simple system for respiratory monitoring.

Finding the Right Material for Humidity Detection

As the need for health management has grown, numerous attempts have been made in recent years to develop sensors for respiratory signals, including humidity, airflow, and pressure for real-time respiratory monitoring.

Due to the relatively high humidity around the mouth and nose during breathing, it may be possible to monitor respiration habits by sensing humidity changes in these areas.

Numerous materials that are sensitive to humidity have been studied, including semiconductors, perovskites, and polymers. However, many of these humidity sensors either depend on external power sources or batteries or have potential biological toxicity and poor sensitivity.

Owing to their high stability, strong biocompatibility, and low cost, carbon nanodots have been frequently utilized in humidity sensors. Along with these characteristics, carbon nanodots possess a variety of hydrophilic functional groups and large specific surface areas, which are advantageous to attracting a lot of water molecules and enhancing humidity sensing capabilities.

The Role of Triboelectric Nanogenerator

A self-powered respiratory monitoring device that is adaptable and stable is promising for regular usage. In this respect, triboelectric nanogenerators (TENGs), which can transform irregular or randomly distributed mechanical energy into electrical energy, have recently emerged as energy harvesting tools. These TENGs have numerous potentials in self-powered systems.

A TENG is an energy harvesting tool that uses electrostatic induction and triboelectric effect to combine mechanical energy from the outside world into electricity.

Among the energy harvesting strategies, TENGs provide various advantages, including a variety of materials, low cost, easy construction, and application to various power sources. Additionally, the TENG may generate electricity by separating two dielectric materials from external physical motions via a simple contact separation.

TENG-based carbon nanodots’ humidity sensors, therefore, make it possible to develop a low-cost and self-powered sensing mechanism for accurate respiratory monitoring.

What Did the Researchers Do?

This work presented a CD-based humidity sensor with minimal cost and effective performance possessing good repeatability, high sensitivity, long-lasting stability, and wise sensing range.

Microwave heating was used to produce carbon nanodots. In 10 mL of deionized water, 1 gram of citric acid monohydrate and 2 grams of urea were dissolved. Afterward, to create a dark solid, the mixture was heated for five minutes in a microwave. The product was then cooled to room temperature, dissolved in deionized water, and purified to produce a solution of carbon nanodots for future use.

A self-powered humidity sensor system has been created for real-time respiratory monitoring that can be utilized to analyze breath conditions by fusing it with TENG.

Important Findings of the Research

In this study, CD-based humidity sensors were designed, and these humidity sensors utilizing carbon nanodots were used to monitor the respiratory process in real-time. The humidity sensors displayed exceptional repeatability and stability over a broad RH range of 11-94% for one month and a comparatively high humidity sensitivity of 5318% at 94% RH.

The hydrophilic functional groups on the surface of carbon nanodots, which are useful for collecting water molecules, were responsible for these exceptional sensing abilities. TENG-based humidity sensors with carbon nanodots were ultimately developed to recognize various human breathing patterns effectively.

The findings outline a plan for CDs-based humidity sensors and indicate their potential uses in respiratory monitoring.


Qin, J., Yang, X. et al. (2022). Carbon nanodot-based humidity sensor for self-powered respiratory monitoring. Nano Energy. Available at:

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Shaheer Rehan

Written by

Shaheer Rehan

Shaheer is a graduate of Aerospace Engineering from the Institute of Space Technology, Islamabad. He has carried out research on a wide range of subjects including Aerospace Instruments and Sensors, Computational Dynamics, Aerospace Structures and Materials, Optimization Techniques, Robotics, and Clean Energy. He has been working as a freelance consultant in Aerospace Engineering for the past year. Technical Writing has always been a strong suit of Shaheer's. He has excelled at whatever he has attempted, from winning accolades on the international stage in match competitions to winning local writing competitions. Shaheer loves cars. From following Formula 1 and reading up on automotive journalism to racing in go-karts himself, his life revolves around cars. He is passionate about his sports and makes sure to always spare time for them. Squash, football, cricket, tennis, and racing are the hobbies he loves to spend his time in.


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