Symposium FE
Functional Nanomaterials for New Generation Solid State Chemical Sensors


FE-1:IL01  Gas Sensing of NiO-SCCNTs Core-shell Heterostructures: Optimization by Radial Modulation of the Hole-accumulation Layer
M.H. Raza1, K. Movlaee2,3, S.G. Leonardi3, N. Barsan4, G. Neri3, N. Pinna1, 1Institut für Chemie and IRIS Adlershof, Humboldt-Universität zu Berlin, Berlin, Germany; 2Center of Excellence in Electrochemistry, School of Chemistry, College of Science, University of Tehran, Iran; 3Department of Engineering, University of Messina, Messina, Italy; 4Institute of Physical and Theoretical Chemistry, University of Tübingen, Tübingen, Germany

Hierarchical core-shell (C-S) heterostructures composed of a NiO shell deposited onto stacked-cup carbon nanotubes (SCCNTs) were synthesized using atomic layer deposition (ALD). A controlled film of NiO particles was uniformly deposited onto the inner and outer walls of the CNTs. The NiO thickness was precisely controlled between 0.80 and 21.8 nm, by varying the number of ALD cycles from 25 to 700. The as-synthesized NiO-SCCNTs C-S heterostructures were thoroughly characterized by high-resolution transmission electron microscopy (HRTEM), energy dispersive X-ray (EDX) elemental mapping, X‐ray diffraction (XRD) and X ray photoelectron spectroscopy (XPS). The electrical resistance of the samples was found to increase of many orders of magnitude with the increasing of the NiO thickness. The behavior of NiO-SCCNTs sensors with various thicknesses of the NiO shell layers was investigated for low concentrations of acetone and ethanol at 200 °C. The sensing mechanism is based on the modulation of hole-accumulation region in the NiO shell layer, during the interaction of the reducing gas molecules with the adsorbed oxygen species, which account for a marked change in the resistance. The electrical conduction mechanism was further studied by developing NiO-Al2O3-SCCNTs heterostructures...

FE-1:IL02  High-performance Flexible Gas Sensors based on Carbon-based Nanostructures
SEON-JIN CHOI, Division of Materials of Science and Engineering, Hanyang University, Seoul, South Korea

Flexible and wearable chemical sensors are gaining much attention considering the requirement for the real-time and on-site detection of hazardous gas species. Various carbon nanomaterials such as graphene have been demonstrated for applications in flexible gas sensors with high mechanical stability. In this presentation, unique synthesis and fabrication strategies for flexible gas sensors integrated with multi-dimensional carbon-based nanostructures are highlighted. There are three technological innovations for the fabrication of flexible gas sensors: i) Synthesis of thermally and mechanically stable transparent flexible substrate, ii) embedding conductive networks for a flexible heater, and iii) integration of various carbon-based nanostructures on the flexible substrate. The composition and structural optimizations of carbon-based nanomaterials were performed on the flexible substrate by optical-thermal treatment. In addition, the flexible sensors exhibited improved reaction kinetics assisted by the heating property to accelerate the surface chemical reaction. We demonstrated real-time detection of environmental gases using multi-dimensional nanostructures integrated with an IoT sensing module to transmit the sensing data to a smartphone.

FE-1:L04  Dual-hydrogen Bond Donor Functionalized Single-walled Carbon Nanotubes for improved NO2 Sensing
JOON-SEOK LEE, S.H. Choi, W.J. Choi, J.W. Seo, S.J. Choi, Division of Materials of Science and Engineering, Hanyang University, Seoul, South Korea

The development of chemical sensors for the on-site detection of hazardous gases is gaining much attention for applications in internet-of-things (IoTs) and point-of-care tests (POCTs) in recent years. Among the various air pollutants, nitrogen dioxide (NO2) is one of the toxic gases causing severe health problems. Excess exposure to NO2 can damage the human respiratory system and cause asthma. In this work, gas sensing receptors composed of dual-hydrogen bond donor groups (e.g., thiourea and squaramide) were incorporated with single-walled carbon nanotubes (SWCNTs) to detect polar NO2. The receptors were covalently linked to poly(4-vinyl pyridine). To transduce chemical interaction into electrical signals, the polymeric receptors were non-covalently functionalized on SWCNTs. Gas sensing characterization was performed to investigate NO2 detection capabilities at different operating temperatures (25, 50, and 100°C). The result revealed the improved NO2 sensing proeprties using the thiourea-based receptor functionalized SWCNTs as a result of a strong binding affinity between –NH protons and the polar NO2. The improved NO2 sensing mechanism was investigated based on the density functional theory (DFT) calculations to elucidate strong binding affinity to NO2.

FE-1:IL05  Agro-industrial Biocarbon Nanomaterials for Advanced Gas Sensing Application
C. ESPRO, University of Messina, Messina, Italy

One of the most important goals of green chemistry and resource efficiency, is the use of renewable raw materials, for a sustainable production of novel advanced carbon nanostrutures, as opposed to their unsustainable production from non-renewable fossil resources such as oil, coal and natural gas. We have recently described a simple, scalable, and cost-effective synthetic way for producing high-quality biocarbon nanomaterials based on the conversion of agro-industrial citrus wastes by hydrothermal carbonization processes (HTC) under mild conditions (180−300°C) and autogenous pressure. They exhibit unique electrical and electrochemical properties depending on the hydrothermal treatment temperature, which could be attributed to their special surface characteristics, as evidenced by the characterization investigation carried out. The so obtained hydrochar was used for fabricating a high performance conductometric sensors for the monitoring of environmental pollutants, experiencing the sensing of low concentration of NO2 in air as target gas. Moreover, bio-carbons can be post-functionalized by simple and green procedure, due to the abundant presence superficial functional groups, as well as, their valuable nanodots (CNDs) fraction can be easily separated and recovered. During this talk, we will communicate our latest results in this fast developing field.

FE-2:IL01  The Role of Surface Oxygen Vacancies in the Sensing Mechanism of SnO2
C.S. BLACKMAN, Department of Chemistry, University College London, UK

Materials such as complex oxides (doped, quaternary, etc) and heterojunctions are finding wide application in fields such as solar devices, heterogenous catalysis and gas sensing, amongst numerous others. The controlled and reproducible synthesis of such materials are obviously therefore key to progress in these fields. Amongst competing synthesis technologies chemical vapour deposition techniques (CVD, ALD) allow reproducible synthesis of a wide range of thin and ultra-thin film materials, and nanomaterials, and provides direct integration of the functional material with a device platform. Here I will discuss our use of vapour deposition techniques for synthesis of functional gas sensing semiconductor nanomaterials.

FE-2:IL03  Improvement of Sensing Properties of Semiconductor Gas Sensors by Controlling Gas Diffusivity and Reactivity
Yasuhiro Shimizu, T. Hyodo, Graduate School of Engineering, Nagasaki University, Nagasaki, Japan

To improve the sensing performance of semiconductor metal oxide gas sensors, strict design and control of meso- and macro-porous structure of sensor materials are of primary importance, i.e. controlling of diffusivity of target gases in the sensing layer toward the position of sensor electrodes, which is the most sensitive region of the sensors, in addition to controlling of catalytic activities of sensor materials. The present paper reports our recent approaches directed to improving gas sensing properties based on the control of gas diffusivity and reactivity. Those include controlling both the diffusivity and the reactivity of target gases by adjusting porous structure and catalytic properties of sensor materials. The main sensor materials tested are mesoporous SnO2 and macroporous In2O3 decorated with and without noble metals, and WO3 decorated with and without siloxane. Target gases tested are H2, NOx and CH3SH. The mesoporous structure is controlled by utilizing self-assembly of surfactants and the macroporous structure is controlled by a colloidal crystal template method by using polymethylmethacrylate (PMMA) microspheres and an ultrasonic spray pyrolysis method of oxide precursor solutions containing PMMA microspheres.

FE-2:IL07  Recent Advances in Thin Films of Metal Oxides as Gas Sensing Materials
K. Zakrzewska, AGH-University of Science and Technology, Faculty of Computer Science, Electronics and Telecommunications, Institute of Electronics, Kraków, Poland

Metal oxide thin films have been recognized as an attractive alternative to other forms of gas sensors. Their planar structure combined with high surface-to-volume ratio make possible integration with the majority of sensing platforms and provides quite significant response. This presentation will highlight the importance of magnetron sputtering as the most promising technology applied for deposition of thin film bilayers of n-n and n-p metal oxides. The examples of SnO2/TiO2 and CuO/TiO2 heterostructures for NO2 sensing will be demonstrated. Recent advances in development of thin film gas sensors will be discussed.

FE-2:L09  A CuO/SiO2 Nanocomposite for Highly Selective H2S Gas Sensing
A. Paul, C. Weinberger, T. Wagner, M. Tiemann, Paderborn University, Department of Chemistry, Paderborn, Germany

We present a composite of CuO nanoparticles inside the pores of nanoporous SiO2. The material is used for dosimetric detection of H2S gas (low ppm). The system is based on the chemical conversion of CuO to CuS at low temperature (160 °C). Since CuS is highly conductive ('metallic' CuS), the reaction results in a strong increase of conductivity (measureable). The sensor is, therefore, highly selective to H2S. The reaction is reversible; CuO is regenerated by heating to 350 °C in air (with or without H2S). Long-time stability of our system allows for repeated cycles of measurement/regeneration. This is possible because the CuO/CuS nanoparticles are embedded in the nanoporous matrix. Despite severe volume expansion and shrinkage of the particles, no overall morphological changes in the sensing material occur. The sensor response is marked by a percolation-type mechanism. Upon exposure to H2S the conductance remains low for a certain induction time while CuS is gradually formed. Once the percolation threshold is reached, a continuous conduction path forms and the conductance shows a steep increase. The length of the induction period depends on the H2S concentration; hence, measuring this time period allows for assessment of the H2S concentration (after calibration).

FE-3:IL03  Layered Amorphous Metal Oxide Gas Sensors by Controlled Oxidation of 2D-MDs
V. PAOLUCCI1, J. De Santis1, G. Giorgi2, 3, C. Cantalini1, 1Department of Industrial and Information Engineering and Economics, University of L’Aquila, Italy; 2Department of Civil and Environmental Engineering (DICA), University of Perugia, Italy; 3CNR-SCITEC, Perugia, Italy

Despite their potential in gas sensing applications, 2D exfoliated metal dichalcogenides (MDs) suffer from spontaneous oxidation showing poor chemical stability under dry/wet conditions even at room temperature, limiting their practical exploitation. Aim of this work is to validate synthesis strategies allowing microstructural and electrical stabilization of the oxides that inevitably form on the surface of 2D dichalcogenides. Taking advantage from spontaneous oxidation of MDs in air, we report on exfoliated SnSe2 flakes annealed in static air at a temperature below the crystallization temperature of the native a-SnO2 oxide, yielding a new class of 2D Layered Amorphous Metal Oxides Sensors (LAMOS), specifically few-layers of a-SnO2, with excellent gas sensing properties. Sensing tests were carried out at 100°C operating temperature exposing a-SnO2 to NO2 and H2 gases and different relative humidities ranging from 40% to 80% RH. The formation of a stable layer of amorphous a-SnO2 guarantees excellent reproducibility and stability if the response over one year. The synthesis strategy here described can be likely extended to all TMDs/MDs 2D materials.

FE-4:IL03  Optical Detection of Chemicals and Biological Entities on Gold Nanostructured Solid Supports
R.E. Ionescu, Laboratoire Lumière, Nanomatériaux et Nanotechnologies- L2n, CNRS ERL 7004, Université de Technologie de Troyes, Troyes, France

The talk will discuss the analytical performances of genuine cost-effective bio-sensing strategies based on controllable formed metallic nano-structures on glass substrates using either natural micrometric labels (Escherichia coli bacteria) or metallic staples or microscopic TEM grids. Such sensitive substrates are used for high nano-scale throughput and multiplexing plasmonic sensitive detection of (bio)molecules for medical and environmental applications. Moreover, the toxicity of carbonaceous nanomaterials to engineered bioluminescent bioreporters: Escherichia coli, TV 1061 strain sensitive to protein damage, and Escherichia coli DPD 2794 strain sensitive to DNA damage will be presented. A scanning electron microscope was used to assess changes in (bio)entities after exposure to powdered nanomaterials.

FE-5:L02  Flexible Plasmonic PEGDA Hydrogels for Biosensing Applications
B. MIRANDA1, 2, S. De Martino3, R. Moretta1, P. Dardano1, I. Rea1, C. Forestiere2, L. De Stefano1, 1Institute of Applied Sciences and Intelligent Systems, Napoli, Italy; 2DIETI, Università degli Studi di Napoli “Federico II”, Napoli, Italy; 3Materias s.r.l., Napoli, Italy

Localized Surface Plasmon Resonance (LSPR)-based biosensors provide unique advantages compared to other sensing technologies. These benefits include single-molecule sensitivity and the possibility to scale down the whole detection setup, this being crucial while realizing point-of-care (POC) diagnostic tools. Among the many nanofabrication technologies, a good trade-off between costs, time and large-scale production is still missing. Motivated by this necessity, we propose a rapid large-scale fabrication strategy of a novel optical platform based on bottom-up chemically synthesized gold nanoparticles (Au-NPs) embedded in Poly(ethylene glycol) diacrylate (PEGDA) hydrogels. PEGDA is a biocompatible, flexible, transparent material that can be used as a substrate to design wearable plasmonic biosensors adaptable to non-planar surfaces (e.g. skin). We analyze the absorbance spectra of spherical Au-NPs with controlled size and embedded in PEGDA hydrogel. We aim to apply the newly designed wearable and flexible platforms to the detection of specific target analytes (cancer biomarkers, viruses, or toxins) in LSPR and Fluorescence, to obtain a dual-mode optical sensor. We finally propose a reverse engineering model to predict the absorption spectra of the realized biosensor.

FE-5:L04  Single Walled Carbon Nanotube-polymer Composite for Real-time Wireless Heavy Metal Ion Sensing
SEUNG-HO CHOI, J.S. Lee, W.J. Choi, J.W. Seo, S.J. Choi, Hanyang University, Seoul, South Korea

Heavy metal ions (HMIs) are toxic pollutants that can cause severe health problems such as HMI poisoning, and several diseases. For these reasons, precise determination and rapid screening of HMI in aqueous solution is imperative. Herein, chemiresistive HMI sensors were developed utilizing polymer-SWCNT composites functionalized with zinc 5,10,15,20-tetra(4-pyridyl)-21H,23H-porphines (ZnTPyP). Firstly, homogenous dispersion was prepared by wrapping SWCNTs with P4VP in dimethylformamide. P4VP-SWCNT composites were anchored on a glass substrate by forming bromo alkyl chains through a quaternization reaction. Subsequently, ZnTPyP was functionalized on the P4VP-SWCNT composite (ZnTPyP-P4VP-SWCNT) by coordination reaction between residual pyridyl groups and the Zn center. HMI sensing characteristics were investigated toward various HMIs in an aqueous solution. The result revealed that ZnTPyP-P4VP-SWCNT exhibited a response [(R0¬–RHMI)/R0] (%) of 32.4% toward 6.25 mM Hg2+ in an aqueous buffer solution, which was over 6-fold improved response (5.1%) as compared to the P4VP-SWCNT composite. Selective sensing properties were evaluated with different HMIs. Finally, wireless HMI detection is demonstrated by transmitting sensor signals to a smartphone using a smart-card type sensor module.

FE-5:IL05  Gas Sensors based on Metal Oxide Nano-heterojuntions
E. Llobet, E. Navarrete, Universitat Rovira i Virgili, MINOS, Tarragona, Spain

Single crystalline, metal oxide semiconductor nanowires (NWs) loaded with metal oxide nanoparticles (NPs) are very promising for developing a new generation of inexpensive, yet highly sensitive and more stable gas sensors. By supporting p-type metal oxide NPs (e.g. Pd, Cu, Ni, Co or Ir oxides) on n-type metal oxide NWs, both chemical and electronic sensitization effects can be obtained, which can dramatically tune the response to target gases of the resulting hybrid nanomaterials, thus enabling the engineering of selectivity. Here we discuss the aerosol-assisted chemical vapour deposition (AACVD) as a technique that enables growing single crystalline, n-type metal oxide NWs supporting homogeneously distributed, mono-modal, p-type metal oxide NPs in a wide range of loading levels. SEM, TEM, XRD, XPS, Raman, ToF-SIMS and PL are used to analyse the morphology, crystalline phase, chemical composition and defects. Their gas sensing properties (response, selectivity and stability) towards different species (e.g., ethanol, ammonia, nitrogen dioxide, hydrogen sulphide) are obtained and the sensing mechanisms are discussed in detail. In addition, the integration of these nanomaterials in different transducer substrates (MEMS, ceramics, flexible polymeric) is discussed as well.

FE-5:IL07  Nanoparticle Networks for Label-free Biosensing
D. Tsoukalas, E. Skotadis, M. Kainourgaki, Dept. of Applied Physics, National Technical University of Athens, Greece; G. Tsekenis, Biomedical Research Foundation of the Academy of Athens, Athens, Greece

We present research on biosensing devices based on the use of nanoparticles (NPs) formed in vacuum using a gas condensation process combined with sputtering. The technique allows the fabrication of platinum nanoparticles with mean diameter of 4-5 nm and controlled surface coverage. The sputtering method provides high flexibility, since it is fully compatible with semiconductor manufacturing technology/batch fabrication and the physically produced NPs can self-assemble on top of silicon dioxide substrates without the need for a functionalization layer. A NP network of varying surface coverages, formed in between interdigitated electrodes, has been implemented towards the development and optimization of electrochemical biosensing devices for the highly specific, label free and fast in-situ detection of biomolecules. Various cases will be presented based on the change of electrical parameters measured between the electrodes upon a detection event. For example platinum nanoparticles, detect a DNA hybridization event via a drop in the resistance of the device the performance of the sensor being optimized by the nanoparticle surface density and inter-finger electrode spacing while impedance measurements have been proved more efficient for high sensitive pesticide molecule detection.


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