Polymer-based gas sensors to detect meat spoilage: A review

Highlights

• The methods for the detection of food spoilage.

• The sensors for the determination of toxic ammonia gas and vapors.

• The fabrication aspect of gas sensors using conducting polymer such as polyaniline (PAni) as the active layers.

• Efficient methods to predict the growth of microorganisms with vapor changes as well as mathematical modeling.

• The selective gas sensor suitable for intelligence packaging applications.

Abstract

Due to adequate response even at sub-ppm concentrations and ambient temperature, conducting polymer sensors has gained practical applications in the detection of ammonia gas, which originates from biological changes at the early stage of food decays. This review article focuses on electrochemical gas sensors based on conducting polymers for the application of food safety control. Herein, a broad summary of cutting-edge research works is provided on polymer sensor structures, the sensing characteristics, and sensing polymer films for a wide variety of sensors of gaseous ammonia. In this review, the methods for detecting food spoilage are discussed, followed by considering the sensors to determine toxic vapors and ammonia gas. Furthermore, the fabrication aspect of gas sensors using conducting polymer such as polyaniline (PAni) as the active layer and the performance of modified electrodes are covered. State of the art in respective polymer gas sensors to detect food spoilage and ammonia volatile is also reviewed. Besides, efficient methods to predict the growth of microorganisms with vapor changes and mathematical modeling are addressed. Finally, the perspective of commercial gas sensors is regarded to identify meat spoilage based on the conducting polymers.

Introduction

An intelligent packaging must be capable of control food storage conditions during the cold chain (such as detecting [1], sensing [2], recording [3], tracing [4], communicating [5], and applying scientific logic [6]). Intelligent packaging(IP) monitors the conditions of packaged food during the life cycle to communicate [7] (i.e., indicate) information such as the quality or safety of the food material [8,9]. The largest share of the global IP market is due to environmental changes and microbial attacks [[10], [11], [12]]. Intelligent packaging can also help to enhance food protection and convenience.

Using gas sensors as an intelligent packaging tool can detect some gas given off poisonous food at the beginning of the decay process [13].

Spoilage of meat, poultry, and fish products has a close correlation with the increased production of nitrogen-containing compounds [14,15]. On the other hand, ammonia volatile has the most considerable odor release strength [16]. The survey of the ammonia volatile in spoilage food is the primary purpose of this research. A gas sensor consists of a gas-sensitive chemical that initiates a chemical reaction in the presence of the target gas at the critical temperature defined, depending on the type of sensor changing [16]. When an analyte comes into contact with the immobilized biological material, the transducer produces a measurable output, such as electrical current [17], change in mass [18], or a change in color [19,20]. There are common electrochemical polymer-based transducers such as conductometric and impedimetric sensors [21]. In addition, visible [22], colorimetric [[23], [24], [25], [26]], fluorescent [27], piezoelectric sensor works based on detection of change in colorimetric, photometric, mass or elastic properties [28,29].

Conductometric and impedimetric sensors operate on the principle that electrical conductivity (resistivity) can change in the presence or absence of some chemical species. The possibility of miniaturization and suitability of these sensors is for food safety in the device or into the food package.

In summary, simple structure, low cost, compatibility with different types of circuits, ease of construction, miniaturization [30], and good interchangeability are some of the reasons why resistance sensors are favorable for printed and flexible sensors [31].

Commercial conventional sensing structures include polymers and metal oxide semiconductors (MOS) [32] for using resistive-type gas sensors. The polymers, due to good sensitivity, reproducibility, and operate at room temperature, are good candidates for printed sensors [33]. In contrast, metal oxide sensors also require elevated operating temperatures between 200 °C and 450 °C [34] and power ranges between 300 mW and 600 mW [35].

In recent years, the development of a polymer-based gas sensor for fast and accuracy-detection of volatile at the beginning of the decay process is the concern of many researchers, and the number of publications (2010 to 2020) on polymer gas sensors is increasing every year (PubMed), resembling that the polymers have grabbed more interest in the current research on gas sensor technology.

In the first section of this review, the selective gas sensor suitable for intelligent packaging applications and their performances is studied. Then, polymer sensors as a candidate are introduced. We also present the methods of deposition and polymerization of the polymer as a sensor followed by taking into account of types of dopants in the polymer and characterization of the active polymeric layer. The response of gas sensors to factors such as the morphology of the active ingredient depends on the sensor, the added compounds, and the polymerization time. In the next section, the working principle of the polymer is discussed. The experimental progress of polymer gas sensors applicable to food spoilage based on ammonia gas detection is surveyed in the fourth section, and finally, the final section deals with mathematical models to describe the dynamic changes of microorganisms over time.