Rhodamine-triazole Functionalized Fe3O4@SiO2 Nanoparticles as Fluorescent Sensors for Heavy Metal Ions

Article abstract of DOI:10.13005/ojc/350318

Rhodamine-triazole sensor functionalized Fe₃O₄@SiO₂ nanoparticles were developed for the detection of heavy metal ions, namely Cu²⁺, Ni²⁺, Hg²⁺, Co²⁺, Fe³⁺, and Pb²⁺. Rhodamine conjugated with a triazole moiety (RBT) was utilized as the metal ion binding site. The RBT-Fe₃O₄@SiO₂ nanoparticles were fully characterized by XRD, FTIR, TGA, SEM and TEM techniques. Additionally, RBT-functionalized Fe₃O₄@SiO₂ nanoparticles can be separated from aqueous phase by application of an external magnet, leading to clear naked-eye observation of the color changes and fluorescence enhancement. From UV-Vis absorption spectra, aqueous solutions of RBT-Fe₃O₄@SiO₂ in the presence of heavy metal ions show an absorption peak at 554 nm. Fluorescence titration experiments reveal that the intensity of the fluorescence emission band at 574 nm is linearly dependent on Cu²⁺ concentration over a 100-800 μM range. Furthermore, complexation of Cu²⁺ by RBT-Fe₃O₄@SiO₂ nanoparticles can induce ring-opening of the rhodamine spirolactam ring followed by hydrolysis, confirmed by mass spectrometry.

Full text of DOI:10.13005/ojc/350318

ISSN: 0970-020 X
CODEN: OJCHEG
2019, Vol. 35, No.(3):
Pg. 1054-1061
ORIENTAL JOURNAL OF CHEMISTRY
An International Open Access, Peer Reviewed Research Journal
www.orientjchem.org
Rhodamine-triazole Functionalized Fe3O4@SiO2 Nanoparticles
as Fluorescent Sensors for Heavy Metal Ions
KANOKORN WECHAKORN1*, PAIRSUNAN CHANPANICH2, PIMFA KAMKALONg2
and SURANAN ANANTACHISILP2
1Department of Chemistry, Faculty of Science and Technology, Rajamangala University of Technology
Thanyaburi, Pathum Thani 12110, Thailand.
2Kamnoetvidya Science Academy, Rayong 21210, Thailand.
*Corresponding author E-mail: kanokorn_w@rmutt.ac.th
http://dx.doi.org/10.13005/ojc/350318
(Received: May 30, 2019; Accepted: June 06, 2019)
AbSTRACT
Rhodamine-triazole sensor functionalized Fe3O4@SiO2 nanoparticles were developed for the
detection of heavy metal ions, namely Cu2+, Ni2+, Hg2+, Co2+, Fe3+, and Pb2+. Rhodamine conjugated
with a triazole moiety (RBT) was utilized as the metal ion binding site. The RBT-Fe3O4@SiO2
nanoparticles were fully characterized by XRD, FTIR, TGA, SEM and TEM techniques. Additionally,
RBT-functionalized Fe3O4@SiO2 nanoparticles can be separated from aqueous phase by application
of an external magnet, leading to clear naked-eye observation of the color changes and fluorescence
enhancement. From UV-Vis absorption spectra, aqueous solutions of RBT-Fe3O4@SiO2 in the
presence of heavy metal ions show an absorption peak at 554 nm.Fluorescence titration experiments
reveal that the intensity of the fluorescence emission band at 574 nm is linearly dependent on Cu2+
concentration over a 100-800 µM range. Furthermore, complexation of Cu2+ by RBT-Fe3O4@SiO2
nanoparticles can induce ring-opening of the rhodamine spirolactam ring followed by hydrolysis,
confirmed by mass spectrometry.
Keywords: Fluorescent sensor, Magnetic nanoparticles, Heavy metal ions, Triazole, Rhodamine.
INTROdUCTION
tools for their detection. Although conventional
analytical techniques such as atomic absorption
spectrometry (AAS)1, flame atomic absorption
spectroscopy (FAAS)2, inductively coupled plasma
mass spectrometry (ICP-MS)3 and voltammetry4
are typically used in metal ion detection, they have
drawbacks in requiring expensive and sophisticated
hardware, long analysis time, and a high level of
technical expertise. Fluorescence spectroscopy, on
the other hand, is an emerging technique for metal
Contamination of water sources by heavy
metal ions (e.g. Co2+, Cu2+, Fe3+, Hg2+, Ni2+ and Pb2+)
is a major environmental concern. In addition, their
toxicity and accumulation in living organisms can
have profound impacts on the overall ecology of
environmental systems. Accordingly, great effort is
being extended into devising ways of removing such
pollutants and the development of new analytical
This is an
Open Access article licensed under a Creative Commons license: Attribution 4.0 International (CC- BY).
Published by Oriental Scientific Publishing Company © 2018

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ion detection in environmental science due to its
high selectivity, rapid response allowing real-time
detection for potential field use and low cost5.
yields and appreciable photostability19. In these
systems, rhodamine having the closed-form of
the spirolactam ring is colorless and shows no
fluorescence emission, while the solutions of
the open-form of rhodamine exhibit a pink color
and fluorescence emission. As a consequence,
rhodamine has been appended to the surface of
magnetic nanoparticles to form sensors for Fe3+
and Hg2+. In 2010, rhodamine 6G-ethylenediamine
was conjugated to the surface of Fe3O4@SiO2
nanoparticles via a polyethylene linker, which
exhibited fluorescence emissions in the presence of
Fe3+ ion20. Substituting the polyethylene linker in the
previous system by an isocyanate linker resulted in
the selectivity of the sensor with the binding of Hg2+,
Cr3+ and Fe3+ ions21,22.In the context of Hg2+ removal,
rhodamine hydrazide was grafted onto the magnetic
nanoparticle surface via 3-glycidyloxy moiety23,
or chloroacetyl aminopropane linkers24. From the
previous literatures, rhodamine-based fluorescent
sensor immobilized on the magnetic nanoparticles
have not been widely developed for heavy metal ion
detection.
Overthelastdecade,magneticnanoparticles
have been extensively studied since they have large
surfaceareatovolumeratiosandarereadilyseparated
from liquid phase by application of an external field.
Conjugation of organic groups on the nanoparticle
surface allows these systems to be utilized in
analytical applications such as metal ion detection.
For example, amino-functionalized Fe3O4@SiO2
magnetic nanomaterials were developed as sorbents
for the toxic metal ions including Cu2+, Pb2+, and Cd2+
ions6-9. In addition, thiol-functionalized Fe3O4@SiO2
nanoparticles were synthesized for Pb2+ and Hg2+
sequestration from water samples10-13. Appending
fluorescent groups (dansyl, naphthalimide, Nile
red, or BODIPY) to the nanoparticle surface allows
the potential of fluorescence as a detection method
to be built into the nanoparticle system. As an
example, Ma’s group developed reusable dansyl-
functionalized Fe3O4@SiO2 nanoparticles for Hg2+
detection, and subsequent removal from water
samples14. In this case, the fluorescence intensity
of nanoparticles was quenched in the presence
of Hg2+, with the limit of detection being 10 mM in
HEPES buffer containing 50% (v/v) CH3CN/H2O.
In 2013, “Turn-off” naphthalimide functionalized
Fe3O4@SiO2 nanoparticles were observed to
aggregate in the presence of Hg2+, forming imide-Hg-
imide complexes in aqueous solution15. In another
development, Zhu’s group designed thioether-crown
conjugated naphthalimide modified Fe3O4@SiO2
nanoparticles via click chemistry for Hg2+ sensing16.
Recently, magnetic nanoparticles appended with
4-acetamidobenzaldehyde functionalities were able
to detect Hg2+ at the nanomolar level17. Meanwhile,
dipicolylamine-naphthalimide conjugated magnetic
nanoparticles exhibited fluorescence emission
allowing feasible Zn2+ detection in environmental
water samples18.In the case of Co2+ ion, chelation by
Nile red-functionalized Fe3O4@SiO2 nanoparticles
leads to fluorescence emission through the inhibition
of photoinduced electron transfer (PET)14.
This work reports the synthesis of a
rhodamine-triazole sensor appended Fe3O4@SiO2
nanoparticles for the detection of heavy metal ions
(Cu2+, Ni2+, Hg2+, Co2+, Fe3+ and Pb2+). The sensor-
functionalized nanoparticles could be easily removed
from the solution by applying an external magnetic field.
Additionally, the 1,2,3-triazole moiety plays several
important roles, being both the metal chelator and the
linkerbetweenthefluorescencereporterandthemetal
ion binding site25.The selectivity and sensitivity of the
sensor system as well as a rationale for the sensing
mechanism, are also reported herein.
MATERIALS ANd METHOdS
Materials and Instruments
All chemicals and reagents of standard
analytical grade were purchased from commercial
suppliersandusedwithoutfurtherpurification.Allsolvents
forcolumnchromatographyweredistilledbeforeuse.The
stock solutions (10 mM) of the metal ions including Co2+,
Cu2+, Fe2+, Fe3+, Hg2+, Ni2+ and Pb2+ were prepared in
deionized water from their acetate salt.
Rhodamine derivatives have been widely
reported as fluorescent entities due to their long
absorption and emission wavelengths, large molar
extinction coefficients, high fluorescence quantum
1H and 13C NMR spectra were recorded
on an Advance Bruker-600AV spectrometer in

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CDCl3 with tetramethylsilane (TMS) as an internal
reference.Fourier transform infrared (FT-IR) spectra
were collected on a Perkin Elmer Spectrum two
spectrometer using KBr pellets in the 4000-370 cm-1
region. High resolution mass spectra (HRMS) were
obtained on a Bruker MicrOTOF mass spectrometer.
Scanning electron microscope (SEM) images were
obtained on a Jeol JAM-7610F with normal mode
and EDS mode. Transmission electron microscopy
(TEM) images were performed on a Jeol JEM-
2100Plus electron microscope.X-ray diffraction (XRD)
studies were performed on a Bruker d8Venture powder
diffractometer (2theta 20 to 80O) with Cu Kα radiation.
Thermogravimetric analysis (TGA) was utilized on a
Linseis STA PT1600 instrument. UV-Vis absorption
spectra were measured on a Hitachi U-2900/2910
UV-Visible spectrophotometer. Fluorescence spectra
were performed on an Edinburgh fluorescence lifetime
spectrometer.
mixture was filtered and the filtrate was evaporated
under reduced pressure to provide the product as
a colorless liquid in 90% yield. 1H NMR (600 MHz,
CDCl3) d (ppm): 3.80 (d, J = 6 Hz, 6H), 3.24 (d, J =
6 Hz, 2H), 1.70 (d, J = 6 Hz, 2H), 1.21 (t, J = 6 Hz,
9H), 0.66 (t, J = 6 Hz, 2H); 13C NMR (150 MHz,
CDCl3) d (ppm): 58.5, 53.9, 22.8, 18.3, 7.7.
Synthesis of Rhodamine-N-propargyl alkyne
Rhodamine-N-propargyl alkyne was
preparedaccordingtoapreviouslyreportedprocedure27.
The crude product was purified by silica column
chromatography with 1% (v/v) CH3OH/CH2Cl2 systemas
amobilephasetoobtainalightbrownsolidin75%yield.1H
NMR (600 MHz, CDCl3) d(ppm): 7. 91.(d, J = 6Hz,1H),
7.45(s,2H),7.1(d,J = 6Hz,1H),6.41-6.46(m,4H),6.27
(d,J = 6Hz,4H),4.57(s,1H),3.32(t,J = 6Hz,10H),2.10
(s, 1H), 1.16(t, J = 6Hz,12H);13CNMR(150MHz, CDCl3)
d(ppm):166.64, 153.70, 151.78, 149.52, 148.84, 132.75,
129.83, 128.54, 128.51, 128.10, 123.98, 122.89, 122.86,
109.74, 107.86, 105.65, 100.07, 98.46, 80.10, 72.42,
65.43, 45.53, 44.44, 44.34, 40.42, 12.63.
Synthesisofsilica-coatedmagneticnanoparticles
(Fe3O4@SiO2)
The magnetic nanoparticles were
synthesized according to a previously reported
procedure26. Briefly, a solution of Fe(acac)3 (5.65 g,
0.016 mol), benzyl ether (80 mL) and oleylamine (80
mL) was heated to 110 OC and allowed to reflux for 1
h with vigorous stirring.The temperature was raised
to 210 OC and then refluxed for 2 h under an argon
atmosphere. After cooling to room temperature, the
reaction mixture was centrifuged at 10,000 rpm for
20 min, affording the magnetic nanoparticles (Fe3O4)
as a black solid. The magnetic nanoparticles were
then dispersed in a mixture of 1-propanol (180 mL),
conc. NH4OH (25 mL) and deionized water (18 mL)
in a 500 mL round-bottom flask by ultra-sonication
for 30 min under an argon atmosphere. Following
this, tetraethylorthosilicate (TEOS) (6 mL, 0.027
mol) was added dropwise for 30 min with vigorous
stirring.After stirring at room temperature for 6 h, the
silica-coated magnetic nanoparticles (Fe3O4@SiO2)
were separated from the solution using an external
magnet and then washed twice successively with
1-propanol and deionized water, respectively. The
Fe3O4@SiO2 nanoparticles (brown solid) were then
dried under vacuum at 60 OC for 6 h, prior to use.
Synthesis of chemosensor-functionalized
magnetic nanoparticles (RbT-Fe3O4@SiO2)
The Fe3O4@SiO2 nanoparticles (1.5 g)
were suspended in toluene (80 mL) under an
argon atmosphere, and then sonicated for 30 min.
3-Azidopropyl triethoxysilane (1.5 g, 6.1 mmol)
was slowly added dropwise into the mixture for
15 min and the mixture was then heated at reflux
for 12 h. The Fe3O4@SiO2-N3 nanoparticles were
then separated by applying an external magnet
and then washed three times successively with
toluene, 1-propanol and deionized water (30 mL),
respectively. Subsequently, the Fe3O4@SiO2-N3
nanoparticles were dispersed in acetonitrile (50 mL)
with the sonication for 30 min while maintaining an
argon atmosphere. In a separate flask, a solution
of rhodamine-N-propargyl alkyne derivative (0.5 g,
1 mmol) and CuBr(PPh3)3 (50 mg, 0.05 mmol) in
acetonitrile (50 mL) was prepared and after being
stirred for 30 min then it was added into the Fe3O4@
SiO2-N3 nanoparticle dispersion with vigorous
stirring under an argon atmosphere. After 24 h, the
RBT-Fe3O4@SiO2 nanoparticleswereseparatedusing
an external magnet and washed twice successively
with acetonitrile, methanol and dichloromethane
(15 mL), respectively.
Synthesis of 3-azidopropyl triethoxysilane
3-Chloropropyl triethoxysilane (5 mL, 0.021
mol) and sodium azide (NaN3) (2.70 g, 0.042 mol,
2 equiv.) were dissolved in DMF (40 mL), and the
mixture was heated at 90 OC for 6 h. After that the

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RESULTS ANd dISCUSSION
followed by nucleophilic substitution with electrophilic
propargyl bromide, as shown in Scheme 1.Magnetic
nanoparticles (Fe3O4) were prepared from a thermal
decomposition process and the surface of the Fe3O4
nanoparticles was coated with silica via a sol-gel
process. Subsequent appending of azide groups
to the silica surface, followed by application of the
click chemistry protocol (CuAAC) with rhodamine-
N-propargyl alkyne afforded RBT-Fe3O4@SiO2
nanoparticles.
RBT-functionalized Fe3O4@SiO2
nanoparticles were synthesized by the click
chemistry protocol (copper(I)-catalyzed azide
alkyne cycloaddition, CuAAC) which involved
grafting rhodamine-N-propargyl alkyne moieties
on the surface of Fe3O4@SiO2 nanoparticles27.
Rhodamine-N-propargyl alkyne was synthesized
in good yield from the condensation of rhodamine
B with hydrazine to obtain rhodamine hydrazide,
Scheme 1. Synthesis of RbT-functionalized Fe3O4@SiO2 nanoparticles
The presence of RBT on the surface of the
Fe3O4@SiO2 nanoparticles was confirmed by FT-IR
spectroscopy, as highlighted in Fig.1. Both Fe3O4@
SiO2 and RBT-Fe3O4@SiO2 nanoparticles exhibit
characteristic Fe-O stretching frequencies at 592
cm-1 and 586 cm-1, respectively. Absorption peaks at
797 cm-1, 963 cm-1 and 1104 cm-1 in RBT-Fe3O4@
SiO2 nanoparticles are assigned to Si-O stretching
vibrations which are also observed in Fe3O4@SiO2
nanoparticles (797 cm-1, 956 cm-1 and 1101 cm-1).
Strong intensity bands at 468 cm-1 and 464 cm-1,
ascribed to Si-O-Si bending are presented in Fe3O4@
SiO2 and RBT-Fe3O4@SiO2 nanoparticles, respectively.
The absorption bands around 1634 cm-1 in Fe3O4@
SiO2 nanoparticles and 1628 cm-1 in RBT-Fe3O4@SiO2
nanoparticles can be attributed to O-H bonds in silanol
groups. Furthermore, the FT-IR spectrum of RBT-
Fe3O4@SiO2 nanoparticles shows absorption peaks
at 635 cm-1, 1397 cm-1, 1490 cm-1 and 1573 cm-1
which can be assigned to C-H bending in aromatic
groups, alkyl (C-H) bending, aromatic C=C stretching,
and aromatic C=C bending, respectively, consistent
with surface functionalization of nanoparticles with
rhodamine-triazole entities. TGA analysis of RBT-
Fe3O4@SiO2 nanoparticles was further confirmed
the presence of organic functional groups on the
surface. From the TGA curves in Fig. 2, initial weight
loss occurred below 200 OC consistent with removal
of adsorbed water. Thermal decomposition of RBT-
Fe3O4@SiO2 occurs at 450-560 OC with a total weight
loss of 10.2%, in contrast to < 1% for both Fe3O4@SiO2
and azide-Fe3O4@SiO2 nanoparticles.
Fig. 1. FT-IR spectra of Fe3O4@SiO2 (blue line) and
RbT-Fe3O4@SiO2 (red line)
Fig. 2.TgA curves of (a) Fe3O4@SiO2 (blue line), (b) Fe3O4@SiO2-
N3 (red line) and (c) RbT-Fe3O4@SiO2 nanoparticles (black line)

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The magnetic property of Fe3O4@SiO2
nanoparticles was proved by XRD analysis. XRD
pattern inFig.3showsthecharacteristicdiffractionpeaks
ofmagnetiteFe3O4nanoparticlesat(220),(311),(400),(511),
RBT-Fe3O4@SiO2 nanoparticles was elucidated by
TEM image.Fig.4d shows that the average diameter
of the RBT-Fe3O4@SiO2 nanoparticles was about
155 nm. EDX analysis and elemental mapping of the
Fe3O4@SiO2 nanoparticles provide a further insight
into their composition with the elemental distribution of
iron (Fe) and silica (Si), as highlighted in Fig.5b.The
atomic percentages of carbon (C, 62.73%), oxygen
(O, 30.06%), silica (Si, 4.33%), and iron (Fe, 2.87%)
for RBT-Fe3O4@SiO2 nanoparticles are indicative of
the existence of organic and silica surface layers, as
shown in Fig. 5c.
(440) and (533),corresponding to previous reports28,29
.
Silica shows a broad peak around 20-28o suggesting
that Fe3O4 nanoparticles were coated with silica.
Fig. 3. XRd pattern of Fe3O4@SiO2 nanoparticles
The morphologies of the RBT-functionalized
Fe3O4@SiO2 nanoparticleswereobservedusingSEM
imaging (Fig. 4). Magnetic Fe3O4 nanoparticles are
spherical with the diameter approximately at 67 nm
(Fig. 4a). After the modification, silica-coated Fe3O4
nanoparticles(Fig.4b)andRBT-functionalizedFe3O4@
SiO2 nanoparticles (Fig. 4c) also remain spherical,
but they have larger sizes as expected from the
addition of surface coatings, respectively.The size of
Fig. 4. SEM images of (a) Fe3O4, (b) Fe3O4@SiO2, and (c)
RbT-Fe3O4@SiO2 nanoparticles, and (d) TEM image of
RbT-Fe3O4@SiO2 nanoparticles
Fig. 5. SEM images of Fe3O4@SiO2 in (a) normal mode, (b) EdS mode showing Fe (red), Si (green), and (c) the EdS mapping
profile of Fe3O4@SiO2 depicting elemental ratios
The selectivity of RBT-Fe3O4@SiO2
nanoparticles towards sensing of heavy metal ions
(Cu2+, Ni2+, Hg2+, Co2+, Fe2+, Fe3+ and Pb2+) in MeOH/
H2O (9:1, v/v) was investigated by UV absorption

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and fluorescence measurements. While initially
exhibiting colorless, the RBT-Fe3O4@SiO2 solutions
exhibit visible color changes on the addition of
metal ions, becoming pink in the presence of Cu2+,
Co2+, Ni2+ ions, and pink-orange when challenged
with Hg2+, Pb2+ and Fe3+ ions (Fig. 7b). However, no
change results from the presence of Fe2+ ion. From
Fig. 7a, the RBT-Fe3O4@SiO2 solutions exhibit an
absorption maximum at 554 nm when exposed to all
of the above metal ions, with Fe3+ ion resulting in the
highest absorption intensities.Fluorescence spectra
in Fig.8a indicate that the RBT-Fe3O4@SiO2 (control)
solution is only weakly fluorescent on excitation at
530 nm. Nevertheless, the addition of metal ions
with the exception of Fe2+ results in significant
fluorescence enhancements with maximum emission
wavelengths at 572 nm on addition of Co2+, 574 nm
for Cu2+ and Hg2+, 576 nm for Ni2+, 578 nm for Fe3+,
and 580 nm for Pb2+ ions.Furthermore, fluorescence
enhancement of the RBT-Fe3O4@SiO2 solution
displayed 1.5-fold upon the addition of Cu2+ in MeOH/
H2O (9:1, v/v) by excitation at 530 nm, as shown in
Fig. 8b. In case of Fe3+ ion, fluorescence emission
revealed 0.8-fold compared to the absence of metal
ions because of fluorescence quenching effect of
Fe3+ ion. From these results, the RBT-Fe3O4@SiO2
nanoparticles can act as a “naked-eye” colorimetric
and fluorescent sensor for certain heavy metal ions
(Cu2+, Hg2+, Co2+, Fe3+ and Pb2+).
investigated by ESI-MS analysis, with the results
shown in Fig. 10. As indicated above, the addition
of these ions results in both color changes and
fluorescence emission, resulting from the metal
ions promoted ring-opening of the spirolactam ring
in rhodamine19. The mass spectrum of the RBT-
Fe3O4@SiO2 solution in the presence of Cu2+ (in
MeOH) displayed a new molecular ion peak at m/z
of 457.2615, which is suggestive of formation of a
rhodamine methyl ester (calcd for C29H33N2O3, 457.
2486). This outcome is consistent with rhodamine
ring-opening followed by hydrolysis as postulated
previously27.
Fig. 6. Separation method of the RbT-Fe3O4@SiO2
nanoparticles in the aqueous phase using an external magnet
Due to the fluorescence enhancement
being greatest in the case of Cu2+, the fluorescence
response of the RBT-Fe3O4@SiO2 nanoparticles
to this metal ion was investigated in more detail
using titration experiments (Fig. 9). From the
fluorescence spectra in Fig. 9a, increasing the Cu2+
concentration results in fluorescence enhancements
with the maximum intensity being reached at 800 mM.
Excitation at 530 nm results in a linear relationship
(Fig. 8b) (y = 82.986X + 8677.2, R2 = 0.9909) at
574 nm between fluorescence intensity and Cu2+
concentration (range 100-800 mM). The detection
limit was determined to be 9.8 mM based on 3s/S,
where s is the standard deviation of the fluorescence
intensity of the RBT-Fe3O4@SiO2 solution and S is
the slope of the calibration curve. Moreover, naked
eye color changes in the RBT-Fe3O4@SiO2 solution
were observable for Cu2+ ion concentrations > 50
mM, as shown in Fig. 9c.
Fig. 7. (a) UV-absorption spectra of the RbT-Fe3O4@SiO2 (20
mg) solutions in MeOH/H2O (9:1, v/v) in the presence of
various metal ions (1 mM), and (b) a bar graph showing the
relative absorbance (554 nm) of the RbT-Fe3O4@SiO2 (20
mg) solutions in the presence of these metal ions (1 mM),
in MeOH/H2O (9:1, v/v); Inset: Color changes of the
RbT-Fe3O4@SiO2 (20 mg) solutions on the addition of
metal ions (1 mM), in MeOH/H2O (9:1, v/v)
The binding mechanism of Cu2+ to RBT-
Fe3O4@SiO2 nanoparticles in MeOH was further

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Fig. 10. Mass spectrum of the RbT-Fe3O4@SiO2 (20 mg)
solution upon the addition of Cu2+ in MeOH
CONCLUSION
Wehavesuccessfullysynthesizedrhodamine-
triazole functionalized Fe3O4@SiO2 nanoparticles,
based on the click chemistry approach. Upon the
addition of heavy metal ions (Cu2+, Co2+, Ni2+, Hg2+, Fe3+,
and Pb2+), the solutions of these nanoparticles exhibited
distinctnakedeyecolorchanges(maximumabsorption
wavelength at 554 nm), and intense fluorescence
emissions at 572-580 nm. As Cu2+ ion displayed
optimum binding behavior, the limit of detection was
found to be 9.8 mM with fluorescence responses
showing a linear correlation with Cu2+ concentration in
the range of 100 to 800 mM.
Fig. 8. (a) Fluorescence spectra obtained by excitation of
the RbT-Fe3O4@SiO2 (20 mg) solutions in MeOH/H2O (9:1,
v/v) at 530 nm in the presence of metal ions (1 mM), and (b) a bar
graph depicting the relative fluorescence enhancement (574 nm)
(DF/F0) of the RbT-Fe3O4@SiO2 (20 mg) solutions on the addition
of metal ions (1 mM) in MeOH/H2O (9:1, v/v)
ACKNOWLEdgMENT
This work was financially supported
by the Institute of Research and Development,
Rajamangala University of Technology Thanyaburi
(Project No.NRF62D0602).We wish to thank Assoc.
Prof. Dr. Palangpon Kongsaeree (Department of
Chemistry, Mahidol University) for experimental
supports and Associate. Prof. Dr. Christopher
Smith (Kamnoetvidya Science Academy) for his
suggestions. We would also like to thank the
Kamnoetvidya Science Academy (KVIS) and
Vidyasirimedhi Institute of Science and Technology
(VISTEC) for use of equipment for characterization
purposes.
Fig. 9. (a) Fluorescence spectra obtained by excitation of the
RbT-Fe3O4@SiO2 (20 mg) solutions at 530 nm in MeOH/H2O (9:1,
v/v) with the addition of Cu2+ (10-1,000 mM), (b) calibration curve
and (c) color changes of the RbT-Fe3O4@SiO2 (20 mg) solutions
in MeOH/H2O (9:1, v/v) on the addition of Cu2+ (10-1,000 mM)
Conflict of Interest
The authors declare that they no conflict of
interest.

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