Peptide Modified ZnO Nanoparticles as Gas Sensors Array for Volatile Organic Compounds (VOCs)

Mechanistic Analysis of Peptide Affinity to Single-Walled Carbon Nanotubes and Volatile Organic Compounds Using Chemiresistors

Peptides, due to their diverse and controllable properties, are used as both liquid and gas phase recognition elements for both biological and chemical targets. While it is well understood how binding of a peptide to a biomolecule can be converted into a sensing event, there is not the same mechanistic level of understanding with regard to how peptides modulate the selectivity of semiconductor/conductor-based gas sensors. Notably, a rational, mechanistic study has not yet been performed to correlate peptide properties to the sensor response for volatile organic compounds (VOCs) as a function of chemical properties. Here, we have designed a peptide that has (1) two amino acid residues that bind the sensor surface, (2) two flexible linkers (GG) that eliminate steric strain, and (3) a five amino-acid repeat that can bind the analyte of interest either by formation of a binding pocket (such as from peptides selected by phage display) or by forming a semiselective adsorption layer. The nine peptide sequences containing both a six amino acid constant sequence (WGGWGG) and a five amino acid variable sequence (XXXXX) were synthesized, and their impact on the selectivity and sensitivity of carbon nanotube (CNT) gas sensors was explored. The response of each sensor to the following VOCs with diverse chemical properties: isopropyl alcohol (polar protic), acetone (polar aprotic), isoprene (nonpolar, linear hydrocarbon), and toluene (nonpolar aromatic), was then recorded and analyzed. This study revealed multiple key factors that influence the response of peptides on CNTs to select VOCs. First, the stability of the CNT-peptide aqueous dispersion correlated to the aromaphilicity of the side chain, strongly suggesting that the side chains of peptides are interfacing with the CNT, and not the peptide backbone. Second, the sensing response profile cannot solely be explained by peptides adsorbing to the gas molecules with similar polarities/dielectrics and may instead be due to analyte displacement of the peptide side chain on the CNT surface as measured by changes in the peptide bond orientation using near-edge X-ray absorption fine structure spectroscopy (NEXAFS). These two observations create a new paradigm to explain how peptides confer selectivity to semiconductor-/conductor-based gas sensors and can provide insights into future design and implementation of peptide-coated solid state sensors for gas targets.

Non-Destructive Pest Detection: Innovations and Challenges in Sensing Airborne Semiochemicals

Pests, especially invasive ones, pose significant threats to the global ecosystem, crop security, and agriculture economy. Sensing airborne semiochemicals as a nondestructive detection method has been recognized as a promising strategy to detect the presence of these living pests on site. However, sensing airborne semiochemicals in fields is challenging, as they are transmitted in concentrations as low as several nanograms per cubic meter in chemically diverse environments. This low vapor pressure together with similarity in functional groups of pheromones among different species have curtailed the practical deployment of corresponding sensors for real world applications. This review describes the advances in semiochemical detection methods and technologies including traditional analytical instruments, trained animals, and electroantennography with a focus on electronic noses (e-noses). Several key types of volatile organic compound (VOC) sensors used in e-noses are summarized, including their transduction methods, sensing materials, and sensing performance for semiochemical and simulants detection. Notably, it was found that many commercial VOC sensors failed to respond to airborne semiochemicals effectively, leading to a reduced efficiency of e-noses. Future work may focus on developing stable and robust sensing materials with higher sensitivity and selectivity to pheromones and understanding the feasibility of the deployment of the sensors under field conditions.

Peptide Linked Diacetylene Amphiphiles for Detection of Epitope Specific Antibodies

Antibodies produced in response to adaptive immunity provide a receptor with multiple sites for binding to a distinct epitope of an antigen. Determining antibody levels to specific antigens has important clinical applications in assessing immune status or deficiency, monitoring infectious or autoimmune diseases, and diagnosing allergies. Leveraging that a specific antibody will bind to a distinct small peptide epitope without requiring the entire antigen to be present, we demonstrate in this work a proof-of-concept assay to detect the presence of an antibody by using peptide epitopes linked to an amphiphile to generate a vesicle-based sensing system. By affording multiple copies of the epitope site on the vesicle, we revealed that the vesicles visibly aggregate in response to an antibody specific for that epitope due to multivalent binding provided by the antibody. We also uncovered the role of peptide surface density in providing accessible epitopes on the vesicles for antibody binding. In summary, using a peptide derived from the coat protein of human influenza virus directly linked to a diacetylene-containing amphiphile afforded peptide-laden vesicles that proved capable of detecting the presence of antibodies specific for human influenza hemagglutinin.

High-performance olfactory receptor-derived peptide sensor for trimethylamine detection based on Steglich esterification reaction and native chemical ligation connection

Trimethylamine (TMA) commonly exists in daily life and is harmful to human health, therefore the convenient and sensitive monitoring of TMA is highly desired. In this study, we developed a method to fabricate a high-performance TMA sensor by chemically conjugating olfactory receptor-derived peptides (ORPs) to single-walled carbon nanotubes (SWCNTs) on interdigital electrodes. First, the SWCNTs were modified with thioester by Steglich esterification reaction. Next, the ORPs with a cysteine residue at the N-terminus were connected to the thioester by native chemical ligation and modified to the surface of the SWCNTs. The chemical connection method enabled more effective loading of ORPs to the SWCNTs compared to the previously reported physical connection method. Using this approach, the ORPs-SWCNTs sensor for gaseous TMA was fabricated and enabled detection of TMA with a concentration as low as 0.01 parts per trillion, which was three orders of magnitude lower than the reported lowest detection limit up to date. Furthermore, we tested the performance of the ORP-sensor with vaporized TMA and TMA generated from various spoiled food, and the sensor exhibited excellent sensitivity, selectivity, and stability for TMA detection. The results demonstrated the effectiveness of the proposed chemical connection method for the fabrication of ORP-sensor and the great potential of using these sensors for applications in environmental safety, food quality evaluation, and healthcare.

A p-n Heterojunction Based Pd/PdO@ZnO Organic Frameworks for High-Sensitivity Room-Temperature Formaldehyde Gas Sensor

As formaldehyde is an extremely toxic volatile organic pollutant, a highly sensitive and selective gas sensor for low-concentration formaldehyde monitoring is of great importance. Herein, metal-organic framework (MOF) derived Pd/PdO@ZnO porous nanostructures were synthesized through hydrothermal method followed by calcination processes. Specifically, porous Pd/PdO@ZnO nanomaterials with large surfaces were synthesized using MOFs as sacrificial templates. During the calcination procedure, an optimized temperature of 500°C was used to form a stable structure. More importantly, intensive PdO@ZnO inside the material and composite interface provides lots of p-n heterojunction to efficiently manipulate room temperature sensing performance. As the height of the energy barrier at the junction of PdO@ZnO exponentially influences the sensor resistance, the Pd/PdO@ZnO nanomaterials exhibit high sensitivity (38.57% for 100 ppm) at room temperature for 1-ppm formaldehyde with satisfactory selectivity towards (ammonia, acetone, methanol, and IPA). Besides, due to the catalytic effect of Pd and PdO, the adsorption and desorption of the gas molecules are accelerated, and the response and recovery time is as small as 256 and 264 s, respectively. Therefore, this MOF-driven strategy can prepare metal oxide composites with high surface area, well-defined morphology, and satisfactory room-temperature formaldehyde gas sensing performance for indoor air quality control.

Coating-Based Quartz Crystal Microbalance Detection Methods of Environmentally Relevant Volatile Organic Compounds

Volatile organic compounds (VOCs) that evaporate under standard atmospheric conditions are of growing concern. This is because it is well established that VOCs represent major contamination risks since release of these compounds into the atmosphere can contribute to global warming, and thus, can also be detrimental to the overall health of worldwide populations including plants, animals, and humans. Consequently, the detection, discrimination, and quantification of VOCs have become highly relevant areas of research over the past few decades. One method that has been and continues to be creatively developed for analyses of VOCs is the Quartz Crystal Microbalance (QCM). In this review, we summarize and analyze applications of QCM devices for the development of sensor arrays aimed at the detection of environmentally relevant VOCs. Herein, we also summarize applications of a variety of coatings, e.g., polymers, macrocycles, and ionic liquids that have been used and reported in the literature for surface modification in order to enhance sensing and selective detection of VOCs using quartz crystal resonators (QCRs) and thus QCM. In this review, we also summarize novel electronic systems that have been developed for improved QCM measurements.

A Hairpin DNA-Based Piezoelectric E-Nose: Exploring the Performances of Heptamer Loops for the Detection of Volatile Organic Compounds

A hairpin DNA (hpDNA) piezoelectric gas sensors array with heptamer loops as sensing elements was designed, realized, and challenged with pure volatile organic compounds VOCs and real samples (beer). The virtual binding versus five chemical classes (alcohols, aldehydes, esters, hydrocarbons, and ketones) of the entire combinatorial library of heptamer loops (16,384 elements) was studied by molecular modelling. Six heptamer loops, having the largest variance in binding the chemical classes, were selected to build the array. The six gas sensors were realized by immobilizing onto gold nanoparticles (AuNPs) via a thiol spacer the hpDNA constituted by the heptamer loops and the same double helix stem of four base pairs (GAAG at 5′ and CTTC at 3′ end). The HpDNA-AuNP was used to modify the surface of 20 MHz quartz crystal microbalances (QCMs). The realized E-nose was able to clearly discriminate among 15 pure VOCs of different chemical classes, as demonstrated by hierarchical cluster analysis. The analysis of real beer samples during fermentation was also carried out. In such a challenging matrix consisting of 23 different VOCs, the hpDNA E-nose with heptamer loops was able to discriminate among different fermentation times with high success rate. Class assignment using the Bayes theorem gave an excellent 98% correct beer samples classification in cross-validation.

Gas sensors based on mass-sensitive transducers. Part 2: Improving the sensors towards practical application

Within the framework outlined in the first part of the review, the second part addresses attempts to increase receptor material performance through the use of sensor systems and chemometric methods, in conjunction with receptor preparation methods and sensor-specific tasks. Conclusions are then drawn, and development perspectives for gravimetric sensors are discussed.

Peptides, DNA and MIPs in Gas Sensing. From the Realization of the Sensors to Sample Analysis

Detection and monitoring of volatiles is a challenging and fascinating issue in environmental analysis, agriculture and food quality, process control in industry, as well as in 'point of care' diagnostics. Gas chromatographic approaches remain the reference method for the analysis of volatile organic compounds (VOCs); however, gas sensors (GSs), with their advantages of low cost and no or very little sample preparation, have become a reality. Gas sensors can be used singularly or in array format (e.g., e-noses); coupling data output with multivariate statical treatment allows un-target analysis of samples headspace. Within this frame, the use of new binding elements as recognition/interaction elements in gas sensing is a challenging hot-topic that allowed unexpected advancement. In this review, the latest development of gas sensors and gas sensor arrays, realized using peptides, molecularly imprinted polymers and DNA is reported. This work is focused on the description of the strategies used for the GSs development, the sensing elements function, the sensors array set-up, and the application in real cases.

Volatile organic compounds gas sensor based on quartz crystal microbalance for fruit freshness detection: A review

In this review article, the state of the art of gas sensors based on quartz crystal microbalance (QCM) for fruit freshness detection is overviewed from the aspects of development history, working principle, selection and modification of sensitive materials, and volatile organic compounds detection of fruits. According to the characteristics of respiratory intensity at the stage of fruit ripening, fruits can be divided into respiration climacteric fruits and non-climacteric fruits. In recent years, research has mainly focused on respiration climacteric fruits, such as bananas and mangoes, etc., while related studies on non-climacteric fruits have been rarely reported, except for citrus fruits. The preparation methods and structure design of sensitive materials based on physical/chemical adsorption mechanisms are further discussed according to the odor components that affect the freshness of fruits, namely alkenes, esters, aldehydes and alcohols.

Flower-Like ZnO Nanorods Synthesized by Microwave-Assisted One-Pot Method for Detecting Reducing Gases: Structural Properties and Sensing Reversibility

In this work, flower-like ZnO nanorods (NRs) were successfully prepared using microwave-assisted techniques at a low temperature. The synthesized NRs exhibited a smooth surface and good crystal structure phase of ZnO. The sharp peak of the XRD and Raman spectrum confirmed the high crystallinity of these ZnO NRs with a pure wurtzite structure. The nanorods were ~2 μm in length and ~150 nm in diameter, respectively. The electron diffraction pattern confirmed that the single crystal ZnO nanorods aligned along the [001] plane. The NRs were applied to fabricate a gas sensor for reducing gases such as CH4, CO, and H2. The sensor showed a good performance and sensitivity toward the target gases. However, its response toward CH4 and CO was higher compared to H2 gas. Although the operating temperature was varied from room temperature (RT) up to 350°C, the sensor did not show a response toward any of the target gases in the range of RT-150°C, but dramatic enhancement of the sensor response was observed at 200°C, and up to higher temperatures. This behavior was ascribed to the activity of the smooth surface and the reactivity of surface oxygen species with the targeted gases. The sensor response was measured at various gas concentrations, where the calibration curve was shown. The gas sensing mechanism was described in terms of the reaction of the gases with the transformed oxygen species on the surface of the oxides.

Bio-Inspired Strategies for Improving the Selectivity and Sensitivity of Artificial Noses: A Review

Artificial noses are broad-spectrum multisensors dedicated to the detection of volatile organic compounds (VOCs). Despite great recent progress, they still suffer from a lack of sensitivity and selectivity. We will review, in a systemic way, the biomimetic strategies for improving these performance criteria, including the design of sensing materials, their immobilization on the sensing surface, the sampling of VOCs, the choice of a transduction method, and the data processing. This reflection could help address new applications in domains where high-performance artificial noses are required such as public security and safety, environment, industry, or healthcare.

Bulk and Surface Acoustic Wave Sensor Arrays for Multi-Analyte Detection: A Review

Bulk acoustic wave (BAW) and surface acoustic wave (SAW) sensor devices have successfully been used in a wide variety of gas sensing, liquid sensing, and biosensing applications. Devices include BAW sensors using thickness shear modes and SAW sensors using Rayleigh waves or horizontally polarized shear waves (HPSWs). Analyte specificity and selectivity of the sensors are determined by the sensor coatings. If a group of analytes is to be detected or if only selective coatings (i.e., coatings responding to more than one analyte) are available, the use of multi-sensor arrays is advantageous, as the evaluation of the resulting signal patterns allows qualitative and quantitative characterization of the sample. Virtual sensor arrays utilize only one sensor but combine it with enhanced signal evaluation methods or preceding sample separation, which results in similar results as obtained with multi-sensor arrays. Both array types have shown to be promising with regard to system integration and low costs. This review discusses principles and design considerations for acoustic multi-sensor and virtual sensor arrays and outlines the use of these arrays in multi-analyte detection applications, focusing mainly on developments of the past decade.

Gas Identification by a Single Metal-Oxide-Semiconductor Sensor Assisted by Ultrasound

The gas identification technology has huge potential applications in medical diagnoses, food industries, early warning of poisonous gas leakage, fire prevention, antiterrorism, military, etc. Although electronic noses may be used to identify different gases, it has been a big challenge to identify gases by a single sensor. In this work, we demonstrate a novel gas identification strategy based on a single metal-oxide-semiconductor (MOS) sensor assisted by an ultrasound. The identification is based on different ultrasonic effects on the steady sensing responses of an ultrasonically radiated MOS gas sensor to different target gases. It does not need a complicated feature extraction computation. Our experiments show that the success rate of identification can be up to 100% if strong enough ultrasound is employed. The identification process can also give the concentration of the gas to be identified. The identification result is immune to the interference of impurity gases to some extent. The anti-interference capability may be strengthened by increasing the vibration velocity and choosing proper sensing materials.

Headspace Volatile Evaluation of Carrot Samples-Comparison of GC/MS and AuNPs-hpDNA-Based E-Nose

The performances of a quartz crystal microbalances (QCMs) based on an electronic nose (E-nose), modified with hairpin-DNA (hpDNA) for carrot aroma profiling has been evaluated. Solid phase micro-extraction (SPME) headspace sampling, combined with gas chromatography (GC), was used as a reference method. The changes in carrot aroma profiles stored at different temperatures (−18 °C, 4 °C, 25 °C, and 40 °C) were monitored during time up to 26 days. The principal component analysis of the data evidenced the different aroma patterns related to the presence of different key compounds. The output data achieved with the hpDNA-based E-nose were able to detect aroma patterns similar to gas chromatography with mass spectrometry (GC-MS). This work demonstrates that hpDNA has different sizes of loops that can be used for the development of sensor arrays able to detect aroma patterns in food and their changes with advantages in terms of easiness of usage, rapidity, and cost of analysis versus classical methods.

Critical review of electronic nose and tongue instruments prospects in pharmaceutical analysis

Electronic nose (enose, EN) and electronic tongue (etongue, ET) have been designed to simulate human senses of smell and taste in the best possible way. The signals acquired from a sensor array, combined with suitable data analysis system, are the basis for holistic analysis of samples. The efficiency of these instruments, regarding classification, discrimination, detection, monitoring and analytics of samples in different types of matrices, is utilized in many fields of science and industry, offering numerous practical applications. Popularity of both types of devices significantly increased during the last decade, mainly due to improvement of their sensitivity and selectivity. The electronic senses have been employed in pharmaceutical sciences for, among others, formulation development and quality assurance. This paper contains a review of some particular applications of EN and ET based instruments in pharmaceutical industry. In addition, development prospects and a critical summary of the state of art in the field were also surveyed.

Protein- and Peptide-Based Biosensors in Artificial Olfaction

Animals' olfactory systems rely on proteins, olfactory receptors (ORs) and odorant-binding proteins (OBPs), as their native sensing units to detect odours. Recent advances demonstrate that these proteins can also be employed as molecular recognition units in gas-phase biosensors. In addition, the interactions between odorant molecules and ORs or OBPs are a source of inspiration for designing peptides with tunable odorant selectivity. We review recent progress in gas biosensors employing biological units (ORs, OBPs, and peptides) in light of future developments in artificial olfaction, emphasizing examples where biological components have been employed to detect gas-phase analytes.