Ligand replacement induced chemiluminescence for selective detection of an organophosphorus pesticide using bifunctional Au-Fe3O4 dumbbell-like nanoparticles

Article abstract of DOI:10.1039/c4cc07430k

A facile ligand replacement induced chemiluminescence method is developed for selective detection of the organophosphorus pesticide parathion-methyl based on the use of bifunctional Au-Fe₃O₄ dumbbell-like nanoparticles to overcome th

Full text of DOI:10.1039/c4cc07430k

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Ligand replacement induced chemiluminescence
for selective detection of an organophosphorus
Cite this:DOI: 10.1039/c4cc07430k
pesticide using bifunctional Au–Fe O4
dumbbell-like nanoparticles†
3
Received 20th September 2014,
Accepted 16th October 2014
a
ab
a
a
a
Jian Zhang, Jianping Wang, Liang Yang, Bianhua Liu, Guijian Guan,
DOI: 10.1039/c4cc07430k
a
a
Changlong Jiang* and Zhongping Zhang*
www.rsc.org/chemcomm
A facile ligand replacement induced chemiluminescence method is for insect and disease eradication, but they also cause wide-
developed for selective detection of the organophosphorus pesticide spread residues in food products and contamination of the
1
0–12
parathion-methyl based on the use of bifunctional Au–Fe
like nanoparticles to overcome the interference from coexisting cannot be detected by the traditional luminol–H
substances in a real sample. because there are no redox groups in these molecules, such
3
O
4
dumbbell- environment.
Most of the organophosphorus compounds
2 2
O
CL system
5a,13,14
as –NH
2
, –OH and –SH groups.
In this paper, we report a
As a facile, sensitive, and cost-effective analytical technique, chemi- surface ligand replacement induced CL switch-on mechanism
luminescence (CL) has widely been investigated for chemical for detection of the organophosphorus pesticide parathion-
analyses, biological assays, clinical diagnoses, and environmental methyl (PM) with high sensitivity and selectivity, based on
detection due to its absence of an unwanted excitation light source, bifunctional Au–Fe O DBNPs. The Au–Fe O DBNPs have been
3
4
3 4
1
–3
low noise signals, and wide linear dynamic range. However, prepared by thermal decomposition of an iron–oleate complex
classical CL systems have very low efficiency for converting in the presence of 12 nm Au NPs. The DBNPs significantly
chemical energy into light, it is very urgent to improve their CL enhanced the CL signals by catalyzing the decomposition of
efficiency in order to give an intense emission intensity for H O into superoxide anions and hydroxyl radicals at their
2
2
4
accurate quantitative detection. With the increasing availability of surface. As illustrated in Fig. 1, the CL signals could be quenched
nanomaterials, various nanocatalysts such as noble metal nano- after modification of the surface of the Au–Fe O DBNPs with
3
4
particles, metal oxide nanostructures and carbon-based nano- methionine. However, the quenching effect can be effectively
materials have been introduced into CL systems for the enhancement inhibited by replacement of the methionine through a specific
5–7
of the CL signals by several to tens of times. Although, these binding reaction of the hydrolyzate of parathion-methyl on
conventional single-component catalysts could be used for enhance- the surface of Au–Fe O DBNPs and a magnetic separation–
3
4
ment of the CL efficiency, the operating procedures are also tedious redispersion process. On the basis of this new finding, a CL
and time-consuming for in-field real sample detection, thus hamper- switch-on chemosensor was facilely established and would have
ing the further application of nanomaterials in CL systems. In
comparison, the discovery of bifunctional Au–Fe
nanoparticles (DBNPs), which contain both a magnetic (Fe
3
O
4
dumbbell-like
) and a
3 4
O
CL catalyst active (Au) unit, has driven a growing interest in low-
8
temperature catalysis and magnetic separation, not only to keep the
high catalytic activity for enhancement of the CL efficiency but also to
take advantage of superparamagnetic properties to overcome inter-
9
ference from environmental pollutants in real sample detection.
Organophosphorus compounds are the most widely used
pesticides in the agricultural field due to their high effectiveness
a
Institute of Intelligent Machines, Chinese Academy of Sciences, Hefei, Anhui,
Fig. 1 Illustration of the CL switch-on mechanism for selective detection
of PM molecules. The CL of the luminol–H –DBNPs system is first quenched
by the coordination of methionine to the surface of the Au–Fe DBNPs and
2
30031, China. E-mail: cljiang@iim.ac.cn, zpzhang@iim.ac.cn
2 2
O
b
Department of Chemistry, University of Science & Technology of China, Hefei,
Anhui, 230026, China
3 4
O
subsequently switched on by the replacement of the methionine with
dimethylphosphorothioate (DMP) and combining with a magnetic separation–
redispersion process in a basic system.
†
Electronic supplementary information (ESI) available. See DOI: 10.1039/
c4cc07430k
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two unique advantages in CL detection: (1) the selectivity is CL signal intensity could be amplified by at least 5 times (see
determined by the coordination capacity of the organophos- Fig. S2, ESI†). Meanwhile, the maximum emission wavelength of
phorus pesticide molecules on the surface of Au–Fe O DBNPs, the CL spectrum was B425 nm, which clearly indicated that the
3
4
therefore, the novel sensing concept can be used to sensitively luminophor was still the excited state 3-aminophthalate anions.
detect nonredox targets without the need for costly antibodies or Therefore, the use of Au–Fe O DBNPs did not lead to the
3
4
enzymes, or any additional techniques; (2) the superparamagnetic generation of a new luminophor for this CL system. The enhanced
properties of the Au–Fe DBNPs provide a simple magnetic CL signals were thus ascribed to the catalysis by the Au–Fe
separation approach to attain interference-free measurements for DBNPs. In order to investigate the effect of Au–Fe DBNPs on
the improvement of the CL intensity, a series of experiments was
DBNPs were synthesized using performed (Fig. 2D). Under the same conditions, the catalytic CL
3
O
4
3 4
O
3 4
O
real sample detection.
Water-soluble Au–Fe
3 4
O
Wu’s method with minor modifications for achieving the high activity of Fe O and Au nanoparticles was 35.4% and 41.9% of
3
4
CL catalytic activity. Fig. 2A presents representative transmission that of the Au–Fe O DBNPs, respectively. Similarly, when a
3
4
electron microscopy (TEM) images of the as-prepared Au–Fe O
mixture of Fe O and Au NPs with the same content as the
3 4
3
4
DBNPs consisting of 12 nm Au NPs and 18 nm Fe
NPs appear black and the Fe NPs are a light colour in the was only 48.9% of that for the DBNPs nanostructure. From the
image because Au NPs have a higher electron density and allow above analyses, the CL-enhancing phenomena of the luminol–
3 4 3 4
O NPs. The Au Au–Fe O DBNPs was used as the catalyst, its catalytic activity
3 4
O
1
5
fewer electrons to transmit. The crystallinity of the Au–Fe
O
3 4
2 2 3 4
H O system by Au–Fe O DBNPs might result from the special
DBNPs was characterized by XRD (Fig. 2B). The position and electron structure in the composites. It has been reported that
relative intensity of all the diffraction peaks match well with coupling Pt NPs with Fe O NPs in dumbbell-like Pt–Fe O NPs
3
4
3 4
standard inverse spinel structured Fe O (Joint Committee on increased the catalytic activity of Pt NPs towards the redox reaction
3
4
Powder Diffraction Standards (JCPDS) card no. 03-0863) and face- and the catalytic enhancement was proposed to arise from partial
centered cubic (fcc) Au (JCPDS card no. 01-1174), and the results electron transfer from Fe to Pt at the nanoscale interface,
indicate that the products have good crystallinity. Like Fe NPs, improving O adsorption and activation on the Pt surface adjacent
the hysteresis loop measurements show that Au–Fe
3 4
O
3
O
4
2
6–18
1
3
O
4
DBNPs to Fe
are super- electronic structure at the interface which may accelerate electron
paramagnetic at room temperature (Fig. 2C). Thus, the Au–Fe transfer, facilitate H adsorption and catalyze the decomposi-
DBNPs could be quickly separated from a suspension under an tion of H O into oxygen-related radicals such as the superoxide
3 4
O .
3 4
In the present system, Au–Fe O DBNPs changed the
À1
with a saturation moment reaching 26 emu g
3
O
4
2 2
O
2
2
ꢀ
À
ꢀ
external magnetic field, providing a rapid method to overcome the radical anion O and the hydroxyl radical OH. The resultant
2
interference of coexisting substances in a real sample. When oxygen-related radicals further oxidize luminol in basic media to
adding the Au–Fe
3
O
4
DBNPs into the luminol–H
2
O
2
solution, the produce a strong CL emission (see Fig. S6, ESI†). Thus, these
characteristics will provide Au–Fe DBNPs with versatility and
power as a CL enhancer, sensing probe, and separation tool.
When the Au–Fe DBNPs were mixed with methionine
3 4
O
9b
3 4
O
solution, the methionine was thus bound onto the surface of
À
the Au–Fe O DBNPs through the COO bond coordination
3
4
effect. Meanwhile, the CL of the luminol–H O –DBNPs was
2
2
quenched due to the reducing groups –NH and –SCH3 of
2
1
9
methionine. Fig. 3A shows the CL quenching behaviour due
to the modification of methionine onto the surface of Au–Fe
3 4
O
DBNPs. The CL intensity decreased gradually upon the addition
of methionine, and the CL was nearly completely quenched at
a concentration of 50 mM. The quenching process follows a
nonlinear behaviour and shows a saturation concentration of
methionine. Methionine is well-known as a radical scavenger
and consequently quenches the CL signals from the luminol–
H
2
O
2
–DBNPs system due to the loss of oxygen-related radicals.
3 4
On the other hand, methionine may cooperate with Au–Fe O
DBNPs to reduce the active surface area, interrupting the
formation of luminol radicals and hydroxyl radicals taking
place on the surface of nanoparticles. The TEM images of the
new DBNPs, the maximum emission CL wavelength and the
shape of the emission spectra are still retained, which implies
that the methionine ligand cannot alter the size and size
distribution of the DBNPs but can only reduce the CL intensity.
Fig. 2 (A) Typical TEM image of Au–Fe
3
O
4
DBNPs in water. (B) XRD of the
DBNPs. (C) Room-temperature magnetization curve for the
DBNPs. (Inset: photos of Au–Fe DBNPs in water (a) and with
Au–Fe
Au–Fe
3
3
O
O
4
4
3
O
4
3 4
Therefore, a methionine–Au–Fe O dumbbell-like nanoparticle
a magnet (b).) (D) The enhancement effectiveness of various nanoparticles
on luminol–H CL system.
2
O
2
(me–Au–Fe
3
O
4
DBNP) probe can be constructed by the modification
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do not have any direct effect on pure Au–Fe
3
O
4
DBNPs and the
luminol–H O CL system. To understand the mechanism of CL
2 2
switching, we studied in detail the interaction between DMP
and me–Au–Fe O DBNPs through the infrared spectrum,
3
4
which further confirmed that DMP bonds to the nanocrystal
surface in place of methionine. Fig. S8 (ESI†) is the infrared
spectrum before and after the surface modification of Au–Fe O
3 4
DBNPs with methionine and replacement with DMP ligand.
À1
The absorption bands at 1245 and 1508 cm in the infrared
spectrum are assigned to C–N bond stretching vibration and
deformation of the –NH2 group of the methionine on the
À1
surface of the Au–Fe O DBNPs, the peak at 1391 cm is from
3
4
the asymmetric deformation vibration mode of the –CH
groups. After DMP replacement of the methionine on the
3
2
3
surface of the Au–Fe
characteristic absorption bands (1508 cm ) disappear. Mean-
while, two new bands (1154 and 950 cm ) appeared, which
3
O
4
DBNPs, the methionine molecule’s
À1
À1
were attributed to the SQP and P–O–Fe stretching vibrations of
2
4
the organophosphorus pesticide.
To better understand the mechanism of the CL sensor, the
CL switch-on selectivity for various pesticides was determined
using four typical pesticide structures. As shown in Fig. 4, only
Fig. 3 (A) CL quenching of a luminol–H
2
O
2
–DBNPs system upon the
and methionine
and I are the CL intensity in the absence and
addition of methionine. (B) The relationship between I/I
concentration (where I
0
0
presence of methionine, respectively). (C) CL enhancement of the me–Au– PM, with a phosphorothioate moiety, was able to switch-on the
Fe DBNPs probe in a luminol–H
system with the addition of PM. (D) CL of the probe and resulted in a remarkable CL enhancement.
The relationship between I/I and PM concentration (where I and I are the
O
3 4
2 2
O
0
0
Although the other organophosphorus pesticides, methamidophos
MP), profenofos (PF) and ethoprophos (EP), can also be hydrolyzed
into organophosphorus moieties with a PQO bond in basic media,
CL intensity before and after methionine on the surface of the Au–Fe
3 4
O
(
DBNPs was replaced with a DMP ligand, respectively).
these moieties are very weak coordinative ligands that are not able
of methionine onto the surface of DBNPs. This probe shows to replace methionine on the surface of the Au–Fe O4 DBNPs.
3
an extremely weak CL intensity compared with that of the bare Therefore, the addition of these three pesticides did not cause any
Au–Fe O DBNPs at the same concentration level in the luminol– change in the CL intensity from that of the blank sample. This
3 4
H
2
O
2
CL system. The weak CL of the probe stays fairly stable over indicates that the PQS double bond, but not the P–S single bond,
À
a relatively long time. Thus, the CL of the probe will switch on if COO or PQO double bond, can replace methionine to form a
the surface methionine ligands are replaced by an appropriate more stable complex at the surface of the Au–Fe
3 4
O DBNPs.
analyte, which is expected for ultrasensitive CL detection. Therefore, the me–Au–Fe O DBNP probe shows very high specifi-
3
4
In a strongly basic system, parathion-methyl (PM) molecules city for the detection of parathion-methyl pesticides by a CL turn on
are rapidly hydrolysed to dimethylphosphorothioate (DMP) and mechanism through surface ligand replacement.
2
0
p-nitrophenol (PNP). The DMP moiety with a PQS bond
The utility of the chemosensor is largely dependent upon the
exhibits a very strong coordinative ability with many metal direct detection of ultratrace PM residues in a real sample. However,
2
1
ions. Accordingly, the methionine ligands at the surface of for detection of analytes in a real sample, general CL techniques
the DBNPs are rapidly replaced by strongly binding DMP either show the sample as undetectable or need complicated sample
ligands, to form a more stable complex because the PQS bond pretreatments, such as solid phase extraction (SPE) and high
has a stronger coordinative ability to Au–Fe O DBNPs than the performance liquid chromatography (HPLC). In this work, we chose
3
4
À
22
COO bond. Then, combined with the magnetic separation–
redispersion process for overcoming the methionine inter-
ference effect, a significant CL enhancement can be clearly
observed with an increase in PM concentration. Fig. 3C shows
that about a 12-fold CL enhancement was measured when the
concentration of PM reached 100 mM. Even at a concentration
as low as 10 nM, CL enhancement can be clearly observed,
demonstrating an ultrasensitive response to the hydrolyzate
DMP of the PM pesticide. In the absence of methionine,
3 4
however, the direct addition of PM to a pure Au–Fe O DBNPs
solution with basicity does not result in any CL enhancement
and even causes a slight quench of the strong CL. This also
Fig. 4 The CL switch-on selectivity for various OP pesticides (100 mM):
parathion-methyl (PM), ethoprophos (EP), 2,4-dichlorophenoxyacetic acid
reveals that the phosphorothioate analyte and its hydrolyzates (2,4-D), profenofos (PF), and methamidophos (MP).
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green tea as the test sample. As shown in Fig. S9 (ESI†) the me–Au–
Fe O DBNPs were first dispersed in real samples spiked with PM
3 4
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molecules at three different concentrations (100, 200, 400 nM).
Through the ligand replacement reaction, most of the hydrolyzate of
the PM molecules will bind on the me–Au–Fe O DBNPs in the
4
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4
5
basic system. When a small magnet was put near the vial, the
DBNPs with DMP were drawn to the wall of the vial. After discarding
the remaining sample solutions, the reddish brown aggregates were
redispersed in a certain amount of water for measuring of the CL
signals. The above separation–redispersion procedure was repeated
two times, and noninterference detection was achieved. The
recovery for an added known amount of PM in the green tea
samples was in the range of 95–104% (Fig. S9C, ESI†), which
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In summary, this work has proposed a sample selective CL
switch-on chemosensor by the modification of the radical scaven-
ger methionine on the surface of Au–Fe O DBNPs. The sensing
9
3
4
mechanism is based on our new findings that the replacement of
methionine ligands by the hydrolyzate of organophosphorothioate
pesticides and a magnetic separation–redispersion process for
inhibiting the scavenging of surface radicals, leads to the switch-
on of the CL. The CL switch-on chemosensor was used to
selectively detect the nonredox organophosphorothioate pesticide
molecule parathion-methyl and exhibited high anti-interference
in real samples after a simple magnetic separation. Moreover, the
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