Optoelectronic Nose Research Articles

Reliable chiral recognition with an optoelectronic nose

Chiral discrimination is a key problem in analytical chemistry. It is generally performed using expensive instruments or highly-specific miniaturized sensors. An electronic nose is a bio-inspired instrument capable after training of discriminating a wide variety of analytes. However, generality is achieved at the cost of specificity which makes chiral recognition a challenging task for this kind of device. Recently, a peptide-based optoelectronic nose which can board up to hundreds of different sensing materials has shown promising results, especially in terms of specificity. In line with these results, we describe here its use for chiral recognition. This challenging task requires care, especially in terms of statistical reliability and experimental confounds. For these reasons, we set up an automatic gas sampling system and recorded data over two long sessions, taking care to exclude possible confounds. Two couples of chiral molecules, namely (R) and (S) Limonene and (R) and (S) Carvone, were tested and several statistical analyses indicate the almost perfect discrimination of their two enantiomers. A method to highlight discriminative sensing materials is also proposed and shows that successful discrimination is likely achieved using just a few peptides.

Optical Index Prism Sensitivity of Surface Plasmon Resonance Imaging in Gas Phase: Experiment versus Theory

Recent advances in SPR imaging detection in the gas phase have led to the development of an optoelectronic nose (opto-eN) requiring the need for optical sensitivity characterization of such devices...

Development of an optoelectronic nose based on surface plasmon resonance imaging with peptide and hairpin DNA for sensing volatile organic compounds

Nowadays, the analysis of volatile organic compounds (VOCs) is very important in various domains. In the last decades, electronic noses have emerged as promising alternatives to traditional analytical methods. Nevertheless, their wide use is still limited by their performances such as low selectivity. Herein, we developed an optoelectronic nose using virtually screened peptides and hairpin DNA (hpDNA) with improved selectivity as sensing materials and surface plasmon resonance imaging (SPRi) as the detection system. Thanks to the complementarity of their binding properties towards target VOCs, the obtained optoelectronic nose has very good selectivity, being able to discriminate not only between VOCs of different chemical families, but also VOCs of the same family with only 1-carbon difference. The combination of these sensing materials with SPRi is relevant for the development of optoelectronic nose with large sensor arrays and improved performances.

Optical Gas Sensor based on Al-doped ZnO/ZnTPP hybrid thin film

Hybrid optical gas sensors based on Al-doped ZnO/Zinc porphyrin (AZO/ZnTPP) thin films have been fabricated and demonstrated to detect ethanol vapor. Double-sensing layer of AZO and ZnTPP films were deposited on a cleaned glass substrate by RF magnetron sputtering and spin-coating techniques, respectively. We have investigated the influences of Al-doping concentration (0%, 2% and 3 wt% Al2O3) on ZnO structure with regarding to enhancing optical gas sensing properties when exposed the films to the volatile. Structural, electrical and optical properties of the AZO thin films were characterized and related to the optical gas sensing responses. It was found that an increase of Al-doped concentration in ZnO structure can also induce a potentially optical sensing response. These results were mentioned that an enhancement of carrier concentration due to Al3+ substitution in Zn2+ on ZnO structure can generate the adsorbed oxygen ion on the AZO surface as well. Absorption spectra of AZO thin films showed blue shift in near UV region due to releasing of electrons when the adsorbed oxygen ions were interacted with ethanol molecules. According to the introduced the AZO layer to form AZO/ZnTPP sensing film, the results could be demonstrated significantly enhanced the optical responses to the ethanol in broaden range of near UV-visible region at room temperature. Finally, the authors have suggest that the A3ZO/ZnTPP thin film exhibiting a good performance to detect ethanol vapor and overcome a conventional ZnTPP, ZnO/ZnTPP and A2ZO/ZnTPP thin films may be promoted as one of the optical gas sensor in an optoelectronic nose system due to broaden responses at room temperature.

Colorimetric Sensor Array for Monitoring CO and Ethylene.

Developing miniaturized and inexpensive detectors remains an important and practical goal for field-deployable monitoring of toxic gases and other bioactive volatiles. CO (a common toxic pollutant) and ethylene (the phytohormone primarily responsible for fruit ripening) share the capability of strong back-π-bonding to low-oxidation-state metal ions, which has proved important in the development of metal-ion-based sensors for these gases. We report herein cumulative colorimetric sensor arrays based on Pd(II)-silica porous microsphere sensors and their application as an optoelectronic nose for rapid colorimetric quantification of airborne CO and ethylene. Quantitative analysis of two gases was obtained in the range of 0.5 to 50 ppm with detection limits at the sub-parts-per-million level (∼0.4 ppm) after 2 min of exposure and ∼0.2 ppm after 20 min (i.e., <0.5% of the permissible exposure limit for CO and <10% of the ethylene concentration needed for fruit ripening). We further validate that common potential interfering agents (e.g., changes in humidity or other similar air pollutants such as NO x, SO2, H2S, or acetylene) are not misidentified with CO or ethylene. Finally, the sensor is successfully used for the quantification of ethylene emitted from ripening bananas, demonstrating its potential applications in the monitoring of fruit ripening during storage.

The Optoelectronic Nose: Colorimetric and Fluorometric Sensor Arrays.

A comprehensive review on the development and state of the art of colorimetric and fluorometric sensor arrays is presented. Chemical sensing aims to detect subtle changes in the chemical environment by transforming relevant chemical or physical properties of molecular or ionic species (i.e., analytes) into an analytically useful output. Optical arrays based on chemoresponsive colorants (dyes and nanoporous pigments) probe the chemical reactivity of analytes, rather than their physical properties (e.g., mass). The chemical specificity of the olfactory system does not come from specific receptors for specific analytes (e.g., the traditional lock-and-key model of substrate-enzyme interactions), but rather olfaction makes use of pattern recognition of the combined response of several hundred olfactory receptors. In a similar fashion, arrays of chemoresponsive colorants provide high-dimensional data from the color or fluorescence changes of the dyes in these arrays as they are exposed to analytes. This provides chemical sensing with high sensitivity (often down to parts per billion levels), impressive discrimination among very similar analytes, and exquisite fingerprinting of extremely similar mixtures over a wide range of analyte types, in both the gas and liquid phases. Design of both sensor arrays and instrumentation for their analysis are discussed. In addition, the various chemometric and statistical analyses of high-dimensional data (including hierarchical cluster analysis (HCA), principal component analysis (PCA), linear discriminant analysis (LDA), support vector machines (SVMs), and artificial neural networks (ANNs)) are presented and critiqued in reference to their use in chemical sensing. A variety of applications are also discussed, including personal dosimetry of toxic industrial chemical, detection of explosives or accelerants, quality control of foods and beverages, biosensing intracellularly, identification of bacteria and fungi, and detection of cancer and disease biomarkers.

Highly-Selective Optoelectronic Nose Based on Surface Plasmon Resonance Imaging for Sensing Volatile Organic Compounds

Monitoring volatile organic compounds (VOCs) is an important issue, but difficult to achieve on a large scale and on the field using conventional analytical methods. Electronic noses (eNs), as promising alternatives, are still compromised by their performances due to the fact that most of them rely on a very limited number of sensors and use databases devoid of kinetic information. To narrow the performance gap between human and electronic noses, we developed a novel optoelectronic nose, which features a large sensor microarray that enables multiplexed monitoring of binding events in real-time with a temporal response. For the first time, surface plasmon resonance imaging is demonstrated as a promising novel analytical tool for VOC detection in the gas phase. By combining it with cross-reactive sensor microarrays, the obtained optoelectronic nose shows a remarkably high selectivity, capable of discriminating between homologous VOCs differing by only a single carbon atom. In addition, the optoelectronic nose has good repeatability and stability. Finally, the preliminary assays using VOC binary and ternary mixtures show that it is also very efficient for the analysis of more complex samples, opening up the exciting perspective of applying it to "real-world" samples in diverse domains.

Colorimetric sensor arrays: development and application to art conservation

ABSTRACT Acceptable air pollutant concentration limits for sensitive artwork are generally at or below a few ppb: this is only ∼1% of the permissible exposure limits for humans. Monitoring pollutants at such low levels is an exceptional challenge, especially to do so in a cost-effective fashion for a large number of locations and microenvironments (e.g., every display case in a museum). To meet this challenge, we have extended our portable “optoelectronic nose,” by using new sensor array chemistry to develop cumulative colorimetric sensor arrays with dosimetric sensitivities that are dramatically better than commercial sensor tubes. The color changes of each sensor in a disposable printed array produce a composite response to volatiles. Using cell phone camera imaging, we have made field trials to monitor pollutant exposure of artwork from the Walt Disney Animation Research Library during shipping to and exhibition in Beijing. This exhibition, “Drawn from Life: the Art of Disney Animation Studios,” featured animation drawings, story sketches, layouts, and concept art spanning the 90 years of the Disney Animation Studio’s history. Sensor arrays monitored exterior and interior environments of passe-partout artwork frames during exhibition and inside shipping crates during transport providing quantitative information on oxidant, aldehyde, and sulfide pollutant exposure.

A digitally printed optoelectronic nose for the selective trace detection of nitroaromatic explosive vapours using fluorescence quenching

We report on a fluorescent optoelectronic nose for the trace detection of nitroaromatic explosive vapours. The sensor arrays, fabricated by aerosol-jet printing, consist of six different commercially available polymers as transducers. We assess the within-batch reproducibility of the printing process and we report that the sensor polymers show efficient fluorescence quenching capabilities with detection limits of a few parts-per-billion in air. We further demonstrate the nose’s ability to discriminate between several nitroaromatics including nitrobenzene, 1,3-dinitrobenzene and 2,4-dinitrotoluene at three different concentrations using linear discriminant analysis. Our approach enables the realization of highly integrated optical sensor arrays in optoelectronic noses for the sensitive and selective detection of nitroaromatic explosive trace vapours using a potentially low-cost digital printing technique suitable for high-volume fabrication.

Portable Optoelectronic Nose for Monitoring Meat Freshness

A disposable colorimetric sensor array (CSA) made from printing various chemically responsive dyes was combined with a hand-held device for on-site assessment and monitoring of the freshness of five meat products: beef, chicken, fish, pork, and shrimp. The hand-held device takes advantage of an on-board diaphragm micropump and a commercial 1D CMOS camera (CIS) which enables the real-time collection of colorimetric data. The sensor array shows excellent sensitivity to gaseous analytes, especially amines and sulfides at low ppb levels; excellent discrimination among meat volatiles in terms of meat type and storage time was demonstrated with multiple chemometric approaches including principle component analysis, hierarchical cluster analysis, and support vector machine analysis. This optoelectronic nose proves to be a promising supplement to other available techniques for meat product inspection.

Rapid Quantification of Trimethylamine

Sensitive detection of trimethylamine both in aqueous and gaseous phases has been accomplished using an inexpensive colorimetric sensor array. Distinctive color change patterns provide facile discrimination over a wide range of concentrations for trimethylamine with >99% accuracy of classification. Calculated limits of detection are well below the diagnostically significant concentration for trimethylaminuria (fish malodor syndrome). The sensor array shows good reversibility after multiple uses and is able to cleanly discriminate trimethylamine from similar amine odorants. Portable sensing of trimethylamine vapors at ppb concentrations is described using a cell phone camera or a hand-held optoelectronic nose. Application of the sensor array in detecting mouth and skin odor as a potential tool for portable diagnosis of trimethylaminuria is also illustrated.

Bacterial culture detection and identification in blood agar plates with an optoelectronic nose.

Clinical microbiology automation is currently limited by the lack of an in-plate culture identification system. Using an inexpensive, printed, disposable colorimetric sensor array (CSA) responsive to the volatiles emitted into plate headspace by microorganisms during growth, we report here that not only the presence but the species of bacteria growing in plate was identified before colonies are visible. In 1894 trials, 15 pathogenic bacterial species cultured on blood agar were identified with 91.0% sensitivity and 99.4% specificity within 3 hours of detection. The results indicate CSAs integrated into Petri dish lids present a novel paradigm to speciate microorganisms, well-suited to integration into automated plate handling systems.

An optoelectronic nose for identification of explosives.

Compact and portable methods for identification of explosives are increasingly needed for both civilian and military applications. A portable optoelectronic nose for the gas-phase identification of explosive materials is described that uses a highly cross-reactive colorimetric sensor array and a handheld scanner. The array probes a wide range of chemical reactivities using 40 chemically responsive colorimetric indicators, including pH sensors, metal-dye salts, redox-sensitive chromogenic compounds, solvatochromic dyes, and other chromogenic indicators. Sixteen separate analytes including common explosives, homemade explosives, and characteristic explosive components were differentiated into fourteen separate classes with a classification error rate of <1%. Portable colorimetric array sensing could represent an important, complementary part of the toolbox used in practical applications of explosives detection and identification.

Differentiation among peroxide explosives with an optoelectronic nose.

Forensic identification of batches of homemade explosives (HME) poses a difficult analytical challenge. Differentiation among peroxide explosives is reported herein using a colorimetric sensor array and handheld scanner with a field-appropriate sampling protocol. Clear discrimination was demonstrated among twelve peroxide samples prepared from different reagents, with a classification accuracy >98%.

Development of a colorimetric sensor array for squid spoilage assessment

The aim of this work was to develop and evaluate a rapid, easy-to-use optoelectronic system for the shelf-life assessment of squid in cold storage. For this purpose, an optoelectronic nose was designed, which consisted of an array containing six sensing materials prepared by combining different dyes and two inorganic supports (aluminium oxide and silica gel). Samples were packaged with the colorimetric array and kept in cold storage for 12days. Squid spoilage was monitored simultaneously by the colorimetric array and by the physico-chemical and microbial analyses during storage. Samples exceeded the acceptability limits for microbial counts on the third day. PCA analysis carried out with CIELab showed that the colorimetric array was able to discriminate between fresh squid fit for consumption and spoiled squid. The statistical models obtained by PLS, with the optoelectronic nose, successfully predicted CO2 and O2 content in the headspace as well as microbial growth.

Monitorization of Atlantic salmon (Salmo salar) spoilage using an optoelectronic nose

An optoelectronic nose for monitoring Atlantic salmon (Salmo salar) spoilage has been developed. The chromogenic array uses eight sensing materials containing pH and a Lewis acid indicator adsorbed in aluminium oxide or silica gel. Colour modulations as RGB coordinates are measured on day 0 and for the salmon samples held in cold storage for 2, 5, 7 and 9 days. For the same days volatile basic nitrogen (TVB-N) and (mesophilic, psychrotrophic and H2S-producing bacteria) analyses were carried out. Changes in the RGB coordinates in the chromogenic array are processed with qualitative (PCA) and quantitative (PLS) tools. The chromogenic data obtained from the array is correlated with the physico-chemical and microbiological parameters (TVB-N, H2S producing, mesophilic and psychrotrophic bacteria) via PLS statistical studies. The influence of the use of two cross-validation methods (Venetian and Random) and diverse number of data splits (NDS) (2–4) to determine the number of PLS components is discussed. The suitability of the PLS models is also studied via t–u score plots. The results suggest the potential feasibility of this system for S. salar freshness monitoring.

Identification of pathogenic fungi with an optoelectronic nose.

Human fungal infections have gained recent notoriety following contamination of pharmaceuticals in the compounding process. Such invasive infections are a more serious global problem, especially for immunocompromised patients. While superficial fungal infections are common and generally curable, invasive fungal infections are often life-threatening and much harder to diagnose and treat. Despite the increasing awareness of the situation's severity, currently available fungal diagnostic methods cannot always meet diagnostic needs, especially for invasive fungal infections. Volatile organic compounds produced by fungi provide an alternative diagnostic approach for identification of fungal strains. We report here an optoelectronic nose based on a disposable colorimetric sensor array capable of rapid differentiation and identification of pathogenic fungi based on their metabolic profiles of emitted volatiles. The sensor arrays were tested with 12 human pathogenic fungal strains grown on standard agar medium. Array responses were monitored with an ordinary flatbed scanner. All fungal strains gave unique composite responses within 3 hours and were correctly clustered using hierarchical cluster analysis. A standard jackknifed linear discriminant analysis gave a classification accuracy of 94% for 155 trials. Tensor discriminant analysis, which takes better advantage of the high dimensionality of the sensor array data, gave a classification accuracy of 98.1%. The sensor array is also able to observe metabolic changes in growth patterns upon the addition of fungicides, and this provides a facile screening tool for determining fungicide efficacy for various fungal strains in real time.

A novel colorimetric sensor array for monitoring fresh pork sausages spoilage

We report herein the development of a new optoelectronic nose composed of seven sensing materials prepared by the incorporation of pH indicators and chromogenic reagents selective to metabolites into inorganic materials (UVM-7 and alumina). The nose has been applied to monitor fresh pork sausage ageing. Sausages were packaged together with the disposable array in a modified packaging atmosphere (30% CO2, 70% N2) and colour changes were measured at seven day intervals. Simultaneously, microbiological and sensory analyses were performed. Colour modulations of the chromogenic array were processed with standard analytical tools, including principal component analysis (PCA) and partial least squares (PLS). According to the PCA, the array was able to monitor the sausage spoilage process and to distinguish between each sampled day. Moreover, the PLS statistical analysis of the chromogenic data displayed a linear correlation between the predicted and measured values of the storage days, mesophilic bacteria (cfu g−1) and the sensory score with regression coefficients of 0.9300, 0.9472 and 0.9381, respectively.

Smelling in Chemically Complex Environments: An Optofluidic Bragg Fiber Array for Differentiation of Methanol Adulterated Beverages

A novel optoelectronic nose for analysis of alcohols (ethanol and methanol) in chemically complex environments is reported. The cross-responsive sensing unit of the optoelectronic nose is an array of three distinct hollow-core infrared transmitting photonic band gap fibers, which transmit a specific band of IR light depending on their Bragg mirror structures. The presence of alcohol molecules in the optofluidic core quenches the fiber transmissions if there is an absorption band of the analyte overlapping with the transmission band of the fiber; otherwise they remain unchanged. The cumulative response data of the fiber array enables rapid, reversible, and accurate discrimination of alcohols in chemically complex backgrounds such as beer and fruit juice. In addition, we observed that humidity of the environment has no effect on the response matrix of the optoelectronic nose, which is rarely achieved in gas-sensing applications. Consequently, it can be reliably used in virtually any environment without precalibration for humidity or drying the analytes. Besides the discussed application in counterfeit alcoholic beverages, with its superior sensor parameters, this novel concept proves to be a promising contender for many other applications including food quality control, environmental monitoring, and breath analysis for disease diagnostics.

Evaluation of sea bream (Sparus aurata) shelf life using an optoelectronic nose

A new optoelectronic nose for the shelf-life assessment of fresh sea bream in cold storage has been developed. The chromogenic array used eight sensing materials (based on aluminium oxide and silica gel) containing pH indicators, Lewis acids and an oxidation–reduction indicator. The colour changes of the sensor array were characteristic of sea bream spoilage. Colour modulations were measured on day 0 and for the samples held in cold storage for 2, 4, 7, 9 and 11days. Determination of moisture content, pH, total volatile basic nitrogen (TVB-N), drip loss, ATP-related compounds and K1-value and microbial (mesophilic bacteria and Enterobacteriaceae) analyses were carried out on the same days. The changes in the chromogenic arrays data were processed by statistical analysis (PCA). Moreover, PLS statistical studies allowed the creation of models to correlate the chromogenic data with concentrations of mesophilic and Enterobacteriaceae. The results suggest the feasibility of this system to help develop optoelectronic noses for fish freshness monitoring.