Food Spoilage Detection Research Articles

Porous and Nanostructured CuBr Networks for Selective Ammonia Sensing at Room-Temperature

Introduction Ammonia (NH3), a major industrial commodity (142 Mt in 2017 [1]), is toxic as well as a tracer for food spoilage detection and important breath marker for impaired kidney function [2]. As a result, there is a strong interest in selective sensors that detect NH3 concentrations over a large range: from 250 to 2900 ppb in mouth-exhaled breath down to few ppb in indoor air at high relative humidity. Also, it occurs usually in gas mixtures containing a myriad of compounds requiring also high NH3 selectivity. Most promising as a solid-state and low-cost sensor material is CuBr featuring high selectivity and sensitivity to low NH3 concentrations (e.g. 20 ppb [3]) even at room temperature. However, current fabrication methods usually result in micro-sized CuBr particles [3] and rather dense film morphologies [4] that could impede efficient NH3 diffusion in the film and interaction with the CuBr surface. Here, we introduce a novel fabrication route yielding highly porous and nanostructured CuBr films for improved NH3 sensitivity and fast response dynamics at room temperature. Methods Porous and nanostructured CuBr films are obtained by a flame-aerosol based method on interdigitated electrodes. Their sensing performance was evaluated at room temperature in gas mixtures prepared with high-resolution mass flow controllers, as described in detail elsewhere [5]. In brief, analyte gases (i.e. NH3, isoprene, ethanol, methane, acetone, hydrogen, acetic acid, methanol, formaldehyde and CO) were supplied from calibrated cylinders (10 or 50 ppm in synthetic air, PanGas) and dosed to dry synthetic air (Pangas 5.0, CnHm and NOx ≤ 100 ppb) with calibrated mass flow controllers. Humidity was added by bubbling dry synthetic air through distilled water and admixing it to the analyte flow. All transfer lines were made of inert Teflon to minimized analyte gas adsorption and heated to 55 °C to avoid water condensation. The sensor film resistance was continuously monitored with a multimeter (Keithley, Integra Series 2700, USA). Results and Conclusions The porous CuBr films were tested for sensing of 5 - 5000 ppb NH3 at 90% RH (Figure 1a). When exposed to 5000 ppb of NH3, the resistance rapidly increases from 47 kΩ to 13 MΩ corresponding to a response (S) of 276. When exposed to NH3, the Cu+ as charge carriers are immobilized by forming that results in the observed resistance increase. Remarkably, this interaction is rapid and reversible even at room temperature, as indicated by the full recovery of the initial resistance baseline (dashed line, Figure 1a) and in line with literature [3]. Most impressively, NH3 concentrations down to 5 ppb (see also inset of Figure 1a for higher magnification) are detected and can be distinguished clearly from 10 and 20 ppb. The signal-to-noise-ratio (SNR, > 70) is remarkable and should enable the detection of even lower concentrations with an extrapolated lower limit of detection (LOD) of 210 parts-per-trillion (ppt) considering a typical SNR of 3. This is superior to state-of-the-art room temperature NH3 sensors: For instance, polyaniline sensors detect 40 ppb NH3 at ≥ 90% RH [6], but these are usually for single-use only as they recover too slowly.The porous CuBr sensor was tested with isoprene, ethanol, methane, acetone, hydrogen, acetic acid, methanol, formaldehyde and carbon monoxide (CO), all at a concentration of 1 ppm and 90% RH (Figure 1b). Most remarkably, the sensor responds strongest to NH3 with selectivity > 30 with CO being the highest one (> 290). This is similar to thermally deposited CuBr films with a CeO2 overlayer [3] for some of these analytes. Other NH3 sensors feature lower selectivities to these analytes. In fact, polymer-based PEDOT:PSS nanowires [7] are quite sensitive to ethanol (NH3 selectivity ~15 vs. CuBr ~40).In conclusion, such nanostructured and porous CuBr films are quite attractive for wearable breath analyzers [8] and detectors for distributed air and food quality monitoring networks with stringent power requirements.

Selective Ammonia Detection at Ppb-Level with Si-Doped MoO3 Sensors for Food and Environmental Applications

Introduction Ammonia (NH3) is an important marker for food spoilage[1] as well as a toxic environmental pollutant emitted from concrete walls, fertilizers or refrigeration systems[2]. Therefore, low-cost compact sensors for the detection of hazardous NH3 are urgently needed. Metal-oxide (chemo-resistive) gas sensors are attractive for NH3 detection as they offer simple operation, low power consumption and can be integrated into portable devices.[3] In specific, the α-phase of MoO3 is promising for detection of NH3 down to 50 parts per billion (ppb) at dry conditions. However, due to the high operating temperatures of MoO3 gas sensors (250 to 500 °C), the material must be stabilized by doping or the addition of foreign oxides. Here, we show how tailoring material morphology, phase composition and particle size enables high NH3 sensing performance[4]. Method Pure and Si-doped MoO3 (0 – 20 wt%) nanoparticles were made by flame spray pyrolysis (FSP) and directly deposited onto Al2O3 sensor substrates with interdigitated Pt electrodes[4]. Subsequently, the sensor films were annealed at 450 °C for 5 h in an oven for thermal stabilization. The nanoparticles were analyzed using X-ray diffraction (XRD) patterns, nitrogen adsorption (Brunauer-Emmett-Teller, BET) as well as transmission electron microscopy (TEM) and electron diffraction (ED). The sensing performance was characterized as a function of SiO2 content with synthetic gas mixtures at a sensor temperature of 400 °C on a dynamic mixing setup. Furthermore, the selectivity towards possible interfering molecules of different chemical classes (e.g. acetone, CO and NO) was evaluated. Results and Conclusions The as-prepared, pure MoO3 powder shows fine crystallinity confirmed by transmission electron microscopy (TEM) (Figure 1a) and ED patterns (Figure 1b). By annealing the sensor substrates at 450 °C for 5 h, pure MoO x particles grow to ribbon-like structures (Figure 1d) with large crystallites, as indicated by XRD (triangles) and BET (open circles) and confirmed by bright spots in ED patterns (Figure 1c). Doping with Si reduces particle and crystal growth significantly, decreasing the crystal size from 147 to 65 nm and the particle size from 272 to 83 nm resulting in superior thermal stability. Excess Si (above 3 wt%) is not incorporated into the MoO3 lattice, but forms amorphous SiO2 domains, inhibiting further crystal growth, as subjected by the constant dXRD (Figure 1) and visible by TEM. Due to those structural changes, the sensor response and selectivity depend on the SiO2 doping content.Figure 2 shows the response of pure and Si-doped MoO3 sensors to 1000 ppb NH3 (triangles), acetone (circles), NO (squares) and CO (diamonds) at 400 °C. Increasing the SiO2 content from 0 to 3 wt% almost triples the NH3 response from 0.22 to 0.53 with only minor changes for the other analytes. This results from the reduced sinter neck size of MoO3 due to segregated SiO2 domains which locally narrow the conduction channel leading to an increased electron depletion and change the morphology resulting in a higher surface-to-volume ratio[4]. Therefore, charge carrier mobility and thus film resistance are dominated by surface phenomena increasing the sensor’s sensitivity. Moreover, Si-doping (3 wt%) improved the NH3 selectivity toward other interfering gases achieving a response ratio to acetone (S NH3 / SA ) of 3.6 and to NO of 7.9 and no sensitivity for CO (Figure 2). Above 3 wt% SiO2 content, the film resistance continuously increases (inset in Figure 2) due to the formation of large and inert SiO2 domains. In addition to the enhanced response and selectivity towards NH3, the sensor could clearly detect NH3 down to 400 ppb even in the presence realistic relative humidity (up to 90%)[4]. As a result, this sensor is promising for integration into a portable device for food spoilage detection and environmental monitoring.

Amine-Reactive Activated Esters of meso-CarboxyBODIPY: Fluorogenic Assays and Labeling of Amines, Amino Acids, and Proteins.

Fluorescence-based amine-reactive dyes are highly valuable for the sensing of amines and the labeling of biomolecules. Although it would be highly desirable, large changes in emission spectra and intensity seldom accompany the conjugation of known amine-reactive dyes to their target molecules. On the contrary, amide bond formation between amines and the pentafluorophenyl (2-PFP) and succinimidyl (2-NHS) esters of meso-carboxyBODIPY results in significant changes in emission maxima (Δλ: 70-100 nm) and intensity (up to 3000-fold), enabling the fast (down to 5 min) and selective fluorogenic detection and labeling of amines, amino acids, and proteins. This approach further benefits from the demonstrated versatility and high reliability of activated ester chemistry, and background hydrolysis is negligible. The large "turn-on" response is a testament of the extreme sensitivity of meso-carboxyBODIPYs to the minimal changes in electronic properties that distinguish esters from amides. Applications to the detection of food spoilage, staining of proteins on electrophoretic gels or in living cells, and the expedited synthesis of organelle-specific fluorescence microscope imaging agents are further demonstrated.

A simple electrochemical approach to fabricate functionalized MWCNT-nanogold decorated PEDOT nanohybrid for simultaneous quantification of uric acid, xanthine and hypoxanthine

Medical diagnostics and detection of food spoilage require estimation of hypoxanthine (HX), xanthine (XN), and uric acid (UA). A selective sensing platform has been proposed for simultaneous detection of all these species. Functionalized multi-walled carbon nanotube (fMWCNT) stabilized nanogold decorated PEDOT:TOS polymeric nanocomposite (Au-PEDOT-fMWCNT) was synthesized through rapid one-step electropolymerization to enhance conductivity and active surface area by several folds. Electrochemical activities of the proposed sensing platform were analyzed by cyclic voltammetry (CV) and differential pulse voltammetry (DPV), electrochemical impedance spectroscopy (EIS). Analyses through SEM, FESEM and TEM were performed to explore the surface morphology and elemental analysis of the polymeric nanohybrid was investigated by XPS, Raman, FTIR, XRD spectroscopy. Electro-catalysis of UA, XN and HX occurred at low oxidation potentials i.e. 0.082, 0.463 and 0.808 V, respectively in the optimized conditions. The uniquely designed simple, interference free Au-PEDOT-fMWCNT/GCE sensor exhibited high selectivity, good reproducibility, reusability (∼180 times) and stability (∼3 month) with excellent sensitivity of 1.73, 14.31 and 3.82 μA μM−1 cm−2 for UA, XN and HX, respectively. The sensor exhibited linear ranges of detection as 0.1–800, 0.05–175 and 0.1–150 μM with detection limits of 199.3, 24.1 and 90.5 nM for quantification of UA, XN and HX respectively. The performance of the proposed sensor was validated by addition of UA, XN and HX in human serum, urine and fish samples by comparing to those using HPLC. The results indicated good applicability of the proposed sensor for simultaneous detection of UA, XN, HX in real biological fluids.

Acid-base Vapor Sensing Enabled by ESIPT-attributed Cd(II) Coordination Polymer with Switchable Luminescence

Fluorescence materials based on excited state intramolecular proton transfer(ESIPT) have attracted great attention due to the unique four-level energy states. Herein, we report the assembly of a Cd-LF coordination polymer from purposely designed LF(H2hpi2cf) ligand, which can present switchable luminescence behavior by gain or loss protons originated in uncoordinated ESIPT sites and serve as acid-base vapor sensors. Fabricated into in-situ grown film or transparent ink by simple methods, Cd-LF presents facile and portable amine sensor for food spoilage detection and fluorescent anti-counterfeiting ink applications.

Colorimetric Sensing of Putrescine and Cadaverine Using Ninhydrin as a Food Spoilage Detection Reagent

A simple colorimetric method is demonstrated for the quantitative detection of aliphatic biogenic amines, putrescine and cadaverine using ninhydrin. The protocol is based on the formation of a complex equivalent to that of Ruhemann’s purple with a molar ratio of 1:2.5 between putrescine and ninhydrin which exhibited an absorption peak at 564 nm. The observation was theoretically verified using density functional theory (DFT). It is observed that the colorimetric detection protocol was rapid at 80 °C. Putrescine and cadaverine exhibited a similar colour on reaction with ninhydrin at pH 8.0, since the structure of both the biogenic amines is quite similar except for an addition of a methylene group, a distinguishable colour change was not observed. The analytical response was studied at 564 nm and 570 nm for putrescine and cadaverine respectively. Putrescine exhibited a linear range of 25–150 ppm, while cadaverine showed a non-linear range of 35–150 ppm. The detection limit for putrescine and cadaverine was observed to be 10 ppm and 40 ppm respectively. The specificity of the method was tested employing nine amino acids in comparison with that of aliphatic biogenic amines.

Identification of the bacteria and their metabolic activities associated with the microbial spoilage of custard cream desserts

The famous French dessert “ile flottante” consists of a sweet egg white foam floating on a vanilla custard cream, which contains highly nutritive raw materials, including milk, sugar and egg. Spoilage issues are therefore a key concern for the manufacturers. This study explored the bacterial diversity of 64 spoiled custard cream desserts manufactured by 2 French companies. B. cereus group bacteria, coagulase negative Staphylococcus, Enterococcus and Leuconostoc spp. were isolated from spoiled products. Thirty-one bacterial isolates representative of the main spoilage species were tested for their spoilage abilities. Significant growth and pH decrease were observed regardless of species. While off-odours were detected with B. cereus group and staphylococci, yoghurt odours were detected with Enterococcus spp. and Leuconostoc spp. B. cereus group bacteria produced various esters and several compounds derived from amino acid and sugar metabolism. Most Staphylococci produced phenolic compounds. Enterococcus spp. and Leuconostoc spp. isolates produced high levels of compounds derived from sugar metabolism. Each type of spoilage bacteria was associated with a specific volatile profile and lactic acid was identified as a potential marker of spoilage of custard cream-based desserts. These findings provide valuable information for manufacturers to improve food spoilage detection and prevention of chilled desserts made with milk and egg.

Use of colorimetric hydrogel as an indicator for food packaging applications

A novel hydrogel was synthesized from N,N-dimethyl acrylamide (DMAAm), gelatin, citric acid (CA) and Basilicum extract (BE). This study was aimed at creating an advanced food packaging material that allows the detection of food spoilage, which can be monitored colorimetrically. The poly(gelatin-co-DMAAm)/CA–BE was synthesized in the form of a film on Petri dishes using a redox polymerization technique. Mechanical and water resistance properties of the hydrogel were further improved by the addition of CA and N,N-methylene-bis-acrylamide as crosslinkers; BE was added to the reaction mixture and entrapped in the polymer chains with the aim to introduce antimicrobial, antioxidant and anthocyanin properties for the desired utilization. The characterization of the synthesized hydrogel was carried out using a dynamic and mechanical analyser, thermo gravimetric analyser, Fourier transform infrared spectroscopy and scanning electron microscopy. The antimicrobial activity of the hydrogel was observed as it was tested against Escherichia coli, Bacillus subtilis and Staphylococcus aureus. Furthermore, total antioxidant and anthocyanin activities of the hydrogels were also studied at different pH values to monitor the colour change capabilities. It was concluded that the hydrogel was a strong candidate for use in food packaging.

ForceSpun polydiacetylene nanofibers as colorimetric sensor for food spoilage detection

Due to health and economic concerns, increasing attention has been attracted to the safety and quality control of food, particularly meat and seafood. Ammonia and biogenic amines (BAs), such as trimethylamine, putrescine and cadaverine, are released during the decomposition of meat protein. Therefore, the sensitive detection of the released BAs is crucial to the assessment of the safety and quality of meat products during storage, transportation and consumption. In this study, we have developed silica-reinforced polydiacetylene (PDA) nanofiber mats by a novel Forcespinning® technique. These PDA nanofibers demonstrate optical sensing of BAs owing to their strong electrostatic interaction with carboxylate ions of the PDA and amine ions in the BA molecules. Specifically, the PDA nanofibers produce a color transition from blue-to-red plus an enhancement of its fluorescence. PDA nanofibers were prepared from two different monomers and their amine sensing properties are evaluated and compared. The PDA nanofibers made from 5,7-eicosadienoic acid (ECDA) demonstrate higher performance and can determine amine vapor concentration with a detection limit of ˜7 ppm in a few minutes. An effective colorimetric response was also obtained when evaluating the sensing ability of the nanofibers to BA vapors from actual spoiling meat products including chicken, beef, fish and pork. Overall, our forcespun PDA nanofibers demonstrated promising colorimetric detection of meat spoilage based on the released amine vapors during the food degradation. These nanofibers are suitable for real-time and in situ monitoring and assessment of meat deterioration and freshness.

Excitation Wavelength Dependent Fluorescence of an ESIPT Triazole Derivative for Amine Sensing and Anti-Counterfeiting Applications.

Excitation wavelength dependent (Ex-De) emission materials have potential applications in anti-counterfeiting labels and bioimaging. Nevertheless, few purely organic chromophores are used in these areas. In this study, multiple excited states were incorporated into a molecule that was excited state intramolecular proton transfer (ESIPT) active, with the goal of manipulating the relaxation pathways of the excited states. The triazole derivative exhibits Ex-De photoluminescence (PL), and the maximum PL wavelength is located at 526 nm and 593 nm under a series of excitation wavelengths. Spectral identification indicates that the excimer and ESIPT processes are responsible for the green (526 nm) and orange (593 nm) fluorescence, respectively. Importantly, the quick response code and test strip prepared with this triazole derivative can be used for anti-counterfeiting and food spoilage detection applications, respectively. This research opens the door for developing novel Ex-De materials for anti-counterfeiting purposes.

Excitation Wavelength Dependent Fluorescence of an ESIPT Triazole Derivative for Amine Sensing and Anti‐Counterfeiting Applications

AbstractExcitation wavelength dependent (Ex‐De) emission materials have potential applications in anti‐counterfeiting labels and bioimaging. Nevertheless, few purely organic chromophores are used in these areas. In this study, multiple excited states were incorporated into a molecule that was excited state intramolecular proton transfer (ESIPT) active, with the goal of manipulating the relaxation pathways of the excited states. The triazole derivative exhibits Ex‐De photoluminescence (PL), and the maximum PL wavelength is located at 526 nm and 593 nm under a series of excitation wavelengths. Spectral identification indicates that the excimer and ESIPT processes are responsible for the green (526 nm) and orange (593 nm) fluorescence, respectively. Importantly, the quick response code and test strip prepared with this triazole derivative can be used for anti‐counterfeiting and food spoilage detection applications, respectively. This research opens the door for developing novel Ex‐De materials for anti‐counterfeiting purposes.

Highly Sensitive Air-Stable Easily Processable Gas Sensors Based on Langmuir–Schaefer Monolayer Organic Field-Effect Transistors for Multiparametric H2S and NH3 Real-Time Detection

A combination of low limit of detection, low power consumption, and portability makes organic field-effect transistor (OFET) chemical sensors promising for various applications in the areas of industrial safety control, food spoilage detection, and medical diagnostics. However, the OFET sensors typically lack air stability and restoration capability at room temperature. Here, we report on a new design of highly sensitive gas sensors based on Langmuir-Schaefer monolayer organic field-effect transistors (LS OFETs) prepared from organosilicon derivative of [1]benzothieno[3,2- b][1]-benzothiophene. The devices fabricated are able to operate in air and allow an ultrafast detection of different analytes at low concentrations down to tens of parts per billion. The sensors are reusable and can be utilized in real-time air-quality monitoring systems. We show that a direct current response of the LS OFET can be split into the alteration of various transistor parameters, responsible for the interactions with different toxic gases. The sensor response acquiring approach developed allows distinguishing two different gases, H2S and NH3, with a single sensing device. The results reported open new perspectives for the OFET-based gas-sensing technology and pave the way for easy detection of the other types of gases, enabling the development of complex air analysis systems based on a single sensor.

Photochromic Paper Indicators for Acidic Food Spoilage Detection.

A photoresponsive microstructured composite is fabricated through the impregnation of cellulosic filter paper (FP) with a spiropyran-modified acrylic polymer. The polymer enwraps uniformly each individual cellulose fiber, increases the thermal stability of cellulose, and ensures the preservation of the composite functionalities even upon removal of the surface layers through mechanical scratching. The photochromic spiropyran moieties of the polymer, even while embedded in the cellulosic sheet, can reversibly interconvert between the colorless spiropyran and the pink merocyanine isomeric states upon irradiation with UV and visible light, respectively. Moreover, the photochromic polymer presents a faster photochromic response and a higher resistance to photodegradation, with an outstanding reusability for more than 100 switching cycles when it is incorporated in the cellulose network. Most importantly, the acidochromism of the modified FP, attributed to the spiropyran molecules after UV activation, allows the real-time optical and visual detection of acidity changes and spoilage in food products, such as wine and milk. Spoilage due to bacterial degradation and oxidation processes generates acidic vapors that induce the protonation of the merocyanine. This results in a visually detectable chromic transition from pink to white of the treated cellulose fibers, corresponding to a blue shift in the absorption spectrum. The developed photoresponsive cellulose composite can serve as cost-effective robust optical component in integrated functional platforms and consumer-friendly indicators for smart food packaging, as well as portable on demand acidoresponsive interfaces for gas monitoring in industrial and environmental applications.

Highly Sensitive, Printable Nanostructured Conductive Polymer Wireless Sensor for Food Spoilage Detection

Near-field communication (NFC) labeling technology has been recently used to endow smartphones with nonline-of-sight sensing functions to improve the environment, human health, and quality of life. For applications in detecting food spoilage, the development of a sensor with high enough sensitivity to act as a switch for an NFC tag remains a challenge. In this Letter, we developed a nanostructured conductive polymer-based gas sensor with high sensitivity of Δ R/ R0 = 225% toward 5 ppm ammonia NH3 and unprecedented sensitivities of 46% and 17% toward 5 ppm putrescine and cadaverine, respectively. The gas sensor plays a critical role as a sensitive switch in the circuit of the NFC tag and enables a smartphone to readout meat spoilage when the concentration of biogenic amines is over a preset threshold. We envision the broad potential use of such intelligent sensing for food status monitoring applications in daily life, storage and supply chains.

A pH-Sensing Film from Tamarind Seed Polysaccharide with Litmus Lichen Extract as an Indicator.

A new pH-sensing film was developed by using tamarind seed polysaccharide (TSP) and natural dye extracted from litmus lichen (LLE). The addition of LLE from 0 to 2.5% decreased the tensile strength and elongation at break from 30.20 to 29.97 MPa and 69.73% to 60.13%, respectively, but increased the water vapor permeability from 0.399 × 10−9 to 0.434 × 10−9 g·s−1·m−1·Pa−1. The UV–Vis spectra of the litmus lichen extract (LLE) in the pH range of 4–10 showed that the color clearly changed from orange to blue. The characterization results showed that TSP interacted with LLE through hydrogen bonds. The color of the film varied from orange (pH 4.0) to blue-violet (pH 10.0). The full cream milk spoilage test indicated that the film is suitable for application in full cream milk spoilage detection. The developed pH-sensing film could be used as a promising diagnostic tool for the detection of food spoilage.

A Highly Sensitive Bimodal Detection of Amine Vapours Based on Aggregation Induced Emission of 1,2-Dihydroquinoxaline Derivatives.

The detection of food spoilage is a major concern in food safety as large amounts of food are transported globally. Direct analysis of food samples is often time-consuming and requires expensive analytical instrumentation. A much simpler and more cost-effective method for monitoring food fermentation is to detect biogenic amines generated as a by-product during food decomposition. In this work, a series of 1,2-dihydroquinoxaline derivatives (DQs) with aggregation-induced emission (AIE) characteristics were synthesised and their protonated forms, that is, H+ DQs, can be utilised for the sensitive detection of biogenic amines. For example, upon exposure to amine vapours, deprotonation occurs that converts the red-coloured, non-emissive H+ DQ2 back to its yellow-coloured, fluorescent parent form. The bimodal absorption and emission changes endow the system with high sensitivity, capable of detecting ammonia vapour at a concentration of as low as 690 ppb. Taking advantage of this, H+ DQ2 was successfully applied for the detection of food spoilage and was established as a robust and cost effective technique to monitor food safety.

Low-cost chemiresistive sensor for volatile amines based on a 2D network of a zinc(II) Schiff-base complex

A marked chemiresistive behavior is revealed in a nanostructured material obtained by spin-coating a solution of a bis(salycilaldiminato)Zn(II) Schiff-base (ZnSB) complex. The resulting submicron 2D network exhibits reversible changes in absorbance and resistance under the cycles of absorption and desorption of a volatile amine. These results are explained in terms of a Lewis donor-acceptor interaction between the ZnSB (acceptor) and the chemisorbed amine (donor). The 2D network of ZnSB was employed as a sensing element to fabricate a low-cost device for the volatile amines detection, showing promising results for food spoilage detection.

Intelligent pH indicator film composed of agar/potato starch and anthocyanin extracts from purple sweet potato

A new colorimetric pH indicator film was developed using agar, potato starch, and natural dyes extracted from purple sweet potato, Ipomoea batatas. Both agar and potato starch are solid matrices used to immobilize natural dyes, anthocyanins. The ultraviolet-visible (UV-vis) spectrum of anthocyanin extract solutions and agar/potato starch films with anthocyanins showed color variations to different pH values (pH 2.0–10.0). Fourier transform infrared (FT-IR) and UV-vis region spectra showed compatibility between agar, starch, and anthocyanin extracts. Color variations of pH indicator films were measured by a colorimeter after immersion in different pH buffers. An application test was conducted for potential use as a meat spoilage sensor. The pH indicator films showed pH changes and spoilage point of pork samples, changing from red to green. Therefore, the developed pH indicator films could be used as a diagnostic tool for the detection of food spoilage.

Simple detection of food spoilage using polydiacetylene/poly(vinyl alcohol) hybrid films

Polydiacetylene (PDA)/poly (vinyl alcohol) (PVA) hybrid films are investigated for detection of ammonia gas generated by the food spoilage process. The films were obtained by mixing solutions containing diacetylene vesicles and aqueous PVA, and then drying. The films, which consist of carboxylic-acid-terminated PDA, showed a blue-to-red color transition upon reaction with ammonia gas. Through Fourier transform infrared (FTIR) analysis, we found that the observed color transition resulted from an ionic interaction between the carboxyl group of PDA and ammonia gas. In addition, patterned films were fabricated by selective UV irradiation through a photomask. Finally, the PDA/PVA hybrid films were found to show a color transition after reaction with real proteinic food at 25 °C. These results verify that the PDA/PVA hybrid films can be used for easier and more convenient real- time detection of food spoilage by the naked eye.

Fluorescent Light-Up Detection of Amine Vapors Based on Aggregation-Induced Emission

Amines play vital roles in agricultural, pharmaceutical, and food industries, but volatile amine vapors are serious threats to human health. Previously reported fluorescent sensors for amine vapor detection usually suffer from aggregation-caused quenching (ACQ) effect and need to be dispersed in solution or matrix materials. Herein, based on the fluorogen of 2-(2-hydroxyphenyl)quinazolin-4(3H)-one (HPQ) with aggregation-induced emission (AIE) properties, we have developed a fluorescent sensor HPQ-Ac for light-up detection of amine vapors through aminolysis reaction. The portable HPQ-Ac sensor can be easily prepared by directly depositing on filter paper, and it can only light up via exposure to amine vapors among various volatile organic compounds. Taking advantage of its portability and high sensitivity for amine vapors, HPQ-Ac sensor can also be used for food spoilage detection and fluorescent invisible ink.