Discrimination and Identification of Flavors with Catalytic Nanomaterial-Based Optical Chemosensor Array

Heterothermic Cataluminescence Sensor System for Efficient Determination of Aldehyde Molecules

A simple and stable cataluminescence (CTL) sensing platform based on a single sensing material for effective and rapid detection of aldehydes is an urgent need due to growing concerns for the environment, security, and health. Here, an effective and user-friendly identification method is successfully proposed to determine six common aldehydes of homologous compounds via a heterothermic CTL sensor system. Using Gd2O3 with excellent catalytic activity as a sensing material, thermodynamic and kinetic insights into the interactions between Gd2O3 and aldehydes at different temperatures were extracted and integrated to generate a unique constellation profile for each tested aldehyde, whereby achieving their effective and prompt determination. Moreover, the sensor system allowed the quantitative analysis of aldehydes with detection limits of 0.001, 0.009, 0.011, 0.011, 0.007, and 0.003 μg mL-1. Significantly, the sensor system had an excellent stability of up to 30 days. The CTL sensing platform was constructed based on a thermal regulation strategy that can provide a new approach to chemical agent identification.

Dual-Mode Optical Sensor Array for Detecting and Identifying Perillaldehyde in Solution Phase and Plant Leaf with Smartphone

Promising techniques for detecting and quantifying active components in the plants and foods have received global concern in smart agriculture. Dual-mode optical assays are becoming more attractive and popular thanks to robust and reliable analysis parameters. We herein unveil a novel turn-on and dual-mode sensor array comprising three kinds of reactive indicators including ring-closed rhodamine-hydrazine, squaraine-hydrazine, and 2,4-dinitrophenylhydrazine for evaluating perillaldehyde. Significant colorimetric and fluorescent changes were triggered through reacting primary amine/hydrazine with the active aldehyde group in perillaldehyde, thus turning on the chromogenic responses of all the indicators. Optimal colorimetric sensing showed good responses to perillaldehyde ranged up to 100 mM in ethanol. Dramatic fluorescence enhancement was also exhibited, illustrating good selectivity as well as high sensitivity (detection limit ∼20.0 μM). Inspired by rapid chemical reactions and distinct optical changes, distinct sensor array strips loaded with the optimal solid-state reactive indicators were developed for evaluating the perillaldehyde content in the perilla frutescence leaves. Smartphone-enabled readout system and digital data processing were further performed for chemometric analysis. A good correlation was obtained and the semiquantitative evaluation of the perillaldehyde content could be achieved within 15 min, possessing the significant features of naked-eye recognition, easy operation, and disposability. To the best of our knowledge, present work demonstrated the use of chromogenic sensing strips to evaluate the active perillaldehyde content in solution and vapor phases for the first time. Taken together, these characteristics also indicate that the present turn-on sensor array has great potential applications in the precise detection and evaluation of perillaldehyde in the forthcoming smart agriculture.

Portable and Label-Free Sensor Array for Discriminating Multiple Analytes via a Handheld Gas Pressure Meter

Cross-reactive sensor arrays are useful for discriminating multiple analytes in a complex sample. Herein, a portable and label-free gas pressure sensor array was proposed for multiplex analysis via a handheld gas pressure meter. It is based on the interaction diversity of analytes with catalase-like nanomaterials, including Pt nanoparticles (PtNP), Co₃O₄ nanosheets (Co₃O₄NS), and Pt-Co alloy nanosheets (PtCoNS), respectively. Thus, the diverse influence of analytes on the catalase-like activity could be output as the difference in the gas pressure. By using principal component analysis, eight proteins were well distinguished by the gas pressure sensor array at the 10 nM level within 12 min. Moreover, different concentrations of proteins and mixtures of proteins could likewise be discriminated. More importantly, the effective discrimination of proteins in human serum and discrimination of five kinds of cells further confirmed the potential of the gas pressure sensor array. Therefore, it provides a portable, cheap, sensitive, and label-free gas pressure sensor array, which is totally different from the reported sensor arrays and holds great potential for portable and cheap discrimination of multiple analytes.

A chemiluminescence sensor array for discrimination of seven toxicants

A chemiluminescence (CL) sensor array was developed based on 11 CL systems cross-combined by three luminescence reagents and four oxidants. Using the CL sensor array, we measured seven toxicants, including morphine, ketamine, diazepam, chlorpromazine, strychnine, paraquat, and fenpropathrin, which represent psychotropic drugs, sedatives and hypnotics, rodenticides, herbicides, and insecticides, respectively. The CL response pattern or 'fingerprints' were obtained for a given compound on the sensor array and then discriminated through principal component analysis. The established sensor array has been applied to real-life samples and the results showed that it possesses excellent discrimination.

Meso-pyrrolyl BODIPY based colorimetric optical sensor for Cu2+ ions

A simple meso-pyrrolyl BODIPY-Schiff base conjugate was synthesized by reacting ([Formula: see text]-formylpyrrolyl) BODIPY with 2-aminophenol in ethanol at reflux followed by recrystallization from CH2Cl2/petroleum ether, affording the conjugate in 72% yield. The conjugate was thoroughly characterized by HR-MS, 1D and 2D NMR and X-ray crystallographic techniques. The X-ray structure of the meso-pyrrolyl BODIPY-Schiff base conjugate revealed that the meso-pyrrole and the phenyl substituents were deviated by an angle of [Formula: see text] and [Formula: see text], respectively, from the plane of the BF2-dipyrrin core. The absorption spectrum of the conjugate was similar to the ([Formula: see text]-formylpyrrolyl) BODIPY with a strong absorption band at 508 nm, whereas the fluorescence of the ([Formula: see text]-formylpyrrolyl) BODIPY was completely quenched in the BODIPY-Schiff base conjugate. Furthermore, cation sensing studies revealed that the conjugate has a specific sensing ability for the Cu(II) ion even in the presence of the other metal ions, as verified by the visual, absorption and mass spectral studies. The DFT optimized structure revealed that the Cu(II) ion was bound to pyrrolic nitrogen, imine nitrogen, phenolic oxygen and two water molecules in a distorted square pyramidal fashion. TD-DFT studies accounted well for the absorption spectra of the BODIPY-Schiff base conjugate and its Cu[Formula: see text] bound complex.

Multistage Signals Based on Cyclic Chemiluminescence for Decoding Complex Samples

Identification of complex samples presents a difficult challenge for modern analytical techniques, and the differentiation among closely similar mixtures often remains indeterminate. In this article, we designed a simplified cyclic chemiluminescence (CCL) system that is able to measure multistage signals in a single sample injection. The system was used to investigate the CCL reactions of the binary, ternary, and multicomponent mixtures. Results showed that each mixture has a unique exponential decay equation (EDE) with a constant decay coefficient (k-value) to describe the change law of its multistage signals. Further studies found that different brands of liquor, beer, toner, and baby powder have different k-values, and the same brand of the commodities between different batches have the same k-values, which allows facile identification of these complex samples. We then used different catalysts to design digital codes of the k-value for further improving the identifying ability of CCL. Moreover, the multistage signals are like fingerprints and could be used for linear discriminate analysis, which provides another complementary approach for identification of complex samples. Finally, we demonstrated that CCL shows potential applications in certification and quality assurance according to the change of the k-values of the sample. This work demonstrates that excellent discrimination ability of CCL for the identification of complex samples and provides a promising technology for quality assurance.

Cataluminescence sensor for highly sensitive and selective detection of iso-butanol

In this paper, a gaseous sensor was described for detection of iso-butanol on the basis of its strong cataluminescence (CTL) emission on nano-MgO surface. The sensor showed high sensitivity and specificity to iso-butanol with response time less than 1 s and recovery time less than 18 s. A good linearly relationship between CTL intensity and the concentration of iso-butanol was observed in the range of 7.6-3350 mg/m³ (r = 0.9992), the limit of detection was 2.5 mg/m³. The proposed CTL sensor exhibits good specificity to iso-butanol against other compounds including common alcohols. The possible reaction paths of iso-butanol on the MgO surface were investigated in detail. Results shows that the hydrogen atom abstraction of iso-butanol to form β-R_iso following consumption via Waddington mechanism possible is a major reaction channel for CTL emission. The sensor was applied to analyze iso-butanol in spiked samples, satisfactory recoveries were obtained in the range of 96.6-112.8% and the RSDs were 5.0-10.1%, indicating that the proposed sensor is a promising candidate for rapid analysis of iso-butanol.

A naked-eye fluorescent sensor for copper(ii) ions based on a naphthalene conjugate Bodipy dye

A novel naphthalene-Bodipy dye (N-Bodipy) was designed, prepared and characterized. N-Bodipy showed a selective and sensitive recognition toward Cu(ii) ions as a fluorescent antenna group in acetonitrile/water over other metal cations. The complexation between Cu(ii) ions and N-Bodipy gave a specific color change as well as caused fluorescence quenching under long-wavelength light (365 nm). The remarkable quenching effect in fluorescence intensity centered at 538 nm was only observed in the presence of copper(ii) ions. Moreover, the orange color of N-Bodipy solution turned pale-yellow depending on the complexation effect in daylight. The complex stoichiometry was determined using a Job's plot and it was found to be 2 : 1 (ligand/metal). The binding constant was calculated with the Benesi-Hildebrand equation to be 1.39 × 1010 M-1 and the detection limit was 1.28 μM (LOD = 3α/slope, α is the standard deviation) for Cu(ii). The data proved that the binding between N-Bodipy and Cu(ii) is chemically reversible.

Nanoparticle-based optical sensor arrays

As in many other methods that have integrated nanoparticles (NPs), the chemical nose/tongue strategy has also progressed greatly since the entrance of NPs into this field. The fascinating tunable physicochemical properties of NPs have made them powerful candidates for array-based sensing platforms and have enabled the development of real-time, sensitive and portable systems that are able to target complex mixtures of analytes. In particular, the unique optical properties of NPs have a key role in providing promising array-based sensing approaches. This review will describe the main aspects and processes of most common NP-based optical sensor arrays. The fundamental steps in the design of a sensor array together with details of each step would be provided. The review begins with the principles of optical sensor arrays and presents the concept of cross-reactivity as the main criterion in the selection of sensing elements. Changes in the absorption and emission properties of the assembled sensing elements are categorized into two main classes of optical signals (colorimetric and fluorometric). Popular chemometric methods used for analyzing the data acquired by a sensor array have also been briefly introduced. On the basis of the objective and the desired application, different types of plasmonic and fluorescent NP that possess unique opto-physical properties have been presented as available choices in the design of sensing elements. The vast number of applications of NP-based optical sensor arrays published throughout the literature have then been reviewed according to their mechanism of interaction and the type of optical signal. Finally, the remaining challenges and future directions in this topic have been highlighted.

Carbon Nanodots-Based Fluorescent Turn-On Sensor Array for Biothiols

Biothiols play important roles in biological processes. In this study, a novel sensor array-based method was proposed to detect and differentiate biothiols. The sensor array was constructed using three kinds of Ag⁺-sensitive carbon nanodots (CDs). The CDs were synthesized with amino acids and urea as carbon sources via a simple microwave method. Results revealed that Ag⁺ can bind with CDs and depress the fluorescence of CDs, while the subsequently joined biothiols can take Ag⁺ away from CDs and recover the fluorescence of CDs. Due to the different binding ability between Ag⁺ and various CDs, as well as Ag⁺ and various biothiols, the CD-Ag⁺ array exhibits a unique pattern of fluorescence variations when interacting with six biothiol samples (cysteamine, dithiothreitol, mercaptosuccinic acid, glutathione, mercaptoacetic acid, and mercaptoethanol). Principal component analysis (PCA) was applied to analyze the pattern and generate a clustering map for a clearer identification of these biothiols. PCA can also be employed to simplify the established three-sensor array into a two-sensor array. Both the three- and two-sensor arrays can identify these biothiols in a wide biothiol concentration range (>10 μM).

Functionalized Ionic Microgel Sensor Array for Colorimetric Detection and Discrimination of Metal Ions

A functional ionic microgel sensor array was developed by using 1-(2-pyridinylazo)-2-naphthaleno (PAN)- and bromothymol blue (BTB)-functionalized ionic microgels, which were designed and synthesized by quaternization reaction and anion-exchange reaction, respectively. The PAN microgels (PAN-MG) and BTB microgels (BTB-MG) were spherical in shape with a narrow size distribution and exhibited characteristic colors in aqueous solution in the presence of various trace-metal ions, which could be visually distinguished by the naked eye. Such microgels could be used for the colorimetric detection of various metal ions in aqueous solution at submicromolar levels, which were lower than the U.S. Environmental Protection Agency standard for the safety limit of metal ions in drinking water. A total of 10 species of metal ions in aqueous solution, Ba²⁺, Cr³⁺, Mn²⁺, Pb²⁺, Fe³⁺, Co²⁺, Zn²⁺, Ni²⁺, Cu²⁺, and Al³⁺, were successfully discriminated by the as-constructed microgel sensor array combined with discriminant analysis, agglomerative hierarchical clustering, and leave-one-out cross-validation analysis.

Recent advances in cataluminescence-based optical sensing systems

Recent advances in the development of cataluminescence focused on oxygen, temperature, catalyst and instrumentation are summarized.

A cataluminescence sensor with fast response to diethyl ether based on layered double oxide nanoparticles

This work proposed a cataluminescence (CTL) sensor for rapid and highly selective detection of diethyl ether using Mg-Al-layered double oxide (Mg-Al LDO). The linear range of the CTL intensity versus the concentration of diethyl ether was 0.1-8.0 mM, with a correlation coefficient (R) of 0.9915. The limit of detection (signal-to-noise ratio (S/N) = 3) was 0.02 mM. The half decay time was ~15 s, indicating a fast CTL process. The CTL sensor showed an excellent selectivity toward diethyl ether and good operational stability. Relative standard deviation (RSD) was less than 3 % in 20 consecutive measurements for diethyl ether. The CTL process was monitored by gas chromatography-mass spectrometry (GC/MS), pH indicator, and CTL spectrum. The results showed that the strong CTL signals were from the specific basic sites of Mg-Al LDO nanoparticle, which was further confirmed by temperature-programmed desorption of carbon dioxide (CO₂-TPD). This work not only provides a facile approach to obtain a CTL sensor based on LDO but also systematically investigates the catalytic mechanism of LDO. Graphical abstract ᅟ.

Facial synthesis of hexagonal metal oxide nanoparticles for low temperature ammonia gas sensing applications

A surfactant assisted facial hydrothermal process has been employed for the synthesis of rutile and wurtzite phase SnO₂ and ZnO nanoparticles, respectively, confirmed by X-ray diffraction studies.

Colorimetric sensor array with unmodified noble metal nanoparticles for naked-eye detection of proteins and bacteria

Herein we report a novel strategy for the detection and identification of proteins using unmodified noble metal nanoparticles.

A sensitive cataluminescence-based sensor using a SrCO3/graphene composite for n-propanol

Adding graphene to SrCO₃ enhanced the CTL intensity of n-propanol, and the SrCO₃/graphene composite was used for sensitive detection of n-propanol.

An array sensor consisting of a single indicator with multiple concentrations and its application in ion discrimination

Optical sensor arrays typically require a large set of chemically responsive colorants to enhance discrimination capability. Conversely, we have proven that by using multiple concentrations of one indicator, the discrimination of various analytes could be realized.

Hybrid mesoporous colloid photonic crystal array for high performance vapor sensing

A hybrid mesoporous photonic crystal vapor sensing chip was developed by introducing fluorescent dyes into mesoporous colloidal crystals. The sensing chip was capable of discriminating various kinds of vapors, as well as their concentrations, according to their fluorescence and reflective responses to vapor analytes.

An optical nose chip based on mesoporous colloidal photonic crystal beads

An optical nose chip is developed using surface functionalized mesoporous colloidal photonic crystal beads as elements. The prepared optical nose chip displays excellent discrimination among a very wide range of compounds, not only the simplex organic vapors from the different or same chemical family, but also the complex expiratory air from different people.

Harmful gas recognition exploiting a CTL sensor array

In this paper, a novel cataluminescence (CTL)-based sensor array consisting of nine types of catalytic materials is developed for the recognition of several harmful gases, namely carbon monoxide, acetone, chloroform and toluene. First, the experimental setup is constructed by using sensing nanomaterials, a heating plate, a pneumatic pump, a gas flow meter, a digital temperature device, a camera and a BPCL Ultra Weak Chemiluminescence Analyzer. Then, unique CTL patterns for the four types of harmful gas are obtained from the sensor array. The harmful gases are successful recognized by the PCA method. The optimal conditions are also investigated. Finally, experimental results show high sensitivity, long-term stability and good linearity of the sensor array, which combined with simplicity, make our system a promising application in this field.

BODIPY-based fluorometric sensor array for the highly sensitive identification of heavy-metal ions

A BODIPY(4,4-difluoro-4-bora-3a,4a-diaza-s-indacene)-based fluorometric sensor array has been developed for the highly sensitive detection of eight heavy-metal ions at micromolar concentration. The di-2-picolyamine (DPA) derivatives combine high affinities for a variety of heavy-metal ions with the capacity to perturb the fluorescence properties of BODIPY, making them perfectly suitable for the design of fluorometric sensor arrays for heavy-metal ions. 12 cross-reactive BODIPY fluorescent indicators provide facile identification of the heavy-metal ions using a standard chemometric approach (hierarchical clustering analysis); no misclassifications were found over 45 trials. Clear differentiation among heavy-metal ions as a function of concentration was also achieved, even down to 10(-7)M. A semi-quantitative interpolation of the heavy-metal concentration is obtained by comparing the total Euclidean distance of the measurement with a set of known concentrations in the library.

Monitoring of chicken meat freshness by means of a colorimetric sensor array

A new optoelectronic nose to monitor chicken meat ageing has been developed. It is based on 16 pigments prepared by the incorporation of different dyes (pH indicators, Lewis acids, hydrogen-bonding derivatives, selective probes and natural dyes) into inorganic materials (UVM-7, silica and alumina). The colour changes of the sensor array were characteristic of chicken ageing in a modified packaging atmosphere (30% CO(2)-70% N(2)). The chromogenic array data were processed with qualitative (PCA) and quantitative (PLS) tools. The PCA statistical analysis showed a high degree of dispersion, with nine dimensions required to explain 95% of variance. Despite this high dimensionality, a tridimensional representation of the three principal components was able to differentiate ageing with 2-day intervals. Moreover, the PLS statistical analysis allows the creation of a model to correlate the chromogenic data with chicken meat ageing. The model offers a PLS prediction model for ageing with values of 0.9937, 0.0389 and 0.994 for the slope, the intercept and the regression coefficient, respectively, and is in agreement with the perfect fit between the predicted and measured values observed. The results suggest the feasibility of this system to help develop optoelectronic noses that monitor food freshness.

A chemiluminescence sensor array based on nanomaterials for discrimination of teas

In recent years, electronic tongue and nose devices have been developed that consist of an array of cross-responsive sensors. In this study, we report a chemiluminescence (CL) sensor array based on oxidation at twelve different catalytic nanomaterial locations for the discrimination of eight teas. CL response patterns or "fingerprints" were obtained for a given compound on the sensor array and then discriminated through linear discriminant analysis. The experiments demonstrate that the sensor array had excellent differentiability and reversibility.

Analysis of 2-propanol in exhaled breath using in situ enrichment and cataluminescence detection

We report a simple gaseous sensor for the sensitive detection of trace 2-propanol in exhaled breath using in situ enrichment and cataluminescence detection method on the surface of nanomaterials. The influences of heating voltage and absorption time on the CTL intensity were discussed, respectively. In the selected conditions, the linear range of 2-propanol concentration is 60-600 ppbv and the detection of limit is 11 ppbv. Moreover, the lifetime and selectivity of the sensor were also investigated. It has the potential to diagnostic volatile organic compounds in human breath.