Table Of ContentMaterials for Chemical Sensors
Editors
Subhendu Bhandari
Department of Plastic and Polymer Engineering
Maharashtra Institute of Technology
Aurangabad, Maharashtra
India
Arti Rushi
Electronics and Telecommunication Department
Maharashtra Institute of Technology
Aurangabad, Maharashtra
India
p,
p,
A SCIENCE PUBLISHERS BOOK
A SCIENCE PUBLISHERS BOOK
Cover illustration reproduced by kind courtesy of Dr. Subhendu Bhandari.
First edition published 2023
by CRC Press
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Library of Congress Cataloging‑in‑Publication Data (applied for)
ISBN: 978-0-367-48435-4 (hbk)
ISBN: 978-1-032-45789-5 (pbk)
ISBN: 978-1-003-03977-8 (ebk)
DOI: 10.1201/9781003039778
Typeset in Times New Roman
by Radiant Productions
Preface
Sensors constitute the intelligent class that can be useful for the detection of various
organic/inorganic contaminants. The sensors are the devices which belong to the
category of transducers. They accept one form of signal and convert it into another
form. Sensors can be classified into various sub-categories which may be either in
terms of the sensing material that is being employed in designing of the sensor, or
the target parameter for which the sensor is intended. However, sensors based on
changes of chemical properties are always standing as monarch of research interests
since in such sensors, technology component is considerably less and output signals
are easy to process and analyze. Fundamentally, such sensors consider chemical
reactions as the backbone of its sensing mechanism.
While fabricating any sensor, the main component which requires the highest
attention is nothing but the ‘sensing material’. The overall characteristics of any
sensor are mostly dependent on the sensing material used in the fabrication of the
sensor. ‘Materials with mind’ are the highest sought for resources in sensor science.
Technologies in a sensor appear to be the most subsidiary part, only after the sensor
material is ‘intelligent’ enough to extend a reliable, sensitive, selective and repetitive
performance towards detection of the targeted analyte(s) as the first hand desired
characteristics. Apart from very few instances, naturally occurring substances are
rarely reported to be efficient sensing platforms as they fall short of meeting all
requisites of an ideal sensor in a single material. Therefore, modification/modulation
in naturally occurring substances or chemically/physically engineered substances,
perhaps, constitutes the most significant part of consideration in sensor materials.
Till date, the sensor science has witnessed the most influenced research in this
particular direction.
The primary objective of this book is to discuss various materials which could be
used efficiently in fabrication of chemical sensors. This book would be highly useful
for the research community working in the area of sensor development. Also, for the
material scientists, this book is expected to be a helping guide. The undergraduate
and post graduate faculty members and students interested to work with various
sensor materials may find this book as a guiding platform.
This book constitutes a spectrum of sensing materials used in the fabrication
of chemical sensors. In this book, eight chapters are devoted to some of the most
efficient sensing materials that have been used in the development of chemical
sensors. This book begins with one of the classical materials viz. metal oxide which
has attracted research attention through decades, back from 1950s. The important
properties of metal oxides which are important in sensing applications are discussed
iv Materials for Chemical Sensors
in the first chapter. Also, sensing mechanism involved in metal oxide-based
sensor and characteristics of this class of sensor are discussed in this chapter. The
second chapter encompasses information related to one of the most promising one-
dimensional nanomaterials—carbon nanotubes. Authors have provided an insight in
design architecture, fabrication methods, functionalization methods, mechanism of
CNT based sensors and sensing parameters. The third chapter focuses on graphene, a
two-dimensional sensing material. The discussion of the physiochemical properties
of this material, used in the demonstration of chemical sensor, is provided here. The
fourth chapter includes review of hydrogel-based sensors. The operational principle,
sensor design, sensing parameters and various sensing applications are explained
in this chapter. The fifth chapter provides comprehensive idea about luminescent
metal-organic frameworks (MOF) as chemical sensors. The uses of MOF materials
in the detection of inorganic and organic compounds such as VOCs, ionic species,
biomolecules, environmental pollutants, toxic molecules, etc., have been discussed in
the chapter. The sixth chapter is assigned for biomaterials and biosensing technology.
The applications of biomaterials for the detection of cancer cells, enzymes and
human motions have been discussed in this chapter. The seventh chapter is based
on the theme of application of textiles in chemical sensor. In this chapter, discussion
is given on textile based wearable sensors for detection of sweat, wound extrudates,
etc. The last chapter encompasses the information about various materials used in
the chemical sensing which are not discussed in the previous chapters. The sensing
capabilities of materials such as pyrylium, hydrazone, black phosphorus, diamond,
electrolyte materials, quantum dots, fluorine derivatives, meta materials, ligands,
crown ethers, porphyrin, etc., are discussed in this chapter. The discussion of all such
‘intelligent’ materials used in the chemical sensing is a herculean task; the inventory
is epical that might require volumes altogether. Therefore, discussion on highly
efficient materials that are used in the chemical sensing has been included in this
book with a preferred orientation of different classes of materials.
The credit of initiation of this book project goes to the publishers. It is our
honour to serve as the editor for this book. The contribution for the proposed chapter
has been invited by the editors. Renowned scientists across the globe having interest
in this particular topic have been requested to contribute in this book project. We
would like to declare that all the submitted chapters are thoroughly reviewed and
have undergone the revision process.
The timely submission from all the authors is appreciated in view of completion
of this book project. We would like to extend our sincere thanks to all the contributing
authors and co-authors for their timely submission and for their dedication in this
entire journey. We owe our heartfelt regards to the publishing staff (especially,
Mr. Raju Primlani) for their initiative, co-ordination, continuous support and time-
to-time guidance.
Subhendu Bhandari
Arti Rushi
Contents
Preface iii
1. Metal Oxides as Chemical Sensors 1
Bhagwan G. Toksha and Sagar E. Shirsath
2. Carbon Nanotube-Based Chemical Sensors 19
Sovan Lal Banerjee and Matthew V. Tirrell
3. Graphene Based Chemical Sensors 56
Bhagwan G. Toksha, Prashant Gupta and Sagar E. Shirsath
4. Hydrogel Based Chemical Sensors 75
Moumita Shee, Piyali Basak, Amit K. Das and Narayan Ch. Das
5. Luminescent Metal-Organic Frameworks as Chemical Sensors 96
Yogeshwar D. More, Sahel Fajal, Subhajit Dutta and Sujit K. Ghosh
6. Biomaterials as Chemical Sensors 135
Benny Ryplida, Ji Hyun Ryu and Sung Young Park
7. Textile Chemical Sensors 163
Marta Tessarolo, Isacco Gualandi, Luca Possanzini and Federica Mariani
8. Miscellaneous Materials for Chemical Sensing 207
Prashant Gupta, Aastha Dutta and Mostafizur Rahaman
Index 231
About the Editors 233
C 1
hapter
Metal Oxides as Chemical Sensors
Bhagwan G. Toksha1 and Sagar E. Shirsath2,*
Introduction
The first attempt at using metal oxide materials as chemical sensors dates seven
decades back (Brattain and Bardeen 1953). The discovery revolved around the logic
that semiconducting materials modify their resistance as they come in contact with
some active substance depending on the atmosphere they are in contact with. This
scientific exploration further expanded with continuous blood monitoring through
biosensors and ion concentration monitoring through field effect based devices
(Clark and Lyons 1962, Bergveld 1972). Further, the form of devices that could
detect gases through heat arrangement and resistivity change could be realized
(Taguchi 1972, Yagawara et al. 1990). Ideally, a sensor is a device carrying the
virtues of being inexpensive, portable, accurate and instantaneous in response to
some stimulus. The chemical sensors offer selective, measurable, and reproducible
response to a certain target chemical substance (Fowler et al. 2009, Bandodkar et al.
2016). This ‘chemical of interest’ could be present in the surrounding in liquid/
gaseous phase at any concentration level. These devices are fabricated with wide
spectrum of material recipes to work as chemical sensors. However, with tremendous
advancements in recent times, a thing such as ‘ideal chemical sensor’ is yet to be
achieved. The chemical parameters, mostly of interest for sensing applications other
than selective applications, are pH, salinity/conductivity, dissolved oxygen/carbon
dioxide, etc. (Buono et al. 2021, Deji et al. 2021, Luo and Wang 2021, Sinha et al.
2021). The presence/absence of a chemical entity as a step change in any parameter,
identifying a particular analyte, concentration in terms of magnitude are detected
in sensing mechanisms. The metal oxide sensors reduced in size possess flexibility,
simple operation, structural designs able to wrap/twist, and compatibility to integrate
1 Electronics and Telecommunication Department, Maharashtra Institute of Technology, Maharashtra,
India.
2 School of Materials Science and Engineering, University of New South Wales, Sydney, NSW 2052,
Australia.
* Corresponding author: [email protected]
2 Materials for Chemical Sensors
with IoTs (Internet of Things), which most importantly takes the sensing applications
into automated versions (Gomes et al. 2019).
The worldwide usage of chemical sensors is going to produce a business of
more than 30 billion USD before 2030 (www.marketresearchfuture.com 2021). The
research interest in chemical sensors is projected to witness significant increase in
the forthcoming decade. The prominent reason for this growth is the increased use of
chemical sensors in healthcare, oil and gas, industrial, agricultural, and biochemical
sectors. The use of chemical sensors is going to be inevitable in detection of
various chemical entities involved in vehicle industry, processing industry, and
safety protocol and monitoring industry. In the healthcare industry in particular,
the chemical sensors are of great help in treatments, portable monitors, diagnosis,
and drug/alcohol abuse diagnosis. The developments in this field jointly with lower
manufacturing costs involved will lead to higher clamour and mobilize the demands.
Metal oxides are materials of interest for the researchers working in the field of
sensors due to their affordability, adaptability in terms of properties by compositional
changes, and ease in designing the connection with single recording devices. These
materials also exhibit sizable step change in response parameter on exposure to the
target molecule, adaptability in terms of properties by compositional changes, and
ease in designing the connection with single recording devices (Sun et al. 2012). The
sensors having metal oxides as active material display better results as compared to
other materials in the detection of baneful pollutants, and explosive gases, and serious
health-related symptoms in human exhaled breath (Fernandez et al. 2018, Yang et al.
2021).
The output of research activities in terms of publications and patents usually
report sensing mechanisms limited to individual gas or chemical entities. The
laboratory level experiments are found to be falling much short to real world working
conditions where all other ambient conditions such as humidity, other interfering
gases and temperature are present. The understanding of various mechanisms leading
to sensing action could be broadly classified as ‘chemiresistive’ wherein the designed
sensing material changes its electrical resistance in response to the chemical reaction
with the target material or ‘cataluminescent’ where the electromagnetic radiation
would be the output of a chemical reaction between the sensing material and the
target material (Liu et al. 2016, Hu et al. 2019, Park et al. 2019). The structure and
working mechanism of a chemical sensor is depicted in Figure 1. As the target entity
to be sensed comes in contact with the sensing material, a signal as a step change in
the sensing material is produced and detected through transducer action. This output
from the transducer is a weak electronic pulse which is made as a measurable electrical
signal in the next step. The recognition of the target entity results in some product
of interaction between the sensing material and the target entity. This reaction has to
be a reversible process which is indicative of the life time cycles of the sensor. The
cycles of the recognition process are the results of the non-covalent chemical bonds,
i.e., ionic/hydrogen bonds and van der Waals interactions. The major challenges in
the effective sensing mechanism lie with the magnitude of product between sensing
material and target entity. There is always a possibility of getting the same product
from sensing material and some other non-intended entities in the same environment.
This defeats the purpose of selectivity. The next step is to transduce them into a
Metal Oxides as Chemical Sensors 3
Figure 1. The layered structure and working mechanism of chemical sensors. As the target entity to be
sensed comes in contact with the sensing material, a signal as a step change is produced in the sensing
material and detected through transducer action with an electric signal. Reprinted with permission from
Mandoj et al. (2018).
measurable electronic response. The change in the electrical property of sensing
material as a function of the target entity is transduced to be a detectable signal. The
change in the electrical property could be changed in resistance and/or change in the
dielectric constant. The dielectric constant is measured with the use of the sensing
material as a dielectric in the capacitor and the capacitance of such a capacitor is
measured.
The research in the metal oxide sensing materials has benefitted from the rapid
and relentless advancements due to newer nanoscale technologies. The nanoscale
processing brought the possibilities of controllable manipulation of matter at the
molecular level. The understanding of properties and usage of nanomaterials has
led to substantial changes in sensor designs and capabilities. The reduction in size,
weight, power requirements has created opportunities for previously unavailable
sensitivity, and specificity. In the present chapter, the contemporary developments
of various metal oxide nanostructures will be discussed in the light of the latest
requirements and future directions. The present book chapter is not intended to present
an exhaustive account of the metal oxide as a chemical sensor. Rather, the chapter
focuses on reviewing the developments in the field of chemical sensors on the basis
of various metal oxide systems. The synthesis, i.e. designing and development of the
metal oxide sensors with the important sensor operating characteristics involved is
also elaborated.
Metal Oxide Properties for Sensing Applications
The metal oxide nanoparticles are bestowed with properties such as high density and
optimal structural features on their surfaces. Owing to their appropriate porosity,
reliable electrical performance, possibility to surpass Moore’s law limitation, metal
4 Materials for Chemical Sensors
oxide nano-wires have attracted research interest (Zeng et al. 2021). This class
of materials have structural properties such as variation in lattice parameters and
increased number of surfaces and interfaces. This leads to structural modifications
which generate strain/stress and adjoining structural perturbations (Bansal et al.
2006, Shaikh et al. 2021). The nanometric phase of metal oxides exhibit specific
size-dependent magnetic, chemical, and electronic properties (Liu 2006, Toksha et
al. 2017). The peculiar electrical properties useful in sensing applications are strongly
dependent on the particle size (Franke et al. 2006). The TiO nanoparticles exhibit
2
ionic conductivity modulating its usability in the field of sensors. These nanoparticles
are demonstrated to work effectively at high temperature harsh conditions where the
increase in the n-n junctions available between anatase and rutile at high temperatures
contributes positively towards conductivity (Fomekong et al. 2020). The chemical/
mechanical stability enables sustainability under harsh environments. The metal
oxide materials possess wider band gap creating possibilities of high energy photon
emission. The wide band-gap semiconducting behaviour of metal oxides makes
the operation possible at higher temperatures (Pearton et al. 2010). The GaO
2 3
thin film sensor for sensing oxygen was devised and tested for stability, sensitivity
and response time at 1000ºC (Baban et al. 2005). The ZnO material synthesized
in one-dimensional nano-wire structure demonstrated superior potential in sensor
applications with biocompatibility and improved sensing properties (Rackauskas et al.
2017). The metal oxide structural blend in case of ZnO and CuO nanowires was
studied by Park et al. (Park et al. 2013). The charge carrier type junctions with other
materials are designed for improvement in response and selectivity of sensors. It was
reported that the ZnO nano-wire formed the hetero-junction with p-type materials,
forming local p-n junctions as depicted in Figure 2.
As a well-known fact about nanomaterials, the reduction in size in nano range
brings escalation in the chemical reactivity due to its larger surface area to unit mass
ratio (Bhati et al. 2020). The surface area is increased with decrease in particle size and
contributes towards the improvement in the performance of sensing materials. This
could be further enhanced in case of 1-D nanostructure with hollow nanostructures.
The study involving SnO fibrous morphology with the role of sintering time reported
2
the critical role of specific surface area and mesopore diameter (Wu et al. 2015).
In another case, where WO thin film morphology was synthesized by magnetron
3
Figure 2. The contrast among the three variations of contacts between ZnO and CuO nano-wires along
with current-voltage characteristics and schematic depicting energy bands. Reprinted with permission
from Park et al. (2013).
