Fabrication of highly sensitive ethanol sensor based on doped nanostructure materials using tiny chips

Article abstract of DOI:10.1039/c5ra08224b

Doped CuO-Fe₂O₃ nanocubes (NCs) are prepared via a facile wet-chemical process using active reactant precursors with reducing agents in high pH medium (pH > 10). The NCs are totally characterized in detail using various methods, such as FTIR spectroscopy, X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), dynamic light scattering (DLS), powder XRD, UV/vis spectroscopy, FESEM coupled XEDS, FE-SEM, etc. A thin-layer of NCs is deposited on tiny chips (surface area, ～0.02217 cm²) to fabricate a selective ethanol sensor with short response time in liquid-phase medium. The fabricated chemi-sensor also exhibits higher sensitivity, large dynamic concentration ranges, long-term stability, and improved electrochemical performance towards ethanol. The calibration plot is linear (r² = 0.9937) over a wide ethanol concentration range (0.1 nM to 0.1 mM). The sensitivity and detection limit are ～7.258 μA cm^-2 mM^-1 and ～0.08 ± 0.02 mM (SNR, signal-to-noise ratio of 3), respectively. This novel effort establishes a well-organized way of developing efficient nanomaterial-based sensors for toxic pollutants in environmental and health-care fields on large scales.

Full text of DOI:10.1039/c5ra08224b

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ARTICLE
Fabrication of highly sensitive ethanol sensor based on doped
nanostructure materials using tiny chips
Mohammed M. Rahman, Abdullah M. Asiri
Received 00th January 20xx,
Accepted 00th January 20xx
2 3
Doped CuOꢀFe O nanocubes (NCs) are prepared by facile wetꢀchemical process using active reactant precursors with
reducing agents at higher pH medium (pH>10). NCs are totally characterized in details using various methods, such as FTIR
spectroscopy, Xꢀray photoelectron spectroscopy’s (XPS), transmission electron microscope (TEM), dynamic light
scattering (DLS), powder XRD, UVꢀvis. spectroscopy, FESEM coupled XEDS, and FEꢀSEM etc. The thinꢀlayer of NCs
DOI: 10.1039/x0xx00000x
2
onto tiny chips (surface area, ~0.02217 cm ) is deposited for fabricating a selective ethanol sensor in short response time in
www.rsc.org/
liquidꢀphase medium. The fabricated chemiꢀsensor is also exhibited higher sensitivity, largeꢀdynamic concentration ranges,
2
longꢀterm stability, and improved electrochemical performances towards ethanol. The calibration plot is linear (r = 0.9937)
ꢀ2
ꢀ1
over the large ethanol concentration ranges (0.1 nM to 0.1 mM). The sensitivity and detection limit is ~7.258 µAcm mM
and ~0.08±0.02 mM (signalꢀtoꢀnoise ratio, at a SNR of 3) respectively. This novel effort is initiated a wellꢀorganize way of
efficient nanomaterialsꢀbasedꢀsensor development for toxic pollutants in environmental and healthꢀcare fields in large
scales.
Key words: CuOꢀFe
2
O
3
nanocubes; Wetꢀchemical method, IꢀV technique; Selectivity; Sensitivity; Ethanol
Introduction
generators [14], and many other functional devices [15]. Transition
metal doping semiconductor nanostructure is also an competent
method to regulate the energy level surface states of ZnO, which can
further progress by the changes of doping concentrations into
semiconductor materials. The doped nanostructure materials have
achieved substantial attention due to their catalysis, optoꢀelectronics,
bioꢀchemicals, magnetic, photoꢀcatalysis, electronics, mechanical
properties and their prospective applications in various fields. Doped
nanostructure materials would be good candidates due to their higher
The significance of safety for lives as well as ecological
plants has been studied with great attention in semiconductor sensors
for toxic chemical detection by reliable methods [1]. Semiconductor
nanostructure materials are very sensitive and efficient due to their
smaller sphericalꢀsize and high active surface to volume ratio as
contrasted to the conventional nanomaterials in microꢀ or nanoꢀmeter
ranges. Nanostructure metal oxides have demonstrated an enormous
deal of consideration due to their outstanding properties occurring of
huge active surface area, high stability, quantum confinement
consequence, and high porosity as well as permeability (mesoꢀ
porous nature), which are reliant on the shape and size of the
nanocrystal [2,3]. Nanomaterials have attracted a wide interest
owing to their unique properties and potential application in
chemical sensors fabrication [4,5]. Semiconductor material has been
recognized as a promising host nanomaterial for doping transition
metal at room temperature. It is revealed a stable morphology and
composed of a number of disorder phases with geometricallyꢀ
coordinated metal and oxide atoms, piled alternately along the axes
&
specific surfaceꢀarea, higherꢀaspectꢀratio & active surface area,
lowerꢀpotentials, lowerꢀresistances, higherꢀcatalytic activity, and
smart electrochemical as well as optical characteristics. Transition
material has been recognized as an attractive guestꢀobjects for
doping into semiconductor materials (as hostꢀobject), which exhibits
a stable and controlled morphology contained a significant amount
of repeated crystalꢀphases coordinated with cationic and anionic
parts [16]. Nanostructure materials have potential characteristics for
their outstanding and excellent electroꢀcatalytic properties towards
various chemical, physicoꢀchemical, and chemicalꢀsensor
applications [17]. In last decade, a widespread progress has been
introduced by transitionꢀmetal doped semiconductor materials in
advancedꢀsciences with sophisticatedꢀtechnologies [18,19]. The lowꢀ
dimensional nanomaterial displays exciting uses in the field
significance electronics (i.e., diode, LED, transistors) [20], ultraꢀ
violate photoꢀdetectors [21], chemiꢀ or immunoꢀsensors (bioꢀassays)
[
6]. Transition metals coꢀdoped in semiconductor materials have
concerned profound research effort for its exceptional and
outstanding properties as well as versatile applications [7]. Recently,
an extensive development has been made on the research leading of
metalꢀoxides coꢀdoped ZnOꢀbased nanomaterials actuated by both
fundamental sciences and potential advanced technologies [8]. The
doped semiconductor nanostructures exhibit promising uses as fieldꢀ
effect transistors [9], UV photoꢀdetectors [10], gas sensors [11], field
emission electron sources [12], nanomaterials [13], nanoscale power
[
[
22,23], magneticꢀfiled (i.e., paraꢀmagnetic) [24], dopedꢀmaterials
25], energyꢀgenerator [26], and various bioꢀchips, and microꢀ
devices [27,28]. The doped nanomaterial is prepared by an effective
thermalꢀmethod to control the surfaceꢀenergy of metallic states that
can promote/growth by the changing in doping concentration in
semiconductor nanostructure materials. Undoped copper oxide
nanomaterials have significant characteristic behaviours due to the
potential applications in fabrication of nanoꢀelectronics, optoꢀ
electronics, bioꢀsensors, bioꢀchemicalꢀchips, fieldꢀemission displays,
and surfaceꢀactive properties [29ꢀ31]. Guest (CuO) and host
Center of Excellence for Advanced Material Research (CEAMR) and Chemistry
department, Faculty of Science, King Abdulaziz University, Jeddah 21589, P.O.
Box 80203, Saudi Arabia
*
Corresponding author (Prof. M.M. Rahman )
Center of Excellence for Advanced Material Research (CEAMR) and Chemistry
department, Faculty of Science, King Abdulaziz University, Jeddah 21589, P.O. Box
nanostructure materials (Fe O ) were exhibited a majorꢀfunction in
2
3
8
0203, Saudi Arabia
improvement
of
accurate,
higherꢀreproducibility,
highly
Email: mmrahman@kau.edu.sa, Phone/Fax (b): +966-59-642-1830
electrosensitive & reliable toxic chemical chemiꢀsensors using tiny
This journal is © The Royal Society of Chemistry 20xx
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chips. Doped nanostructure materials have been also attracted the by powder Xꢀray diffractometer at room conditions. Ramanꢀshift
considerable attention for the researchers, generally to control was employed to determine the bandꢀshift of CuOꢀFe O NCs by
2
3
growth monitoring owing to the increasing demand in healthcare and Raman spectrometer in different radiation sources. The size of CuOꢀ
bioꢀmedical fields [32ꢀ34]. Semiconductor nanomaterials are being Fe nanocubes was performed by transmission electron
comprehensively investigated owing to their exclusive surface microscope (TEM; JEMꢀ2100F, Japan). TEM sample was prepared
behaviours communed by largeꢀactive surfaces, which can construct as follows: the synthesized CuOꢀFe NCs were dispersed into
2
O
3
2
O
3
them perfect chemical recognizing elements as ionoꢀsensor or ethanol under ultrasonic vibration for 2 min, and then the TEM film
chemoꢀsensors. Lately, development of chemiꢀsensors using doped is dipped in the solution and dried for investigation. The particle size
nanostructure metalꢀoxides, active conducting polymers and was determined by DLS (photon correlation spectroscopy) with
nanocomposites are the key motive for the detection of Zetasizer NanoZS (Zetatrac NPA 152ꢀ31A, USA) at 25.0 °C. The
2 3
determination carcinogenic elements and hazardousꢀchemicals [35ꢀ CuOꢀFe O nanocubes were dispersed with 3.0 mL distilled water in
38]. Ethanol detection is important in different technological order to obtain accurate scattering intensity before the measurement.
scientific areas i.e., ecological & environmental monitoring, clinicalꢀ Equivalent amount of sample was dispersed into 3.0 ml distilled
o
diagnosis, & various practical industrial applications [39ꢀ41]. It has water at 25.0 C before analysis. All the samples were analyzed in
been also increasing the attention for toxicity analysis in recent triplicate (n=3). Currentꢀvsꢀvoltage (IꢀV) method (two electrodes
years, particularly hazardous and carcinogenic chemicals, owing to composed onto fabricated microꢀchip) was measured for ethanol ions
concerns about ecoꢀenvironmental protection and healthꢀcare fields. by using KeithleyꢀElectrometer from USA.
Ethanol is a toxic analytes, which is generally applied in various
research resolution and industrial laboratories for R&D purposes.
2 3
Preparation and growth mechanism of CuOꢀFe O NCs:
Longꢀtime revelations to ethanol can consequences in various
infections, such as healthꢀtroubles and nervalꢀdiseases, and probably
cell damages. Therefore, the determination and recognition of
The term "wet chemical methods" emerged in contrast to
conventional and solidꢀstate synthesis methods of nanostructural
materials widely used in preparation of doped or undoped
nanomaterials. The term refers to a group of methods of powder and
material production using liquid phase at one of the preliminary
process stages. The wet chemical products of solids in liquidꢀphase
synthesis are much smaller grains (crystallites) and, usually, lower
temperature and shorter duration of phase formation. Here, Facile
ethanol in liquid phase is a significant task using doped CuOꢀFe
2 3
O
nanocubes coupled onto tiny chips. The doped CuOꢀFe NC has
2
O
3
interesting behaviours i.e., large and activeꢀsurface area, nontoxicity,
chemicalꢀinstability, elemental activities, and goodꢀconductivity,
which offered goodꢀelectron communication characteristics that
encouraged electron transfer to the target analytes. Typically, it is
also demonstrated that transition metal doped semiconductor
nanomaterials (such as mesoꢀporous nanomaterials) can propose
huge surfaceꢀarea, higherꢀstability, nanoꢀporosity, and consistency,
which could develop the potential chemical sensors.
and lowꢀtemperature synthesis of CuOꢀFe
wetꢀchemical process using active reactant precursors such as copper
chloride (CuCl ), iron chloride (FeCl ), and sodium hydroxide
NaOH). In a usual reaction procedure, 0.1 M CuCl was dissolved
in 50.0 ml deionized (DI) water mixed with 50.0 ml FeCl solution
0.1 M) under continuous stirring. pH of resultant solution was
2 3
O NCs was prepared by a
2
3
(
2
3
Ethanol is extremely toxic and usually serious to health
and environment, it is immediately required the detection by using a
(
adjusted over 10.0 by the addition of NaOH and resulting mixture
was shaken and stirred continuously for 10.0 minutes at room
conditions. After stirring, the solution mixture was then put into
2 3
reliable sensing method with prepared doped CuOꢀFe O NCs using
tiny chips. The investigation of ethanol by doped CuOꢀFe O NCs
2
3
films on chips is prepared and studied in details of the chemical
sensors. The easyꢀcoating method for the construction of CuOꢀFe
o
conical flux and heatꢀup at 120.0 C for 6.0 hours. The temperature
2
O
3
of solution was controlled manually throughout the reaction process
NCs thinꢀfilm within conductor bindingꢀagents is developed in
preparation of nanomaterial films onto smart chips. In this approach,
doped CuOꢀFe O NCs fabricated films with conducting binders is
2 3
utilized towards the target carcinogenic analytes using reliable
CurrentꢀvsꢀVoltage (IꢀV) method. It is confirmed that the fabricated
chemical sensor by IꢀV method is the unique and efficient approach
o
at 90.0 C. After heating the reactant mixtures, the flux was kept for
cooling at room conditions until reached the room temperature. The
final CuOꢀFe O doped products were prepared, which was washed
2
3
with DI water, ethanol, and acetone for several times subsequently
and dried at roomꢀtemperature. The asꢀgrown product was kept for
air dry for few hours and then used for structural, elemental,
morphological, and optical characterizations. The growth mechanism
of the CuOꢀFe O nanocube materials can be explained on the basis
2 3
for ultraꢀsensitive recognition of ethanol with CuOꢀFe O NCs onto
tiny chips in short responseꢀtime.
2
3
of chemical reactions and nucleation, as well as growth of doped
nanocrystals. The probable reaction mechanisms (iꢀiv) are presented
Experimental
2 3
here for obtaining the CuOꢀFe O nanomaterials in below.
+
ꢀ
Materials and Methods:
NaOH(aq) → Na (aq) + OH (aq)
(i)
(ii)
(iii)
(iv)
2
+
+
+
ꢀ
CuCl
2
+ NaOH(aq) → Cu (aq) + OH (aq) + Na (aq) + 2Cl (aq)
ꢀ
Copper chloride, binders (butyl carbitol acetate and ethyl
acetate), iron chloride, sodium hydroxide, and all other chemicals
were in analytical grade and purchased from SigmaꢀAldrich
Company. They were used without further purification. The
absorption maxima (λmax) of CuOꢀFe O NCs was investigated by
2 3
UVꢀvis spectrometer, where the bandꢀgap energy (Ebg) calculated
based on this study. A FTꢀIR spectrum of CuOꢀFe O NCs was
investigated using FTꢀIR spectrophotometer, which used for the
metalsꢀoxygen bonds (CuꢀO and FeꢀO) confirmation. The XPS
2 3
measurement of doped CuOꢀFe O NCs was measured with Thermoꢀ
Scientific KꢀAlpha spectrometer (Germany), for the calculation of
binding energy (KeV) of Cu, Fe, and O. Morphology, particleꢀsize,
and arrangement of CuOꢀFe O NCs was recorded by using a
FESEM instrument from JEOL (JSMꢀ7600F, Japan). The
crystallinity and crystalꢀpatterns of CuOꢀFe NCs was measured
3
+
ꢀ
+
FeCl3(s) + 2NaOH(aq) → Fe (aq) +2OH (aq) + 2Na (aq) + 3Cl (aq)
2
+
3+
+
Cu (aq) + 2Fe (aq) + 6NaOH(aq) → CuO.Fe
2
O3 (s)↓ +6Na +2H
2
O
The reaction is forwarded slowly according to the equation
(
i) to equation (iii). During preparation, the pH value of the reaction
medium plays an important role in the doped nanoꢀmaterial oxide
formation. Over pH 10, when CuCl is hydrolyzed with NaOH
2
2
3
solution, copper hydroxide is formed instantly according to the
equation (ii). During the whole synthesis route, NaOH operates a pH
buffer to control the pH value of the solution and slow contribute of
ꢀ
ꢀ
2+
hydroxyl ions (OH ). When the concentrations of the Cu and OH
ions are achieved above in critical value, the precipitation of CuO
3
+
nuclei begin to start. As there is high concentration of Fe ions
according to the reactions (iii)] in the solution, the nucleation of
Fe crystals become slower due to the lower activation energy
2
3
[
2
O
3
2
O
3
barrier of heterogeneous nucleation. Hence, as the concentration of
2
| J. Name., 2012, 00, 1-3
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2
+
Cu existences, a number of larger CuOꢀFe
aggregated cubeꢀlike morphology form after the reactions [equation stored into the desiccators, when not in use. Resist on µꢀchip surface
iv)]. The shape of asꢀprepared CuOꢀFe NCs is approximately is removed by acetone and cleaned with isopropyl alcohol (IPA).
2 3
O crystals with executed. Silicon wafer is diced into pieces by dicing apparatus and
(
2 3
O
reliable with the growth pattern of copper oxide doped iron oxides The opposite side of the chip is roughed by a sandpaper sheet for
nanocrystals [42,43]. Then the solution was washed thoroughly with better adhesion and electrical stability. The µꢀchip is bonded with die
acetone, ethanol, and water successively and kept for drying at room and packaged by silver paste. It is dried in a drying oven. Pads on
condition. In NCs growth technique, initially CuO and Fe
nucleus growth takes place by selfꢀaggregation, which then reꢀ machine. Finally, siliconꢀbased adhesive is put on the periphery of
aggregates and produced CuOꢀFe nanocrystal according to the the chip to protect pads and gold wire from sample solution.
2
O
3
chip are connected to the package through gold wire with bonding
2
O
3
Ostwald ripening method. Nanostructure material crystallizes and reꢀ Adhesive is dried for 24 hours at room temperature. The
aggregates with each other through VanderꢀWaals forces and forms semiconductor smart µꢀchips were fabricated on silicon wafer.
doped CuOꢀFe O nanocubes morphology, which is presented in Aluminum was sputtered to fabricate as wiring and bonding pads.
2 3
Scheme 1. Finally, the asꢀgrown CuOꢀFe O3 NCs were fully PtꢀTiꢀTiN was sputtered on thermal oxide of silicon and patterned by
2
characterized in detail of their morphological, structural, elemental, photolithography to fabricate counter electrode (CE). TiꢀTiN layers
and optical properties, and applied for detection of ethanol chemical were used for strong adhesion. AuꢀTi were sputtered and
sensor for the first time. The phases of the dried in air and doped lithographed, which made circular working electrode (WE) with a
powder materials were examined using XRD. The morphology and diameter of 1.68 mm in the centre of the µꢀchip. After electrodes
cross section of the powders were observed with SEM equipped with fabrication, palylene layer was fabricated by evaporation method as
XEDS. The evaluation of bandꢀgap energy and metalꢀoxygen bond a passivation layer. The wafer was diced to 5.0 mm square µꢀchips.
formation (CuꢀO and FeꢀO) was examined by using UV/vis. and This µꢀchip was bonded to a package by silver paste. Aluminum
FTIR Spectroscopy.
pads were connected to the package by gold wire. Finally, adhesive
Araldite, Hantsman, Japan) was put on the periphery of the chip,
which prevents target solution from contacting pads.
(
2 3
Fabrication of doped CuOꢀFe O NCs/µꢀchip assembly:
Construction of µꢀchip by conventional photolithography
method has been already explained in previous section. Here, a tiny
µꢀchip is fabricated by asꢀgrown CuOꢀFe O NCs with conducting
2
3
coating agents (ethyl cellulose powder, EC & butyl carbitol acetate
solvent, BCA). After that, CuOꢀFe NCs fabricated µꢀchip
2
O
3
o
assembly is moved into heatingꢀoven at 65.0 C intended for 2 hours
to make complete drying and uniformꢀfilm formation. Fabricated
NCs/microꢀchip and Pt microꢀline (onto microꢀchip) are worked a
working and counter electrode respectively. As purchased ethanol is
used to make target solution to formulate different concentration (1.0
nM ~ 1.0 mM) in 0.1M phosphate buffer solution with deionised
system (0.1M PBS is made in deionised water) and use as a selective
target toxicꢀanalyte. 15.0 µL of target analyte solution (in phosphate
buffer solution, 0.1M PBS) is dropped onto the NCs/chip during
investigation. The Current/Voltage (IꢀV, slope of calibrationꢀcurve)
is utilized to calculate of target NCs sensitivity. Limit of detection
Scheme 1: Probable growth mechanism of doped CuOꢀ
Fe O NCs at lowꢀtemperature by wetꢀchemical process
2
3
Construction of µꢀChips using photolithography method:
Electrochemical µꢀchips were fabricated by conventional
photolithographic technique, where electrodes and passivation layers
are developed on silicon wafer followed by dicing and packaging
[
44,45]. Nitrogenꢀdoped silicon wafers are prepared and overflowed
by extraꢀpure water. In this step, all contaminations on the surface
and native SiO layer are removed perfectly. At first, the wet
2
oxidation is employed and then dry oxidation is executed, where,
wafers are annealed in the nitrogen environment. Aluminum is
sputtered with aluminumꢀ1% Si target. Then the photolithograph
processes are applied. Resist coating, baking, exposure, and
development are employed by Kanto chemicals, and then it is rinsed
thoroughly by ionic water. Aluminum is etched by etching solution
and resistance layer is removed perfectly by plasma etching
instrument. Then silicon wafers are cleaned by acetone, methanol,
(
LOD) is manipulated from the 3N/S ratio vs. sensitivity (~3×Noise
vs. Sens.) in linear portion of total concentration range of
calibrationꢀplot. CurrentꢀVoltage technique is evaluated as
potentialꢀsources by electrometer in two (workingꢀcounter)
electrodes assembly. CuOꢀFe NCs is made and exhibited for the
detection of target ethanol in solutionꢀphase system.
a
2
O
3
and finally by plasma simultaneously. Silicon nitride (SiN) layer is Results and discussion
deposited by chemical vapor deposition and then pad electrode
surfaces are etched by reactive ion etching. Finally residual resist Evaluation of Morphological and Elemental property:
layer is removed by plasma etching. After photolithographic process,
platinum is sputtered by SP150ꢀHTS. Then it is patterned by liftꢀoff presented in Figure 1(aꢀc). It exhibits the images of the NCs
method, in which wafers are immersed into the remover, and then with nanoꢀdimensional sizes of asꢀgrown CuOꢀFe O NCs. The
2
FESEM images of asꢀgrown CuOꢀFe O3 NCs are
2
3
washed with isopropyl alcohol. Photolithographic process is again
investigated, where titanium is sputtered as a binding layer, and then
gold is evaporated by deposition method. Finally, gold layer is
patterned by liftꢀoff method. Parylene passivation layer is formed for
the protection of the µꢀchip from water. Photolithographic process is
performed again for pad protection. Then paryleneꢀdimer is
evaporated by deposition apparatus. Photolithography process is
done again for patterning. Parylene layer is patterned by etching.
Finally, unꢀnecessary resists are removed by acetone and then wafer
is cleaned by isopropyl alcohol (IPA). Resist is coated on a whole
surface of the silicon wafer for protection during dicing process is
dimension of NC is calculated as
from the FESEM images that the facile synthesized CuOꢀFe
∼0.11µm. It is clearly exposed
2
O
3
NCs is nanostructures in cubicꢀshape, which grown in very
highꢀdensity and possessing almost uniform cubes. When the
size of doped material decreases into nanometerꢀsized scale, the
surface area is increased significantly, this improved the energy
of the system and made reꢀdistribution of Cu and Fe ions
possible. The nanometerꢀsized cube could have tightly packed
into the lattice, which is an agreement with the publish reports
[
46,47].
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Where Ebg is the bandꢀgap energy and λmax is the wavelength (648.0
nm) of the CuOꢀFe NCs. No extra peak associated with
2
O
3
impurities and structural defects are observed in the spectra, which
proved that the synthesized microstructure controlled crystallinity of
asꢀgrown CuOꢀFe O NCs [48].
2 3
Figure 1. (aꢀc) FESEM images and (d) elemental analysis of asꢀ
grown CuOꢀFe O NCs at room conditions.
2
3
The Xꢀray electron dispersive spectroscopy (XEDS) analysis
of these CuOꢀFe NCs are indicated the presence of copper (Cu),
2
O
3
iron (Fe), and oxygen (O) composition in the pure asꢀgrown
nanostructure material, which is presented in Figure 1d. It is clearly
displayed that the prepared nanomaterials contained only Cu, Fe, and
O elements with the 4.99, 90.75, 4.26 wt% respectively, which is Figure 2. (a) FTꢀIR, (b) UV/visible, and (c) Xꢀray powder
presented in Figure 4d (inset). No other peak related with any diffraction of asꢀgrown CuOꢀFe O NCs at room conditions
2
3
impurity has been detected in the FESEM coupled XEDS, which
confirms that the nanocubes are composed only with Cu, Fe, and O.
Crystallinity and crystal phase of asꢀprepared CuOꢀFe O3
2
NCs were investigated. Powder Xꢀray diffraction patterns of doped
nanocubes are represented in Figure 2c. The CuOꢀFe O NCs sample
Evaluation of Optical and Structural property:
2
3
were investigated and exhibited as faceꢀcentered cubic shapes.
Figure 2c reveals characteristic crystallinity of the CuOꢀFe NCs
2 3
The asꢀgrown CuOꢀFe O NCs is also investigated in terms
O
3
of the atomic and molecular vibrations. To predict the functionalꢀ
recognition, FTIR spectra fundamentally in the region of 400~4000
2
and their crystalline arrangement, which is investigated by powder
Xꢀray crystallography. The peaks were found to match with CuO
phase (Tenorite) having faceꢀcentered monoclinic geometry [Joint
Committee on Powder Diffraction Standards, JCPDS#073ꢀ6234].
The major phases are indicated the characteristic peaks (Hash
symbol, #) with indices for 2θ values at 35.5(110), 38.2(111),
ꢀ
1
cm is investigated at room conditions. Figure 2a displays the FTIR
ꢀ
1
spectrum of NCs, which represents band at 532 cm . These observed
ꢀ
1
broad vibration bands (at 532 cm ) could be assigned as metalꢀ
oxygen (CuꢀO and FeꢀO mode) stretching vibrations, which
demonstrated the configuration of CuOꢀFe
The optical property of the asꢀgrown CuOꢀFe
one of the significant characteristics for the assessment of its photoꢀ
2 3
O NCs materials.
5
3.1(020), 57.1(202), 67.8(113), 74.1(221), and 76.1(ꢀ222) degrees.
2
3
O NCs is
The monoclinic lattice parameters are a=4.662, b=3.417, c=5.118,
catalytic activity. UV/visible absorption are a technique in which the β=99.48, Point group: C2/c, and Radiation: CuKα1 (λ= 1.5406).
outer electrons of atoms or molecules absorb radiant energy and These indicate that there is significant amount of crystalline CuO
undergo transitions to high energy levels. In this phenomenon, the present in semiconductor nanomaterials. The reflection peak is found
spectrum obtained due to optical absorption can be analyzed to to match with iron oxide phase (Hematite, αꢀFe
acquire the energy bandꢀgap of the doped metal oxides. For Rhombohedral geometry [JCPDS#080ꢀ2377]. In Fig 2c, the phases
UV/visible spectroscopy, the absorption spectrum of CuOꢀFe O
(with indices) are represented to the major characteristic peaks (star
2 3
O ) having
2
3
NCs solution is measured as a function of wavelength, which is symbol, *) for asꢀgrown crystalline iron oxide at 2θ values of
presented in Figure 2b. It presents a broad absorption band around 24.1(012), 32.5(104), 39.4(006), 40.7(113), 43.4(202), 49.3(024),
6
48.0 nm in the visibleꢀrange between 200.0 to 800.0 nm 54.1(116), 57.6(018), 62.3(214), 64.1(300), 69.2(208), 71.6(1010),
wavelengths indicating the formation of CuOꢀFe
NCs. Bandꢀgap and 75.5(220) degrees. The lattice parameters are a=5.03521;
2
O
3
energy (E ) is calculated on the basis of the maximum absorption c=13.7508, Z=6, point group: Rꢀ3c(167), and radiation: CuK 1 (λ=
bg
α
band of CuOꢀFe
following equation (v).
2
O
3
NCs and found to be ∼1.9135 eV, according to 1.5406). These indicate that there is considerable amount of
crystalline iron oxide present in doped nanostructure materials.
These confirmed that there is major number and amount of
crystalline doped CuOꢀFe O NCs present in NCs [49]. Crystallite
2 3
size was calculated by DebyeꢀScherrer’s formula given by equation
(vi)
1
240
Ebg
=
(eV)
λ
(v)
D= Kλ/(βcos θ)
(vi)
4
| J. Name., 2012, 00, 1-3
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Where D is the crystal size; λ is the wavelength of the Xꢀray morphology of the CuOꢀFe
View Article Online
DOI: 10.1039/C5RA08224B
COMMUNICATION
2
O
3
nanostructures assembled in
radiation (λ=0.15406 nm) for CuKα; K is usually taken as 0.9; and β cubicꢀshape morphology as found in FESEM and revealed the
is the line width at halfꢀmaximum height (FWHM) [50]. The average full consistency in terms of shape and dimension.
cross sectional diameter of CuOꢀFe
2
O
3
NCs is close to ~0.11 µm.
The size distribution of CuOꢀFe
2
O
3
nanocubes was
measured by DLS at 25.0 °C. Before investigation, NCs were
wellꢀdispersed into 3.0 mL distilled water in order to obtain the
Evaluation of Binding energy:
Xꢀray photoelectron spectroscopy (XPS) is a quantitative accurate scattering intensity. The dispersed solution of NCs
spectroscopic method that determines the chemicalꢀstates of the were analyzed in triplicate (n=3). The size distribution was
elements that present within doped materials. XPS spectra are measured by DLS showed approximately normal distribution
2 3
acquired by irradiating on a nanomaterial with a beam of Xꢀ (Fig 4b). The hydrodynamic sizes of CuOꢀFe O NCs were
rays, while simultaneously determining the kinetic energy and 0.1274 µm in the 0.1001~0.1558 µm ranges. SEM, TEM, and
number of electrons that getꢀaway from the top one to ten nm of the XRD could determine the morphous and original diameter of
material being analyzed. Here, XPS measurements were measured the particles. DLS mainly reflects the hydrodynamic size in
for CuOꢀFe
chemical states of Fe
2 3
O
2 3
NCs semiconductor nanomaterials to investigate the dispersion media. The hydrodynamic size of CuOꢀFe O NCs
O
3
and CuO. The XPS spectra of O1s, Fe2p, was measured in distilled water as stock media. The
2
and Cu2p are presented in Fig. 3a. The O1s spectrum shows a main observation showed that owing to the Van der Waals force and
peak at 531.3 eV in Fig. 3b. The peak at 531.3 eV is assigned to hydrophobic interaction with surrounding media the
ꢀ
lattice oxygen may be indicated to oxygen (ie, O
CuOꢀFe
state of the doped Fe
2
) presence in the hydrodynamic size is generally larger (~0.1274 µm) than
O
3
NCs [51]. XPS was also used to resolve the chemical original (~0.11 µm). The zeta potential (particle charge) was
nanomaterial and their depth. Here, the spin also measured by determining the nanocubes electrophoretic
2
2
O
3
orbit peaks of the Fe2p(3/2) and Fe2p(1/2) binding energy for all the mobility using the same instrument Zetasizer NanoZS at 25.0
samples appeared at around 713.2 eV and 724.1 eV respectively, °C. The values were calculated using Helmholtz–
2 3
which is in good agreement with the reference data for Fe O
2 3
[52]. Smoluchowski equation. The CuOꢀFe O NCs were diluted 10
In Figure 3d, the spin orbit peaks of the Cu2p(3/2) and Cu2p(1/2) times with filtered deionized water to obtain ideal concentration
binding energy for all the samples appeared at around 932.5 eV and range for optimal measurement. (Viscosity values of the
9
53.1 eV respectively, which is in good agreement with the dispersion media were made less than equivalent to water [1.0
reference data for CuO [53]. XPS compositional analyses evidenced mPas] at 25.0 °C). Here, it was also measured the zeta
the coꢀexistence of the two singleꢀphase of CuO and Fe O
potential, mobility, conductivity, charge, and dielectric constant
nanomaterials. Therefore, it is concluded that the wetꢀchemically as 5.7 mM, 0.44 u/s/V/cm, 415.0 uS/cm, 0.056 fC, and 79
prepared doped CuOꢀFe
NC materials have NCs phase contained respectively.
2
3
2
O
3
two materials. Also, this conclusion is reliable with the XRD data
noticeably.
Figure 3. XPS of (a) doped CuOꢀFe O NCs, (b) O1s level, (b) Fe2p
2
3
level, and (d) Cu2p level acquired with MgKα1 radiation.
2 3
Figure 4. Particle size analysis of CuOꢀFe O NCs by (a) TEM
and (b) DLS.
Particle size analysis by TEM and DLS:
Further structural characterization of CuOꢀFe
was investigated and found in cubeꢀshaped morphology by
2
O
3
materials Application: Chemical sensor with NCs/µꢀChips assembly
The potential application of CuOꢀFe O NCs assembled
2
3
TEM analysis. As shown in Figure 4a, the TEM images of onto µꢀchip as chemical sensors (especially ethanol analyte) has
CuOꢀFe O nanomaterials had a cubicꢀshape with an average been monitored for detecting hazardous chemicals, which are
2
3
diameter of 0.11 µm. The TEM observation shows the exact not environmental affable. Improvement of doping of these
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Journal Name
CuOꢀFe
stage and no other reports are available. The NCs sensors have (grayꢀdotted) and coated (darkꢀdotted) µꢀchip working electrodes
advantages such as stability in air, nonꢀtoxicity, chemical with CuOꢀFe NCs in absence of target ethanol. With NCs
2
O
3
NCs on µꢀchip as chemical sensors is in the initial
In Figure 6a shows the current responses of unꢀcoated
2
O
3
inertness, electrochemical activity, simplicity to assemble or fabricating surface, the current signal is slightly reduced compared to
fabrication, and bioꢀsafe characteristics. As in the case of toxic uncoated NCs/µꢀchip surfaces, which indicates the surface is slightly
ethanol sensors, the phenomenon of reason is that the current inhibited with CuOꢀFe
response in IꢀV method of CuOꢀFe NCs considerably curve. The current changes for the without target (darkꢀdotted) and
changes when aqueous ethanol are adsorbed. The calcined with target analyte (blueꢀdotted) injecting of towards target ethanol
CuOꢀFe
2 3
O NCs during the measurement of IꢀV
2
O
3
2
3
2 3
O NCs were applied for modification of chemical (∼15.0 µL) ethanol (∼0.1 µM) onto with CuOꢀFe O NCs modified
sensor, where ethanol was measured as target analyte. The µꢀchips is showed in Figure 6b. A significant current enhancement is
magnified construction view of internal µꢀchip center (sensing exhibited with the CuOꢀFe O NCs modified µꢀchips compared with
2
3
area) is presented in the Figure 5(aꢀc). Figure 5(aꢀc), platinum uncoated µꢀchips due to the presence of nanostructures, which has
line (PtE) and goldꢀcentralꢀcircle onto microꢀchip is employed higherꢀspecific surface area, largerꢀsurface coverage, excellent
as CE and WE electrodes (potential sources on 2ꢀelectrodes absorption and adsorption capability into the porous NCs surface
system) respectively. Figure 5d, the probable detection towards the target ethanol. A control experiment is performed for the
mechanism of NCs/chips is presented with fabricated ethanolꢀ comparison of current response in various compositions of NCs,
sensors using IꢀV methods. Figure 4e, expected experimental Iꢀ such as CuO NCs, Fe O NCs, and CuOꢀFe O NCs embedded µꢀ
2
3
2
3
V responses with NCs/chips by reliable conducting coating chips. Here, IꢀV responses of undoped CuO NC coating uꢀchip,
agents are developed. The fabricatedꢀsurface of CuOꢀFe O3 undoped Fe O coating NC uꢀchip and doped CuOꢀFe O3 NC
2
2
3
2
NCs sensor was made with conducting binders on the µꢀchip coating uꢀchip are measured by deducting the background current
surface, which is presented in the Figure 5(cꢀd). The fabricated (0.001mM analyte). In this control experiment, the doped CuOꢀ
µꢀchip electrode was placed into the oven at low temperature Fe O NC coating uꢀchip exhibits the highest current response
2
3
o
(
60.0 C) for two hours to make it dry, stable, and uniform the compared to unꢀdoped CuO or Fe O NCs, which is presented in
2 3
surface totally. IꢀV signals of chemical sensor are anticipated Electronic Supplemental section (S1). This significant change of
having NCs doped thin film as a function of current versus surface current is monitored in every injection of the target ethanol
potential for hazardous ethanol. The real electrical responses of onto the CuOꢀFe O NCs modified µꢀchips by electrometer. IꢀV
2
3
target ethanol are investigated by simple and reliable IꢀV responses with CuOꢀFe O NCs modified µꢀchip surface are
2
3
2 3
technique using CuOꢀFe O NCs fabricated µꢀchip, which is investigated from the various concentrations (0.1 nM to 1.0 mM) of
presented in Figure 4e.The time holding of electrometer was set ethanol, which is showed in Figure 6c. It shows the current changes
for 1.0 sec. A significant amplification in the current response of fabricated µꢀchip films as a function of ethanol concentration in
with applied potential is noticeably confirmed. The simple, room condition. It was also found that at low to high concentration
reliable, possible reaction mechanism is generalized in Figure of target analyte, the current responses were enhanced regularly. The
4d in presence of ethanol on NCs sensor surfaces by IꢀV potential current changes at lower to higher potential range
technique. The ethanol is converted to water and carbon dioxide (potential, +0.1 V to +1.3 V) based on various analyte concentration
ꢀ
in presence of doped nanomaterials by releasing electrons (ꢀ6e ) are observed, which is clearly presented in Figure 5c. A large range
to the reaction system (conduction band, C.B.), which improved of analyte concentration is measured the probable analytical limit,
and enhanced the current responses against potential during the which is calculated in 0.1 nM to 0.1mM. The calibration (at +0.5V)
IꢀV measurement at room conditions.
and magnifiedꢀcalibration curves are plotted from the various
ethanol concentrations, which are presented in the Figure 6d. The
sensitivity is estimated from the calibration curve, which is close to
ꢀ
2
ꢀ1
~7.258 µAcm mM . The linear dynamic range of this sensor
displays from 0.1nM to 0.1mM (linearity, R= 0.9937) and the
detection limit was considered as 0.11±0.02 nM [3×noise
(
N)/slope(S)].
Figure 5. Schematic diagram of (a) real cameraꢀview from top of
bared chips, (b) expected magnifiedꢀview of CuOꢀFe
2 3
O NCs
fabrication onto chips, (c) expected magnified view of CuOꢀFe
2
O
3
NCs /chips assembly with conducting coating binders onto sensingꢀ
area of tiny chips, (d) probable reaction mechanism of targetꢀethanol
ions in presence of doped NCs, and (e) expected responses of IꢀV
methods in the experimental results.
6
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Fig. 6. IꢀV responses of (a) uncoated and coated µꢀchip with CuOꢀ
Fe O NCs; (b) in absence and presence with 0.1µM ethanol with
2
3
CuOꢀFe
2
O
3
NCs/chip; (c) concentration variations (0.1 nM to
NCs
0.1mM) of analyte; and (d) calibration plot of with CuOꢀFe O
2 3
fabricated on µꢀchip surfaces. Potential was chosen in +0.1 to +1.5 V
ranges. Error limit of IꢀV measurement was ± 0.01. There are three
trial has been done in same experimental concentration at similar
condition.
The resistance value of doped semiconductor materials are
decreased (current increased) with increasing surrounding active
oxygen, which are the fundamental characteristics of nanomaterials
[
54]. Actually, oxygen adsorption demonstrates
a significant
responsibility in the electrical properties of the CuOꢀFe O NCs onto
2
3
tiny µꢀchip. The oxygen ion adsorption is removed the conduction
electrons and increased the resistance of CuOꢀFe NCs. Unstable
& O ) are adsorbed on the doped NC
surface at room temperature, and the quantity of such chemisorbed
oxygen species is directly depended on morphological and structural Figure 7. Mechanism of ethanol detection with active CuOꢀFe
2
O
3
−
−
oxygen species (i.e., O
2
2
O
3
−
properties. At room condition, O
2
is chemisorbed, while on NCs/µꢀchip is presented at ambient conditions.
−
−
nanocubes morphology, O
For this reason, the active O
ethanol sensing mechanism on CuOꢀFe
executed due to the presence of semiconductors oxides. The
2
and O are chemisorbed significantly.
The sensor response time was ~10.0 sec for the CuOꢀ
2 3
is disappeared quickly [55]. Here, Fe O NCs coated µꢀchip sensor to achieve saturated steady state
−
2
current in IꢀV plots. The major sensitivity of µꢀchip sensor can be
attributed to the good absorption (porous surfaces NCs fabricated
2
3
O NCs/µꢀchip sensor is
oxidation or reduction of the semiconductor NCs is held, according with binders), adsorption ability, highꢀcatalytic activity, and good
to the dissolved
O
2
in bulkꢀsolution or surfaceꢀair of the bioꢀcompatibility of the CuOꢀFe NCs/µꢀchip. The expected
2 3
O
neighbouring atmosphere according to the following equations (viiꢀ sensitivity of the NC fabricated sensor is relatively better than
ix).
previously reported ethanol sensors based on other composites or
materials modified electrodes [59]. Due to perceptive surface area,
O
2 3
2(diss) (CuOꢀFe O NCs/µꢀchip) → O2(ads) (vii)
ꢀ
ꢀ
here the doped nanoꢀmaterials developed
a
beneficial
e (CuOꢀFe
2
O
3
NCs/µꢀchip) + O
2
→ O
2
(viii)
ꢀ
ꢀ
ꢀ
microenvironment for the toxic chemical detection (by adsorption)
and recognition with excellent quantity. The prominent sensitivity of
CuOꢀFe O NCs affords high electron communication features which
2 3
improved the direct electron communication between the active sites
of nanoꢀsheets composed microstructures and µꢀchips. The modified
e (CuOꢀFe O NCs /µꢀchip) + O → 2O (ix)
2
3
2
These reactions are held in bulkꢀsystem or air/liquid
interface or adjacent atmosphere due to the small carrier
concentration which enhanced the resistances. The ethanol
sensitivity could be attributed to the high oxygen deficiency on CuOꢀ
Fe O NCs/µꢀchip (eg. MO ) and higher density conducts to increase
thin CuOꢀFe
2
O
3
NCs/µꢀchip sensor film had a better reliability as
NCs/µꢀchip
2
3
x
well as stability in ambient conditions. CuOꢀFe
2
O
3
oxygen adsorption. Larger the quantity of oxygen adsorbed on the
fabricated sensor surface, larger would be the oxidizing potential as
well as faster would be the oxidation of ethanol. The reactivity of
ethanol would have been very large as compared to other fabricated
material surfaces surface under identical condition [56,57]. When
ethanol reacts with the adsorbed oxygen on the exterior/interior of
exhibits several approaching in providing ethanol chemical based
sensors, and encouraging improvement has been accomplished in the
research section.
It was also investigated the sensing selectivity
performances (interferences) with other chemicals like acetone,
dichloromethane, methanol, chloroform, ethanol, 4ꢀnitrophenol,
methanol, propanol, and butanol (Figure 8a). Ethanol exhibited the
maximum current response by IꢀV system using CuOꢀFe O NCs
2 3
fabricated microꢀchip electrodes. Therefore, it was specific towards
ethanol compared to all other chemicals. Current responses (at
the CuOꢀFe O NCs/µꢀchip layer, it oxidized to carbon dioxide and
2 3
ꢀ
water by releasing free electrons (6e ) in the conduction band, which
is expressed through the following reactions (x).
ꢀ
ꢀ
CH
3
CH
2
OH(ads) + 6O (ads) →2CO
2
+ 3H
2
O + 6e (C.B.)(x)
In the reaction system, these reactions referred to oxidation
+
0.5V) of all inferring analytes converted into percentile (%
of the reducing carriers. This method is enhanced the carrier
concentration and consequently decreased the resistance on adjacent
reducing analytes. The elimination of ionosorbed oxygen amplified
the electron concentration onto CuOꢀFe
the surface conductance is increased in the film [58]. The reducing
analyte (ethanol) gives electrons to CuOꢀFe O NCs/µꢀchip surface.
Consequently, resistance is reduced, and hence the conductance is
increased. This is the cause why the analyte response (current)
amplifies with increasing potential. Thus produced electrons
responses) by deducting the blank current (reading only in PBS
system) are calculated and presented in Figure 8b. By deducting the
current value of blank solution, it was found the current value less
than 10% for all chemicals (acetone 4.1%; dichloromethane 3.7%;
chloroform 4.3%; 4ꢀnitrophenol 2.7%; methanol 3.5%, propyl
alcohol 8.6%, butanol 7.4%, and isoꢀpropyl alcohol 5.4%, and blank
2 3
O NCs/µꢀchip and hence
2
3
0
%) compared to target ethanol (90.0%). Therefore, it is clearly
demonstrated the sensor is most selective towards ethanol compared
with other chemicals.
contribute to rapid increase in conductance of the thick CuOꢀFe
2 3
O
NCs/µꢀchip film. The CuOꢀFe NCs unusual regions dispersed on
2
O
3
the surface would progress the capability of nanomaterial to absorb
more oxygen species giving high resistance in air ambient, which is
presented in Figure 7.
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Journal Name
Range
LOD
ꢀꢀ
e
,
LDR
Pote
ntial
3
.08
µAm
M
cm
Ni/Pt/Ti
ampe
rome
try
ꢀꢀ
−1
ꢀꢀ
ꢀꢀ
[60]
[61]
[62]
[63]
[64]
−2
Niꢀdoped
2.3148
µA
1
.0nM
SnO
2
0.84
40
10.0
s
IꢀV
~1.0m
−2
0.6 nM
nanostru
cture
cm m
M
−1
M
Pote
ntial
ampe
rome
try
Pd–
Ni/SiNW
s
0.76
mAm
0.99
70
10.0
µM
ꢀꢀ
−1
ꢀꢀ
M cm
−2
electrode
ZnOꢀ
2.1949
µA
cm−2
mM−1
1
.7m
CeO
2
0.94
63
0.6±0.0 10.0
IꢀV
M~1.7
M
Nanopart
icles
5 mM
s
Cycli
c
volta
mme
try
RuOꢀ
modified
Ni
4.92
100~1
000
ppm
µApp
13.0
s
Figure 8. IꢀV responses of CuOꢀFe
2
O
3
NCs coated µꢀchip are
ꢀꢀ
ꢀꢀ
ꢀ
1
ꢀ
m cm
presented for ethanol sensors (a) selectivity, (b) Current responses of
analytes at +0.5V (Presented in percentage), (c) control experiment,
and (d) reproducibility study. Ethanol and other chemicals
2
electrode
0
.92
CeO
2
0.17m
M~0.1
7M
0.124±
0.010
mM
ꢁ
Acm
0.74
58
10.0
s
concentration are taken as 0.1µM for selectivity study. Delay time: nanopart
IꢀV
[65]
[66]
[67]
−
2
−
m1M
1.0s. Potential range: 0 to +1.5V.
icles
Alꢀdoped
ZnO
nanomat
erial
1000
ppm
ethano
l
IꢀV
meth
od
Up to
3000p
pm
A control experiment was performed with the various
nanomaterial fabricated microchip using individually Fe O CuO,
∼8.0
ꢀꢀ
ꢀꢀ
2
3,
s
and CuOꢀFe
method (Figure 8c). A significant enhancement of current responses
was observed by CuOꢀFe NCs/chip compared to undoped Fe
and CuO individually. To investigate the reproducibly and storage
stabilities, IꢀV response for CuOꢀFe NCs coated µꢀchip sensor
was examined (up to 2 weeks). After each experiment, the fabricated
CuOꢀFe NCs/µꢀchip substrate was washed gently and observed
2 3
O NCs at 0.001mM analytes concentration by IꢀV
~0.972
2
CuO
nanoshee
ts
2
O
3
2
O
3
up to
0.78
06
0.143
mM
10.0
s
IꢀV
IꢀV
–
1
.7M
ꢁAcm
mM
2
–1
2
O
3
Smꢀ
Doped
2.1991
1.0nM
~10.0
mM
2
O
3
±0.10
0.90
65
0.63±0. 10.0
Co
3
O
4
ꢀ
[68]
[69]
ꢁ
Acm
02 nM
s
that the current response was not significantly decreased (Figure 8d).
The sensitivity was retained almost same of initial sensitivity up to
Nanoker
nels
2
ꢀ1
mM
st
nd
week (1 to 2 week), after that the response of the fabricated
electrode gradually decreased. series of six successive
measurements of 0.1µM ethanol in solution yielded a good
reproducible signal at CuOꢀFe NCs/µꢀchip sensor in different
5.845
uA
Sb
2
O
3
ꢀ
0.17m
M~0.8
5M
0.11±0.
02
mM
A
0.99
89
10.0
s
ZnO
MFs
IꢀV
ꢀ
cm
2
ꢀ1
mM
2 3
O
7
.258
conditions with a relative standard deviation (RSD) of 3.1%. The
sensorꢀtoꢀsensor and runꢀtoꢀrun repeatability for 0.1µM ethanol
CuOꢀ
Fe
NCs
0.1nM
~0.1m
M
This
wor
k
uA
0.99
37
0.087
nM
10.0
s
2
O
3
IꢀV
ꢀ
cm
detection were found to be 1.8% using CuOꢀFe
2
O
3
NCs/µꢀchip. To
2
ꢀ1
mM
investigate the longꢀterm storage stabilities, the response for the NCs
sensor was determined with the respect to the storing time. The longꢀ
term storing stability of the CuOꢀFe
investigated significantly at room conditions. The sensitivity retained
2% of initial sensitivity for several days. The above results clearly
2 3
O NCs/µꢀchip sensor was
Conclusions
9
CuOꢀFe O NCs were synthesized by easy, simple,
2 3
suggested that the fabricated sensor can be used for several weeks efficient, reliable, and economical approaches using active reducing
without any significant loss in sensitivity. The dynamic response agents. The optical, elemental, structural, and morphological
(0.1 nM to 0.1 mM) of the sensor was investigated from the practical properties were investigated by FTIR, XRD, XEDS, XPS, FESEM,
concentration variation curve. The sensor response time is TEM, DLS, and UVꢀvisible techniques. CuOꢀFe O NCs/µꢀchip was
2
3
mentioned and investigated using this sensor system at room prepared by simple fabrication technique and displayed higher
conditions. In Table 1, it is compared the performances for ethanol sensitivity for chemical sensing. NCs/µꢀchips were efficiently
chemical detection based various modified electrode materials [60ꢀ prepared for sensitive and selective ethanol sensor based on doped
6
9]. It exhibits the higher sensitivity using CuOꢀFe O NCs/chip CuOꢀFe O NCs embedded chips with conducting coating binders.
2 3
2 3
compared other nanomaterials fabricated electrodes with the similar The analytical performances of fabricated ethanol NCs sensors were
target analytes.
excellent in terms of sensitivity, detection limit, linear dynamic
ranges, and in short response time. CuOꢀFe NCs/µꢀchips were
exhibited higherꢀsensitivity (∼7.258 uAcm mM ) and lowerꢀ
detection limit (∼0.087±0.02 nM) with good linearity in short
response time, which efficiently utilized as chemical sensor for
ethanol onto tiny µꢀchips. This novel approach is introduced a wellꢀ
2
O
3
ꢀ
2
ꢀ1
Table 1: Comparison the performances for ethanol detection based
on various nanomaterials fabricated sensor.
Linea
r
Dyna
mic
Limit
of
Detecti
Res
pon
se
Line
Met
hods
Sensit
ivity
Materials
arity
Ref
2
,
r
on,
Tim
8
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organized route of efficient chemical sensor development for
environmental pollutants and healthꢀcare fields in broad scale.
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