A switchable electrochemical redox ratiometric substrate based on ferrocene for highly selective and sensitive fluoride detection

Article abstract of DOI:10.1039/c6ra14416k

A novel latent electrochemical probe based on a ferrocenyl carbamate derivate (FCCD) was synthesized for the highly selective ratiometric detection of fluoride (F^-). FCCD was synthesized through an easy, one step reaction using ferrocenyl azide and silyl protected benzyl alcohol as precursors through a Curtius rearrangement. In presence of F^-, FCCD undergoes a nucleophilic substitution reaction, which led to the removal of silyl protecting group through 1,6-quinone-methide rearrangement with concomitant release of ferrocenyl amine (FA). As the concentration of F^- increases, the amount of FCCD is dissipated, while that of FA accumulated in the reaction medium were monitored through the linear changes in their redox couples. Compared with a conventional ion selective electrode, the use of a cheaper unmodified electrode as a transducer coupled with FCCD displayed higher stability, excellent selectivity and better sensitivity with LOD of 5.1 × 10^-7 M (9.69 ppb). Moreover, FCCD is a selective and sensitive colorimetric visualization probe for F^-. The proof-of-concept of the approach is demonstrated in direct toothpaste sample (non-transparent solutions), biological and water samples. The important advantages of this approach are high selectivity, the use of cheaper unmodified electrode, adoption of simple electrochemical methods, dual channel detection, low overpotential of the reporter, naked-eye detection, and ability to detect F^- in non-transparent samples.

Full text of DOI:10.1039/c6ra14416k

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A switchable electrochemical redox ratiometric substrate based
on ferrocene for highly selective and sensitive fluoride detection
Kesavan Manibalan,a Veerappan Mani,a,b Sheng-Tung Huanga,b*
Received 00th January 20xx,
Accepted 00th January 20xx
A novel latent electrochemical probe based on ferrocenyl carbamate derivate (FCCD) was synthesized for highly selective
ratiometric detection of fluoride (F–). FCCD was synthesized through easy one step reaction using ferrocenyl azide and silyl
protected benzyl alcohol as precursors through Curtius rearrangement. In presence of F–, FCCD undergoes nucleophilic
substitution reaction and led to the removal of silyl protecting group through 1,6 quinone-methide rearrangement with
concomitant release of ferrocenyl amine (FA). As the concentration of F− increases, the amount of FCCD is dissipated, while
that of FA accumulated in the reaction medium which were monitored through the linear changes in their redox couples.
Compared with conventional ion selective electrode, the use of cheaper unmodified electrode as transducer coupled with
FCCD displayed higher stability, excellent selectivity and better sensitivity with LOD of 5.1×10–7 M (9.69 ppb). Besides,
FCCD is selective and sensitive colorimetric visualization probe for F−. The proof-of-concept of the approach is
demonstrated in direct toothpaste sample (non-transparant solutions), biological and water samples. The important
advantages of this approach are high selectivity, the use of cheaper unmodified electrode, adoption of simple
electrochemical methods, dual channels detection, low overpotential of reporter, naked-eye detection, and ability to
DOI: 10.1039/x0xx00000x
www.rsc.org/
detect
F–
in
non-transparent
samples.
probes for anions is of great importance.4-7 In the present
work, we desired to develop a novel latent electrochemical
redox ratiometric probe for detection of fluoride anion (F–), a
smallest known anion for its significance in environmental and
biochemical processes.8 It is an essential trace element and
hence it is useful additive added in toothpaste, pharmaceutical
agents and drinking water. However, F– is potentially toxic if its
concentrations exceed cellular requirements which will cause
severe health risks.9 The permissible overall quantity of F−
present in toothpaste is regulated within the range of 0.50 to
1.50 mg g–1. the US Environmental Protection Agency (US EPA)
has recommended upper allowed limit of 2 ppm (105 µM) F– in
drinking water.10 However, detection of low concentrations of
F– in polar and aqueous solutions remains challenging without
expensive analytical equipment. Ion selective electrode (ISE) is
the standard method employed in current F– detection.11
However, it encounters certain disadvantages, such as,
interference from hydroxide/hydrogen ions, poor selectivity
due to the non-covalent complexations and low stability.12 The
optical probes developed based on specific chemical affinity
between F– and Si are the most successful in selectivity since
the recognition is highly selective; wherein, F– triggers the
cleavage of Si-O bond installed in probes and releases optical
reporters.3,13,14 Nevertheless, so far only two electrochemical
substrates are reported for F– detection based on TBDMS (tert-
butyltrimethylsilane) trigger; (1) hydroquinone probe reported
by our group,6 however it requires higher organic electrolyte
phase (2) spiropyran derivative, although it showed good
sensitivity, the probe preparation involves multi-step
Introduction
The design of chemosensors for determination of anions
through specific anion-induced reactions couples with
selective changes in optical signals is renowned sensing
approach in environmental safety.1 To date many optical
(fluorogenic and chromogenic) chemosensors have been
developed for the detection of anions.2,3 Importantly, optical
methods require transparent samples and rely on additional
expensive optical tools to convert underlying chemical signal
(analyte-probe interaction) into electronic signal. In addition,
optical methods encounter certain limitations such as low
quantum yield, pre-sampling steps, auto-absorption/auto-
fluorescence, bulky and laborious. In contrary, electrochemical
instruments does not require transparent solutions and they
can directly convert the chemical reaction into electronic
signal. In addition, electrochemical methods are simple, fast,
low-cost, portable, easy to handle, miniaturizable and require
low power and minimal sample. In recent years,
electrochemical methods are emerging as potential alternative
to optical methods and hence design of latent electrochemical
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procedures and the probe should be immobilized on the
electrode surface using carbon nanotubes which involves
additional fabrication procedures, cost and extra-time.12
Experimental section
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DOI: 10.1039/C6RA14416K
Materials and Instrumentation
Ferrocence carboxylic acid and diphenylphosphorylazide
were purchased from Tokyo Chemical Industry Co., Ltd. 1,2-
dichloroethane triethyl amine and trimethylamine were
purchased from TEDIA and Acros organics respectively. 4-
hydroxy benzaldehyde, toluene imidazole, methanol,
Herein, we sought to develop a switchable electrochemical
substrate, ferrocene based carbamate derivative (FCCD) for
simple and facile F– detection using cheaper unmodified
electrode at interference-free potential without compromising
sensitivity and selectivity (Scheme 1). The synthesis of FCCD is
easy one step reaction using ferrocenyl azide (1) and silyl
protect benzyl alcohol (2) through Curtius rearrangement.
Ferrocenyl amine (FA) is a sustainable redox reporter due to its
favourable electrochemical properties, excellent stability and
easy derivatization. Under optimal voltammetric conditions,
FCCD (substrate) and FA (reporter) delivered distinct redox
couples, RCFA and RCFCCD at formal potentials (E0’) of – 0.0026 V
and + 0.30 V with fairly high potential separation of 302.6 mV
(inset, Fig. 1A). In presence of F–, FCCD undergoes nucleophilic
substitution reaction at Si-O bond due to the special affinity of
F– for Si and led to the removal of silyl protecting group
sodiumborohydride,
2-[4-(2-hydroxyethyl)piperazin-1-
yl]ethanesulfonic acid, tert-butyldimethylsilylchoride, sodium
fluoride and other common anions were obtained from Sigma
Aldrich and used as received. Bovine serum isolated from cows
is bought from Sigma-Aldrich. Rain water and tap water
samples were collected from National Taipei University of
Technology, Taipei, Taiwan. Sensodyne toothpaste was
1
purchased from Taiwan local medical shop. H NMR and 13C
NMR were acquired using BRUKER AVANCE 300 spectrometer
in CDCl3 using TMS as an internal standard. Mass spectra were
recorded using a Finnigan TSQ 700 triple quadrupole mass
spectrometer equipped with an electrospray ionization (ESI)
ion source. UV-visible and Fourier-transform infrared
spectroscopies were performed using Jasco 630 spectrometer
and HORIBA 720 spectrometer, respectively. All the
electrochemical experiments were carried out on a CHI 612D
electrochemical workstation at ambient conditions. The three-
electrode cell comprises a glassy carbon electrode (GCE) as a
working electrode (area 0.071 cm2), platinum-wire as a
counter electrode, and saturated Ag|AgCl (saturated KCl) as a
reference electrode.
through
1,6
quinone-methide
rearrangement
with
concomitant release of reporter ferrocenyl amine (FA). As the
concentration of F− increases, the amount of FCCD dissipated,
while that of FA accumulates in the reaction medium. The
concentration of reacted F− is related to the dissipated
amounts of FCCD and accumulated amounts of FA which in
turn linearly related to their electrochemical redox couples,
RCFA and RCFCCD, respectively. The redox reaction is related to
one electron-one proton reversible process between ferrocene
and ferrocenium cation.4 The important advantages of this
approach are the use of cheaper unmodified electrode,
adoption of simple electrochemical methods, dual channels
detection, low overpotential of reporter, high selectivity,
naked-eye detection, ability to detect both aqueous and
organic F− and promising practicality in non-transparent
samples.
Synthesis of ferrocenyl carbamate derivative: (2-((((4-((tert-
butyldimethylsilyl)oxy)benzyl)oxy)carbonyl)amino)cyclopenta-2,4-
dien-1-yl)(cyclopenta-2,4-dien-1-yl)iron
Compound
procedures.15,16 Next, 250 mg (1 equivalents) of compound
was treated with 230 mg (1 equivalents) of compound in 3
ml of toluene and refluxed for 1 h at 115°C under N2
atmosphere to give final compound (FCCD). The overall yield
1 and 2 were prepared by previously reported
2
1
3
was 74% after column chromatography separation using ethyl
acetate-hexane (10:90, v/v). 1H NMR (300 MHz; CDCl3, ppm):
δ= 0.7.22 (2H, d, J = 8.2 Hz), 6.86 (2H, d, J = 8.1 Hz) 5.12 (2H, s),
4.27 (2H, s), 4.13 (5H, s), 3.93 (2H, s), 0.96 (9H, s), 0.16 (6H, s)
(Fig S11). 13C NMR (300 MHz; CDCl3, ppm): δ=18.3, 25.68,
69.17, 95.47, 120.2, 128.87, 130.01, 153.83 (Fig S12). MS
(ESI+): Calcd for C24H31FeNO3Si: m/z 465.14, found 465.1 (Fig
S13). FT-IR of compound 1: ν = 1673.91 cm–1 (azide C=O);
2150.24 cm–1 (azide N3). FT–IR of compound
3 (FCCD):
3478.95 cm–1 (amide NH), 1700.97 cm–1 (amide C=O).
Electrochemical testing conditions
The GCE surface was cleaned by polishing it with 0.05 µm
alumina slurry using Buehler polishing kit. Next, it was
ultrasonicated for 5 min in ethanol and water respectively, and
dried in oven for 20 min. The optimized parameters for cyclic
voltammetry experiments: potential range= − 0.30 to + 0.50 V
Scheme 1 Synthesis of FCCD and its reaction with F−. TBDMS=
tert-Butyldimethylsilyl ether
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and scan rate= 50 mV s–1. The optimized supporting electrolyte
used all over the cyclic voltammetry (CV) and differential pulse
voltammetry (DPV) experiments is 50/50% (v/v%) of
DMF/HEPES (pH 7.8) buffer unless otherwise specified. The
optimized parameters for DPV measurements: amplitude =
0.05 V, sampling width = 0.0167 s and pulse period = 0.5 s. In
all over the manuscript, RCFA (E0’= – 0.0026 V) and RCFCCD (E0’=
+ 0.30 V) are representing redox couples responsible for the
redox reactions of FA (released through reaction between
FCCD and F–) and FCCD respectively.
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DOI: 10.1039/C6RA14416K
Experimental conditions and parameters optimization
In order to achieve better sensing performance, the
reaction conditions such as incubation time and temperature
were optimized. The incubation time of 2 h and incubation
temperature of 50°C showed maximum F– interaction ability.
HEPES buffer with pH of 7.8 has shown better performance. 50
μM concentration of FCCD showed measurable redox signals
and hence it is kept as optimum concentration for all the
experiments. Next, the volume ratio between DMF and HEPES
buffer is optimized. Here, the use of DMF is necessary to
solvate FCCD. The performances of FCCD in absence (Fig S1A,
C) and presence of 100 μM F− (Fig S1B, D) were investigated
under different volume ratios of DMF and HEPES. As can be
seen from the figures and plots, the response current
increases as the volume of DMF increases from 1% to 50% and
then started to decrease. The optimum performance was
observed when the volume ratio is 50/50% for FCCD in either
absence or presence of F− and hence 50/50% DMF/HEPES is
used as supporting electrolyte in all the experiments.
The present F− assay system consists of two steps: (1)
Incubation of 50 µM FCCD with appropriate concentrations of
F− in 50/50 (v/v%) of DMF/HEPES buffer (pH 7.8) for 2 h at
50°C, (2) electrochemical measurements of RCFCCD and RCFA
using voltammetry under optimized parameters.
Fig. 1 (A) CVs recorded at GCE in 50/50% DMF/HEPES buffer
containing 50 μM FCCD (a), 50 μM FA (b) and 50 μM FCCD+50
Real sample preparation
To assay for water samples, 10 mM F− stock solutions were μM F− (c). Inset: CV for the mixture of 50 μM FA and 50 μM
prepared by spiking F− in 10 ml of tap water and rain water. FCCD. (B) CVs responses of 50 μM FCCD in presence of F−
Likewise, 10 mM F− stock solution was prepared in 1 ml bovine (a=10, b= 20, c=30, d=40, f=50, g=60, h=70, i=80, j=90, k=100
serum sample. Thereafter, appropriate volumes of F− with µM)
known concentrations were distributed into aliquots (1 mL) in
eppendorf tubes. Next, 50 µM FCCD have been added to each
3.1 Electrochemical sensing mechanism of FCCD
tubes, wherein 50/50 (v/v%) of DMF/HEPES was maintained as
The fluoride−FCCD interaction and its signal revealing
supporting electrolyte in all reaction mixture. Afterwards, the mechanism were investigated through voltammetric study of
tubes were transferred to water bath and incubated for 2 h at RCFA and RCFCCD. In absence of F−, the voltammogram of FCCD
50°C. The electrochemical experiments were carried out by featured with RCFCCD at + 0.30 V (curve a, Fig. 1A). In presence
DPV and monitored the RCFA and RCFCCD
.
To prepare of F−, the peak currents of RCFCCD started to decrease,
’
toothpaste solution, 2 g of toothpaste sample containing 0.22 concomitantly a new redox couple is appeared at E0 of –
w/w% of NaF was dissolved in 10 mL water via ultrasonicated 0.0026 V (curve c, Fig. 1A). The newly appeared redox couple
for 5 min. The amount of F− present in the resulting toothpaste of FCCD in presence of F– is consistent with the voltammogram
solution is estimated to be 10 mM and this solution is directly of pristine FA (curve b, Fig. 1A). From these voltammetric
analyzed.
results, we elucidated that F– triggered the silyl deprotection of
FCCD and released FA which was observed as new redox
couple in the voltammogram of FCCD. Furthermore, as the
concentration of F− increases, the redox peak currents of
3. Results and Discussions
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RCFCCD linearly decrease, while those of FA linearly increase selective electrode.19-24 Besides, the LOD of FCCD probe is about
View Article Online
DOI: 10.1039/C6RA14416K
(Fig. 1B). Thus, two different electrochemical channels, i.e 4.7 fold more sensitive than our previously reported
OFF/ON (RCFA) and ON/OFF (RCFCCD) were stimulated hydroquinone redox substrate (LOD= 2.38 µM) which clearly
simultaneously at two different potential regions in response revealed the outstanding sensitivity of FCCD and FA redox
to F–. The linear range for the quantitative detection of F− systems.
through CV method is 10-100 µM (Fig. S2). The limit of
detection (LOD) is 7.7 µM and the sensitivity is 0.0282 µAµM−1
cm−2. The redox peak currents increased linearly as the scan
rate increases (Fig. S3). A plot between peak currents and
square root of scan rate exhibited good linearity indicating
that the redox reactions are diffusion-controlled.
Fig. 2 (A) DPVs recorded at RCFCCD and (B) RCFCCD for 50 μM
FCCD in presence of F− (0−100 µM). Insets: (I−Io) vs. [F−].
Fig. 3 (A) DPVs recorded at GCE in 50/50% DMF/HEPES
containing 500 μM FCCD in presence of 2 mM concentrations
of various anions. (B) Chart for interference study: response
3.2 Determination of fluoride
Similarly, DPV experiments were carried out for FCCD in current of RCFA vs. F− (50 µM) and other anions (2 mM). (C)
presence of different concentration of F− (Fig. 2A and Fig. 2B). Chart for interference study monitored via RCFCCD
The DPV results are similar to CV, but showed better sensitivity
even at low concentrations of F− (Fig. S4). A calibration plot
3.3 Selectivity
derived between normalized current response and
concentration of F− exhibited good linearity (insets to Fig. 2A
Several possible competitive interferents species such as
and 2B) in a wide linear concentration range of 1–100 µM. The (NaI, NaCl, KBr, NaH2PO4, Na2HPO4, LiClO4, potassium acetate
LOD were calculated to be 5.1×10–7 (9.69 ppb) and 20.1×10–7 (KoAc), KCN, NaN3, Na2CO3, KNO3, and NaHCO3 were tested
(38.1 ppb) via FCCD and FA channels, respectively which with FCCD in order to investigate selectivity of FCCD for F-
surpassed the sensitivity of several optical probes and Ion detection (Fig. 3A). High concentrations of anions (2 mM) were
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incubated with FCCD for 2 h at 50°C. Their corresponding DPVs
featured with RCFA and RCFCCD were monitored (Fig. S5). None
of the other anions were able to produce any current
responses even at such high concentrations (2 mM) via both at
RCFA (Fig. 3B) and at RCFCCD (Fig. 3C). Thus, the silyl
deprotection of FCCD is highly specific for F− and hence the
developed approach offers highly selective F− detection
platform. The redox potentials of reporter observed at low
overpotential –0.0026 V which is free from biological interferences,
and this probe is suitable for future development of F− sensors in
View Article Online
DOI: 10.1039/C6RA14416K
Table 1 Determination of F− in real samples
Samples Added/µM Found/µM Recovery/% RSD*/%
Bovine
Serum
6
8
5.78
8.1
96.33
101.25
99.40
103.3
97.63
97.40
97.50
98.63
102.5
101.67
103.38
97.6
2.23
3.70
4.03
4.73
3.45
3.05
2.17
2.61
3.60
4.93
4.51
2.64
10
6
8
10
6
8
9.94
6.20
7.81
9.74
5.85
7.89
10.25
6.1
Tap
water
biological assay. In contrary, direct sensing of F− on modified Rain
electrodes usually occurs at high overpotential and severely water
suffers interferences from biological interferents.
Tooth-
10
6
3.4 FCCD: a sensitive and selective colorimetric indicator for F−
paste
8
10
8.27
9.76
Next, the absorption spectra of FCCD in presence and
absence of F− have been investigated, because this could add
additional evidence to support our proposed mechanism.
Also, direct, sensitive and selective detection of intrinsic F−
present in whole toothpaste sample is analysed. The whole
toothpaste is composed of F− along with several other active
ingredients. FCCD was added to toothpaste solution and
incubated at 50°C for 2 h and subsequently analysed. As the
amount of toothpaste sample increases, the response current
for FA increases, while that of FCCD decreases which is
consistent with lab sample results (Fig. S6D and fig. S7D).
Hence, this study validated the proof-of-concept of our new
electrochemical probe FCCD for successful detection of F− in
real complex systems. We noticed that the as-prepared
toothpaste sample is cloudy (i.e., non-transparent), still we
able to get good recovery, because electrochemical methods
does not require transparent solution.
In the past decades, several optical probes have been
reported for F−, however they are relying on hydrogen bonds
or Lewis acid coordination, and most of them able to operate
only in organic solvents to detect tetrabutylammonium (TBA+)
fluoride rather than inorganic F− which limited their
applicability for F− detection in biological samples.28 Overall,
the detection of low concentrations of F− in aqueous solutions
still remains challenging without expensive analytical
equipment. The electrochemical methods based on chemically
modified electrodes encounter interferences from other
anions and biological interferents. Besides, the electrochemical
fluoride recognition strategies based on Lewis acid
coordination with arylboronic acids/esters are encounter
difficulties in detection of aqueous fluoride F−.7 Interestingly,
our approach is able to solve several aforementioned issues.
For instance, our electrochemical approach does not require
electrode modification and pre-sampling procedures, yet
sensitive and selective. The FCCD is highly selective to F− even
other anions are coexisted in high concentrations. Additionally,
the less overpotential of reporter FA facilitates biological
interferences-free analyses. Besides, the voltammograms does
not encounter any interference from dissolved O2 and hence
oxygen removal step performed in usual voltammetric analysis
can be avoided. Moreover, our approach enables detections at
two voltammetric channels either at OFF/ON (RCFA) or ON/OFF
(RCFCCD) redox signals. Also, the LOD is within the relevant
FCCD was incubated with appropriate amounts of F− for 2 h at
50°C and then absorption spectra studies were performed. In
the absence of F−, the spectrum of FCCD featured with only
one absorption peak at 250 nm (curve a, Fig. S6). However, in
presence of F−, the absorption peak at 250 nm is red shifted to
270 nm and additionally a new peak is observed at 420 nm
which could be originated from the F− triggered release of FA
(curves b, c; Fig. S6). The observed new peak at 420 nm is
consistent with the absorbance spectrum of pristine FA (curve
d, Fig. S6). Thus, the absorption spectra results also consistent
with electrochemical results. The solution of FCCD solution is
ivory colour in the absence of F−, however it turned to yellow
in presence of F− and hence FCCD is a good colorimetric
indicator for F− visual detection. As the concentration of F−
increases, the colour of the solution is converted to darker
yellow (Fig. S7). 50 µM of F− can be detectable on naked eye
which makes FCCD as an outstanding colorimetric visualization
probe. Also, the LOD of 50 µM is surpassed the LOD of our
previously reported colorimetric probe13 as well other
literature reports.25-27 The incubation of other anions (2 mM)
with FCCD din not produce any colour changes which proved
the selectivity of FCCD (Fig. S8). Hence, the colorimetric studies
added additional evidence for the proposed scheme and
mechanism along with voltammetric results.
3.5 Real sample analysis
Practical feasibility of the developed latent electrochemical
approach has been demonstrated in real samples such as
water samples (tap and rain water), biological sample (bovine
serum) and toothpaste sample (Fig. S9, S10). Known
concentrations of F− were spiked (6, 8 and 10 µM) and
incubated with FCCD for 2h at 50°C. Then, found and recovery
values are satisfactory (97–103%) (Table 1) and hence FCCD
possess good practical feasibility.
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13 J.-A. Gu, Y.-J. Lin, Y.-M. Chia, H.-Y. Lin and S.-T. Huang,
window of US EPA’s mandated upper limit and surpassed the
sensitivity of several previously reported probes. FCCD is also
an outstanding selective colorimetric visualization probe which
can detect even 50 µM F− on naked eye. This approach is
works well in non-transparent solutions directly prepared from
toothpaste.
View Article Online
Microchim. Acta, 2013, 180, 801-806.
14 J.-A. Gu, V. Mani and S.-T. Huang, Analyst, 2015,
DOI: 10.10319/4C06,R3A41464-16K
352.
15 I.S. Turan and E.U. Akkaya, Org. lett., 2014, 16, 1680-1683.
16 X.-F. Yang, Spectrochim. Acta, Part A, 2007, 67, 321-326.
17 E. Corey and A. Venkateswarlu, J. Am. Chem. Soc., 1972, 94
6190-6191.
,
18 E. Corey and B. B. Snider, J. Am. Chem. Soc., 1972, 94, 2549-
2550.
Conclusions
19 A.K. Mahapatra, S.K. Manna, B. Pramanik, K. Maiti, S.
Mondal, S.S. Ali and D. Mandal, RSC Adv., 2015, 5, 10716-
10722.
In summary, a new electrochemical substrate FCCD is
synthesized for highly selective and sensitive detection of
aqueous F−. The approach is simple, inexpensive and possible
alternative for laborious optical methods of F– detection. The
20 J. Hu, M.R. Whittaker, T.P. Davis and J.F. Quinn, ACS Macro
Lett., 2015, 4, 236-241.
21 S.J. Butler, Chem. Commun., 2015, 51, 10879-10882.
special chemical affinity between F− and Si enabled high 22 G. Jha, N. Anoop, A. Rahaman and M. Sarkar, Phy. Chem.
Chem. Phy., 2015, 17, 3525-3533.
23 P. Ashokkumar, H. Weißhoff, W. Kraus and K. Rurack, Angew.
Chem. Int. Ed., 2014, 53, 2225-2229.
selectivity over other anions and the oxidation of FA observed
at lower overpotential is greatly beneficial to eliminate
biological interferences. Compared with conventional F– Ion
selective electrode and previously reported electrochemical
24 A. Roy, D. Kand, T. Saha and P. Talukdar, Chem. Commun.,
2014, 50, 5510-5513.
substrates, FCCD displays better sensitivity with LOD of 5.1×10–7 25 Y. Kai, Y. Hu, K. Wang, W. Zhi, M. Liang and W. Yang,
Spectrochim. Acta, Part A, 2014, 118, 239-243.
26 D. Buckland, S.V. Bhosale and S.J. Langford, Tetrahedron
Lett., 2011, 52, 1990-1992.
27 P. Rajamalli and E. Prasad, Org. Lett., 2011, 13, 3714-3717.
28 S. Rivadehi, E.F. Reid, C.F. Hogan, S.V. Bhosale and S.J.
Langford, Org. Biomol. Chem., 2012, 10, 705-709.
(9.69 ppb) using simple bare electrode. Also, FCCD is selective
and sensitive colorimetric visualization indicator for F−. The
practical applicability of FCCD has been demonstrated in direct
toothpaste (non-transparent solution), biological and water
samples which shown satisfactory recoveries. FCCD can also be
suitable electrochemical probe for different analytes by
installing different trigger moieties.
Acknowledgements
This work was supported by the Ministry of Science and
Technology, Taiwan (NSC 103-2811-M-027-002, 102-2113-M-
027-002-MY3, and MOST 104-2622-M-027-001-CC3).
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Ferrocene based electrochemical redox substrate for highly selective and sensitive fluoride
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