Selective chemosensing of spermidine based on fluorescent organic nanoparticles in aqueous media via a Fe3+ displacement assay

Article abstract of DOI:10.1039/c4nj02381a

A novel fluorescent chemosensor based on fluorescent organic nanoparticles (F1) has been synthesized. This tripodal framework shows significant fluorescence quenching for Fe³⁺ ions from among nineteen metal ions due to the formation of a F1·Fe³⁺ complex. The lowest detectable concentration of F1 for Fe³⁺ ions was found to be 1.66 μM. Upon the addition of spermidine (a biologically active amine), the fluorescence intensity of the aqueous solution of complex increases with a detection limit of 3.68 μM indicating that spermidine can displace Fe³⁺ ions from the F1·Fe³⁺ complex. Moreover, the recognition of spermidine was selective with no interference from other biogenic amines studied. Thus, F1·Fe³⁺ acts as a potential sensor for spermidine through a cation displacement assay in aqueous media.

Full text of DOI:10.1039/c4nj02381a

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Selective chemosensing of spermidine based on
fluorescent organic nanoparticles in aqueous
media via a Fe displacement assay†
Cite this:DOI: 10.1039/c4nj02381a
3+
a
b
a
c
Shweta Chopra,‡ Jasminder Singh,‡ Harpreet Kaur, Harpreet Singh,
b
a
Narinder Singh* and Navneet Kaur*
A novel fluorescent chemosensor based on fluorescent organic nanoparticles (F1) has been synthesized. This
3+
tripodal framework shows significant fluorescence quenching for Fe ions from among nineteen metal ions
3+
3+
due to the formation of a F1ÁFe complex. The lowest detectable concentration of F1 for Fe ions was
found to be 1.66 mM. Upon the addition of spermidine (a biologically active amine), the fluorescence intensity
of the aqueous solution of complex increases with a detection limit of 3.68 mM indicating that spermidine
Received (in Montpellier, France)
2
3rd December 2014,
Accepted 10th February 2015
3+
3+
can displace Fe ions from the F1ÁFe complex. Moreover, the recognition of spermidine was selective with
DOI: 10.1039/c4nj02381a
3+
no interference from other biogenic amines studied. Thus, F1ÁFe acts as a potential sensor for spermidine
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through a cation displacement assay in aqueous media.
Therefore, keeping the concern for food safety and human
health in view, the detection of these target amines is bene-
Introduction
The selective recognition and sensing of biologically important ficially required. In contrast to the analytical tools reported
9
–13
analytes such as metal ions and amines with artificial receptors for the investigation of metal ions,
elaborate procedures
1
–3
is an important area of research. Under the class of biogenic such as deproteination, centrifugation, and HPLC analysis
amines (BAs), which are products of the enzymatic decarbox- are known for the determination of BAs due to which research
1
3–15
ylation of amino acids found in living organisms and which in this area is facing challenges.
Thus, a necessary goal is
plays vital role in the regulation of gene expression and cell the development of a rapid and concise procedure for the
growth, histamine, putrescine, cadaverine, tyramine, tryptamine, analysis of biologically active amines with their applicability
b-phenylethylamine, spermine and spermidine are considered in aqueous medium.
4
,5
to be the most important BAs occurring in foods. Despite
To achieve this goal, we focused our attention on the
the important physiological functions displayed by BAs, e.g., fabrication of fluorescent organic nanoparticles of the newly
aliphatic polyamines spermine and spermidine are involved synthesized novel tripodal receptor (1) in 99% aqueous medium.
6
16
in cell proliferation and histamine role in gastric secretion,
In this context, Yao and coworkers have already explained
raised levels of these amines is undesired causing headaches, the reprecipitation method for the formation of FONs in
respiratory distress, heart palpitations and several allergic which a monomer solution is injected rapidly into a solvent
disorders. For example, food-borne intoxication is induced by which reflects the rare solubility of the monomer. Further, it
7
histamine via ingestion of sea food; increased level of spermi- is associated with the addition of water and follows the
dine and spermine in urine can be used as a tool for early general Ostwald type ripening process. Water and DMF are
8
diagnosis and evaluation of effectiveness of cancer therapy.
miscible, so the solubility of hydrophobic tripodal receptor
decreases with the increasing fraction of water, gradually
reaching a critical nucleation condition at which nuclei form
1
a
Centre for Nanoscience and Nanotechnology (UIEAST), Punjab University,
1
7
throughout the solution and begin to grow as nanoparticles.
Chandigarh, 160014, India. E-mail: navneetkaur@pu.ac.in; Tel: +91-1722534464
3
+
b
The chemosensor comprising of association of Fe ions
with FONs is capable of detecting biological amines at a
physiological pH. Upon complexation with metal ion, the
fluorescence from the fluorophore is quenched. However,
Department of Chemistry, Indian Institute of Technology Ropar (IIT Ropar),
Rupnagar, Punjab, 140001, India. E-mail: nsingh@iitrpr.ac.in;
Tel: +91-1881242176
c
SMMEE, Indian Institute of Technology Ropar (IIT Ropar), Rupnagar,
Punjab, 140001, India
3
+
spermidine which was more active for Fe reduction led to
the displacement of the metal ion resulting in the restoration of
the fluorescence of FONs.
†
Electronic supplementary information (ESI) available: Experimental details,
fluorescence spectra, NMR spectra, mass spectra. See DOI: 10.1039/c4nj02381a
Both authors contributed equally.
‡
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Results and discussion
Synthesis
The synthesis of receptor 1 was carried out via the condensation of
3
-(dimethylamino)-1-propylamine and 2-pyridine carboxaldehyde
followed by reduction with NaBH in methanol and further
reaction of the reduced product with 1-naphthyl isocyanate
4
1
8
(
Scheme 1). The compound 1 was fully characterized using
1
13
H NMR, C NMR, and mass spectroscopy (Fig. S1–S3, ESI†).
Preparation of nano-aggregates
With the growing interest in nanotechnology due to its substantial
applications in all the aspects of sciences and engineering, it
has been embraced most frequently in multidisciplinary fields. It
also emphasizes the fabrication and characterization of substances
having sizes in the nano range, as a smaller particle size leads to a
high surface to volume ratio, allowing the distinct spatial domains.
Moreover, nanosized particles facilitates a higher amount of
binding regions on the surface making them ideal multivalent
platforms for the realisation of environmentally and biologi-
1
9,20
cally relevant analytes.
Thus, we focused on the preparation
of fluorescent organic nanoparticles (F1) of tripodal receptor 1
employing a simple reprecipitation method, in which a small
volume fraction from stock solution of receptor in organic solvent
(1 mM) was slowly injected into bidistilled water using a micro-
syringe. The solution was sonicated to ensure the proper mixing
of two solvents, which resulted in aggregation of organic molecules
due to the dramatic change of solvent properties, and an aqueous
dispersion of nanoparticles was ultimately obtained. The particle
size of the nanoaggregates was analysed using TEM (transmission
electron microscopy) showing a spherical size of 18 nm and size
distribution was confirmed from DLS (dynamic light scattering) to
be in 25–60 nm range (Fig. 1).
Fig. 1 (A) TEM image (B) DLS size distribution of FONs of receptor 1
prepared in aqueous solution.
Effect of water content
the stabilization of the excited state of fluorophore undergoing
p–p* transition upon increasing the polarity of the solvent
system (Fig. 2A).
Using the fluorescence spectroscopic technique, the effect
of water on the photophysical properties was monitored. The
fluorescence spectra of receptor 1 (10 mM) in DMF exhibited an
emission peak at 365 nm. As the solvent system was changed
from DMF to water, the bathochromic shift of 5 nm (peak shift
from 365 nm to 370 nm) was observed which could be due to
Recognition studies
To study the ability of F1 to bind metal ions, fluorescence
measurements were performed in water : DMF (99 : 1, v/v)
solution. The responses of F1 (10 mM) of receptor 1 were
interrogated in the presence of 10 equiv. of different metal
+
+
+
+
2+
2+
2+
2+
3+
3+
ions such as Li , Na , K , Cs , Mg , Ca , Ba , Sr , Al , Cr ,
2
+
3+
2+
2+
2+
+
2+
2+
2+
Mn , Fe , Co , Cu , Zn , Ag , Pb , Cd and Hg . The
probe F1 exhibits an emission band at 370 nm when excited at
3
+
3
01 nm. Among the metal ions, only Fe selectively quenches
the fluorescence intensity of F1 (Fig. 2) whereas the others
exhibit no fluorescence quenching response under the same
spectroscopic conditions.
3
+
Moreover, upon the addition of Fe ions from 0–140 mM,
the fluorescence intensity started quenching steadily showing
a good linearity having a linear coefficient of 0.9857 (Fig. 3).
2
1
The detection limit calculated by 3s method was found to be
1.66 mM. In order to test whether FONs (F1) could be used for
Scheme 1 Synthesis of receptor 1.
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+
+
+
+
2+
2+
2+
2+
3+
3+
interferents like Li , Na , K , Cs , Mg , Ca , Ba , Sr , Al , Cr ,
2+
2+
2+
2+
+
2+
2+
2+
Mn , Co , Cu , Zn , Ag , Pb , Cd and Hg (10 equiv. each).
However, no significant change in the fluorescence spectral
3
+
profile of FONs.Fe was observed. This result showed the good
3+
sensitivity and selectivity of F1 for Fe over other competitive
metal ions (Fig. S4, ESI†).
Detection of spermidine
3
+
3+
Since F1 selectively recognized Fe , the utility of the F1ÁFe
complex was studied as a secondary chemosensor for the
selective recognition of biogenic amines (BAs). In this context,
the photonics of the F1ÁFe complex was explored via the addition
of 15 equiv. of a series of biogenic amines (spermidine, spermine,
tyramine, 2-phenylethylamine, histamine, 1,2-diaminopropane,
3+
1
,4-diaminobutane, and 1,5-diaminopentane). Under the influence
of spermidine, the emission band of the solution of complex at
70 nm was greatly resurrected. In contrast, addition of other BAs
did not induce any obvious change (Fig. 4A). Further addition of
3
3+
increasing concentration of spermidine into the F1ÁFe complex
solution showed linear resurrection of the fluorescence profile of
FONs, having good linearity with a regression coefficient of
0
.9876 (inset Fig. 4B), with a detection limit of 3.68 mM
2
1
calculated using the 3s method. The restored fluorescence
Fig. 2 (A) Emission spectrum of F1 in water and receptor 1 in DMF;
3+
(
B) fluorescence spectra of F1 (10 mM) with Fe ions (10 equiv.) in H
2
O :
DMF (99 : 1, v/v) solution.
3+
Fig. 3 Fluorescence spectra of F1 upon addition of Fe ions as nitrate
salt in H O : DMF (99 : 1, v/v) solution. Inset: a plot of fluorescence intensity
depending on the concentration of Fe ranging from 0–140 mM.
2
3+
3+
Fig. 4 (A) Fluorescence emission spectra of complex F1ÁFe (10 mM) with
3+
2
Fe in the absence and presence of different biogenic amines in H O:DMF
3+
(
99 : 1, v/v) solution, (B) fluorescence spectra of F1ÁFe complex (10 mM) in
the presence of different concentrations of spermidine in H O : DMF
99 : 1, v/v) solution. Inset: a plot of fluorescence intensity depending on
3
+
selective sensing of Fe ions even in the presence of other
metal ions, a competitive experiment was conducted for deter-
2
(
3
+
3+
mination of Fe (10 equiv.) in the presence of various metal ion the concentration of Fe ranging from 0–125 mM.
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Fig. 6 Density functional theory calculations and their HOMO & LUMO
energy comparison.
3
+
Fig. 5 Competitive binding assay of F1ÁFe complex towards spermidine
(
(
15 equiv.) in the presence of other biogenic amines, (A) spermidine only,
B) spermine, (C) tyramine, (D) 2-phenylethylamine, (E) histamine, (F) 1,2-
3+
diaminopropane, (G) 1,4-diaminobutane, (H) 1,5-diaminopentane.
signifies the formation of 1 : 1 complex of F1ÁFe . The quenching
in the fluorescence can be attributed to the open shell effect of
3+
22
Fe ions. Similarly, when spermidine is added to the solution of
can be attributed to the fact that spermidine caused the
3+
complex F1ÁFe , a clear shift in the peak and formation of a
3
+
3+
displacement of Fe from the F1ÁFe , indicating that F1 can
peak at m/z = 325.4 is observed (Fig. S10, ESI†), which is due to
be used as a reversible chemosensor (Fig. 4B) for the determination
3+
the formation of a complex between Fe and spermidine along
3+
of both Fe ions and spermidine.
with two nitrate ions. Moreover, in the same mass spectrum,
the pak at m/z = 363 also signifies the recovery of ligand peak.
The competitive experiments were also performed for sermidine
3
+
determination using the F1ÁFe complex, via addition in the
The stoichiometry and the binding constant of the complex was
presence of 15 equiv. of potentially interferent biogenic amines
23,24
calculated using the Lehrer–Chipman equation,
(Fig. S11
(
spermine, tyramine, 2-phenylethylamine, histamine, 1,2-diamino-
propane, 1,4-diaminobutane, and 1,5-diaminopentane). As shown in
Fig. 5, the emission spectra of the complex with spermidine remain
and S12, ESI†). The plotted curves clearly show the stoichiometry
of 1 : 1 for both the complexes, with a binding constant of 3.08 Â
4
À1
3+
4
À1
1
0 M for F1ÁFe and 4.29 Â 10 M for the complex of
3
+
unaffected by different biogenic amines proving F1ÁFe as a
3+
spermidine with Fe .
The selectivity for decomplexation of F1ÁFe is explained on
selective sensor for the detection of spermidine in aqueous medium.
3+
25–28
the basis of DFT calculations carried using the DMol
3
package
pH and salt effect
with DFT (density functional theory) calculations run through GGA
The effect of pH on the fluorescence emission spectrum of with the basis set DNP (double numeric plus polarization). It
developed FONs (F1) solution was studied (Fig. S5, ESI†). The is quite evident from the HOMO and LUMO energies of both
3
+
3+
emission intensity remains unchanged within a wide pH range complexes i.e. F1ÁFe and the complex of spermidine with Fe
3
+
covering the physiological pH. However, a slight change in the ions that the spermidine.Fe complex has stable HOMO and
intensity at very high or very low pH values may be related to the LUMO as compared with that of that receptor or its complex
protonation or deprotonation of the molecule. The experiment with Fe ions (Fig. 6).
was also conducted to see the effect of high ionic strength,
It is also concluded from the studies that spermidine engulfs
3
+
3
+
therefore, tetra butyl perchlorate salt (0–100 equiv.) was added the Fe ion by forming a cage-like cavity around it. The lone pair
but no change in the fluorescence intensity of emission spectra of nitrogen present in spermidine donates their lone pair to
3
+
of F1 (10 mM) was observed (Fig. S7, ESI†). A similar behaviour electron deficient Fe ions. However, other compatriot biogenic
3
+
was observed for the F1ÁFe complex (Fig. S6 and S8, ESI†). amines do not have such multiple heteroatoms forming a cavity
3
+
3+
Thus, both F1 and F1ÁFe complexes exhibited solubility as for complexation with Fe ions. Although, spermine has similar
well as good stability under a wide pH range with no hindrance nitrogen atom but the atoms are in opposite orientation to that
from the salts present in the environment and this feature proves of the centre of the molecule. Therefore it does not converge to a
3
+
their practical application for the determination of spermidine in stable configuration. Iron gets decomplexed from F1ÁFe and
aqueous medium.
the open shell effect gets cancelled leading to enhancement in
the fluorescence intensity.
Authentication of the complexation and decomplexation of F1
3
+
Real sample analysis
For authentication of the complexation of F1 with Fe to form
3
+
F1ÁFe and its decomplexation upon addition of spermidine The artificially prepared samples of spermidine were prepared
were studied using mass spectra. It was quite clearly observed by adding known concentrations of spermidine into water
3
+
that the addition of Fe ions in F1 generated an altogether new solution. The prepared samples were analysed using proposed
3
+
À
peak at m/z = 542.3 [ligand + Fe + 2NO
3
] (Fig. S9, ESI†), which sensors and results are given in Table 1. It is quite evident from
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Table 1 Real sample analysis of artificially prepared samples of spermi- (1.25 ml, 10 mmol) at room temperature. After the reaction
dine and their percentage recovery using proposed sensor
mixture was stirred overnight, the liquid product (Schiff’s base)
obtained was reduced with NaBH4 (1.5 g, 40 mmol), diluted
Concentration Concentrationa
Entry no. Sample
added
of spermidine
Recovery (%) with MeOH (10 mL) and kept stirring overnight at room
temperature. The solvent was concentrated under reduced
1
2
3
Sample 1 20 mM
Sample 2 25 mM
Sample 3 10 mM
18.2 Æ 0.37 mM 91
23.2 Æ 0.51 mM 92.8
9.36 Æ 0.24 mM 93.6
pressure, and the residue was extracted using CHCl
mixture. The organic layer was extracted and dried over Na
3
and water
SO
2
4
a
Mean of three determinations.
and concentrated to acquire the reduced amine. Further, the
reaction of reduced amine with 1-naphthyl isocyanate (425 mL,
3
2.96 mmol) taken in CHCl (12 mL) at 75 1C was refluxed
the Table 1 that proposed sensor can determine spermidine in overnight and solvent was removed under reduced pressure to
given solution with utmost accuracy having a recovery percentage obtain a residue which was recrystallized using EtOH to yield
1
of more than 90% in all the samples.
compound 1. H NMR (CDCl , 400 MHz): 1.83 (q, 2H, CH ), 2.08
3
2
The prepared sensor was compared with the reported sensor (s, 6H, CH
3
), 2.40 (t, 2H, CH
2
), 3.63 (t, 2H, CH
2
), 4.70 (s, 2H,
in the literature. It is quite evident from the comparison table CH2), 7.17 (t, 1H, ArH), 7.44 (m, 5H, ArH), 7.63 (t, 1H, ArH), 7.82
Table S1, ESI†) that proposed sensor for selective determina- (t, 1H, ArH), 8.06 (t, 1H, ArH), 8.56 (d, 1H, ArH), 10.30 (s, 1H,
(
1
3
tion of spermidine clearly holds an edge over the reported NH); C-NMR (CDCl
3
, 400 MHz): 14.71, 25.11, 31.06, 44.37,
sensors, as it determines spermidine in lower micromolar range 61.41, 119.50, 122.09, 122.53, 122.83, 123.74, 125.35, 125.59,
selectively in total aqueous systems.
126.05, 128.55, 134.30, 135.70, 137.17, 148.95, 158.18, 158.99.
CHN analysis: calculated = C 72.88, H 7.93, N 15.46. Obtained =
C 72.90, H 7.98, N 15.27, ESI-MS m/z = 363.3 [M + H] .
+
Conclusions
Synthesis of nano-aggregates
In conclusion, we have developed a fluorescence sensor F1
which is selective and sensitive for detection of Fe ions in
aqueous medium. The influence of Fe ions results in the
quenching of the fluorescence intensity of F1 with no inter-
ference from other metal ions. Further F1ÁFe system has been
used as a chemosensing ensemble for the sensing of biogenic
amine spermidine at a physiologically relevant pH via the
displacement approach i.e. by removal of the metal ion from
the complex, thus, restoring the fluorescence profile of F1.
3
+
The formation of fluorescent organic nanoparticles (F1) of receptor
1 in aqueous solution was carried out successfully using reprecipita-
tion method. During this method, 0.1 ml of stock solution of 1 was
injected slowly into 100 ml of double distilled water followed by
sonication for 10 min. retaining the constant concentration of
3
+
3
+
634 nm in 1 ml DMF which was found to be appropriate amongst
various concentrations of compound 1 dissolved in DMF.
Recognition studies
To study the binding ability of the F1/complex of F1 toward
different analytes, fluorescence measurements were recorded at
Experimental
General information
À3
25 Æ 1 1C. The standard solutions of 5.0 Â 10 M concentration
of analytes were all prepared in double distilled water. For
Analytical grade chemicals purchased from Sigma-Aldrich Co.
were used for the experimentation. H and C NMR spectra were
recorded using an Avance-II (Bruker) instrument (400 MHz and
analysis, the 5 ml solutions of F1 (10 mM) with added analytes
1
13
(100 mM) were kept for half an hour to obtain uniformity and
shaken well before using it for studying the cation binding
100 MHz, respectively). Mass spectra were obtained from a
behaviour of F1 in aqueous medium. Titrations were performed
quadrupole, time-of-flight mass spectrometer (LC-MS Spectro-
meter Model Q-ToF Micro Waters) and CHN analysis was
performed using a Perkin Elmer 2400 CHN Elemental Analyser.
The fluorescence emission spectra were taken on a Shimadzu
RF-5301Pc Fluorescence spectrophotometer. TEM images were
recorded on a Hitachi (H-7500) instrument worked at 120 kV.
This instrument has a resolution of 0.36 nm (point to point) with
a 40–120 kV operating voltage. A 400 mesh formvar carbon-
coated copper grid was used for sample preparation. The particle
size of nano-aggregates was determined using Dynamic Light
Scattering (DLS) using the external probe feature of the Metrohm
Microtrac Ultra Nanotrac Particle Size Analyzer.
using different concentrations of Fe(NO
3 3
) in volumetric flasks.
Following this, competitive experiment was also conducted for
3
+
Fe estimation by preparing solutions of F1 (10 mM) with and
without other metal ions (100 mM each). Further, determination
of spermidine was carried out using a similar pattern for the F1Á
3
+
Fe complex (10 mM) and the evaluation of the interference
behaviour in spermidine was performed using 150 mM solution
of each biogenic amine. The effect of pH and ionic strength was
3
+
studied for both F1 and F1ÁFe complexes. Different concentra-
tions of a TBA salt of perchlorate (0–100 equiv.) were employed to
observe the effect of ionic strength.
Theoretical studies
Synthesis of receptor 1
The geometry of the complex was optimized using the DMol3
2
5,26
To a solution of 2-pyridinecarboxaldehyde (0.95 ml, 10 mmol) package
with GGA-DFT, using double numerical plus polar-
in MeOH (10 mL) was added (3-dimethylamino)-1-propylamine ization (DNP) as the basis set. All electrons of the system were
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2
7,28
treated using the BLYP
correlation potential.
local functions for the exchange– 11 R. M. F. Batista, E. Oliveira, S. P. G. Costa, C. Lodeiro and
M. M. M. Raposo, Tetrahedron, 2011, 67, 7106–7113.
1
1
1
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4 J. Donthuan, S. Yunchaland and S. Srijaranai, Anal. Methods,
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Three different samples with known concentrations of spermidine
were prepared and were analysed using the proposed sensor.
2
014, 6, 1128–1134.
15 J. Lange and C. Wittmann, Anal. Bioanal. Chem., 2002, 372,
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Acknowledgements
2
This work was supported by a research grant provided by UGC,
New Delhi.
1
1
1
1
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