Detection Of Ultra-low Concentrations Research Articles

A biomolecule-free electrochemical sensing approach based on a novel electrode modification technique: Detection of ultra-low concentration of Δ⁹-tetrahydrocannabinol in saliva by turning a sample analyte into a sensor analyte

Cannabis is currently one of the most consumed drugs in many countries. Δ⁹-tetrahydrocannabinol (THC) is the principal psychoactive component of this drug and is present in saliva after consumption. This paper reports a novel biomolecule-free electrochemical approach to detect an ultra-low level of THC in saliva using modified electrodes with molecules of the same analyte (THC) that are detected later via square wave voltammetry. The results from this research revealed that the electrodeposition of THC on the working electrode (sensor analyte) could highly enhance the limit of detection by improving the affinity of the THC molecules present in the sample (sample analyte) to the sensing electrode surface. Detailed descriptions about the optimization of the sensor and its performance in simple media, such as PBS, and complex media, such as simulated and real saliva, are provided. This novel and yet simple electrochemical-based sensing strategy allowed for a low limit of detection of 1.6 ng/mL THC in simulated and real saliva, distinguishing concentrations ranging from 2 to 25 ng/mL, making this technology viable for a real-world application such as roadside testing.

Three-dimensional reduced graphene oxide/cobaltosic oxide as a high-response sensor for triethylamine gas at room temperature

Three-dimensional (3D) reduced graphene oxide (rGO)/cobaltosic oxide (Co3O4) nanocomposites were prepared by a simple and low-cost hydrothermal method. Characterization results confirmed that rGO sheets were self-assembled to form a crosslinked porous network structure and Co3O4 nanoparticles were uniformly attached to the surface of rGO with the specific surface area of 306.49 m2/g. More importantly, the as-obtained 3D rGO/Co3O4 nanocomposites exhibited superior gas sensing property for ultra-low concentration detection of triethylamine (TEA) at room temperature; this was because of the mesoporous structure, large specific surface area, and excellent charge carrier transport properties of the nanocomposites. The response value of the 3D rGO/Co3O4 nanocomposite sensors to 1 ppm TEA gas was approximately 35% at room temperature, with extremely fast response and recovery time. 3D rGO/Co3O4 nanocomposites with excellent sensing performance have potential applications in the field of gas sensors.

(Plenary) Rational Design of Oxide Chemiresistors for Next-Generation Gas Sensors and Artificial Olfaction

Oxide semiconductor chemiresistors have been widely used to detect harmful gases because of their advantages such as high sensitivity, facile integration, and cost effectiveness, and their applications are being expanded to pollutant monitoring, medical diagnosis from exhaled breath, food quality assessment, and smart farming. The collection of big gas sensing data becomes easier than before thanks to the progresses in wireless communication, Internet of Things, and sensor integration. Furthermore, machine learning algorithm and enhanced computing capability are supporting the artificial olfaction. Despite the growth of market demand and relevant technology, oxide semiconductor gas sensors and electronic noses using their array need further improvement since oxide-based chemiresistors often show low gas selectivity and the sensors in the array are frequently insufficient to cover all the complex chemicals. To date, various nanostructures with high surface area to volume ratio have been explored to enhance the gas response and sensing materials have been loaded with noble metal or oxide catalysts for tailoring gas selectivity. Nevertheless, for demand-based design of high performance gas sensors and artificial olfaction, many issues still remain unsolved, which include the detection of ultralow concentration of analyte gas, highly selective detection of a specific gas, moisture-independent gas sensing, and the establishment of distinctive gas sensing library toward numerous analyte gases as well as complex odors [1]. How can we overcome above challenges? The diversity of gas sensing materials provides a rational solution for the complexity of chemicals, which can be accomplished by introducing new sensing materials, designing new nano-architectures, making new methods to tune the reforming/oxidation of analyte/interference gases, establishing new strategies to maximize/control catalytic activity, and using different ways to control electronic/chemical sensitization. In this presentation, various new, promising and general strategies to design sensitive, selective, and reliable chemiresistors for next-generation gas sensors and artificial olfaction will be suggested, which are as follows: Hollow and hierarchical nanostructures with high gas accessibility for rapid gas detection [2]P-type oxide semiconductors with high catalytic activity for detecting new gas species [3]Multi-valence additives for humidity-independent oxide semiconductor gas sensors [4,5]Catalyst-loaded or catalytic micro-reactors for highly selective detection of aromatic compounds [6]Bilayer sensors consisting of sensing layer and nanoscale catalytic overlayer for separating catalytic and sensing reactions and modulating gas sensing behaviors [7,8]Hetero-nanostructures composed of two different materials with dissimilar catalytic activity [9]Monolayer oxide nanofiber sensor with tailored exposure of catalytic electrode for controlling gas selectivity [10] References [1] S.-Y. Jeong, J.-S. Kim, J.-H. Lee, Rational Design of Semiconductor‐Based Chemiresistors and their Libraries for Next‐Generation Artificial Olfaction, Adv. Mater. (online published) doi.org/10.1002/adma.202002075[2] J.-H. Lee, Gas sensors using hierarchical and hollow oxide nanostructures: Overview, Sens. Actuators B 140 (2009) 319-336. doi:10.1016/j.snb.2009.04.026.[3] H.-J. Kim, J.-H. Lee, Highly sensitive and selective gas sensors using p-type oxide semiconductors: Overview, Sens. Actuators B 192 (2014) 607-627. doi:10.1016/j.snb.2013.11.005.[4] H.-R. Kim, A. Haensch, I.-D. Kim, U. Weimar, J.-H. Lee, Role of NiO doping in reducing the humidity impact on the performance of SnO2-based gas sensors: synthesis strategies, phenomenological and spectroscopic studies, Adv. Funct. Mater. 21 (2011) 4229-4240. doi:10.1002/adfm.201101154.[5] J.‐W. Yoon, J.‐S. Kim, T.‐H. Kim, Y. J. Hong, Y. C. Kang, J.‐H. Lee, A new strategy for humidity independent oxide chemiresistors: Dynamic self‐refreshing of In2O3 sensing surface assisted by layer‐by‐layer coated CeO2 nanoclusters, Small 12 (2016) 4456-4463. doi:10.1002/smll.201601507.[6] J.-W. Yoon, Y.J. Hong, G.D. Park, S.-J. Hwang, F. Abdel-Hady, A.A.Wazzan, Y.C. Kang, J.-H.Lee, Kilogram-scale synthesis of Pd-loaded quintuple-shelled Co3O4 microreactors and their application to ultrasensitive and ultraselective detection of methylbenzenes, ACS Appl. Mater. Interfaces 7 (2015) 7717-7723. doi: 10.1021/acsami.5b00706.[7] S.-Y.Jeong, Y.K. Moon, T.-H. Kim, .S-W. Park, K. B. Kim, Y.C. Kang, J.-H. Lee, A New Strategy for Detecting Plant Hormone Ethylene Using Oxide Semiconductor Chemiresistors: Exceptional Gas Selectivity and Response Tailored by Nanoscale Cr2O3 Catalytic Overlayer ethylene sensor Adv. Sci. 7 (2020) 1903093. 10.1002/advs.201903093[8] S.‐Y. Jeong, Y.K. Moon, J.K. Kim, S.‐W. Park, Y.K. Jo, Y.C. Kang, J.‐H. Lee, A General Solution to Mitigate Water Poisoning of Oxide Chemiresistors: Bilayer Sensors with Tb4O7 Overlayer, Adv. Funct. Mater. (online published) 10.1002/adfm.202007895[9] T.-H. Kim, C.-H. Kwak, J.-H. Lee, NiO/NiWO4 composite yolk−shell spheres with nanoscale NiO outer layer for ultrasensitive and selective detection of sub ppm-level p-xylene, ACS Appl. Mater. Interfaces 9 (2017) 32034-32043. doi:10.1021/acsami.7b10294.[10] K. Lim, Y.-M. Jo, J.-W. Yoon, J.-H. Lee, Metal oxide patterns of one-dimensional nanofibers: on-demand, direct-write fabrication, and application as a novel platform for gas detection, J. Mater. Chem. A 7 (2019) 24919-24928. doi:10.1039/C9TA09708B.

GEA Group, Germany

Three-dimensional (3D) reduced graphene oxide (rGO)/cobaltosic oxide (Co3O4) nanocomposites were prepared by a simple and low-cost hydrothermal method. Characterization results confirmed that rGO sheets were self-assembled to form a crosslinked porous network structure and Co3O4 nanoparticles were uniformly attached to the surface of rGO with the specific surface area of 306.49 m2/g. More importantly, the as-obtained 3D rGO/Co3O4 nanocomposites exhibited superior gas sensing property for ultra-low concentration detection of triethylamine (TEA) at room temperature; this was because of the mesoporous structure, large specific surface area, and excellent charge carrier transport properties of the nanocomposites. The response value of the 3D rGO/Co3O4 nanocomposite sensors to 1 ppm TEA gas was approximately 35% at room temperature, with extremely fast response and recovery time. 3D rGO/Co3O4 nanocomposites with excellent sensing performance have potential applications in the field of gas sensors.

People & Appointments

Three-dimensional (3D) reduced graphene oxide (rGO)/cobaltosic oxide (Co3O4) nanocomposites were prepared by a simple and low-cost hydrothermal method. Characterization results confirmed that rGO sheets were self-assembled to form a crosslinked porous network structure and Co3O4 nanoparticles were uniformly attached to the surface of rGO with the specific surface area of 306.49 m2/g. More importantly, the as-obtained 3D rGO/Co3O4 nanocomposites exhibited superior gas sensing property for ultra-low concentration detection of triethylamine (TEA) at room temperature; this was because of the mesoporous structure, large specific surface area, and excellent charge carrier transport properties of the nanocomposites. The response value of the 3D rGO/Co3O4 nanocomposite sensors to 1 ppm TEA gas was approximately 35% at room temperature, with extremely fast response and recovery time. 3D rGO/Co3O4 nanocomposites with excellent sensing performance have potential applications in the field of gas sensors.

Parker Hannifin Corp, USA

Three-dimensional (3D) reduced graphene oxide (rGO)/cobaltosic oxide (Co3O4) nanocomposites were prepared by a simple and low-cost hydrothermal method. Characterization results confirmed that rGO sheets were self-assembled to form a crosslinked porous network structure and Co3O4 nanoparticles were uniformly attached to the surface of rGO with the specific surface area of 306.49 m2/g. More importantly, the as-obtained 3D rGO/Co3O4 nanocomposites exhibited superior gas sensing property for ultra-low concentration detection of triethylamine (TEA) at room temperature; this was because of the mesoporous structure, large specific surface area, and excellent charge carrier transport properties of the nanocomposites. The response value of the 3D rGO/Co3O4 nanocomposite sensors to 1 ppm TEA gas was approximately 35% at room temperature, with extremely fast response and recovery time. 3D rGO/Co3O4 nanocomposites with excellent sensing performance have potential applications in the field of gas sensors.

A simple magnetic-assisted microfluidic method for rapid detection and phenotypic characterization of ultralow concentrations of bacteria

Isolation and enumeration of bacteria at ultralow concentrations and antibiotic resistance profiling are of great importance for early diagnosis and treatment of bacteremia. In this work, we describe a simple, rapid, and versatile magnetic-assisted microfluidic method for rapid bacterial detection. The developed method enables magnetophoretic loading of bead-captured bacteria into the microfluidic chamber under external static and dynamic magnetic fields in 4 min. A shallow microfluidic chamber design that enables the monolayer orientation and transportation of the beads and a glass substrate with a thickness of 0.17 mm was utilized to allow high-resolution fluorescence imaging for quantitative detection. Escherichia coli (E. coli) with green fluorescent protein (GFP)-expressing gene and streptavidin-modified superparamagnetic microbeads were used as model bacteria and capturing beads, respectively. The specificity of the method was validated using Lactobacillus gasseri as a negative control group. The limit of detection and limit of quantification values were determined as 2 CFU/ml and 10 CFU/ml of E. coli, respectively. The magnetic-assisted microfluidic method is a versatile tool for the detection of ultralow concentrations of viable bacteria with the linear range of 5–5000 CFU/ml E. coli in 1 h, and providing growth curves and phenotypic characterization bead-captured E. coli in the following 5 h of incubation. Our results are promising for future rapid and sensitive antibiotic susceptibility testing of ultralow numbers of viable cells.

Carbon Dots Detect Water-to-Ice Phase Transition and Act as Alcohol Sensors via Fluorescence Turn-Off/On Mechanism.

Highly fluorescent carbon nanoparticles called carbon dots (CDs) have been the focus of intense research due to their simple chemical synthesis, nontoxic nature, and broad application potential including optoelectronics, photocatalysis, biomedicine, and energy-related technologies. Although a detailed elucidation of the mechanism of their photoluminescence (PL) remains an unmet challenge, the CDs exhibit robust, reproducible, and environment-sensitive PL signals, enabling us to monitor selected chemical phenomena including phase transitions or detection of ultralow concentrations of molecular species in solution. Herein, we report the PL turn-off/on behavior of aqueous CDs allowing the reversible monitoring of the water-ice phase transition. The bright PL attributable to molecular fluorophores present on the CD surface was quenched by changing the liquid aqueous environment to solid phase (ice). Based on light-induced electron paramagnetic resonance (LEPR) measurements and density functional theory (DFT) calculations, the proposed kinetic model assuming the presence of charge-separated trap states rationalized the observed sensitivity of PL lifetimes to the environment. Importantly, the PL quenching induced by freezing could be suppressed by adding a small amount of alcohols. This was attributed to a high tendency of alcohol to increase its concentration at the CD/solvent interface, as revealed by all-atom molecular dynamics simulations. Based on this behavior, a fluorescence "turn-on" alcohol sensor for exhaled breath condensate (EBC) analysis has been developed. This provided an easy method to detect alcohols among other common interferents in EBC with a low detection limit (100 ppm), which has a potential to become an inexpensive and noninvasive clinically useful diagnostic tool for early stage lung cancer screening.

Sunflower-Like Nanostructure with Built-In Hotspots for Alpha-Fetoprotein Detection.

In the present study, a sunflower-like nanostructure array composed of a series of synaptic nanoparticles and nanospheres was manufactured through an efficient and low-cost colloidal lithography technique. The primary electromagnetic field contribution generated by the synaptic nanoparticles of the surface array structures was also determined by a finite-difference time-domain software to simulate the hotspots. This structure exhibited high repeatability and excellent sensitivity; hence, it was used as a surface-enhanced Raman spectroscopy (SERS) active substrate to achieve a rapid detection of ultra-low concentrations of Alpha-fetoprotein (AFP). This study demonstrates the design of a plasmonic structure with strong electromagnetic coupling, which can be used for the rapid detection of AFP concentration in clinical medicine.

Improvement of SERS for detection of ultra-low concentration of methyl orange by nanostructured silicon decorated with Ag nanoparticles

We studied the effect of nanostructured silicon integrated with Ag nanoparticles (NPs) on surface enhanced Raman scattering (SERS) to detect methyl orange (MO). Ag NPs are deposites on the two types of porous silicon, single-layer porous silicon (s-PSi) and porous silicon photonic crystals (PSi PhCs). Their characteristics were confirmed by scanning electron microscopy (SEM) and reflectance. SERS activity of the substrates was compared by using MO as the probe molecules. The results with SERS experiments showed that SERS activity of Ag NPs/PSi PhCs was much stronger than that of Ag NPs/s-PSi with 6.8-fold improvement. The limit of detection of MO was 10−9 M and the linear range was from 10−9 to 10-3 M.

Plasmonic structure with nanocavity cavities for SERS detection of pesticide thiram

Excessive thiram residues in food have the potential to negatively impact human health. Hence, the development of a convenient and fast detection method is highly desirable. In this study, an efficient, repeatable, and sensitive surface-enhanced Raman scattering (SERS) active chip was manufactured via a low-cost colloidal lithography technique. The plasmonic structure was composed of a series of silver nanospheres and nanowires. Interestingly, this type structure creates a nanocavity space with a characteristic geometry generating a strong electromagnetic field coupling. The finite-different time-domain software was employed to simulate the electromagnetic field distribute on the nanocavity. Accordingly, SERS active chip that displays ultra-low concentration detection of thiram (10−11 M) was realized. Moreover, the excellent reproducibility of thiram (10−6 M) practical detection on an apple pericarp has great potential for application in food safety.

Gold nanoplasmonic particles in tunable porous silicon 3D scaffolds for ultra-low concentration detection by SERS.

A composite material of plasmonic nanoparticles embedded in a scaffold of nano-porous silicon offers unmatched capabilities for use as a SERS substrate. The marriage of these components presents an exclusive combination of tightly focused amplification of Localised Surface Plasmon (LSP) fields inside the material with an extremely high surface-to-volume ratio. This provides favourable conditions for a single molecule or extremely low concentration detection by SERS. In this work the advantage of the composite is demonstrated by SERS detection of Methylene Blue at a concentration as low as a few picomolars. We systematically investigate the plasmonic properties of the material by imaging its morphology, establishing its composition and the effect on the LSP resonance optical spectra.

High enhancement factor of SERS probe based on silver nano-structures deposited on a silica microsphere by laser-assisted photochemical method

The high enhancement factor (EF) of surface-enhanced Raman (SERS) probes is an important parameter for high-sensitivity Raman scattering measurement applied to environment control. In this article, we present a SERS probe based on silver nano-structures deposited on silica microsphere surfaces made by the laser-assisted photochemical method and reflection converging mirror for a high EF Raman measurement of ultralow organic compound concentration inliquid environments. The laser-assisted photochemical method can synthesize and homogeneously deposit nano-silvers on a silica microsphere, and the reflection converging mirror can collect more Raman signal to the photo-detector and give high Raman enhancement of the SERS probe. The SERS-activity of the probe is verified by the detection of ultralow concentrations of Rhodamine 6 G in aqueous solutions in the range of 10−4–10−10 M. The obtained results show that the proposed SERS probe has an increase of collected Raman intensity up to 32% in comparison to a SERS probe without reflection converging mirror, and an EF of the SERS probe achieved up to 1.8 × 1010. We believe that the novel SERS probe has a large potential for applications in biochemical sensing techniques.

A Semi-quantitative method for the detection of fentanyl using surface-enhanced Raman scattering (SERS) with a handheld Raman instrument.

A handheld, spatially offset Raman spectroscopy (SORS) system was successfully used to obtain Surface-enhanced Raman Scattering (SERS) spectra of fentanyl under simulated field conditions. A series of aqueous fentanyl solutions were prepared with commercially available gold nanoparticle solution, at concentrations ranging from 0.003 to 1697μM. These SERS spectra were then used to generate two concentration calibration models (via a plot of peak area (1026cm-1 ) versus concentration, and quantitative spectral decomposition using partial least squares (PLS1)). For both models, the relationship followed Langmuir adsorption and became non-linear at concentrations above ~0.2μM, with a limit of detection (LOD) of approximately 3nM. The same technique was successfully used to measure fentanyl in the presence of two common "cutting agents," heroin and glucose, at 1% and 2% fentanyl proportions (w/w). Fentanyl detection was successfully achieved, but mixture interference from the cutting agents prevented a calibration model being generated. Four fentanyl analogues were also investigated-butyrylfentanyl, furanylfentanyl, acetylfentanyl, and ocfentanyl. A concentration calibration model for each species was successfully generated, but differentiation from fentanyl proved more challenging, although several potential diagnostic peaks were identified. These results identified a pathway forward in using handheld equipment for the reliable detection of ultra-low concentrations of fentanyl and fentanyl analogues via SERS, even when mixed with diluents. However, quantitative detection is negatively impacted in the presence of heroin and glucose. This also provides a starting point for a SERS-based spectral library of fentanyl analogues, in combination with a range of different diluents.

Communication—Fabrication of Uniform Hollow Cubic Ag Cages and The Application for Surface-Enhanced Raman Spectroscopy Detection

In this study, a facial synthesis route for cubic Ag micro structure with well-defined hollow interior was developed. The fabricated hollow micro-cages were applied as the substrate for the detection of ultralow concentration of crystal violet (CV)-a poisonous organic pollutant. The substrate exhibits optimum SERS performance with a detection of 10−6 M of CV due to the unique hollow morphology, proving that it is a good candidate for SERS detection in the chemical and environmental field.

Detection of individual insulating entities by electrochemical blocking

Electrochemical blocking is a type of single-entity electrochemical measurement particularly well adapted to the detection of insulating particles. The digital detection of ultralow concentrations of artificial entities such as polymer particles or biotargets such as proteins and bacteria represents an exceptional opportunity for sensing applications. In this review, we explore the latest development in the field of electrochemical blocking and propose some perspectives. • Electrochemical blocking is sensitive enough to sense individual proteins. • Single-entity electrochemistry may be used to detect subattomolar concentrations of particles. • The size of spherical particles can be estimated within about 10% of error by electrochemical blocking.

Morphology and Microstructure Evolution of Gold Nanostructures in the Limited Volume Porous Matrices.

The modern development of nanotechnology requires the discovery of simple approaches that ensure the controlled formation of functional nanostructures with a predetermined morphology. One of the simplest approaches is the self-assembly of nanostructures. The widespread implementation of self-assembly is limited by the complexity of controlled processes in a large volume where, due to the temperature, ion concentration, and other thermodynamics factors, local changes in diffusion-limited processes may occur, leading to unexpected nanostructure growth. The easiest ways to control the diffusion-limited processes are spatial limitation and localized growth of nanostructures in a porous matrix. In this paper, we propose to apply the method of controlled self-assembly of gold nanostructures in a limited pore volume of a silicon oxide matrix with submicron pore sizes. A detailed study of achieved gold nanostructures’ morphology, microstructure, and surface composition at different formation stages is carried out to understand the peculiarities of realized nanostructures. Based on the obtained results, a mechanism for the growth of gold nanostructures in a limited volume, which can be used for the controlled formation of nanostructures with a predetermined geometry and composition, has been proposed. The results observed in the present study can be useful for the design of plasmonic-active surfaces for surface-enhanced Raman spectroscopy-based detection of ultra-low concentration of different chemical or biological analytes, where the size of the localized gold nanostructures is comparable with the spot area of the focused laser beam.

Detection of N,N-dimethylformamide vapor down to ppb level using electrospun InYbO nanofibers field-effect transistor

The development of ultrasensitive and down to ppb-level gas sensors for the accurate detection of volatile organic compounds (VOCs) in environmental monitoring is still a bottleneck that urgently needed to be overcome. Here, we report a high-performance N,N-dimethylformamide (DMF) gas sensor based on electrospun InYbO nanofibers field-effect transistor (FET). Owing to the high surface area of nanofibers, the gas sensor exhibits a remarkably high sensitivity of 89–2000 ppb DMF, fast response/recovery time (36/67 s), exceedingly low detection limit of 5 ppb and outstanding selectivity towards DMF against other typical gases as well as excellent stability and reliability. In particular, the developed gas sensor can obtain low theoretical limit of detection (LOD) of 1.18 ppb. Moreover, a possible sensing enhanced mechanism is also proposed and verified utilizing the capacitance-voltage (C–V) analysis. This work opens a new route for the electrospun nanofibers FETs as a promising sensing platform to realize high-performance and ultralow-concentration detection gas sensors.

Detection of Ppb-level NO2 using mesoporous ZnSe/SnO2 core-shell microspheres based chemical sensors

Detection of ultralow concentrations of the hazardous gases is the major demand and challenge for the development of biosensors. A novel mesoporous ZnSe-core/SnO2-shell microspheres based chemiresistive-type sensor was fabricated for ppb-level NO2 detection, and the theoretical detection limit is calculated to be 0.87 ppb. The as-fabricated sensor presents an excellent performance for low-concentrations of NO2 up to 2.4 ppm and exhibits significantly higher response approximately 6.94 than those of pristine SnO2 (∼2.86) and ZnSe based sensors (almost no response) to 2.4 ppm NO2 at 160 °C. The response and recovery time of the core-shell microspheres based sensor are 64 s and 52 s, respectively, which are substantially improved compared to those of the pristine SnO2 based sensor (∼149 s and ∼133 s). The sensor demonstrates a superior long-term stability with a deviation in the response of the sensor less than 5 % for one month, and a brilliant selectivity to several possible interferents. The significantly improved sensing performance could be attributed to the obtained mesoporous structures and the formed ZnSe/SnO2 hybrid interfaces. It yields more active sites and promotes the electrons transferred between ZnSe and SnO2 nanocrystals. The density functional theory (DFT) calculations are employed to reveal the potential transducing mechanisms.

(Plenary) Design Strategies for High-Performance Oxide Semiconductor Gas Sensors

Oxide semiconductor gas sensors have been widely used to detect explosive and harmful gases because of their irreplaceable advantages such as high sensitivity, excellent reversibility, simple structure, facile integration, and cost effectiveness, and their applications are being rapidly expanded to environmental monitoring, disease diagnosis from exhaled breath, food quality control, smart farming, and artificial olfaction. In particular, oxide semiconductor chemiresistors and their array can be integrated within smart phones and portable devices, which will open a wide range of new applications through the sensor connection using Internet of Things, multivariate pattern recognition, and machine learning of big gas sensing data in the near future. To date, various nanostructures with high surface area to volume ratio, such as nanoparticles, nanowires, nanosheets have been explored to enhance the gas response and sensing materials have been loaded with noble metal or oxide catalysts for tailoring gas selectivity. However, for demand-based design of high performance gas sensors and artificial olfaction, many issues still remain unsolved, which include the detection of ultralow concentration of analyte gas, highly selective detection of a specific gas, moisture-independent gas sensing, and the establishment of distinctive gas sensing library toward numerous analyte gases as well as complex odors. How can we overcome above challenges? The diversity of gas sensing materials provides a rational solution, which can be accomplished by introducing new sensing materials, designing new nano-archiectures, making new methods to tune the reforming/oxidation of analyte/interference gases, establishing new strategies to maximize/control catalytic activity, and using different ways to control electronic/chemical sensitization. In this presentation, various new, promising and general strategies to design sensitive, selective, and reliable chemiresistors for next-generation gas sensors and artificial olfaction will be suggested, which are as follows: Hollow and hierarchical nanostructures with high gas accessibility for effective and raid gas detection [1]P-type oxide semiconductors with abundant oxygen adsorption, facile redox reaction, and high catalytic activity for detecting new gas species and for expanding the gas sensing materials [2]Multi-valence additives for humidity-independent oxide semiconductor gas sensors [3,4]Catalyst-loaded or catalytic micro-reactors such as yolk-shell spheres and multiroom-structured spheres for highly selective detection of aromatic compounds via the reforming of less-reactive gases into more reactive species [5]Bilayer sensors consisting of sensing layer and nanoscale catalytic overlayer for separating catalytic and sensing reactions as well as for tailoring gas selectivity and response without limiting the gas transport [6]Hetero-nanostructures consisting of two different materials with dissimilar catalytic activity and work function for enhancing catalytic activity and for promoting electronic sensitization via the charge transfer across hetero-interface [7]Semiconducting multinary oxides consisting of two or more catalytic components [8].Monolayer oxide nanofiber sensor with tailored exposure of catalytic electrode for controlling gas selectivity [9] References [1] J.-H. Lee, Gas sensors using hierarchical and hollow oxide nanostructures: Overview, Sens. Actuators B 140 (2009) 319-336. doi:10.1016/j.snb.2009.04.026.[2] H.-J. Lee, J.-H. Lee, Highly sensitive and selective gas sensors using p-type oxide semiconductors: Overview, Sens. Actuators B 192 (2014) 607-627. doi:10.1016/j.snb.2013.11.005.[3] H.-R. Kim, A. Haensch, I.-D. Kim, U. Weimar, J.-H. Lee, Role of NiO doping in reducing the humidity impact on the performance of SnO2-based gas sensors: synthesis strategies, phenomenological and spectroscopic studies, Adv. Funct. Mater. 21 (2011) 4229-4240. doi:10.1002/adfm.201101154.[4] J.‐W.Yoon, J.‐S.Kim, T.‐H. Kim, Y. J. Hong, Y. C. Kang, J.‐H. Lee, A new strategy for humidity independent oxide chemiresistors: Dynamic self‐refreshing of In2O3 sensing surface assisted by layer‐by‐layer coated CeO2 nanoclusters, Small 12 (2016) 4456-4463. doi:10.1002/smll.201601507.[5] J.-W.Yoon, Y.J.Hong, G.D.Park, S.-J.Hwang, F.Abdel-Hady, A.A.Wazzan, Y.C.Kang, J.-H.Lee, Kilogram-scale synthesis of Pd-loaded quintuple-shelled Co3O4 microreactors and their application to ultrasensitive and ultraselective detection of methylbenzenes, ACS Appl. Mater. Interfaces 7 (2015) 7717-7723. doi: 10.1021/acsami.5b00706.[6] S.-Y.Jeong, J.-W.Yoon, T.-H.Kim, H.-M.Jeong, C.-S.Lee, Y.C.Kang, J.-H.Lee, Ultra-selective detection of sub-ppm-level benzene using Pd-SnO2 yolk-shell micro-reactors with a catalytic Co3O4 overlayer for monitoring air quality, J. Mater. Chem. A 5 (2017) 1446-1454. doi:10.1039/C6TA09397C.[7] T.-H. Kim, C.-H. Kwak, J.-H. Lee, NiO/NiWO4 composite yolk−shell spheres with nanoscale NiO outer layer for ultrasensitive and selective detection of sub ppm-level p-xylene, ACS Appl. Mater. Interfaces 9 (2017) 32034-32043. doi:10.1021/acsami.7b10294.[8] K. H. Lee, B.-Y. Kim, J.-W. Yoon, J.-H. Lee, Extremely selective detection of ppb levels of indoor xylene using CoCr2O4 hollow spheres activated by Pt doping. Chem. Commun. 55 (2019) 751-754. doi:10.1039/C8CC08186G.[9] K. Lim, Y.-M. Jo, J.-W. Yoon, J.-H. Lee, Metal oxide patterns of one-dimensional nanofibers: on-demand, direct-write fabrication, and application as a novel platform for gas detection, J. Mater. Chem. A 7 (2019) 24919-24928. doi:10.1039/C9TA09708B.