FRET-based Solid-state Luminescent Glyphosate Sensor Using Calixarene-grafted Ruthenium(II)bipyridine Doped Silica Nanoparticles

Article abstract of DOI:10.1002/cphc.201800447

Calixarene-functionalized luminescent nanoparticles were successfully fabricated for the FRET-based selective and sensitive detection of the organophosphorus pesticide glyphosate (GP). p-Tert-butylcalix[4]arene was grafted on the surface of [Ru(bpy)₃]²⁺ incorporated SiNps to produce self-assembled nanosensors (RSC). FRET was switched on in the presence of GP by means of energy transfer due to binding with p-tert-butylcalix[4]arene grafted on the surface of the RSC. The FRET efficiency of the GP-RSC system was increased gradually with the addition of GP. The FRET efficiency was evaluated as 87.69 % and a high binding affinity was established by the binding constant value, 1.16×10⁷ M^?1, using a Langmuir binding isotherm plot. The estimated limit of detection (LOD) was 7.91×10^?7 M, which was lower than the Environmental Protection Agency (EPA) recommendation. The probe also effectively responds to real sample analysis. The sensitivity and selectivity was realized due to the efficient FRET towards the fluorescence properties of the [Ru(bpy)₃]²⁺ complex.

Full text of DOI:10.1002/cphc.201800447

Accepted Article
Title: FRET based solid state luminescent sensor for glyphosate
using calixarene grafted ruthenium(II) bipyridine doped silica
nanoparticle
Authors: Bosco Christin Maria Arputham Ashwin, Chokalingam
Saravanan, Thambusamy Stalin, Paulpandian Muthu
Mareeswaran, and Seenivasan Rajagopal
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: ChemPhysChem 10.1002/cphc.201800447
Link to VoR: http://dx.doi.org/10.1002/cphc.201800447
A Journal of
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10.1002/cphc.201800447
ChemPhysChem
ARTICLE
FRET based solid state luminescent sensor for glyphosate using
calixarene grafted ruthenium(II)bipyridine doped silica
nanoparticle
Bosco Christin Maria Arputham Ashwin,[a] Chokalingam Saravanan,[a] Thambusamy Stalin,[a]
Paulpandian Muthu Mareeswaran*[a] and Seenivasan Rajagopal*[b]
Abstract: A calixarene functionalized luminescent nanoparticle was
successfully fabricated for the FRET based selective and sensitive
detection of organophosphorus pesticide, Glyphosate (GP). The p-
tert-butylcalix[4]arene was grafted over the surface of [Ru(bpy)3]2+
incorporated SiNps to produce self-assembled nanosensors (RSC).
The FRET was switched on in the presence of GP by means of
energy transfer due to the binding with p-tert-butylcalix[4]arene
grafted on the surface of RSC. The FRET efficiency of GP-RSC
system was increased gradually with the addition of GP. The FRET
efficiency was evaluated as 87.69 % and high binding affinity was
established by the binding constant value, 1.16 × 107 M-1 using
Langmuir binding isotherm plot. The estimated limit of detection
(LOD) was 7.91 × 10-7 M which was lower than Environmental
Protection Agency (EPA) recommendation. The probe also
effectively responds to real sample analysis. The sensitivity and
selectivity was realized due to the efficient FRET towards the
fluorescence properties of [Ru(bpy)3]2+ complex.
synthase enzyme’s activity which leads to plant’s death.[7] The
use of excess quantity of GP causes gene species shift and
leads to genetically modified weeds.[8]
The widespread use of GP requires selective and sensitive
detection. The Environmental Protection Agency (EPA) referred
2 mg/kg/day as a permissible dosage for GP.[9] The maximum
contaminant level of GP in drinking water is reported as 0.7
ppm.[10] Quantitative determination of GP generally relies on
solid-phase extraction followed by GC-MS[11] or LC-MS.[12] The
enzyme-linked immunosorbent assay (ELISA) system is also
used to determine GP.[13] Even though, these methods are
reliable and accurate, they involve high cost and trained
manpower. The various techniques proposed for sensing GP are
fluorescent,[14] colorimetric detection,[15] electrochemical,[16]
biosensor based on surface plasmon resonance[17] and quantum
dot based sensor systems.[18] Optical recognition based on
supramolecular interactions appears to be an appealing
strategy.[19]
The fluorescence resonance energy transfer (FRET)
based sensor systems receive predominant impact in selective
detection of neutral and charged small molecules.[20] The
utilization of FRET with solid state dye doped nanoparticles are
novel strategies developed for selective detection, stability and
reusability.[21] The cavity containing supramolecules are
promising candidates for the selective recognition and sensitive
detection.[22] In particular, the calixarenes are well-known vase
structured supramolecules which are extensively employed in
the field of molecular recognition.[23] Owing to their facile
synthesis, flexibility, easy functionalization of upper and lower
rims and tuning the cavity as per the requirements for particular
analyte made calixarenes as most suitable among other host
molecules.[24] Calixarene derivatives could be grafted over the
luminescent nanoparticles for the optical detection of
analytes.[25] Herein we report, p-tert-butylcalix[4]arene grafted
ruthenium(II)-bipyridine doped silica nanoparticle for the FRET
based selective detection of GP in aqueous medium.
Introduction
The worldwide use of pesticides pollute agricultural lands and
impose toxic effects over the ecosystem.[1] The occurrence of
pesticide residues in food items is a serious threat to food safety
and it is necessary to develop new sensor systems to make sure
the level of pesticides in food.[2] Organophosphates are one of
the classes of herbicides/pesticides which are also used as
chemical warfare agents.[3] Glyphosate (GP) is an important
organophosphate extensively used as herbicide in agriculture.[4]
The utilization of GP beyond the limit causes adverse effects to
animals,[5] plants[4b] and results in the proliferation of breast
cancer in humans.[6] The GP inhibits the aromatic amino acids
synthesis by restricting the 5-enolpyruvylshikimate-3-phosphate
[a]
[b]
B. M. Ashwin, C. Saravanan, Dr. T. Stalin and Dr. P. Muthu
Mareeswaran*
Department of Industrial Chemistry
Alagappa University
Karaikudi, Tamilnadu, India.
Dr. S. Rajagopal*
Results and Discussion
Department of Physical Chemistry, School of Chemistry
Madurai Kamaraj University
Madurai, Tamilnadu, India.
Preparation and characterization of RSC
E-mail: muthumareeswaran@gmail.com,
mareeswaran@alagappauniversity.ac.in,
rajagopalseenivasan@yahoo.com
The RSC have been synthesized by multistep process
(Figure 1).
Supporting information for this article is given via a link at the end of
the document.((Please delete this text if not appropriate))
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10.1002/cphc.201800447
ChemPhysChem
ARTICLE
Figure 1. Multistep synthesis scheme for the [Ru(bpy)3]2+ dye doped silica nanoparticle coupled with tert-butylcalix[4]arene (RSC)
Each step is monitored by analytical techniques, the details are
given in supporting information. A new peak at 450 nm of
[Ru(bpy)3]2+ is observed in the UV-Visible absorption spectrum
of Ru-SiNps which is not appeared in SiNps. The SEM images
(Figure S3) of SiNps and Ru-SiNps explain the variation in the
size of nanoparticles and the EDAX results establish the
incorporation of [Ru(bpy)3]2+ within SiNps. The prepared t-
butylcalix[4]arene tetra-ester and t-butylcalix[4]arene tetra-acid
are characterized by FT-IR, ESI-MS,1H and 13C NMR techniques
and the results are given Figures S4 - S11. The mass peak of
the corresponding product with Na+ ion is appered at 1015.44
and 903.26 m/z in ESI-MS spectrum of t-butylcalix[4]arene tetra-
ester (Figure S5) and t-butylcalix[4]arene tetra-acid (Figure S9),
strongly confirmed the formation of these compounds. The final
product, RSC is characterized by TEM, XRD and FT-IR.
The FT-IR spectra of RSC, Ru-SiNps and calix[4]arene
precursor (Figure 2) confirm the successful grafting of the
calix[4]arene on the surface of Ru-SiNps. From the IR spectra
collected in Figure 2 we realize that RSC shows benzene ring
stretching at 1625 cm−1.[26] The sharp peak at 1090 cm−1 is the
characteristic peak of Si–O–Si.[27] The C ═ O stretching band of
the amide at 1736 cm-1 is significantly shifted and merged with
the absorption band of benzene ring of RSC.[26] The absorption
band at 794 cm-1 belongs to the C−H bending vibration of
aromatic rings. This peak is present in both Ru-SiNps and RSC.
It clearly confirms the presence of aromatic bipyridine moiety in
solid matrix of RSC. The absorption band at 2957 cm-1 belongs
to the C−H stretching vibration of alkanes in calix[4]arene
conjugate. The broad peak at 3430 cm-1 is due to the N−H
stretching frequency of amide formed in RSC. Hence, the FT-IR
results confirm the formation of RSC.
Figure 3. TEM images of Ru-SiNps and RSC
The XRD patterns of RSC and Ru-SiNps show the
amorphous nature of the nanoparticles and distinct patterns
(Figure S12). From TEM images (Figure 3), the remarkable
differences in surface and size are observed. It can be seen that
the prepared RSC is spherical in shape, highly dispersed and
uniform in size (average size: 50 nm). The probe shows high
stability with the environment.
Figure 2. FT-IR spectra of the prepared RSC, calix[4]arene precursor and Ru-
SiNps
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10.1002/cphc.201800447
ChemPhysChem
ARTICLE
FRET Based Selective Detection of GP
which supports the high stability and applicability of the probe in
various conditions. These results confirm the applicability and
reliability of the proposed method for assay of GP in
environmental samples.The reported solid state probe has
possibilities to be extended to the sensor strip like devices for
direct detection of GP in real samples.[30]
In order to examine the selectivity of FRET system towards
GP, the FRET response of RSC with various common pesticides
are carried out. GP only brings the FRET emission peak of
[Ru(bpy)3]2+ dye at 580 nm and others fail to switch on the FRET
emission. The emission intensity of GP-RSC combination at 580
nm is much higher than the others (Figure4). This is due to the
significant interaction and proximity of GP with RSC. Since the
number of GP molecules increases and FRET is rather strong,
the emission intensity of GP (420 nm) also increases stepwise
due to the availability of excess unbound GP and similar
increment was observed in the recent report.[28] Moreover the
probe is excited with the same wavelength of GP for another
pesticide Mancozeb (340 nm), the FRET emission is not
occurred at 580 nm. The competitive recognition is studied using
the mixture of all pesticides with the probe. The interference of
other pesticides in the recognition of GP is very meagre. This
outcome strongly certifies the selective response of the probe.
Figure 5. FRET emission spectrum of RSC with real samples (a) ground water
and (b) rice spiked with different concentrations of GP.
Thus
a very simple calixarene functionalized luminescent
Mechanism for the FRET response towards GP by RSC
nanomaterial RSC worked as a selective and sensitive FRET-
On sensor for GP.
The FRET response of RSC with GP is studied using
fluorescence spectroscopy. The well-defined structure of the
calixarene cavities can be exploited for the inclusion of organic
guests.The calix[4]arene moiety grafted on silica matrix has a
unique cavity with the size around 2.75-3.00 Å.[31] The size of
GP is compatible with this size. However, the cavity of
calix[4]arene is not sufficiently large enough to accommodate
bulk aromatic pesticides excluding a small linear molecule like
GP, which results in the selective FRET response to GP.[32] The
hydrogen bond formation between the GP with the amide which
is located at the lower rim of calix[4]arene is also responsible for
the recognition. Similar recognition of amino acids with the
calix[4]arene having amide group at the lower rim is reported
previously.[33] This inclusion renders stable proximity with SiNps
doped with [Ru(bpy)3]2+.There is a prominent overlap of the
emission of GP with the absorption of [Ru(bpy)3]2+ (Figure S14),
which facilitates the energy transfer between GP and
[Ru(bpy)3]2+.The other pesticides taken for this study are not
able to provide compact binding with RSC. Therefore, the
possibility of FRET is less. The mechanism of FRET switch-on
sensor with GP is explained in Figure 6.
Figure 4. FRET response of RSC with individual common commercial
pesticides including glyphosate (GP) and mixture of all pesticides. (Excited at
individual excitation wavelengths of pesticides). The bar diagram shows the
selective FRET-On response of GP.
Real Sample Analysis
To evaluate the practicality of RSC as a probe for GP, we
carried out the real sample analysis by analyzing environmental
ground water and rice samples.[29] Different concentrations of
GP (1 and 2 µM) were added for each sample to determine
recovery.The FRET spectrum of GP spiked real samples were
measured (Figure 5) and the results were depicted in Table 1.
Table 1.FRET based detection of GP in real samples using RSC
Added
(µM)
Found
(µM)
Samples
pH
6.6
Recovery %
1
2
1
2
0.963
1.896
0.987
1.955
96.3
94.8
98.7
97.7
Ground
water
Rice
4.3
The satisfactory recovery was observed in the range of
94–98% for different GP spiked water and grain samples,
indicating the reported probe is good in precision. The pH of the
real samples were measured and they show varient in pH.
Interestingly all the samples give sufficient results using RSC,
Figure6. Schematic representation of the FRET-On detection system for
glyphosate (GP) using RSC
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10.1002/cphc.201800447
ChemPhysChem
ARTICLE
Binding and Detection Limit Studies of GP with RSC
I/Imax = (1/BImax) + (1/Imax) [GP]
It can be linearized as,
[GP]/I = (1/BImax) + (1/Imax) [GP]
(6)
(7)
The broad absorption peak of RSC overlaps that with GP,
which makes the possibility of the binding constant calculation
by absorption technique difficult. Moreover the reported sensor
probe mainly works on the FRET principle. Hence the
calculation of the binding constant by FRET emission change
seems to be proper and suitable one. The concentration
dependent change in emission intensity follows the binding of
GP in the cavity of the receptor calix[4]arene grafted over the
surface of RSC and the binding is effectively described by a
Langmuir-type binding isotherm.[32, 34] The emission intensity is
increased with increasing GP concentration (Figure7).
As per the Langmuir description, a plot of [GP]/I as a
function of [GP] should be linear when the binding of GP on the
surface of RSC is factual. Here, [GP] is the GP’s concentration
and I is the fluorescence intensity of the RSC produced by FRET
at given GP concentrations. Interestingly a linearity is obtained
for the whole range of GP concentration. The binding constant,
B is calculated as 1.16 × 107 M-1, and the linear fit coefficient is ˃
0.999 (Figure 8). The remarkable Langmuirian fit suggests that,
the binding probability is more than one for each GP to the
surface of an individual Nps.
Figure7. FRET response of RSC with different concentrations of GP (0-2 µM).
Figure8. Langmuir binding isotherm plot of GP with RSC showing a linear fit
(Excited at 340 nm)
The observed emission intensity changes of GP at the
concentration 0 - 2 µM are correlated with the structural
deformation of the calix[4]arene-group shell covering the Ru-
SiNps upon intercalation. This may be due to the production of
an effective and new radiative path involving the bound GP
and/or from the nonradiative process suppression. Whenever
GP is added with RSC, the intercalation of GP restricts the
calixarene-cavity distortion and induces a static arrangement.
Such uniformed orientation and/or conformational rigidity
enhancement due to the surface substituents may restrict the
quenching path to the medium by effective core protection and
which increase the FRET intensity.
From the Langmuir equation, the surface of the RSC
contains limited number of binding sites and each can adsorb
single analyte (GP) from the solution. Ɵ is defined as the fraction
of engaged sites. The binding rate of GP on the surface of RSC
is proportional to the concentration of GP ([GP]) in the sample
and the available binding sites, 1 - Ɵ. The binding rate (Rb) of
GP on the surface of RSC is considered as,
Rb = Kb[GP](1 - Ɵ)
(1)
The desorption rate of GP from the surface of RSC
depends on the engaged binding sites fraction which is
expressed as
The change of FRET intensity can be described to the
amount of GP bound to the sensing interface and the detection
Rb = KdƟ
(2)
At equilibrium, the binding rate is equal to the desorption
limit was calculated from the calibration plot (Figure S15).[35]
A
rate
limit of detection about 7.91 × 10-7 M was found for GP,
significantly lower than the maximum contaminant level allowed
by EPA (0.7 ppm ≈4 μM).[19b]
KdƟ = Kb[GP](1 - Ɵ)
(3)
The solved equation for Ɵ is the function of the ratio, B=
Kb/Kd.
FRET Efficiency Calculation
Ɵ = (B[GP])/(1 + B[GP])
(4)
FRET is responsible for the appearance of acceptor’s
The ratio of the signal received at stated pesticide
(RSC) emission while exciting the donor (GP) atom (Figure
concentration I and the maximum intensity Imax is related to the
fraction of the engaged binding sites, Ɵ.
4).[23a]
According to Förster’s theory,[36] FRET efficiency (E) is
Ɵ = I/Imax
(5)
given by,
6
6
E = (R0 )/(R0 +R6 )
(8)
However, an equation relating the concentration of GP with
the intensity of the signal can be derived as
where, R0 is the Förster radius and R is the distance of acceptor
center from the donor center. Förster radius is given by Eq.(9).
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10.1002/cphc.201800447
ChemPhysChem
ARTICLE
R0 = (8.8 × 1023JK2Q0n-4)1/6A
J = ΣF(λ)ε(λ)λ4λ / Σ F (λ) λ
(9)
Instruments
(10)
UV-Visible absorption spectrometric measurements and
fluorescence emission measurements are performed by SHIMADZU UV-
2401PC and JASCO FP-8200 Spectrofluorometer respectively at room
temperature. FT-IR spectra are recorded on Jasco FT-IR 4600
spectrometer. The X-ray powder diffraction (XRD) is recorded on
XPERT-PRO X-ray diffractometer with Cu-Kα radiation. Surface
morphological studies and EDAX are carried out on FEI QUANTA 250
scanning electron microscope and TEM images are obtained by JEOL
JEM 3010 Microscope.
Here, K2 is the orientation factor of a dipole–dipole
interaction, Q0 is the quantum yield of donor in the absence of
acceptor, J is the spectral overlap integral in M-1cm3 and n is the
refractive index of the medium. Figure S14 in the supporting
information shows the GP’s emission overlap with the RSC’s
absorption. From the overlapping spectrum, J can be estimated
by integrating the spectra from 360 nm to 550 nm. The
estimated overlap integral value is 6.61× 10−19 cm3mol/L and the
R0 is 6.93 Å. For this calculation K2 value is taken as 2/3 for
random orientation, and n = 1.33 for water medium.
Preparation of [Ru(bpy)3]2+ doped SiNps (Ru-SiNps)
Ru-SiNps were prepared by water-in-oil micro emulsion method.[37]
Triton X-100 (1.77 ml), cyclohexane (7.5 ml), 1-hexanol (1.8 ml), water
(400 µL) and concentrated solution of [Ru(bpy)3]2+(50 µL) were taken in a
RB flask and stirred vigorously. After 1 h, TEOS (200 µL) as a precursor
of silica was added to the solution and 100 µL of NH4OH was added to
initiate the polymerization process. The reaction was continued for 24 h
at room temperature. The surface of the SiNps was modified by the
addition APTES (100 µL) and TEOS (50 µL). The reaction mixture was
stirred for further 2 h. The spherical shaped Ru-SiNps were separated by
centrifugation. Then the Ru-SiNps were washed with water, ethanol and
acetone several times. The bare SiNps were synthesized without
[Ru(bpy)3]2+ and compared with Ru-SiNps using HR-SEM and EDAX
(Figure S3).
Interaction between GP and RSC probe system is
associated with the existence of specific binding site on RSC.
RSC has a supramolecular host molecule calix[4]arene as a
binding site. The binding site and the cavity play important role
in the specific interaction of RSC with GP. While binding of
analyte occurs inside the cavity, the fluorophore donor will be
very closer to the acceptor, RSC. The average distance is
assumed from Ru-SiNps surface to the GP which is in the centre
of the cavity and estimated as 5Å for the FRET efficiency, E is
estimated as 87.69 % for GP-RSC system.
Synthesis of t-butylcalix[4]arene precursor
Conclusions
The t-butylcalix[4]arene precursor was synthesized according to the
reported procedure[26] with some modifications. A mixture of p-tert-
butylcalix[4]arene (1g), potassium carbonate (0.42 g) and
ethylbromoacetate (0.68 ml) were taken in 50 ml dry acetone and
refluxed for 15 h. The cooled solution was passed through a bed of celite.
The filtrate and dichloromethane washings of celite were mixed and
evaporated to dryness. Recrystallization from ethanol provided the tetra-
ester. A solution of prepared tetra-ester (98 mg) in a mixture of THF (3
mL), methanol (3 mL) and aqueous KOH (1 mL, 40% weight) was stirred
overnight at room temperature. The organic solvents were removed in
vacuoat 70 ºC and the remaining aqueous solution was acidified to pH 1
by the addition of 4 N HCl and allowed to stand at 0 ºC for 6 h. The
resulting precipitate was filtered, washed with water and dried at 80 ºC.
The tetra-acid was extracted from aqueous solution with CH2Cl2. The
resulting white solids were dried under vacuum. The product was
characterized using FT-IR and discussed in the results and discussion
part.
Luminescent silica nanoparticles grafted with p-tert-
butylcalix[4]arene are synthesised and successfully applied to
the detection of GP by means of FRET process using emission
spectral technique. The FRET switch on process for RSC is
observed in the presence of GP with 87.69% FRET efficiency
and 7.91 × 10-7 M of detection limit. This FRET switch on is not
observed for the pesticides other than GP taken for the study.
The binding constant values establish the efficient binding of GP
with cavity of p-tert-butylcalix[4]arene derivative grafted on the
silica surface. The real time analysis depicts the efficiency of the
RSC towards practical applications. The selective detection of
GP using RSC by means of switch on FRET process shows the
possible usage of FRET process in solid state sensor systems.
The aspect of FRET based stable and simple sensor strips can
be envisaged by means of this study.
Preparation of t-butylcalix[4]arene grafted Ru-SiNps(RSC)
Experimental Section
The prepared t-butylcalix[4]arene tetra-acid (1.76 g) was then
refluxed with 20 ml of thionyl chloride for 2 h to obtain p-tert-butyl-
tetra(chloroformylmethoxy)calix[4]arene in quantitative yield, and the
excessive thionyl chloride was removed in vacuum. The obtained product
was directly used in next step without further purification. A mixture of
calix[4]arene precursor (0 .76 g), Ru-SiNps (0.94 g, content ~90%) and
triethylamine (0.33 g) in freshly distilled dry toluene (120 ml) were stirred
at room temperature in an inert atmosphere of dry nitrogen for 16 h. At
last, the solid product was filtered and washed in sequence with warm
toluene, acetone, methanol and double-distilled water subsequently. The
product was dried under vacuum for 3 h, and kept in a desiccator.The
normalised UV and emission spectra of RSC in water are shown in
Figure S1.
Materials
The
RuCl3.3H2O,
are
2,2’-bipyridine,
procured from
Triton
X-100,
p-tert-
butylcalix[4]arene
Sigma-Aldrich.
(3-
aminopropyl)triethoxysilane (APTES), tetraethyl orthosilicate (TEOS),
ammonium hydroxide, ethanol, acetone,cyclohexane, 1-hexanol,
potassium carbonate and ethyl bromoacetate are procured from Alfa
Aesar. Ultra-pure water (Millipore) is used as solvent throughout the
study. The pesticides Mancozeb (Man), Thiamethoxam (Thia), Cartap
Hydrochloride (Car), Emamectin Benzoate (Ema), Alphamethrin (Alp),
Fenpropathrin (Fen), Triazophos (Tri), Imidacloprid (Imi), Glyphosate
(GP) and Chlorpyrifos (Chl) are purchased as commercial products
SAAF, Pele, Quick, Trust, Alphaguard, Danitol, Tarzan, Pronto, Round
Up and Durmet respectively. The chemical structure and absorption
spectra (Figure S13& S2) of GP are given in Supporting Information.
FRET Studies
The chemical composition of the desired pesticide in the
commercial pesticides were calculated. Each pesticide (1 × 10-6 M) was
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10.1002/cphc.201800447
ChemPhysChem
ARTICLE
taken with RSC (1 mg) in 5 ml SMF separately. Each samples were
sonicated and emission spectra was measured using fluorescence
spectrometer by exciting at the excitation wavelength of corresponding
pesticide. For GP titration study, 1 mg of RSC was taken in a cuvette and
GP was varied from 0 - 2 µM concentration. The whole study was carried
out in double distilled ultrapure water (pH=6.8) and room temperature.
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Real Sample Analysis
To find the potential applicability of the proposed RSA in real
samples, detection of GP residues was carried out in ground water and
rice grains. From the literature, these are the suitable samples for
pesticide detection in real samples.[29b] The collected ground water
sample was filtered using filter paper to remove solid particulates from
the samples. Then the water samples were spiked with different
concentrations of GP (1 × 10-4 M and 2 × 10-4 M) and analyzed by RSC.
The spiked rice sample was prepared according to a previous report.[29a]
Similarly, different concentrations of GP (1 × 10-4 M and 2 × 10-4 M) were
added into the fine powdered rice samples (10.0 g) and kept for 24 h at
room temperature. Then, GP was extracted using 20 mL of methanol in
an ultrasonic bath for 20 min. The extracts were decanted and repeated
the same procedure twice. The extract was filtrated through filter paper
and then the concentration of GP was estimated using RSC as a probe.
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Acknowledgements
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The authors acknowledge the financial support of Department of
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Keywords : FRET-On Sensor• Glyphosate• Pesticide Detection•
Calixarene• Luminescent Nanoparticle
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This article is protected by copyright. All rights reserved.

10.1002/cphc.201800447
ChemPhysChem
ARTICLE
Layout 2:
ARTICLE
B. M. Ashwin, C. Saravanan, Dr.T. Stalin,
Dr. P. Muthu Mareeswaran* and
Dr. S. Rajagopal*
1 – 7
FRET based solid state luminescent
sensor for glyphosate using
calixarene grafted ruthenium(II)
bipyridine doped silica nanoparticle
A calixarene functionalized luminescent silica nanoparticle was prepared and studied for it’s FRET based selective and
sensitive sensor application for glyphosate.
This article is protected by copyright. All rights reserved.