Original article
Detection of ammonia based on a novel fluorescent artificial nose and pattern recognition

https://doi.org/10.1016/j.apr.2015.10.019Get rights and content

Abstract

A simple and rapid fluorescent sensor array for identification and quantification of different concentrations (ppb level) of ammonia was proposed in this paper. Employing porphyrin, porphyrin derivative and chemically responsive dyes as the sensing elements, the developed sensor array of artificial nose showed a unique pattern of fluorescence changes upon its exposure to ammonia for just 4 min. And the eigenvalues from raw fluorescence spectra were analyzed by means of pattern recognition algorithm, including hierarchical cluster analysis (HCA), principal component analysis (PCA) and back-propagation neural network (BPNN). The results showed that HCA and PCA, which were used to assess the feasibility and effectiveness of discrimination of fluorescent sensor array, revealed a distinct separation between samples. BPNN were used for automatically classifying and predicting concentration of ammonia, and the accuracy was 97.55% while the relative standard deviation (RSD) was up to 3.67% for real samples. It indicates the fluorescent artificial nose system is a rapid and feasible sensing platform for the identification and quantitative analysis of gases, and also shows the possibilities in the field of environmental gas detection and environmental gas monitoring.

Introduction

Although ammonia is used in many important fields, such as fertilizers, refrigeration, dyes, drugs, explosives, it is one kind of industrial toxic gases, which can brings environment pollution and health hazards to human body directly or indirect. With the increasing awareness of environmental protection, rapid detection of low-concentration ammonia remains a challenge. In addition to optical absorption detection (Peeters et al., 2000, Mount et al., 2002, PR China. Ministry of Environmental Protection, 2009), which is often used as a standard method and the operation is quite complex, there are two main strategies for detecting gases currently. One is traditional large instruments, such as Gas Chromatography (GC), Mass Spectrometer (MS), and so on, and it is not suitable for on-site detection and is not family-oriented because of poor portability and the high cost of initial investment and ongoing maintenance. The other is based on gas sensors. A number of principles and techniques have been employed to measure ammonia, including metal-oxide sensors (Du et al., 2007, Samotaev et al., 2013, DeMeo et al., 2014), graphene-based sensors (Yavari et al., 2012, Hu et al., 2014), conducting polymer detectors (Kondawar et al., 2012, Zhong et al., 2013), electrochemical sensors (Ji et al., 2007), semiconductor sensors (Khuspe et al., 2013, Fu, 2014), surface acoustic wave (SAW) sensors (Chen et al., 2013, Tang et al., 2014, Wang et al., 2015), field effect transistor sensors (Lu et al., 2011, Yu et al., 2012, Li et al., 2013), and quartz crystal microbalance sensors (Jia et al., 2014, Li et al., 2014, Ogimoto et al., 2015). These approaches have been used successfully in chemical analysis, and continued research efforts are needed to improve the accuracy and reliability.

As a new sensor array method developed by Rakow and Suslick (2000) in recent years, the colorimetric approach has been diffusely adopted in view of the excellent performance on molecular recognition. The colorimetric sensor array are widely used for odor recognition (Lim et al., 2009), molecular recognition (Suslick et al., 2010, Hou et al., 2013), and even complex mixture identification (Bang et al., 2008, Musto et al., 2009, Wu et al., 2014). These sensor arrays, which are based on cross-response mechanism and have characteristics of non-specific recognition, are characterized by imitation of smell or taste in view of a variety of sensitive elements and optimizing their combinations, and then achieve the distinguishing between targets. Therefore, they are possible to avoid the conventional sensors which have highly requirements in specific sensitive element, and have been widely used. In addition, more and more attentions are paid to fluorescence sensor recently due to its high sensitivity. Mayr et al. (2003) proposed a fluorescent cross-reactive array in a micro titer plate and succeed in predicting the presence of metal ions. Thete et al. (2009) used a fluorescent microarray based on hydrogel and achieved the characterization of liquid analytes. Xu et al. (2013) presented a fluorescence sensor for the detection of CO2. More and more reports have indicated that the fluorescence sensor array has high specificity and sensitivity in discrimination of various kinds of analytes (Kang et al., 2014, Liu and Bonizzoni, 2014, Xu et al., 2014). Besides detecting metal ions and liquids, it can also detect gases. Therefore, unlike these principles and techniques for measuring ammonia mentioned above, which mainly depend on single signals, in this paper, based on the cross-response mechanism, a novel rapid and effective artificial nose with fluorescent sensor array for detecting low concentrations of NH3 was proposed and realized.

Section snippets

Fluorescent sensor array

The fluorescent sensor array consisted of seven chemical materials with fluorescent effect as the sensing elements, including porphyrin (H2TTP), porphyrin derivative (TTPS), metalloporphyrin (ZnTTP), zinc porphyrin dimer (ZnPD) and three chemically responsive dyes, which were prepared according to our previous report (Fa et al., 2009, Hou et al., 2011). These kinds of materials can identify interactions between molecules such as π-π molecular complex action, bond formation, acid–base

The dynamic response of the fluorescent sensor array to NH3

The sensor array was exposed to certain concentration NH3 (the lowest concentration, 30 ppb) at different times. And the difference spectra data Yi, which were obtained from the fluorescent artificial nose and analyzed in accordance with the above-described processing methods, were shown in Fig. 3. It showed that specific feature points exhibited significant fluorescence changing until they reached to the equilibrations with the increase of exposure time. When the reaction time was less than

Conclusions

In this paper, a novel fluorescent artificial nose of recognizing and distinguishing toxic gas has been developed. A series of concentrations of NH3 were detected, and the unique fluorescence difference spectra fingerprint of NH3 was obtained. Based on the fluorescent cross-responsive sensor array and data analysis as mentioned above in detail, the dynamic response to the low concentration has been explored, and the response time of chemical reaction reached equilibrium has been determined. By

Conflict of interest

There is no conflict of interest.

Acknowledgment

The authors would like to acknowledge the financial support from NSFC (31171684), Key Technologies R&D Program of China (2014BAD07B02), the Fundamental Research Funds for the Central Universities (106112015CDJRC121210), Liquor Making Bio-Technology & Application of Key Laboratory of Sichuan Province (NJ2014-03) and Chongqing Graduate Student Research Innovation Project (CYB14013).

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    Peer review under responsibility of Turkish National Committee for Air Pollution Research and Control.

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