Sensitive and selective colorimetric sensing of Fe3+ ion by using p-amino salicylic acid dithiocarbamate functionalized gold nanoparticles

Article abstract of DOI:10.1039/c3nj01468a

We have developed a selective and sensitive colorimetric method for determination of Fe³⁺ ion by using p-amino salicylic acid dithiocarbamate functionalized gold nanoparticles (DTC-PAS-Au NPs) as colorimetric probes. The DTC-PAS-Au NPs were characterized by FT-IR, ¹H NMR, UV-visible spectrometry, transmission electron microscopy (TEM), dynamic light scattering (DLS) and atomic force microscopic (AFM) techniques, respectively. The DTC-PAS-Au NPs are aggregated rapidly by addition of Fe³⁺ ions, yielding a color change from red to blue. The characteristic surface plasmon resonance (SPR) peak (520 nm) of DTC-PAS-Au NPs was shifted to longer wavelength, 700 nm, which confirms the ligand-to-metal charge transfer between DTC-PAS-Au NPs and Fe³⁺ ions. Under the optimal conditions, a good linear relationship (correlation coefficient R ² = 0.993) was obtained between the ratio of the extinction at 700 nm to that at 520 nm and the concentration of Fe³⁺ over the range of 40-80 μM, with a detection limit of 14.82 nM. The DTC-PAS-Au NPs acted as colorimetric sensors for the selective detection of Fe³⁺ ions in real samples (blood and urine samples).

Full text of DOI:10.1039/c3nj01468a

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Sensitive and selective colorimetric sensing of Fe3+
ion by using p-amino salicylic acid dithiocarbamate
functionalized gold nanoparticles†
Cite this: New J. Chem., 2014,
38, 1503
Vaibhavkumar N. Mehta,a Suresh Kumar Kailasa*a and Hui-Fen Wubc
We have developed a selective and sensitive colorimetric method for determination of Fe3+ ion by using
p-amino salicylic acid dithiocarbamate functionalized gold nanoparticles (DTC-PAS-Au NPs) as
colorimetric probes. The DTC-PAS-Au NPs were characterized by FT-IR, 1H NMR, UV-visible
spectrometry, transmission electron microscopy (TEM), dynamic light scattering (DLS) and atomic force
microscopic (AFM) techniques, respectively. The DTC-PAS-Au NPs are aggregated rapidly by addition of
Fe3+ ions, yielding a color change from red to blue. The characteristic surface plasmon resonance (SPR)
peak (520 nm) of DTC-PAS-Au NPs was shifted to longer wavelength, 700 nm, which confirms the
ligand-to-metal charge transfer between DTC-PAS-Au NPs and Fe3+ ions. Under the optimal conditions,
a good linear relationship (correlation coefficient R2 = 0.993) was obtained between the ratio of the
extinction at 700 nm to that at 520 nm and the concentration of Fe3+ over the range of 40–80 mM, with
a detection limit of 14.82 nM. The DTC-PAS-Au NPs acted as colorimetric sensors for the selective
detection of Fe3+ ions in real samples (blood and urine samples).
Received (in Montpellier, France)
23rd November 2013,
Accepted 7th December 2013
DOI: 10.1039/c3nj01468a
www.rsc.org/njc
coupled-plasma atomic emission spectrometry (ICP-AES),14
inductively coupled plasma mass spectrometry (ICPMS),15,16
Introduction
Development of novel colorimetric sensors has attracted signi- atomic absorption spectrometry (AAS)17 and voltammetry.18
ficant interest for selective and sensitive detection of metal ions However, these methods are expensive and require tedious
in environmental and biological samples.1–5 Iron is the most sample pretreatment procedures. Therefore, the development
abundant vital transition metal in both plants and the human of a facile, inexpensive, selective and in situ method that allows
body that plays a significant role in cellular metabolism, and real-time monitoring of metal species is a great challenge.
enzymatic catalysis. It acts as a carrier for oxygen and electron
In recent years, significant research efforts have been devoted
transports in hemoglobin and serves as a cofactor in many to the design and preparation of Au NPs as promising colori-
enzymatic reactions.6–10 However, excess amounts of Fe3+ ion metric probes for the analysis of a wide variety of molecules in
can cause damage to cellular lipids, nucleic acids and proteins. environmental and biological samples.19–22 The colorimetric
Furthermore, a deficiency of Fe3+ ion limits oxygen delivery to sensing approaches are based on their SPR spectral shift by a
cells and causes anemia, liver and kidney damage, diabetes, strong overlap between the plasmon fields of the nearby particles,
and heart disease.11–13 Therefore, the detection of Fe3+ ions has and the resulting color change from red to blue.23–25 This is due
become a matter of considerable interest in environmental and to the strong interactions between the tailored organic molecules
biological samples. Conventional Fe3+ assays are performed on the Au NPs and the target analytes, which allow Au NP-
by using several analytical techniques such as inductively induced aggregation with the analytes. Therefore, surface func-
tionalization of Au NPs plays a crucial role in increasing their
analytical applicability for detection of trace analytes with high
a Department of Applied Chemistry, S. V. National Institute of Technology,
selectivity and sensitivity.24,26 In this connection, dithiocarba-
Surat-395007, India. E-mail: sureshkumarchem@gmail.com, skk@ashd.svnit.ac.in;
mate molecular assembly on Au NPs has attracted significant
interest in the area of nanoanalytical science due to their easy
preparation and the very short interatomic distance between the
two sulfur atoms which facilitates a strong binding with the NP
surface.27 As a result, dithiocarbamate derivative functionalized
Au NPs have been used as selective probes for detection of
biomolecules,28 anions29 and cations.30,31
Fax: +91-261-2227334; Tel: +91-261-2201730
b Department of Chemistry and Center for Nanoscience and Nanotechnology,
Institute of Medical Science and Technology, Doctoral Degree Program in Marine
Biotechnology, National Sun Yat-Sen University, Kaohsiung, 804, Taiwan
c School of Pharmacy, College of Pharmacy, Kaohsiung Medical University,
Kaohsiung, 806, Taiwan
† Electronic supplementary information (ESI) available. See DOI: 10.1039/
c3nj01468a
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Research Committee, S. V. National Institute of Technology,
Surat, Gujarat, India.
Synthesis of DTC-PAS-Au NPs
Dithiocarbamate derivative of p-amino salicylic acid was syn-
thesized according to the method reported in the literature.32
Briefly, an equimolar mixture of p-amino salicylic acid and CS2
in ethanolic KOH (50 mL, 5%) and DMF (50 mL) was warmed at
45 1C for 30 minutes and then cooled. The reaction mixture was
acidified with dilute AcOH. The resulting solid product was
filtered and recrystallized from methanol as orange needles.
Citrate-capped Au NPs were prepared according to Frens’
method.33 Briefly, 100 mL of 1 mM HAuCl4 was taken into a
round-bottomed flask and then boiled under vigorous stirring
for 20 min. To this, 38.8 mM of trisodium citrate (10 mL) was
added rapidly into the reaction flask and the mixture was
stirred for another 15 min. The color of the solution changed
from pale yellow to deep red, confirming the formation
of Au NPs. The concentration of the Au NPs was calculated
according to Beer’s law by using an extinction coefficient
of ca. 108 MÀ1 cmÀ1 at 520 nm (ref. 34) and found to be
12.28 nM. To obtain DTC-PAS-Au NPs, 25 mL of 1 mM DTC-
PAS was added into 20 mL of Au NPs and then stirred for 1 h at
room temperature (ESI,† Fig. S1). The resulting Au NP solu-
tion was used for the colorimetric sensing of Fe3+ in biological
samples.
Scheme 1 Schematic representation for colorimetric sensing of Fe3+ by
using DTC-PAS-Au NPs as colorimetric probes.
In this paper, we explore the utility of DTC-PAS-Au NPs as a
colorimetric probe for the detection of Fe3+ in environmental
and biological samples. The DTC-PAS-Au NPs aggregated
rapidly by addition of Fe3+ ions, resulting in a color change
from red to blue, which is induced by ligand-to-metal charge
transfer between the –OH and –COOH groups of DTC-PAS-Au
NPs and Fe3+ (Scheme 1). This colorimetric probe opens up
new possibilities for developing analytical methods for the
monitoring of Fe3+ in biological samples without any sample
pretreatment procedure.
Detection of Fe3+ using DTC-PAS-Au NPs
A stock solution of ferric chloride (1 mM) was prepared by
dissolving ferric chloride in deionised water. For the detection of
Fe3+ by using the DTC-PAS-Au NPs, 100 mL of different concen-
trations of Fe3+ solution were added separately into a 1.5 mL of
DTC-PAS-Au NP solution, and the pH was adjusted to 6.0 by
using PBS buffer. The sample vials were vortexed for 30 s and the
color of the solution changed from red to purple then blue. The
resulting Au NPs UV-visible spectral changes were measured by
using a Maya Pro 2000 spectrophotometer. Furthermore, we also
Experimental
Chemicals and materials
Hydrogen tetrachloroaurate hydrate (HAuCl4ÁxH2O), p-amino evaluated the stability of Au NPs before and after functionaliza-
salicylic acid, metal salts (Zn(NO3)2Á6H2O, Mn(NO3)2Á4H2O, tion. It was noticed that citrate modified Au NPs are stable for
Co(NO3)2Á6H2O, Pb(NO3)2, Cd(NO3)2Á4H2O, Cu(NO3)2Á3H2O, 2 months and well agreed with the literature.35 At the same time,
Hg(NO3)2ÁH2O, FeCl2Á4H2O, Mg(NO3)2Á6H2O, NiSO4Á6H2O, DTC-PAS-Au NPs are stable for 3–4 weeks; after that there is a
FeCl3Á6H2O), phosphate-buffered saline (PBS), Tris-HCl (Tris) slight color change due to the electrostatic interactions and
and sodium acetate (NaAc) were obtained from Sigma-Aldrich, hydrogen bonding formation between DTC-PAS-Au NPs. How-
USA. Dimethyl formaldehyde (DMF) and carbon disulfide were ever, the rapid color change of DTC-PAS-Au NP solution (red to
purchased from Merck Ltd., India. Trisodium citrate dihydrate blue) was attributed to the DTC-PAS-Au NP aggregation induced
was purchased from SD Fine Chemicals Ltd., India. Blood and by Fe3+ ion (10–100 mM).
urine samples were collected from healthy volunteers. All
chemicals were of analytical grade and used without further
Instrumentation
purification. Milli-Q-purified water was used for the sample UV-visible spectra were measured with a Maya Pro 2000 spectro-
preparations. Caution: blood samples were obtained from photometer (Ocean Optics, USA) at room temperature. 1H NMR
Shivam Pathological Laboratory, Surat, Gujarat, India, which spectra were recorded on a Varian 400 MHz instrument. Fourier
is approved by All India Institute of Medical Sciences, transform infrared (FT-IR) spectra were recorded on a Perkin
New Delhi, India. The blood samples were collected by con- Elmer (FT-IR spectrum BX, Germany). Transmission electron
firming informed consent. All experiments were performed microscopy (TEM) images were taken on a Tecnai 20 (Philips,
in compliance with the relevant laws and institutional guide- Holland) at an acceleration voltage of 100 kV. DLS measurements
lines, and this study was also approved by the Institute were performed by using a Zetasizer Nano ZS90 (Malvern, UK).
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Results and discussion
Characterization of DTC-PAS-Au NPs
However, the proton peaks of DTC-PAS-Au NPs disappeared in
the spectrum of DTC-PAS-Au NPs, which confirms the change
in their chemical environment and the presence of water
molecules in the DTC-PAS-Au NPs (ESI† Fig. S3c).
The synthesized DTC-PAS-Au NPs were characterized by spectro-
1
scopic (UV-visible, FT-IR and H NMR) and microscopic (TEM,
It is well known that the average size of NPs can be estimated
by calculating the mean hydrodynamic diameter from the auto-
correlation function of the intensity of light scattered from the
particles via Brownian motion.39 Fig. 2a and b shows the DLS
data of bare Au NPs and DTC-PAS-Au NPs. It is observed that the
bare Au NPs are monodisperse with an average hydrodynamic
diameter of B10 nm. However, the hydrodynamic diameter of
Au NPs was increased to B43 nm due to surface modifications of
Au NPs with DTC-PAS (Fig. 2b). DTC-PAS molecules are bulky
and covalently attached onto the surface of the Au NPs, resulting
in an increase in their hydrodynamic diameter.40 Fig. 3a shows
the TEM image of DTC-PAS-Au NPs and the functionalized Au
NPs are well dispersed with an average size of B40 nm, which
agrees well with the DLS data. The DTC-PAS-Au NPs are spherical
in shape. Furthermore, we also studied the AFM of DTC-PAS-Au
NPs (Fig. 4a). This result indicates that the DTC-PAS-Au NPs are
not aggregated and can be used as colorimetric probes for
sensing of metal ions.
AFM and DLS) techniques. Fig. 1 shows the UV-visible spectra
of bare Au NPs and DTC-PAS-Au NPs. It can be noticed that the
characteristic SPR peak (520 nm) of Au NPs was slightly red-
shifted and the peak intensity was little decreased after func-
tionalization of the DTC-PAS molecules onto the surface of the
Au NPs. ESI† of Fig. S2 illustrates the typical FT-IR spectra of
pure p-amino salicylic acid, DTC-PAS and DTC-PAS-Au NPs.
FT-IR spectrum of pure p-amino salicylic acid shows the two
characteristic bands at 3495 and 3388 cmÀ1 corresponding to
–N–H asymmetric and symmetric stretching modes, respec-
tively. The strongest absorption peak at 1644 cmÀ1 belongs to
CQO stretching mode of COOH group in PAS. Fig. S2b of the
ESI† shows the FT-IR spectrum of DTC-PAS. In this spectrum,
C–S, –S–H and CS–NH group stretching vibrations were observed
at 1100, 2561 and 1228 cmÀ1, respectively. Importantly, it can be
noticed that the mercapto group (–SH) stretching and bending
modes were not observed at 2543–2550 cmÀ1 in the spectrum of
the DTC-PAS-Au NPs, confirming the new bond formation
between DTC-PAS and the Au NP surfaces (Fig. S2c of the ESI†).
These results revealed that the DTC-PAS molecules were success-
fully attached onto the surface of the Au NPs via a simple ‘‘zero-
length’’ covalent coupling.
DTC-PAS-Au NPs as colorimetric probes for sensing Fe3+ ions
To investigate the analytical application of DTC-PAS-Au NPs as
sensors for metal ions, various metal ions (Cu2+, Fe2+, Mg2+,
Mn2+, Hg2+, Zn2+, Ni2+, Co2+, Pb2+, Cd2+ and Fe3+, 500 mM) were
added into DTC-PAS-Au NP solutions (Fig. 5a). It can be observed
that there is a drastic decrease in the SPR peak of DTC-PAS-Au
NPs at 520 nm, and a new absorption peak is generated at
700 nm only with addition of Fe3+ ions, which clearly confirms
the DTC-PAS-Au NP-induced aggregation with Fe3+ ions (Fig. 5a).
This newly generated peak around 700 nm is attributed to the
coordinate covalent bonds between the –OH and –COOH groups
of the DTC-PAS-Au NPs and Fe3+, which leads to ligand-to-metal
charge transfer. As a result, the color of the DTC-PAS-Au NP
solution changed from red to blue, which can be observed with
the naked eye (Fig. 5b). This result strongly indicates that Fe3+
ions show a high ability to interact with the –OH and –COOH
groups of the DTC-PAS-Au NP surfaces, resulting in DTC-PAS-Au
NP-induced aggregations through electric dipole–dipole inter-
actions and coupling between the plasmon of neighboring
nanoparticles.26 ESI† Fig. S4 shows that the colorimetric
sensing ability of DTC-PAS-Au NPs with other metal species
was expressed by the ratio of absorption at 700 nm to that at
520 nm (A700nm/520nm), and indicates that DTC-PAS-Au NPs
showed higher selectivity towards Fe3+ than the other metal
species.
ESI† Fig. S3 shows the 1H NMR spectra of pure p-amino
salicylic acid, DTC-PAS and DTC-PAS-Au NPs. The 1H NMR
spectrum of pure p-amino salicylic acid shows multiplet peaks
at 6.0–7.0 ppm, which are assigned to the aromatic protons of
PAS. The peaks at 11.37 (singlet) ppm and 12.53 (singlet) ppm
corresponded to the –OH protons of PAS. The peak at 5.98
(doublet) ppm corresponds to the –NH2 protons of PAS. The
appearance of a new peak at B1.19 ppm confirms the proton
peak of the mercapto (–SH) group of DTC-PAS (ESI† Fig. S3b).
Sensing mechanism for Fe3+ ions
As shown in ESI† Fig. S1, p-amino salicylic acid contains amino
(–NH2), phenolic (–OH) and carboxylic acid groups (–COOH).
It is well known that the –NH2 group of PAS is already involved
in the preparation of DTC-PAS followed by their molecular
assembly onto the surfaces of Au NPs via a thiolate linkage
(–NH–CS2–Au NPs), which confirms the blocking of free –NH2
Fig. 1 UV-visible spectra of bare Au NPs (black line) and DTC-PAS-Au NPs
(red line). Inset picture shows bare Au NPs and DTC-PAS-Au NPs.
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Fig. 2 DLS of (a) bare Au NPs (b) DTC-PAS-Au NPs and (c) DTC-PAS-Au NPs induced aggregations with Fe3+ ions.
values of PAS are 1.79 and 3.92 respectively, these groups are
effectively coordinated with Fe3+ ions.37,38 Therefore, these
negatively charged groups (–OÀ and –COOÀ) can be effectively
form complexes with Fe3+, which can induce a higher degree of
DTC-PAS-Au NP aggregation.
Effect of pH
We investigated the effect of buffer pH on the colorimetric
sensing ability of DTC-PAS-Au NPs for Fe3+ ion detection. Fig. 6
shows the intensities of the extinction ratios (A700nm/520nm) of
DTC-PAS-Au NPs upon the addition of Fe3+ ions in PBS, Tris
and NaAc buffer systems pH from 2–10. Even though the
intensities of the extinction ratios of DTC-PAS-Au NP–Fe3+
Fig. 3 TEM images of (a) DTC-PAS-Au NPs and (b) DTC-PAS-Au NPs
induced aggregations with Fe3+ ions.
groups and avoids the complex formation of DTC-PAS-Au NPs solutions are good when using the three buffers at low pH 2–4,
with divalent metal ions (Fe2+, Zn2+, Cd2+).36 After function- this pH range is not suitable for colorimetric sensing of Au NPs.
alization of DTC-PAS with Au NPs, only –OH and –COOH are Au NPs surfaces can be neutralized at low pH (o4), which allows
available to form a complex with Fe3+ ions. These groups have Au NP self aggregation without addition of analytes. As shown in
negative charges when the pH is >4. Since the pKa1, and pKa2 Fig. 6, the extinction ratio (A700nm/520nm) of DTC-PAS-Au NP
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induced aggregation with Fe3+ ions reaches its maximum at
pH 6.0. This may be because DTC-PAS-Au NPs have negative
charges when the pH value is higher than 4.0, and this allows a
high degree of DTC-PAS-Au NP-induced aggregation with Fe3+
ions. Therefore, a pH of 6.0 of the PBS buffer solution was
selected.
Confirmation of DTC-PAS-Au NP-induced aggregation with
Fe3+ ions by DLS, TEM and AFM
In order to confirm the DTC-PAS-Au NP-induced aggregation
with Fe3+ ions, we studied DLS, TEM and AFM techniques. As
shown in Fig. 2c, the hydrodynamic diameter of DTC-PAS-Au
NPs was drastically increased to B412 nm by the addition of
Fe3+ ions, yielding the DTC-PAS-Au NP aggregation via the
complex formation between DTC-PAS-Au NPs and Fe3+ ions.
Fig. 3b shows the TEM image of DTC-PAS-Au NP induced
aggregation with Fe3+ ions. It can be seen that the morphology
and sizes of DTC-PAS-Au NPs were greatly influenced by the
addition of Fe3+, which results in a change in their state from
monodisperse to polydisperse. Furthermore, the aggregation
Fig. 4 AFM images of (a) DTC-PAS-Au NPs and (b) DTC-PAS-Au NPs
induced aggregations with Fe3+ ions.
Fig. 5 (a) UV-visible absorption spectra of DTC-PAS-Au NPs upon the addition of different metal ions (Cd2+, Co2+, Cu2+, Fe2+, Fe3+, Hg2+, Mg2+, Mn2+
Ni2+, Pb2+, Zn2+). (b) Photographic images of DTC-PAS-Au NPs in the presence of various metal ions.
,
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Quantification of Fe3+ by using DTC-PAS-Au NPs as colorimetric
probes
The potential of the DTC-PAS-Au NP based UV-visible spectro-
metric method was demonstrated for the quantification of
Fe3+ in aqueous samples as a model analytical problem. At
the optimized conditions, various concentrations (10 to 100 mM)
of Fe3+ were added into a DTC-PAS-Au NP solution separately
and their UV-visible spectra were measured. As shown in Fig. 7b,
the color of the Au NPs solutions gradually changed from red to
purple and then blue upon increasing concentration of Fe3+
ions, which could be observed by the naked eye. It can be
observed that with the increasing concentrations of Fe3+ ions,
the SPR peak of Au NPs at 520 nm decreased gradually, and
along with the increase a new SPR peak appeared at 700 nm
(Fig. 7a). Furthermore, a calibration graph was constructed
between the UV-vis extinction ratio (A700nm/A520nm) and concen-
Fig. 6 The extinction ratio (A700nm/A520nm) of DTC-PAS-Au NP induced
aggregation with Fe3+ ions by using different buffers (PBS, Tris and NaAc) in
the pH range of 2–10.
of DTC-PAS-Au NPs with Fe3+ was also verified by using tration of Fe3+ ions ranging from 40 to 80 mM ( y = 1.923x À 2.846),
AFM. Fig. 4b shows the AFM image of DTC-PAS-Au NP induced which can be used for the quantification of Fe3+ with a
aggregation with Fe3+ ions in three dimensions. This result correlation coefficient of 0.993 (Fig. 8), and the detection limit
confirms the DTC-PAS-Au NP induced aggregation with Fe3+ (LOD) is 14.82 nM, respectively. In addition, we also compared
ions.
the sensitivity of the present method with the reported NP-based
Fig. 7 (a) UV-visible spectra of DTC-PAS-Au NP solutions with increasing concentrations of Fe3+ in the range of 10–100 mM. (b) Visual color change of
DTC-PAS-Au NPs with different concentrations of Fe3+ ranging from 10 mM to 100 mM.
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Table 1 Comparison of DTC-PAS-Au NPs as colorimetric sensor for the detection of Fe3+ with the reported methods
Nanoparticles
Capping agent
Size (nm)
LOD (M)
Detection method
Ref.
Au NPs
Au NPs
Au NCs
Ag NPs
Pyrophosphate
—
L-3,4-Dihydroxyphenylalanine
Pyridyl-appended calix[4]arene
p-STEC4
—
—
15
—
2–6
10
52
3.8
1–4
10
5.6 Â 10À6
50 ppm
UV-visible
UV-visible
Fluorescence
UV-visible
UV-visible
Fluorescence
Fluorescence
UV-visible
41
42
43
44
45
46
47
3.5 Â 10À6
125 Â 10À6
9.4 Â 10À9
0.32 Â 10À6
—
Ag NPs
Carbon dots
Polymer dots
Au NPs
DTC-PAS
14.82 Â 10À9
Present study
UV-visible and fluorescence methods for detection of Fe3+ ions
(Table 1). It indicates that the present method showed higher
sensitivity than the NPs-based UV-visible41,42,44,45 and fluores-
cence43,46,47 methods. Therefore, this analytical system exploits
the advantages of DTC-PAS-Au NPs as colorimetric sensors for
the detection of Fe3+ by using UV-visible spectrometry.
Interference studies
To demonstrate the selectivity of DTC-PAS-Au NPs for Fe3+ ions,
competitive experiments were carried out in the presence of
other metal ions (Cu2+, Fe2+, Mg2+, Mn2+, Hg2+, Zn2+, Ni2+, Co2+,
Pb2+ and Cd2+, 100 mM) for detection of Fe3+ ions. It can be
noticed that the SPR peak shift occurred only with the mixed
solution of metal ions that contained Fe3+ ions, resulting in a
visible color change from red to blue, which was just the same as
for sole addition of Fe3+ ions into a Au NP solution (ESI† Fig. S5).
This result clearly indicates that this method was free from
Fig. 8 Calibration graph was constructed in response to the UV-visible interference from other metal ions, which should be noted for
extinction of DTC-PAC-Au NPs solution upon the addition of Fe3+ ion
practical application to Fe3+ assays in real samples.
(40–80 mM).
Application of DTC-PAS-Au NPs for the analysis of Fe3+ ion in
blood and urine samples
Table 2 DTC-PAS-Au NPs as colorimetric sensor for the analysis of Fe3+
in spiked blood and urine samples
The proposed DTC-PAS-Au NPs sensor has been applied to
detect Fe3+ ion in blood and urine samples. For this, human
serum and urine samples were collected from healthy adult
volunteers. The collected blood samples were centrifuged at
5000 rpm for 15 min. The collected supernatant (serum) were
diluted 100-fold with ultrapure water and used for further analysis.
Urine samples were filtered through a 0.45 mm membrane and
diluted 100-fold with ultrapure water. The above blood and urine
samples were spiked with different known concentrations of Fe3+
(10, 50 and 100 mM) and then the concentration of Fe3+ ions was
Added
(mM)
Found
(mM)
Recovery
(%)
RSD (%)
(n = 3)
Sample
Blood sample
10
50
100
9.50
49.03
98.76
95.00
98.06
98.76
1.17
1.18
0.88
Urine sample
10
50
100
9.22
47.48
98.27
92.20
94.96
98.27
1.21
1.02
0.90
Table 3 Precision and accuracy of the present method for the analysis of Fe3+ in spiked aqueous and urine samples
Intra-day
Inter-day
Found
Found
Known
concentration (mM)
concentrationa (mM)
RSDb (%)
Accuracyc
concentrationa(mM)
RSDb (%)
Accuracyc
Sample
Spiked water
100
50
98.32 Æ 0.0285
49.08 Æ 0.0115
3.00
4.35
À0.0168
À0.0184
98.65 Æ 0.0251
50.81 Æ 0.0101
2.85
4.29
À0.0135
+0.0162
Spiked urine
100
50
101.25 Æ 0.044
3.95
4.31
+0.0125
À0.0462
97.39 Æ 0.0416
3.70
4.05
À0.0261
47.69 Æ 0.0098
51.18 Æ 0.0105
+0.0236
a
b
c
Mean Æ standard deviation (n = 3). Relative standard deviation. Accuracy was calculated from (found concentration À known concentration)/
known concentration.
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estimated by the aforesaid procedure. ESI† Fig. S6 shows the
UV-visible spectra for the spiked blood serum and urine sam-
ples at three different concentrations (10, 50 and 100 mM). The
amount of Fe3+ ion was estimated by using the present method
and the data obtained were shown in Table 2. This result
indicates that this method showed good recoveries in the range
of 95–98.76% and 92.2–98.27% for blood and urine samples,
with relative standard deviation (%RSD) values in the range of
0.88–1.17% and 0.90–1.21% for blood and urine samples, respec-
tively. This indicates the present method exhibits good precision
for the analysis of Fe3+ in blood and urine samples. In order to
estimate the accuracy of the present method, we studied intra- and
inter-day precision and accuracy of the method for the analysis of
Fe3+ ion in spiked aqueous and urine samples. As shown in
Table 3, this method shows good precision (RSD o 4.35%) and
accuracy (À0.0462 to +0.0236) for the analysis of Fe3+ ions in
spiked aqueous urine samples. ESI† Fig. S7 shows the measured
intra- and inter-day UV-visible spectra DTC-PAS-Au NPs upon the
addition of Fe3+ ions (100 mM). These results indicate the reliability
of DTC-PAS-Au NPs as ideal colorimetric probes for Fe3+ determi-
nation in real samples.
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Conclusions
In summary, we present a simple, selective and sensitive DTC-PAS-
Au NP-based UV-visible method for on-site and real-time detection of
Fe3+ in biological samples. The Fe3+ ion-induced aggregates of DTC-
PAS-Au NPs were characterized by UV-visible spectroscopy, DLS,
TEM and AFM, respectively. The extinction ratio A700nm/A520nm is
linear with the concentration of Fe3+ ranging from 40 mM to 80 mM,
which provides a sensitive detection of Fe3+ ions with a detection
limit of 14.82 nM. This method was free from interference from
other metal ions and exhibited good precision and accuracy for
detection of Fe3+ ions in aqueous and urine samples. Therefore,
DTC-PAS-Au NPs can be utilized as a novel colorimetric sensor for
the rapid, selective and real-time in situ detection of Fe3+ in biological
samples, and it offers great potential for practical applications to
Fe3+ ion assays in environmental and biological samples.
Acknowledgements
We gratefully acknowledge the Director, SVNIT for providing all
the facilities to carry out this work. We also thank the Depart-
ment of Science and Technology, India for providing a UV-visible
spectrophotometer for this analysis. We would like to thank
Mr Vikas Patel, SICART, Anand, and V. V. Nagar for their
assistance in TEM data. The authors thank Shivam Pathological
Laboratory, Surat, Gujarat, India for providing blood samples.
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