Analytica Chimica Acta 395 (1999) 17–26
Integrated ethanol biosensors based on carbon paste electrodes modified
with [Re(phen-dione)(CO)
3
Cl] and [Fe(phen-dione)
3
](PF
6
)
2
F. Tobalina
a
, F. Pariente
a
, L. Hernández
a
, H.D. Abruña
b
, E. Lorenzo
a,∗
a
Departamento de Qu´ ımica Anal´ ıtica, Universidad Autónoma de Madrid, Cantoblanco 28049 Madrid, Spain
b
Department of Chemistry & Chemical Biology, Baker Laboratory, Cornell University, Ithaca, NY 14853-1301, USA
Received 4 January 1999; received in revised form 8 April 1999; accepted 11 April 1999
Abstract
The preparation and electrochemical characterization of carbon paste electrodes modified with 1,10-phenantroline-5,6-dione
(phen-dione) complexes of Fe ([Fe(phen-dione)
3
]
2+
) and Re ([Re(phen-dione)(CO)
3
Cl]) as well as their behavior as electro-
catalysts towards the oxidation of NADH are described. These modified electrodes exhibit redox responses very similar to
those of the complexes in aqueous solution, including the pH-dependent response ascribed to the pendant o-quinone groups,
as well as to those observed for films of the complexes electrodeposited onto glassy carbon electrodes. Carbon paste electrodes
modified with either of the complexes, exhibited potent and persistent electrocatalytic activity towards NADH oxidation at
potentials around 0.0 V versus SSCE, which represents a dramatic diminution in the overpotential. Using carbon paste elec-
trodes modified with the Re complex, alcohol dehydrogenase and NAD
+
we have developed an integrated ethanol biosensor.
It exhibited a detection limit of 45 M(S/N = 3), linearity up to 4.0 mM, a sensitivity of 174 nA mM
−1
and a stability of at
least 8 days when stored at 4
◦
C. ©1999 Elsevier Science B.V. All rights reserved.
Keywords: Integrated biosensor; Ethanol
1. Introduction
The development of modified electrodes exhibit-
ing electrocatalytic activity towards the oxidation of
nicotinamide adenine dinucleotide (NAD
+
/NADH)
continues to be an area of great interest in biosensor
technology because over 300 dehydrogenases use it as
a cofactor. NADH dependent dehydrogenases catalyze
the oxidation of numerous compounds of interest in
industry, medicine and other research fields.
The mode of operation of these biosensors involves
enzyme substrate oxidation by the enzyme and transfer
of electrons to the soluble cofactor NAD
+
, which is re-
∗
Corresponding author. Tel.: +34-1-397-5000.
duced to NADH. Enzymatically generated NADH can
be oxidized on bare electrode surfaces but with rather
high overpotentials [1,2] so that other substances such
as ascorbate and uric acid, among others, interfere with
the determination. In addition, the direct oxidation of
NADH is often accompanied by electrode fouling and
interfering background currents in real samples [3–5].
The large overpotentials required can be dimin-
ished through the use of redox mediators [6,7]. These
are usually small molecules that can accept electrons
from NADH and transfer them to the electrode, re-
generating the NAD
+
expended in the enzymatic
step. Materials that have been employed as mediators
include quinones [8–10], catechols [11], phenox-
azines [12,13], phenazines [14], phenothiazines [15],
0003-2670/99/$ – see front matter ©1999 Elsevier Science B.V. All rights reserved.
PII:S0003-2670(99)00332-3