Transcript Nessun titolo diapositiva - Università degli Studi di Roma Tor Vergata

Istituto per lo Studio
dei Materiali Nanostrutturati
NOVEL NON-CONDUCTING FILMSFOR
INTERFERENCE-FREE ELECTROCHEMICAL SENSORS
M.
a
BADEA , A.
CURULLI
b*,
G. PALLESCHI
a,
S. KACIULIS
c , A.
MEZZI
c
a Università
di Roma ‘Tor Vergata’, Dipartimento di Scienze e Tecnologie Chimiche, Rome, Italy
b CNR ISMN Istituto per lo Studio di Materiali Nanostrutturati Sezione Roma 2, Rome Italy
c CNR ISMN Istituto per lo Studio di Materiali Nanostrutturati Sezione di Montelibretti, Rome, Italy
Cyclic voltammograms for electropolymerization of 2,6-DHN, AP-EA and
electrocopolymerization of 2,6-DHN with AP-EA on Pt electrodes
AIM OF WORK
Electropolymerised films based on phenol, aniline, vinylindole and
pyrrole have been used as an alternative to conventional
membranes. The oxidation of different monomers can lead to
modified electrodes with peculiar properties, including selectivity
and protection of the electrode from passivation.
CH 2 CH 2 NH 2
OH
(2,6-DHN)
HO
2,6-DHN & AP-EA
2-(4-aminophenyl)-ethylamine
2,6 - Dihydroxynaphtalene
(AP-EA)
H2 N
Interest vs modified electrodes was focused on conducting films,
but non-conducting films seem to be equivalent to ideal
membranes. Because of non-conducting films self-limited growth,
the formed polymers are very thin (10-100 nm) and the response of
these modified electrodes is very fast. Other advantages are that
such films are usually pinholes free and potentially robust. This
type of films can be used to immobilise enzymes during or after the
electropolymerisation step by covalent attachment.
In our work new non-conducting polymers based on different
dihydroxynaptalenes (DHN) and 2-(4-aminophenyl)-ethylamine (APEA) have been synthesised on the surface of Pt electrodes to
assemble fast-response and
interference-free amperometric
sensors for hydrogen peroxide.
The electropolymerisation was performed by cyclic voltammetry.
Different scan rates and scan ranges were investigated and
selected according to the monomer used. All the sensors obtained
were tested for hydrogen peroxide, ascorbic acid and
acetaminophen by cyclic voltammetry and amperometry. Studies
on reproducibility, interference, response time, buffers, storage and
operational time of the sensors have been performed.
The chemical composition of obtained films was analysed by X-ray
Photoelectron Spectroscopy.
1,0
2,6-DHN (1mM)
AP-EA (100 mM)
copolymer 2,6-DHN (0.5 mM) + AP-EA (10 mM)
25
0,8
current (mA)
Pascorbic acid (%)
20
15
10
0
Conc.
(mM)
Scan rate
(mV/min)
Range
(mV)
No. of
cycles
2,3-DHN
1.0
5
0 - 1200
20
4.1
94.3
97.1
1,6-DHN
1.0
20
-500 - 1200
20
0.65
32.3
94.8
2,6-DHN
0.5
20
0 - 1200
30
0.62
5.4
89.3
1,5-DHN
1.0
20
0 - 1000
20
11.5
17.4
95.8
20
40
60
80
100
0
10
20
30
40
50
days
scan rate (mV/sec)
Influence of the scan rate used in the
film preparation on the permeability
to 1 mM ascorbic acid
Pascorbic acid Pacetaminophen P hydrogen peroxide
(%)
(%)
(%)
0,4
0,0
0
Permeability of various electropolymerized films
to 1mM hydrogen peroxide, 1mM ascorbic acid
and 1mM acetaminophen (E= + 650 mV)
0,6
0,2
5
Monomer
1 mM ascorbic acid
1 mM acetaminophen
0.1 mM hydrogen peroxide
Stability of the response of copolymer/Pt electrode
to hydrogen peroxide, ascorbic acid
and acetaminophen
RESULTS
Five different dihydroxynaphtalenes were tested: 2,3 DHN, 1,6-DHN, 2,6-DHN, 1,5-DHN and 1,2-DHN. For all of these, an oxidation peak
was recorded in positive potential range between 250 – 800 mV. The decrease of the oxidation current after the first cycle indicates the
passivation of the electrode surface. The polymers formed were transparent and strongly adherent on the surface of the platinum
electrode
In our knowledge, the electropolymerisation of a new monomer 2-(4-aminophenyl)-ethylamine (AP-EA), which has a similar structure of
tyramine, is reported, for the first time. The resulting film showed a very good rejection of ascorbic acid, a high permeability for
hydrogen peroxide but a poor stability in time.
In order to improve the stability of poly(AP-EA), a copolymerisation of AP-EA with 2,6-DHN was studied. Different ratios 2,6-DHN /
APAE were studied and the best results in terms of stability and interference rejection were obtained using a mixture 0.5 mM 2,6-DHN
and 10 mM AP-EA.
1,2-DHN
1.0
20
-200 - 1200
20
62.9
87.0
97.5
2-(4AP)-EA
100
50
300 - 1300
20
0.78
7.80
95.6
Different parameters (scan rate, range of potential, monomer concentration, number of cycles, pH buffer) for preparation and storage
of polymers were optimised.
2,6-DHN
+
AP-EA
0.5
+
10
10
100 - 1150
20
0
5.9
93.3
The permeability for hydrogen peroxide and rejection of ascorbic acid and acetaminophen was tested for all the films by cyclic
voltammetry and amperometry (applied potential +650 mV vs Ag/AgCl), in batch and also in flow injection conditions.
The presence of the free amino-groups in the copolymer (2,6-DHN – AP-EA) (see the XPS results) structure permits the covalent
attachment of the enzymes via peptide bond formation. Preliminary experiments for covalent immobilisation of hydrogen peroxide
producing enzymes were carried out using this copolymer and glucose oxidase, as a model enzyme.
P = ( Ifilm / Ibare ) x 100%
Ifilm = current measured at the electrode covered with the electropolymerized film
Ibare = current measured at the naked electrode
XPS results for poly(2,6-DHN), poly(AP-EA)
and (2,6-DHN - AP-EA) copolymer
BE
Poly(2,6-DHN)
Poly(AP-EA)
(eV)
(%)
(%)
Copolymer
(2,6-DHN
with AP-EA)
(%)
aromatic
285.0
58.1
56.0
58.7
C-OH
286.4
15.2
15.5
15.6
H2N-C
399.0
-
1.8
2.7
N
H2N-Ph
400.2
-
4.5
-
O (A)
C-OH
533.6
12.2
-
-
O (B)
532.5
9.2
17.9
18.7
impurities
102.3
5.3
4.4
4.2
Atom
C
XP Spectra relevant to N1s level
recorded for copolymer
Type
CONCLUSIONS
New non-conducting films were electrosynthesised starting from
dihydroxynaphtalenes by cyclic voltammetry. Poly(2,6-DHN)
showed the best characteristics in terms of interference rejection,
permeability for hydrogen peroxide and stability in operational
conditions.
A film with free amino groups on its skeleton has been
synthesised, from AP-EA , which was for the first time reported.
The presence of the free amino-groups on the poly(AP-EA)
backbone allowed the covalent attachment of the enzymes via
peptide bond formation.
In order to improve the poly(AP-EA) stability, a copolymerisation
with 2,6-DHN was performed and optimised. The resulting film was
characterised by a very good rejection of interferents, a long life
time (more then 60 days) associated with the presence of the free
amino groups on its structure.
Preliminary results obtained for the covalent immobilisation of the
glucose oxidase were very promising for a interference free
biosensor assembling.
Acknowledgements: The authors thank the European Community ( MCFA-2000-000725) and the CNR Target Project MSTA II for the financial support.