Development Of Chemical Sensors Research Articles

Anisotropic growth and strain-induced tunable optical properties of Ag–ZnO hierarchical nanostructures by a microwave synthesis method

Effective surface-enhanced Raman scattering (SERS) substrate with hierarchical nanostructure is successfully fabricated by architecturing Ag nanoparticles on the surface of one dimensional (1-D) semiconducting ZnO nanospikes. The influence of anisotropic growth and strain in the ZnO nanostructures through microwave treatment with the different time interval of microwave exposure. Based on the obtained physiochemical characterization results, the Ag–ZnO hierarchical nanostructures facilitates to modify the band structure due to the formation of heterojunction and thus drastically improves the SERS sensing capacity towards the various chemically harmful species. It is proposed that the anisotropic growth and strain-induced effect would be a unique strategy for designing and development of high-performance chemical and real-time molecular sensors.

Structured and functionalized organic semiconductors for chemical and biological sensors based on organic field effect transistors

This review gives an overview of strategies to tailor organic semiconductors with designed physical structures and chemical functionalities for development of chemical and biological sensors based on organic field effect transistors.

Effect of microwave irradiation on the gas sensing properties of SnO2 thin films

Several studies clearly show that the gas sensing activity of metal oxides especially SnO2 is governed by the nature of surfaces exposed to ambient gas. Consequently, control over film morphology, the size and shape of faces in crystallites, defects etc. are required for the development of better chemical gas sensors with increased sensitivity and selectivity. In the formation of nanoparticles, homogenous fast heating is desired and thereupon microwaves exposure is looked upon as supportive to play a fabulous role in the growth and structure of materials. In this work, microwave treated (0.5–4 min.) SnO2 based precursor sol is used to prepare nanoparticulate thin film by spray pyrolysis, and the morphology, as well as the grain characteristics, are modified to enrich the surface physico-chemical, electrical transport and gas sensing properties. The structural characterization via XRD shows the formation of consistent films with tetragonal cassiterite structure accompanied with some local defects. The crystallite size lies in the nano regime (28–36 nm). The texture coefficient of prominent planes shows marked variation upon energy irradiation. The improvement in the gas sensing properties of as prepared films is investigated. The film made from 1 min. irradiated precursor sol shows LPG response of 98.5% and the mechanism of gas sensing has been explained on the basis of structural investigations and morphological aspects. Field Emission Scanning Electron Micrograph (FESEM) and UV characterization confirm that microwave assisted preparation technique helps to modify the gas-sensing properties by tuning the amount of surface defects which is an overriding factor in the gas-sensing process and influences the gas molecule adsorption and catalytic reaction at the surface.

A La3+-doped TiO2 nanoparticle decorated functionalized-MWCNT catalyst: novel electrochemical non-enzymatic sensing of paraoxon-ethyl.

The development of novel chemical sensors for pesticide detection has found particular application in the area of environmental monitoring. However, designing primary sensors as weapons to destroy contaminants (e.g., paraoxon-ethyl) in water and soil remains a challenge. Herein, we show different strategies, such as modification of TiO2 NPs through La3+ doping and decoration of f-MWCNTs, which can provide possibilities for notable developments in electrocatalytic performance. Using this approach, we introduce an active La3+ doped TiO2 NP decorated f-MWCNT electrocatalyst for pollutant monitoring applications. Thereby, our findings move towards an outstanding LOD (0.0019 μM) performance, high selectivity, and exceptional sensitivity (7.6690 μA μM−1 cm−2) on an as-presented catalytic platform for a PE sensor. Interestingly, the practical applicability of the suggested catalyst shows a rich sensing platform for PE-contaminated environmental samples.

Silver Metallization Characterization and Resistivity Performance Potential toward Chemical Sensor Application

Performance of limiting resistive and capacitive signal delays increases gradually depends on the complexity degree of multilayer metallization. Electrodes sensor for electrical applications requires low surface roughness and low resistivity metal layers. Amongst conductive metal series, silver (Ag) has the lowest resistivity. On the other hand, compared to aluminum and copper, this metal also has higher oxidation resistance. This study aims to characterize Ag thin film on the glass substrate and the resistivity performance by using a physical deposition technique for chemical sensor application. A series of Ag thin film with different thickness were prepared from thermal vacuum evaporator at 3.45 x 10-5 Pa with applied current at 28 Ampere in 21 minutes. Four-point resistivity probing instrument was used for resistivity testing of the thin films with different thickness. The prepared Ag thin film shows a low average roughness at 1.89 nm. A smooth and homogeneous of Ag thin film is an advantage to provide a sensitive surface for element recognition in the development of chemical sensor and an adsorbate can be justified whereas it schematically assembled with the arrangement onto smooth and perfectly flat thin film surface. Ag thin film has shown a crystallite size with respect to 50.84 nm. The low rough surfaces have fewer nucleation sites, therefore fewer grains (crystallites) will appear. The optimum thickness was determined at 107 nm and the resistivity of Ag thin film was an average at 1.988 x10-8 Ohm m.  Â

Novel multifunctional molecular recognition elements based on molecularly imprinted poly (aniline-co-itaconic acid) composite thin film for melamine electrochemical detection

The combination of copolymerization and molecularly imprinting technology provides functional materials with improved properties and can enhance the number of binding sites than the individual monomer. In this work, molecularly imprinted poly (aniline-co-itaconic acid) (MI-PANI-PIA) composite thin film was synthesized on glassy carbon electrode (GCE) by using an in-situ electropolymerization method using melamine (MA) as a template. The formation of the thin film was monitored by electrochemical methods and characterized by Fourier transform infrared (FTIR) spectrophotometry and scanning electron microscopy (SEM). Solvent extraction of the template generated the binding cavities in the polymer matrix which fit the target in size, shape and functionality. After the rebinding of MA, the proposed sensor shows a linear range between 0.25 × 10−9 M to 100 × 10−9 M, limit of quantification (LOQ) of 5.98 × 10−11 M and limit of detection (LOD) of 1.79 × 10−11 M respectively. The composite film showed high affinity towards MA through multiple non-covalent interactions, good reproducibility and stability with RSD 4.02% and 4.67% respectively. The developed sensor has an interesting potential for real sample testing applications with good recovery ranging from 95.87% to 101.5%. The new sensing composite material has good sensitivity and selectivity due to the synergistic effects of multi-functionality from the two polymers, porous thin film and imprinting effect. To this end, the MI-PANI-PIA can be regarded as a potential functional material for the chemical sensor development in future.

Fluorescence Turn-On Response Amplified by Space Confinement in Metal-Organic Frameworks.

Sensitive fluorescence turn-on response to specific substances is highly desired for development of chemical sensors and switches. Here we utilized a "two-in-one" strategy to prepare ionic metal-organic frameworks (MOFs) functionalized with the cationic bipyridinium receptors at the frameworks and anionic fluorescent indicators in the pores. The MOFs are rendered a fluorescence-resting state because the indicator's fluorescence is efficiently quenched by the ground-state charge-transfer (CT) complexation between the indicator and receptor. Addition of an alkylamine efficiently turns on the fluorescence because the indicator is displaced by the CT complexation between alkylamine with receptor. The turn-on response is highly specific to alkylamines. The MOFs can be used as recyclable sensors for selective and sensitive detection of alkylamines, with ultralow detection limits (0.5 nM). The fluorescence in solid state can be reversibly switched on and off with high contrast. The sensitive and high-contrast response can be attributed to the space confinement effects of the porous frameworks. The confined space can significantly enhance indicator-receptor and analyte-receptor interactions, and thereby both the quenching efficiency in the off state and the displacement efficiency in the on state are amplified.

A Perspective on Recent Advances in Piezoelectric Chemical Sensors for Environmental Monitoring and Foodstuffs Analysis

This paper provides a selection of the last two decades publications on the development and application of chemical sensors based on piezoelectric quartz resonators for a wide range of analytical tasks. Most of the attention is devoted to an analysis of gas and liquid media and to industrial processes controls utilizing single quartz crystal microbalance (QCM) sensors, bulk acoustic wave (BAW) sensors, and their arrays in e-nose systems. The unique opportunity to estimate several heavy metals in natural and wastewater samples from the output of a QCM sensor array highly sensitive to changes in metal ion activity in water vapor is shown. The high potential of QCM multisensor systems for fast and cost-effective water contamination assessments “in situ” without sample pretreatment is demonstrated.

Interplay Between Silicon Nanocrystal Size and Local Environment Within Porous Silicon on the Analyte-Dependent Photoluminescence Response.

Porous silicon (pSi) exhibits strong photoluminescence (PL) and its PL is often exploited for chemical sensor development. However, the sensor response is not uniform across a pSi specimen. We use co-localized confocal PL and Raman scattering mapping to establish a relationship between the analyte-induced PL response and the silicon nanocrystallite size, size distribution, and amorphous silicon (aSi) contribution across a pSi specimen. Using toluene as a model analyte, high analyte-induced PL response is associated with areas within the specimen that have (i) low aSi content, (ii) silicon nanocrystallites having diameters between 2 and 5 nm, and (iii) silicon nanocrystallites that exhibit a narrow size distributions (≤1% relative standard deviation).

Enhanced plasmonic biosensors based on microstructured optical fibers

Plasmonic devices using microstructured optical fibers are particularly well suited for the development of high sensitivity chemical and biochemical sensors, thanks to their intrinsic microfluidic properties. We review the most recent literature on such sensors, comparing different types and approaches. Then, we present some examples of the design/analysis using finite-element software tools. In particular, a sensor for liquid analytes based on a birefringent solid-core microstructured optical fiber is discussed in detail. This device has six holes, quite a limited number in comparison to other structures with similar performances, whose geometrical characteristics can be tailored to optimize the power fractions carried by the core and plasmon modes at the loss-matching points in the analyte layer depending on the analyte refractive index.

Vapomechanical soft actuators based on graphene-polymer Nanocomposite/Metal hybrid structure for visual detection of chloroform

Vapomechanical actuation triggered through chemical vapors by employing soft smart materials is the most recent and less-explored area of actuators research having powerful applications in the field of chemical sensors/detectors. A tubular shaped actuator driven by chloroform vapors based on graphene-polydimethylsiloxane nanocomposite/gold bilayers has been realized. The tubular shape of actuator is transformed into a planar sheet within about 1.7 s time under the exposure of chloroform vapors with vapor pressure of 57 kPa. The shape switching time of this actuator varies linearly with vapor pressure of chloroform. These vapomechanical actuators may find potential uses in the development of smart chemical sensors which are cheap, easy to use and do not require any electrical power for their operations.

Molecular Design of Solid-State Nanopores: Fundamental Concepts and Applications.

Solid-state nanopores are fascinating objects that enable the development of specific and efficient chemical and biological sensors, as well as the investigation of the physicochemical principles ruling the behavior of biological channels. The great variety of biological nanopores that nature provides regulates not only the most critical processes in the human body, including neuronal communication and sensory perception, but also the most important bioenergetic process on earth: photosynthesis. This makes them an exhaustless source of inspiration toward the development of more efficient, selective, and sophisticated nanopore-based nanofluidic devices. The key point responsible for the vibrant and exciting advance of solid nanopore research in the last decade has been the simultaneous combination of advanced fabrication nanotechnologies to tailor the size, geometry, and application of novel and creative approaches to confer the nanopore surface specific functionalities and responsiveness. Here, the state of the art is described in the following critical areas: i) theory, ii) nanofabrication techniques, iii) (bio)chemical functionalization, iv) construction of nanofluidic actuators, v) nanopore (bio)sensors, and vi) commercial aspects. The plethora of potential applications once envisioned for solid-state nanochannels is progressively and quickly materializing into new technologies that hold promise to revolutionize the everyday life.

Lossy mode resonance sensors based on lateral light incidence in nanocoated planar waveguides

The deposition of an indium oxide (In2O3) thin film on conventional planar waveguides (a coverslip and a glass slide) allows generating lossy mode resonances (LMR) by lateral incidence of light on the waveguide and by registering the optical spectrum in a spectrometer. This novel sensing system becomes an alternative to optical fibre, the substrate where LMR-based sensors have been developed so far, since it is easier to handle and more robust. An additional advantage is that cost effective waveguides, such as slides or coverslips, can be used in a platform that resembles surface plasmon resonance-based sensors in the Kretschmann configuration but without the need for a coupling prism and with the advantage of being able to generate TE and TM LMR resonances with metallic oxide or polymer thin films. The results are corroborated with simulations, which provide in-depth understanding of the phenomena involved in the sensing system. As a proof-of-concept for the optical platform, two refractometers were developed, one with low sensitivity and for a wide range of refractive indices, and the other with higher sensitivity but for a narrower refractive index range. The sensors presented here open up the path for the development of LMR-based chemical sensors, environmental sensors, biosensors, or even the generation of other optical phenomena with the deposition of multilayer structures, gratings or nanostructures, which is much easier in a planar waveguide than in an optical fibre.

Transistor-like Ultra-pH-Sensitive Polymeric Nanoparticles.

Electronic transistors have revolutionized the fields of microelectronics, computers, and mobile devices. Their ability to digitize electronic signals allows high fidelity data transfer as well as formation of logic gates. Inspired by electronic transistors, transistor-like organic materials have been under intensive investigation to amplify biological signals in a broad range of applications such as biosensing, diagnostic imaging, and therapeutic delivery. This Account highlights the inception and implementation of a "proton transistor" nanoparticle that can digitize acidotic pH signals in biological systems. Similar to electronic transistors, the ultra-pH-sensitive (UPS) nanoparticles derive their binary threshold response from phase separation phenomena. Hydrophobic micellization drives nanophase separation from unimers to aggregated polymeric micelles, which is responsible for the all-or-nothing proton distribution between the micelle and unimer states. Depending on the assembly status, conjugated fluorophores are quenched (micelle state) or freely fluoresce (solution unimer state) allowing robust detection of the phase transition behavior across a narrow pH range. Based on this mechanistic insight, we created a UPS nanoparticle library encompassing a broad physiological pH range from 4.0 to 7.4. For biological applications, we engineered a barcode-like nanosensor capable of digitizing multiple pH signals at a single organelle resolution in live cells. The barcode system allowed easy identification of mutant Kirsten rat sarcoma viral oncogene (KRAS), a common mutation involved in tumorigenesis, which leads to rapid cellular proliferation, as the protein driver for accelerated organelle acidification and lysosome catabolism in a broad set of isogenic as well as heterogeneous cancer cell lines. Adoption of the technology to an ON-OFF/Always-ON design allowed the quantification of proton flux across the membranes of endocytic organelles. For medical applications, we demonstrate the ability to achieve binary detection of solid cancers with clear tumor margin delineation by near-infrared fluorescence imaging. Image-guided resection of head/neck and breast tumors resulted in significantly improved long-term survival over white light or tumor debulking surgeries in tumor-bearing mice, catapulting the clinical evaluation of the UPS nanosensor in cancer patients. This Account serves as the first comprehensive summary of the molecular mechanism and biological applications of the digital pH threshold sensors. Building on the concept of cooperative phase transition behavior, we hope this Account will promote the rational design and development of additional transistor-like chemical sensors to digitize analog biological signals.

Sensitive and selective m-tolyl hydrazine chemical sensor development based on CdO nanomaterial decorated multi-walled carbon nanotubes

In this approach, the wet-chemical (co-precipitation) technique was used to prepare the cadmium oxide (CdO) nanoparticles (NPs) decorated with multi-walled carbon nanotubes (CNT) at low temperature. The powder XDR, UV–vis, TEM, XPS, and FTIR spectroscopy were used for detail characterization of the synthesized CdO/CNT nanocomposite (NCs). A thin layer of CdO/CNT NCs was deposited onto a glassy carbon electrode (GCE) with conducting coating binder to obtain a chemical sensor which was subsequently used to detect m-tolyl hydrazine hydrochloride (m-THyd) in buffer medium by electrochemical approach for environmental safety. The proposed m-THyd chemical sensor exhibited long-term stability, good selectivity, broad linear dynamic range, lower detection limit, and enhanced electrochemical response. The calibration curve of the current vs concentration of m-THyd was found to be linear (r2 = 0.9903) over the linear dynamic range (LDR) of 0.01 nM to 0.1 mM. The sensitivity (25.7911 μA μM cm−2) of chemical sensor was calculated from the slope of calibration curve and surface area of GCE (0.0316 cm2) and the detection limit (4.0 ± 0.2 pM) was estimated from the signal to noise ratio at 3. These preliminary results suggest that the newly developed CdO/CNT NCs nanocomposite could be promising electrochemical sensors for the detection of hazardous toxins to clean the environment in broad scales.

Chiral Selectivity of Porphyrin-ZnO Nanoparticle Conjugates.

Recognition of enantiomers is one of the most arduous challenges in chemical sensor development. Although several chiral systems exist, their effective exploitation as the sensitive layer in chemical sensors is hampered by several practical implications that hinder stereoselective recognition in solid state. In this paper, we report a new methodology to efficiently prepare chiral solid films, by using a hybrid material approach where chiral porphyrin derivatives are grafted onto zinc oxide nanoparticles. Circular dichroism (CD) evidences that the solid-state film of the material retains supramolecular chirality due to porphyrin interactions, besides an additional CD feature in correspondence of the absorbance of ZnO (375 nm), suggesting the induction of chirality in the underlying zinc oxide nanoparticles. The capability of hybrid material to detect and recognize vapors of enantiomer pairs was evaluated by fabricating gas sensors based on quartz microbalances. Chiral films of porphyrin on its own were used for comparison. The sensor based on functionalized nanostructures presented a remarkable stereoselectivity in the recognition of limonene enantiomers, whose ability to intercalate in the porphyrin layers makes this terpene an optimal chiral probe. The chiroptical and stereoselective properties of the hybrid material confirm that the use ofporphyrin-capped ZnO nanostructures is a viable route for the formation of chiral selective surfaces.

Recent Advances in 2D Inorganic Nanomaterials for SERS Sensing.

Surface-enhanced Raman spectroscopy is a powerful and sensitive analytical tool that has found application in chemical and biomolecule analysis and environmental monitoring. Since its discovery in the early 1970s, a variety of materials ranging from noble metals to nanostructured materials have been employed as surface enhanced Raman scattering (SERS) substrates. In recent years, 2D inorganic materials have found wide use in the development of SERS-based chemical sensors owing to their unique thickness dependent physico-chemical properties with enhanced chemical-based charge-transfer processes. Here, recent advances in the application of various 2D inorganic nanomaterials, including graphene, boron nitride, semiconducting metal oxides, and transition metal chalcogenides, in chemical detection via SERS are presented. The background of the SERS concept, including its basic theory and sensing mechanism, along with the salient features of different nanomaterials used as substrates in SERS, extending from monometallic nanoparticles to nanometal oxides, is comprehensively discussed. The importance of 2D inorganic nanomaterials in SERS enhancement, along with their application toward chemical detection, is explained in detail with suitable examples and illustrations. In conclusion, some guidelines are presented for the development of this promising field in the future.

Cross-Reactive, Self-Encoded Polymer Film Arrays for Sensor Applications.

The development of chemical sensors continues to be an active area of research, especially the development of a practical electronic nose. Here, we present a spectroscopic chemical sensor based on an array of 64 self-encoded polymer films deposited on a microfabricated silicon substrate. The polymer arrays were analyzed by FTIR and Raman spectroscopy before and after exposure to a series of organic volatiles to monitor changes in their vibrational fingerprints. We show here that the spectroscopic changes of self-encoded polymer films can be used to distinguish between volatile organic analytes. Changes induced in the sensor arrays by the analyte vapor were denoted by a spectroscopic response of the self-encoded polymer sensors and transformed into a response pattern by multivariate data analysis using partial least squares regression. The results indicated that the polymer sensors provide a unique and reproducible pattern for each analyte vapor and can potentially be used in the fabrication of a novel electronic nose device.

Ionic Current Rectification by Laminated Bipolar Silica Isoporous Membrane.

Ionic current rectification (ICR) is one of interesting characteristics displayed by nanochannels with asymmetric geometry, ionic concentration or charge distribution, which has been utilized for the development of chemical sensors and biosensors. Herein we report the ICR phenomenon observed with ultrathin silica isoporous membrane (SIM), which was prepared by laminating two layers of SIM with opposite charges and different pore diameters, designated as bipolar SIM (bp-SIM). The negatively charged layer, called as n-SIM, was 86 nm-thick and consisted of channels with a diameter of 2-3 nm. The positively charged layer with a thickness of 59 nm, termed as p-SIM, was comprised of channels of 4.5-5.5 nm in diameter. They were primarily grown on the solid surface using the Stöber-solution and biphasic-stratification growth approaches, respectively, and then exfoliated to obtain perforated structures by the polymer-protected chemical etching and transfer method. The negative charges of n-SIM and positive ones of p-SIM were generated by the deprotonation of pristine surface silanol and postmodified ammonium groups, respectively. Neither n-SIM nor p-SIM alone displays the ICR characteristic, because of their symmetric structure and uniform charge distribution. When laminating two of them, an apparent ICR characteristic was observed for the bp-SIM with a typical diode-like current-voltage response. This behavior was rationalized to arise from the asymmetric charge distribution on two layers by finite element simulations. Considering the facile preparation and diverse surface functionalities, as well as its uniform and highly porous structure, the bp-SIM provides an attractive platform for designing ICR-based sensors.

Semiconductor α‐Fe2O3 Hematite Fabricated Electrode for Sensitive Detection of Phenolic Pollutants

AbstractHematite (α‐Fe2O3) semiconductor is an abundant and non‐toxic catalyst for different (photo)electrochemical reactions. In this work, a selective p‐nitrophenol sensor was developed by fabricating a thin‐layer of a glassy carbon electrode (GCE) with 5% nafion coating binders onto α‐Fe2O3 thin film synthesized by a simple and inexpensive process. High sensitivity including linear dynamic range, long‐term stability, and enhanced electrochemical performance towards p‐nitrophenol were achieved by a reliable current‐voltage method. A linear calibration curve was observed over a wide range of p‐nitrophenol concentrations. Very low detection limit (0.6±0.02 nM), good limit of quantification (2.0 nM) and high sensor sensitivity (K=74.1 μA⋅cm−2) are calculated based on noise to signal ratio of ∼3 N/S. Very importantly, the detection range covers over 7 orders of magnitude concentrations, from nM to mM. Figures of merits are comparable with best reported results whilst using a very simple device configuration. We show that hematite is an excellent material for the development of chemical sensors to detect hazardous compounds for environmental safety in a broad scale of concentrations.