We develop a fast-response and flexible nanocrystal-based humidity sensor for real-time monitoring of human activity: respiration and water evaporation on skin A silicon-nanocrystal film is formed on a polyimide film by spin-coating the colloidal solution and is used as a flexible and humidity-sensitive material in a humidity sensor The flexible nanocrystal-based humidity sensor shows a high sensitivity; current through the nanocrystal film changes by 5 orders of magnitude in the relative humidity range of 8–83% The response/recovery time of the sensor is 40 ms Thanks to the fast response and recovery time, the sensor can monitor human respiration and water evaporation on skin in real time Due to the flexibility and the fast response/recovery time, the sensor is promising for application in personal health monitoring as well as environmental monitoring

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Fast-Response and Flexible Nanocrystal-Based Humidity Sensor for Monitoring Human Respiration and Water Evaporation on Skin

Breath analysis is an attractive strategy that holds tremendous potential to achieve non-implantable physical health management enabled by flexible humidity sensors for breathing behaviors (e.g., continuity, frequency) related to disease monitoring and chemiresistive gas sensors related early disease diagnosis. Compared to other techniques for breath component detection, non-invasive breathing diagnostics based on chemical sensors can offer several advantages like miniaturization, low power consumption, simple structure and cost-saving, which is helpful to enhance the portability of practical tests. Although extensive research has been carried out over the past two decades to improve sensing performances of breath gas sensors, many problems need to be further addressed when it comes to clinical disease diagnosis. Developing integrated gas sensor arrays have become one of the efficient solutions to improve detection accuracy. To get rid of external power supply, various novel sensors combining with self-powered technology are designed to exhibit a desirable development prospect in breath analysis. Thus, this review aims to summarize the latest research advances on wearable humidity-enabled breathing behaviors monitoring and typical biomarker gases-based disease screening, and also provides the prospects of future development from individual sensors to integrated devices and self-powered health monitoring systems.

Evolution of breath analysis based on humidity and gas sensors: Potential and challenges

Carbon nanocoils (CNCs) are employed to fabricate fast, high-resolution, and reversible humidity sensor based on a flexible liquid crystal polymer (LCP) substrate. The humidity sensor displays fast-response (1.9 s) and recovery time (1.5 s), a broad relative humidity (RH) detection range (4-95%), linearity, repeatability, and stability. The rapid response and recovery are considered to benefit from the hydrophobic effect of the LCP substrate and high purity of the CNCs, which give rise to weak physical adsorption. Meanwhile, the high sensitivity results from both the unique helical structure of CNCs and the microporous structure of the LCP substrate. The distinctive structure-related properties enable the sensor to reliably perceive an extremely small RH variation of 0.8%, which is too small to be detected by most humidity sensors reported previously. These features allow the sensor to monitor a variety of important human activities, such as respiration, speaking, blowing, and noncontact fingertip sensation, accurately. Furthermore, different human physical conditions can be distinguished by recognizing the respiration response patterns. In addition, the long-term operation and mechanical bending do not adversely affect the sensing performance.

Carbon Nanocoil-Based Fast-Response and Flexible Humidity Sensor for Multifunctional Applications.

Lead halide perovskites have demonstrated outstanding achievements in photoelectric applications owing to their unique properties. However, the moisture sensitivity of lead halide perovskite has ra ...

Lead-Free Cs2BiAgBr6 Double Perovskite-Based Humidity Sensor with Superfast Recovery Time

Recent Progress in Essential Functions of Soft Electronic Skin

We have reviewed the humidity sensors based on ceramic materials. We first discuss the operating principle of ceramic humidity sensors. This is followed by a section on the relationship between the conduction mechanism and microstructure characteristics of the sensing elements of ceramic humidity sensors. This part of the review is also focused on the methods for optimization of the microstructure of ceramic porous elements. The next section summarizes the information on the materials used for the ceramic humidity sensors fabrication and effect of dopants or hybrid compositions on the sensing ceramic-based materials. Then we analyze state-of-the-art techniques for producing ceramic sensors. The key research and technological challenges in the field are discussed at the end of the review. The review is based on 424 references published during from 1998–2013.

Recent trends of ceramic humidity sensors development: A review

The papers takes stock of different methods for evaluating the detection (c
 min) and determination (c
 lim) limits of components described in the literature and presents a comparative analysis of the results of such evaluations. It is shown that use of the data on the fluctuations of the blank experiment, in spite of their wide application for such evaluations, gives ambiguous estimates for c
 min and c
 lim. The most correct method for evaluating the specified parameters is the experimental determination of the actual analyte concentration (content) from the empirical concentration dependence of the relative standard deviation. In case when this estimation method cannot be used, it is recommended to evaluate c
 lim by the lower boundary of the calibration graph. The article may be useful for inexperienced analysts experimenters in choosing a method for evaluating the results obtained.

Once again about determination and detection limits

Conditions for eliminating systematic errors and minimizing random errors in the determination of water in methanol and α-alumina using Karl Fisher reagent with visual end-point detection are studied. The concentration dependence of the relative standard deviation of the determination of water by the Karl Fisher method is found to be linear in RSD-1/c coordinates. To exclude the effect of moisture contained in the titration flask, it is suggested to bind water with a titrant in the presence of a small amount of methanol. The methanol effect (that is, the dependence of the titration results on the water: methanol ratio and the total amount of the titrated water-methanol mixture) is shown to be eliminated in the presence of the products of water interaction with Karl Fisher reagent that form on the water binding stage. It is found that the use of a background dye, methylene blue, eliminates significant systematic errors in the determination of water by the Karl Fisher method, particularly, at low concentrations. It is noted that the visual detection of the titration end-point has some advantages over the automated electrometric versions of the method; in particular, it is characterized by a better reproducibility of the determination of low concentrations of water.

T. A. Blank

Papers

Recent trends of ceramic humidity sensors development: A review

Once again about determination and detection limits

Some aspects of the determination of water by the karl fisher method

Study on the sorption properties of (NH4)2TiOF4 particles

Modified Greener Procedure for the Synthesis of Cucurbit[6]uril