Synthesis and deposition of a Tr?ger's base polymer on the electrode surface for potentiometric detection of a neuroblastoma tumor marker metabolite

Article abstract of DOI:10.1039/c6cc06203b

The development of novel diagnostic tools is a primary goal in bioanalytical chemistry. Here we report the synthesis of Tr?ger's base functionalized with amino- and coumarin-units designed as a monomeric unit for the development of an electrochemical canc

Full text of DOI:10.1039/c6cc06203b

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Synthesis and deposition of Tröger base polymer on
electrode surface for potentiometric detection of
neuroblastoma tumor marker metabolite
Received 00th January 20xx,
Accepted 00th January 20xx
T. V. Shishkanova,a M. Havlík, a M. Dendisová, b P. Matějka b and V. Krála
DOI: 10.1039/x0xx00000x
www.rsc.org/
The development of novel diagnostic tools is a primary goal in
bioanalytical chemistry. Here we report the synthesis of a Tröger
base functionalized with amino- and coumarin-units designed as a
monomeric unit for the development of an electrochemical cancer
sensor. The synthesized receptor was deposited onto a conducting
support using electrochemical polymerization, characterized
spectroscopically and tested potentiometrically towards
metabolites used as tumor markers of neuroblastoma.
Fig. 1 The structures of the tested metabolites for screening
neuroblastoma
The development of detection methods for diseases with high
mortality represents a crucial target of contemporary science.
At present, the classical methodology for cancer detection is
1–5
clinical analysis, and (iii)
a malarial antigen for clinical
research.11 The compatibility of similar devices with any
mobile phone or wearable electronics guarantees that
sophisticated diagnostic testing can be performed by users
with a broad spectrum of needs, resources, and levels of
technical expertise. A few reports have been related to
voltammetric determination of HVA and VMA without using
supramolecular receptors. 12
based on biopolymer analysis.
A modern innovative
approach is based on low-molecular weight non-classical
tumor markers (TMs) and cancer cell metabolite identification
6,7,8. Despite the potential significance to detect low-molecular
weight non-classical TMs, there is no yet reports concerning of
their determination using supramolecular analytical chemistry,
especially potentiometry.9 Neuroblastoma,
a neuroblastic
tumor derived from the perimordial neural crest, remains the
leading cause of disease in infancy. A promising screening test
of neuroblastoma could rely on the monitoring of urine
catecholamine metabolites, namely homovanillic acid (HVA)
and vanillylmandelic acid (VMA) (Fig. 1) which serve as TMs. 10
Ultrasensitive diagnostic devices based on electrochemical
principles could be one quite simple approach to screening the
low-molecular-weight non-classical TMs of neuroblastoma.
Recently, Nemiroski et al. have proposed universal mobile and
highly effective electrochemical devices for the detection of (i)
glucose in the blood for personal health, (ii) sodium in urine for
Since a number of biologically relevant molecules are
electroactive, the selectivity of many electrochemical sensors
based on electroactivity is limited. Therefore, a promising way
to avoid overlapping electrochemical signals and increase
selectivity is the development of a potentiometric sensor
derived from a recognition receptor selective towards the low-
molecular-weight target metabolite. We are pioneered in
potentiometric determination of the metabolites for
neuroblastoma screening.
A Tröger’s base is a molecule containing two arenes
connected to the
b and f sides of 1,5-methano-1,5-
diazocine.13,14 Due to its unique structural features (C2-
symmetry and rigid V-shape geometry) and the possibility of
functionalization, a Tröger’s base is an attractive receptor for
the development of optical and spectroscopic sensors.13–16 The
sensor technology assume immobilization of a supramolecular
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Scheme 1 Stepwise preparation protocol of Tröger base functionalized with amino- and coumarin-units 6.
receptor onto the electrode interface between transducer and metabolite in question potentiometrically. The success of the
measured sample. The practically applicable approach is to supramolecular design was proven using spectroscopic and
immobilize receptor into a suitable matrix. However, a non- nanoscopic experiments, comprising both optical and
covalent immobilized monomer can leach out from the matrix mechanical measurements. Scheme 1 shows the synthesis of
as result of desorption and other physical effects occurring on receptor
6. †
the electrode surface contacting with sample. In contrary, We should note that this is not a case of preparation of a
covalent immobilization of receptor allows to limit the leaching molecularly imprinted polymer. TMs are not present in the
out from sensor surface and to construct microsensors for
electropolymerization mixture.
† A cyclic voltammogram of 6 on a
practical application. In this paper, a Tröger’s base derivative
6
Pt electrode (Fig. 2) exhibits two anodic peaks at ca. 0.55 and 1.02 V
(from the 1st potential scan) and the reduction peak at ca. 0.47 V.
The current intensity increased from 1 up to 4 cycles indicating the
polymer growth (Fig. 2). In the subsequent scans, the current
decreased indicating the growth of the non-conducting polymeric
film. The presence of the anodic peak at 1.02 V is related to the
oxidation of the monomer and initiating the electrosynthesis of the
polymeric film.17 A couple (peaks Ia and Ib) is evident at a potential
of ca. 0.55 V, corresponding to the reduction–oxidation of an
adsorbed product.
(Scheme 1) was designed to allow us to deposit it
electrochemically on the electrode surface and to detect the
Fig. 2 Cyclic voltammogram of
a Tröger’s base derivative 6 in
CH3CN/ TBAFB/HCl on a Pt electrode. The electrode potential was
swept repeatedly between 0.0 and 1.2 V vs. Ag/AgCl at a scan rate of
50mV s–1, number of scans are 4.
†
Fig. 3 SNIM images 5x5 µm of the Au electrode surface. Mechanical
amplitude signal (A) and optical signal (B).
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Scanning near-field infrared microscopy (SNIM) combined ratio of bands at ca. 2960 cm–1 and 2930 cm–1 of asymmetric
with nanomechanical patterning shows that the polymeric film stretching vibrations of CH3 and CH2 groups, respectively, is
on the electrode surface is nanostructured and consists of reversed. These changes may be rationalized as follows: in the
“hills” and “valleys” with a maximal height profile of 0.5 µm methylcoumarin unit, the possible delocalization of electrons
(Fig. 3A). The amplitude of the infrared signal assigned to in the lactone ring taking place during polymerization leads to
aromatic C–C stretching mode suggests that the adhering film the change in the dipole moment of CH3 vibrations and to the
is porous, with grains located on the edges of both “hills” and conformation changes. The bands at 1713 and 1716 cm–1 of
“valleys” (Fig. 3B).
the C=O vibration of the coumarin unit are observed in both
the monomer and polymer spectra, respectively. After
To confirm the formation of the polymer derived from 6,
Fourier transform infrared (FTIR) spectra of the monomer and polymerization, the intensity of the coupled N–H and C–C
polymer prepared by chemical polymerization in CH3CN were vibrations band at 1683 cm–1 is remarkably increased to a
compared (Fig. 4). The polymer spectrum differs substantially comparable intensity to the C=O vibration.19 The aromatic ring
from that of the monomer between 3400 – 3200 cm–1 and modes are shown as a set of bands under 1600 cm–1 (1596,
under 1600 cm–1. In contrast to the monomer spectrum, which 1469, 1288, 1152, 1067, 1050, 942, 829 and 707 cm–1) in both
exhibits bands at
primary amino group, the polymer spectrum exhibits the band stretching vibration at 1483 cm–1 assigned to the benzenoid
∼ ∼
3350 cm–1 and 3237 cm–1 assigned to a spectra with different intensities. We note that the C=N
at
∼
3217 cm–1 of the secondary amino group.18 The intensity
units18 characteristic for polyaniline is observed in the polymer
spectrum. The intense band at 1044 cm–1 results from the
sulfate anion as a product of aniline oxidation by persulfate
and somewhat overlaps with the band at ca. 1140 cm–1
assigned to protonated polyaniline.18 Hence the FTIR spectra
reveal the polymerization of
6 via its amino group according to
the mechanism of aniline polymerization.
The electrochemically modified electrodes were tested for
the potenꢀometric detecꢀon of TMs (Fig. 5).
potentiometric response of –39 mV decade–1 towards VMA
was found in the concentration range from 9.9
10–6 up to 3.3
10–3 mol L–1 (squared correlation coefficient was equaled
† A
×
×
0,9914). The under-Nernstian behavior could be caused by the
roughness of the polymeric film and the effect of surface
morphology of supporting metallic material. In the case of
HVA, the potentiometric response of the prepared electrode
was insignificant (not shown). The tested TMs are structurally
closely related (Fig. 1) and differ by the hydroxy
Fig. 4 FTIR spectra of polymer (blue) and monomer (red) from 4000 to
2000 cm–1 (A) and from 1900 to 600 cm–1 (B). Each spectrum was
averaged from 256 scans with 4-cm–1 resolution.
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The detection was purely potentiometric. The geometry of
electrochemically polymerized receptor enabled it to interact
specifically with VMA in contrast to HVA.
6
This work was supported by the Grant Agency of the Czech
Republic (Project P206/15/02815S).
Notes and references
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modified with polymer based on 6 towards VMA in 0.1 mol L–1 phosphate
buffer at pH=7.
,
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electrode based on the polymer derived from 6 enable the selective
detection of VMA in the presence of HVA (log KPot. VMA, HVA=–0.9).
†
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electrode surface. Actually, our spectroscopic findings confirmed
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electropolymerization. The hydroxyl groups of VMA (Figure 1) may
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24
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proposed electrode based on the Troger's base polymer provide an
alternative device for VMA determination.
In conclusion, we have presented an innovative detection
of neuroblastoma TM which is based on specific and selective
interaction with a polymer film (prepared from 6) and VMA.
4 | J. Name., 2012, 00, 1-3
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