Sensitive Chemical Sensors Research Articles

Design of a highly sensitive and selective bulk optode based on fluorescence enhancement of N,N′-bis-(1-hydroxyphenylimine)2,2′-pyridil Schiff base: Monitoring of zinc(II) ion in real samples and DFT calculation

A novel highly sensitive and selective optical chemical sensor (optode) was fabricated for the determination of Zn2+ ion. The optical sensor was prepared by incorporating recently synthesized ionophore, HPP: N,N′-bis-(1-hydroxyphenylimine)2,2′-pyridil, sodium tetraphenylborate (NaTPB) as an anionic additive, dibutyl phthalate (DBP) as a plasticizer in a poly(vinylchloride) membrane. The novel ionophore was synthesized by conventional condensation reaction between 2,2′-pyridil and 2-aminophenol and characterized using different spectroscopic techniques. The response of the sensor is based on the strong fluorescent emission enhancement of ionophore HPP upon binding to Zn2+ ions. This can be correlated to the efficient Zn2+ binding of HPP which promotes a good chelation-enhanced fluorescence (CHEF) effect and prevents the photoinduced electron transfer (PET) effect. The effect of several parameters in determining Zn2+ were studied and optimized. Under the optimum conditions, a good linear relationship between the fluorescence response and concentration of Zn2+ was achieved with high sensitivity within a wide range from 1.0×10−10 to 1.0×10−2M and a limit of detection (LOD) 6.3×10−11M. Furthermore, the present probe exhibited a high selectivity for Zn2+ over other metal ions and was successfully assessed for determination of Zn2+ ions in real samples including some food and biological samples with satisfactory results. Theoretical calculations were employed to support the sensing mechanism of the sensor toward Zn2+.

Highly sensitive ethanol chemical sensor based on nanostructured SnO2 doped ZnO modified glassy carbon electrode

Chemical sensors represent an essential strategy for the monitoring of environmental constituents at low level exposures, but are often limited by relatively low sensitivity and slow response time. Here we report highly crystalline SnO2 doped ZnO framework with a cave-shaped porous nanostructure synthesized by a facile chemical approach as a high performance ethanol chemical sensor. A simple sensing system in solution is established using the modified glassy carbon electrode and applying the current–potential (I–V) and cyclic voltammetry techniques. With unique pore channels and small crystallite size, efficient electron and ion transport occur, leading to a remarkable sensitivity of 62.56μAcm−2mM−1 which is, to our knowledge, 9 orders of magnitude higher than those previously reported. The calibration plot is linear (r2=0.9887) over ethanol concentration range 0.195–25mM, with a limit of detection 0.137mM. The interaction of ethanol is a diffusion dominated with fast electron-transfer kinetics. The findings can open up exciting opportunities to fabricate highly efficient chemical sensors.

Highly Sensitive Chemical Sensor Based on CuO Rosette-Like Nanostructures.

This paper reports the successful fabrication and characterization of phenyl hydrazine chemical sensor based on CuO rosette-like nanostructures. The CuO rosette-like nanostructures were synthesized by facile hydrothermal process at low-temperature and characterized in detail in terms of their morphological, structural and compositional properties. The detailed morphological studies revealed that the prepared CuO rosettes are made by the accumulation of hundreds of small CuO nanodisks which are arranged in a special fashion that they made rosette-like morphologies. The structural characterization, by X-ray diffraction (XRD), confirmed that the prepared CuO rosette-like structures are nanocrystalline and possessing monoclinic structure. The compositional studies further substantiates that the synthesized rosette-like morphologies are pure CuO. The fabricated phenyl hydrazine chemical sensor based on CuO rosette-like nanostructures exhibited very high sensitivity of -49.532710 μA/cm2 x mM. Due to high sensitivity, it can be concluded that CuO rosette-like nanostructures could be an effective candidate for the fabrication of highly sensitive phenyl hydrazine chemical sensors.

Development of a Potentiometric Chemical Sensor for the Rapid Detection of Carbofuran Based on Air Stable Lipid Films with Incorporated Calix[4]arene Phosphoryl Receptor Using Graphene Electrodes

AbstractThe present article describes a miniaturized potentiometric carbofuran chemical sensor on graphene nanosheets with incorporated lipid films. The graphene electrode was used for the development of a very selective and sensitive chemical sensor for the detection of carbofuran by immobilizing an artificial selective receptor on stabilized lipid films. The artificial receptor was synthesized by transformation of the hydroxyl groups of resorcin[4]arene receptor into phosphoryl groups. This chemical sensor responded for the wide range of carbofuran concentrations with fast response time of ca. 20 s. The presented potentiometric carbofuran chemical sensor is easy to construct and exhibits good reproducibility, reusability, selectivity, rapid response times, long shelf life and high sensitivity of ca. 59 mV/decade over the carbofuran logarithmic concentration range from 10−6 to 10−3 M.

Highly sensitive formaldehyde chemical sensor based on in situ precipitation synthesis of ZnSnO3 microspheres

Highly sensitive formaldehyde chemical sensor was fabricated using uniform and mono-disperse ZnSnO3 microspheres, which were successfully prepared by a template-free, economical in situ precipitation method combined with subsequent calcination. The orientation and morphology of the precursor, ZnSn(OH)6 microspheres, were carefully controlled by adjusting the added amount of NaOH. This facile process may provide an approach to synthesis of functional nanomaterials with unique structures and excellent physicochemical properties. Moreover, the as-fabricated sensors based on the ZnSnO3 microspheres showed high response and short response-recovery time toward formaldehyde. To 50 ppm formaldehyde, the sensor response (S) was 17 at a working temperature of 260 °C, and the response and recovery time were 6 and 18 s, respectively. The gas response of sensors based on the ZnSnO3 microspheres was linear with the concentration of formaldehyde in the range of 5–100 ppm with a correlation coefficient of 0.997. These results showed that the as-prepared ZnSnO3 microspheres have a potential application in gas sensor.

Growth and properties of well-crystalline cerium oxide (CeO2) nanoflakes for environmental and sensor applications

This paper reports the synthesis, characterizations and applications of well-crystalline 2D-cerium oxide (CeO2) nanoflakes prepared by a rapid and facile solution combustion process. The nanoflakes were characterized in detail and applied as photocatalyst for dye-degradation and as an efficient electron mediator to fabricate high-sensitive hydroquinone chemical sensor. The detailed characterizations revealed that the prepared nanoflakes were well-crystalline and grown in very high-density. The synthesized CeO2 nanoflakes exhibited good photocatalytic activity toward the photocatalytic degradation of direct red-23 dye. Further, the synthesized nanoflakes were utilized as an efficient electron mediator to fabricate reproducible and highly sensitive hydroquinone chemical sensor. The fabricated chemical sensor exhibited a reproducible and reliable sensitivity of 2.04μAmM−1cm−2 and the detection limit of 2.914μM with the correlation coefficient (R) of 0.98815 and good linearity from 78μM to 12.5mM. The observed results confirmed that the CeO2 nanoflakes can efficiently be used for photocatalytic and sensing applications.

Rose-like CuO nanostructures for highly sensitive glucose chemical sensor application

This paper reports the synthesis, characterization and glucose chemical sensing applications of well-crystalline rose-like CuO nanostructures. The rose-like CuO nanostructures were synthesized by facile hydrothermal process at low-temperature and characterized in detail in terms of their morphological, compositional, structural, optical and sensing properties. The detailed characterizations revealed that the synthesized rose-like CuO nanostructures are nanocrystalline and possessing monoclinic structure. Further, the synthesized nanostructures were used as efficient electron mediator to fabricate non-enzymatic glucose sensor. The fabricated glucose chemical sensor shows a very high sensitivity of ~4.640μAmM−1cm−2 and an experimental detection limit of ~0.39mM with correlation coefficient (R) of 0.9498. The observed linear dynamic range for the fabricated chemical sensor was from 0.78mM to 100mM. The presented work demonstrates that simply prepared CuO nanomaterials can efficiently be used to fabricate reliable and reproducible glucose chemical sensors.

Development of selective and sensitive bicarbonate chemical sensor based on wet-chemically prepared CuO-ZnO nanorods

We have prepared calcined copper oxide doped zinc oxide nanorods (CuO-ZnO NRs) by a facile wet-chemical method using reducing agents in alkaline medium. The doped NRs were totally characterized by UV/vis, FT-IR, X-ray photoelectron, energy-dispersive X-ray spectroscopy, X-ray powder diffraction, and field-emission scanning electron microscopy. The NRs were deposited on flat silver electrode (AgE) to result in a sensor that has a fast response to selective bicarbonate in buffer system. Features including high sensitivity, lower-detection limit, reliability, reproducibility, ease of integration, long-term stability, selective, and enhanced electrochemical performances were investigated in detail. The calibration plot is linear (r2=0.99) over the large concentration range (1.0nM to 1.0mM). The sensitivity and detection limit are calculated as ∼1.667μAcm−2μM−2 and 0.89±0.02nM (at a signal-to-noise-ratio, SNR of 3) respectively. Finally, the efficiency of the proposed chemi-sensors can be applied and effectively utilized for the detection of bicarbonate in various environmental real water samples with acceptable and reasonable results.

MoS2 Nanosheet-Pd Nanoparticle Composite for Highly Sensitive Room Temperature Detection of Hydrogen.

Highly sensitive hydrogen detection at room temperature can be realized by employing solution-processed MoS2 nanosheet-Pd nanoparticle composite. A MoS2-Pd composite exhibits greater sensing performance than its graphene counterpart, indicating that solvent exfoliated MoS2 holds great promise for inexpensive and scalable fabrication of highly sensitive chemical sensors.

An electrochemical sensing platform based on hollow mesoporous ZnO nanoglobules modified glassy carbon electrode: Selective detection of piperidine chemical

Hollow mesoporous ZnO nanoglobules were synthesized through carbon spheres template assisted sonochemical process followed by annealing at 600°C. The synthesized hollow mesoporous ZnO nanoglobules was applied as a working electrode or electron mediator electrode for the fabrication of reproducible, highly sensitive and reliable chemical sensors for the detection of piperidine chemical. The synthesized nanomaterials possessed the porous hollow globular morphology due to the radial arrangement of nanoparticles on the outer shell of nanoglobules. The formation of hollow mesoporous ZnO nanoglobules was confirmed by analyzing the structural, crystalline and the compositional properties. The electrochemical behavior was examined by performing the cyclic voltammetry using hollow mesoporous ZnO nanoglobules based glassy carbon electrode (GCE) towards the detection of piperidine chemical. The performance of piperidine chemical sensor based on hollow mesoporous ZnO nanoglobules GCE was analyzed by measuring the current (I)–voltage (V) characteristics of different piperidine concentrations in phosphate buffer solution. The hollow ZnO nanoglobules GCE based piperidine chemical sensor exhibited the high sensitivity of ∼59.9μAmM−1cm−2 and a detection limit of ∼3.3μM with a correlation coefficient (R) of ∼0.98782 and a short response time of 10s.

Ag-doped ZnO nanoellipsoids: Potential scaffold for photocatalytic and sensing applications

Well-crystalline Ag-doped ZnO nanoellipsoids (NEs) were synthesized in large quantity and used as effective photocatalyst for the photocatalytic degradation of methyl orange (MO) and efficient electron mediator for the fabrication of highly sensitive, reliable and robust hydrazine chemical sensor. The Ag-doped NEs were synthesized by facile low-temperature (~60°C) solution process and characterized in detail using various characterization techniques. The characterizations revealed that the synthesized nanostructures are well-crystalline, possessing ellipsoidal shapes and were grown in very high density. The photocatalytic activities of these Ag-doped NEs were evaluated by measuring the rate of photodegradation reaction of hazardous methyl orange (MO) dye under UV light irradiation. By comparing the photocatalytic performance of Ag-doped ZnO NEs with those of ZnO nanoflowers, the former was found to be a much superior photocatalyst than the later. Further, Ag-doped ZnO NEs based hydrazine sensor exhibited a high sensitivity of ~9.46µA/cm2µM and detection limit of 0.07µM in a response time of <10s. Thus we find that Ag-doped ZnO nanomaterials synthesized by simple solution process holds potential as efficient photocatalysts and efficient electron mediators for the fabrication of robust and highly sensitive chemical sensors.

Sensitive and fast response ethanol chemical sensor based on as-grown Gd2O3 nanostructures

Well crystalline gadolinium oxide (Gd2O3) nanostructures were grown by annealing the hydrothermally as-prepared nanostructures without using any template. Microscopic studies of Gd2O3 nanostructures were recorded along the [111] direction due to the clearly resolved interplanar distance d(222)∼0.31 nm of the cubic crystal structure Gd2O3. Sensing mechanism of Gd2O3 as efficient electron mediator for the detection of ethanol was explored. As-fabricated sensor demonstrated the high-sensitivity of ∼0.266 μAm/M/cm2 with low detection limit (∼52.2 μmol/L) and correlation coefficient (r2, 0.618). To the best of our knowledge, this was the first report for the detection of ethanol using as-grown (at 1000 °C) Gd2O3 nanostructures by simple and reliable I-V technique and rapid assessment of the reaction kinetics (in the order of seconds). The low cost of the starting reagents and the simplicity of the synthetic route made it a promising chemical sensor for the detection of various toxic analytes, which are not environmentally safe.

Fabrication and characterization of a highly sensitive hydroquinone chemical sensor based on iron-doped ZnO nanorods.

Herein, we report the development of a simple and highly sensitive hydroquinone (HQ) chemical sensor based on an electrochemically activated iron-doped (Fe-doped) zinc oxide nanorod (ZnO NR) modified screen-printed electrode (SPE). The Fe-doped ZnO NRs were prepared using a hydrothermal process and their morphological, crystal, compositional and optical properties were characterized in detail. The detailed characterizations showed that the NRs are densely grown, well-crystalline and possess a wurtzite hexagonal phase. The fabricated HQ electrochemical sensor exhibited high sensitivity of 18.60 μA mM(-1) cm(-2) and a very low experimental detection limit of 0.51 μM. Our results demonstrate that simply prepared doped ZnO nanomaterials are promising candidates to fabricate highly sensitive electrochemical sensors.

Sb2O3–ZnO nanospindles: A potential material for photocatalytic and sensing applications

This paper reports the facile synthesis, characterization and applications of Sb2O3–ZnO nanospindles. The nanospindles were synthesized by facile diethanolammine assisted hydrothermal process and characterized in detail in terms of their morphological, structural, compositional and optical properties. The detailed characterizations revealed that the prepared nanoellipsoids are well-crystalline, grown in high density and possessing good optical properties. Further, the as-synthesized Sb2O3–ZnO nanospindles were found to be an efficient photocatalyst for the degradation of methylene blue (MB) dye under UV light. Sb2O3–ZnO nanospindles were also used as an efficient electron mediator to fabricate a robust, highly sensitive and reproducible chemical sensor for the detection of thiourea in aqueous medium. The fabricated chemical sensor possesses high sensitivity of 6.54µAmmolL−1cm−2. The sensing calibration plot was found to be linear (R2=0.91423) over the large concentration range from 1.56mmolL−1 to 100mmolL−1. The obtained results confirmed that the Sb2O3–ZnO nanospindles may hold great potential for the removal of organic pollutants and for monitoring of thiourea in aqueous solution.

Remarkable improvement of gas-sensing abilities in p-type oxide nanowires by local modification of the hole-accumulation layer.

This paper proposes a method for improving the reducing or oxidizing gas-sensing abilities of p-type oxide nanowires (NWs) by locally modifying the hole-accumulation channel through the attachment of p-type nanoparticles (NPs) with different upper valence band levels. In this study, the sensing behaviors of p-CuO NWs functionalized with either p-NiO or p-Co3O4 NPs were investigated as a model materials system. The attachment of p-NiO NPs greatly improved the reducing gas-sensing performance of p-CuO NWs. In contrast, the p-Co3O4 NPs improved the oxidizing gas-sensing properties of p-CuO NWs. These results are associated with the local suppression/expansion of the hole-accumulation channel of p-CuO NWs along the radial direction due to hole flow between the NWs and NPs. The approach proposed in this study provides a guideline for fabricating sensitive chemical sensors based on p-CuO NWs.

Zinc oxide nanocones as potential scaffold for the fabrication of ultra-high sensitive hydrazine chemical sensor

The fabrication and characterization of ultra-high sensitive hydrazine chemical sensor based on zinc oxide (ZnO) nanocones are reported. The ZnO nanocones were synthesized by a low-temperature solution process and examined by various techniques in terms of their morphological, structural, compositional and optical properties. The studies revealed that the synthesized ZnO materials possessed good-crystallinity and defined nanocone morphologies and exhibited good optical properties. The hydrazine chemical sensor was fabricated on the amperometric principle and shows ultra-high sensitivity and low detection limit. The estimated sensitivity and detection limit of the fabricated hydrazine chemical sensor were 50×104µAµM−1cm−2 and 0.01µM, respectively. The observed response time was <2s.

Sensor system including silicon nanowire ion sensitive FET arrays and CMOS readout

We present a highly sensitive chemical sensor system including a chip with an array of silicon nanowire ISFETs and a CMOS chip with custom-designed signal-conditioning circuitry. The CMOS circuitry, comprising 8 sigma–delta (Σ–Δ) modulators and 8 current-to-frequency converters, has been interfaced to each of the nanowires to apply a constant voltage for measuring the respective current through the nanowire. Each nanowire has a dedicated readout channel, so that no multiplexing is required, which helps to avoid leakage current issues. The analog signal has been digitized on chip and transmitted to a host PC via a FPGA. The system has been successfully fabricated and tested and features, depending on the settings, noise values as low as 8.2pARMS and a resolution of 13.3bits while covering an input current range from 200pA to 3μA. The two readout architectures (Σ–Δ and current to frequency) have been compared, and measurements showing the advantages of combining a CMOS readout with silicon nanowire sensors are presented: (1) simultaneous readout of different silicon nanowires for high-temporal-resolution experiments and parallel sensor experiments (results from pH and KCl concentration sweeps are presented); (2) high speed measurements showing how the CMOS chip can enhance the performance of the nanowire sensors by compensating its non-idealities as a consequence of hysteresis.

Development of efficient chemi-sensor and photo-catalyst based on wet-chemically prepared ZnO nanorods for environmental remediation

Highly sensitive ammonia chemical sensor has been fabricated by using efficient ZnO nanorods (NRs) synthesized by low temperature wet-chemical process. The fabricated ammonia sensor showed excellent sensitivity ∼5.538μA/cm2/mM, lower-detection limit (∼0.11μM), and large-linear dynamic range (LDR, 0.5μM to 0.5mM) with good linearity (R=0.7102) in short response time (10.0s). Additionally, ZnO NRs displayed excellent performance in degrading acridine orange (AO), methylene blue (MB), and amido black (AB). The structural and morphological characterizations of the synthesized ZnO was carried out by field emission scanning electron microscopy (FESEM), powder X-ray diffraction (XRD), Fourier transform infrared spectrophotometer (FT-IR), and UV–vis spectrophotometer, which confirmed that the synthesized product is wurtzite type well-crystalline rod-shape structure with an average diameter of 58.61±5.0nm.

Synthesis and characterizations of ferrite nanomaterials for phenyl hydrazine chemical sensor applications.

This paper presents the synthesis, characterization and phenyl hydrazine chemical sensing applications of Cd0.5Mg0.5Fe2O4 ferrite nanoparticles. The nanoparticles were synthesized by facile and simple co-precipitation method and characterized in detail in terms of their morphological, structural, compositional and electrical properties. The detailed characterization studies revealed that the prepared nanoparticles are grown in high density, possessing Cd0.5Mg0.5Fe2O4 composition and exhibiting spinel cubic structure. Moreover, the prepared Cd0.5Mg0.5Fe2O4 ferrite nanoparticles were used as efficient electron mediators for the fabrication of high-sensitive, robust, reliable and reproducible phenyl hydrazine chemical sensor by simple I-V technique. The fabricated chemical sensor exhibits a highsensitivity of 7.01 microA mM(-1) cm(-2) with an experimental detection limit of 3.125 mM in a short response time of -10.0 s. This work demonstrates that Cd0.5Mg0.5Fe2O4 ferrite nanoparticles can efficiently be utilized for the fabrication of highly sensitive and reliable chemical sensors.

Sensors Research at the NSF-Assist Nanosystems Engineering Research Center:Correlated Sensing of Environmental and Physiological Parameters Using Low-Power Wearable Sensors

This presentation will provide an overview of the technology and system development effort for low-power wearable sensors in the NSF Nanosystems Engineering Research Center (NERC) for Advanced Self-Powered Systems of Integrated Sensors and Technologies (ASSIST). We employ nanotechnology as an enabling factor to achieve low-power, highly specific, multifunctional sensing on compact wearable platforms. Minimizing the power consumption by the sensors and supporting electronic circuits is a critical goal, as these sensors would be powered by harvested energy. To achieve these goals we develop a systems-based approach that optimizes the overall system performance instead of focusing solely on individual components. We envision that nanotechnology-enabled long-term sensing will enable patients, physicians, and scientists to make direct correlations between health and environmental toxins leading to chronic disease prediction, management, and treatment. Furthermore, the self-powered, wearable, correlated sensing platforms we develop will accelerate environmental health research and clinical trials as well as inform environmental policy.Based on the targeted sensing parameter, ASSIST sensors can be grouped in two categories: 1) Environmental sensors (i.e., for sensing pollutant gases and particulate matter); 2) Physiological sensors (i.e., for sensing heart rate, hormonal biomarkers, oxygen saturation, body sounds, and hydration levels). An alternative classification is based on the sensing mechanism: 1) Chemical/particulate sensing (i.e., for sensing gases such as ozone, nitric oxide, nitrogen dioxide, hydrogen sulfide, volatile organic compounds, and particulate matter); 2) Biochemical sensing (i.e., for sensing hormonal biomarkers such as cortisol and epinephrine, as well as electrolytes); 3) Bioelectrical sensing (i.e., electrocardiogram and skin conductivity); 4) Optical and acoustic sensing (i.e., pulse oximetry and body sounds).For sensing the pollutant gases in the environment we develop four different types of sensor technologies: 1) Metal-oxide nanowires deterministically assembled on a custom low-power CMOS integrated circuit. Nanowires offer advantages such as low-power heating and increased surface-to-volume ratio for improved sensitivity. These nanowires are fabricated by coating silicon nanowires by a metal-oxide shell using atomic layer deposition (ALD). After these nanowires are released in a solution they are assembled on a CMOS chip. An alternative approach to make metal oxide nanowires is laser interference lithography. 2) An ALD metal-oxide layer by itself can also function as a gas sensor, which provides a large sensing surface area and low power heating. 3) Mechanically resonant devices with selective polymer coatings can sense gas. We use tuning fork type crystal resonators as well as electrostatically actuated flextensional transducers with nano-patterned selective polymers as functionalization layers. 4) AlGaN/GaN heterostructures to make open gate transistors with metal-oxide or nanoparticle functionalization layers. The high mobility in these heterostructures with specific functionalization layers has the potential to realize a low-power, highly sensitive chemical sensor. For sensing the particulate matter we develop an optical fiber based particle counting system that is suitable for micron-size particle detection. Our biochemical sensing strategy has three main components: 1) Sample extraction. We currently develop hydrogel-based microfluidic interfaces to skin to be able to sample sweat and interstitial fluids for further analysis. 2) Antibody-based functionalization for cortisol detection. 3) Transduction to an electrical signal by electrochemical impedance spectroscopy using nanowire enhanced interdigitated electrodes or tunneling field effect transistors. The major challenges for the described biochemical sensors are: 1) Noninvasive access to interstitial fluid; 2) Assuring antibody stability; 3) Achieving reversible binding of target analyte or finding a way to replenish antibodies for long-term usability of the sensor.The hydrogel-based skin interfaces are designed as multifunctional devices that can provide sweat sampling and facilitate direct measurement of skin conductivity by incorporating metal electrodes in the structure. Furthermore, pH sensing and other electrochemical sensing modalities can be integrated in this device.We have also implemented a low-profile wireless pulse oximetry system in the form of a smart bandage using commercial off-the-shelf components. Future generations of this device will include custom designed optoelectronic components for low-power operation.In summary, we are developing a wide variety of sensing modalities for continuous environmental and physiological monitoring. Low-power operation, compact and comfortable form factor, and multifunctionality are the common features in all of the described sensor systems. The technologies and systems we are developing in ASSIST have a great potential to improve global health by correlating personal health and personal environment. Acknowledgments: This material is based upon work supported by the National Science Foundation under Grant No. 1160483.