Cecilia Lete 1, Daniela Berger 2, Cristian Matei 2, Stelian Lupu 3, (

Electrochemical and microgravimetric studies of poly[3,4-ethylenedioxythiophene]- tyrosinase biocomposite material electrodeposited onto gold electrodes by a sinusoidal voltages method 1

Cecilia Lete 1, Daniela Berger 2, Cristian Matei 2, Stelian Lupu 3,

1 Institute of Physical Chemistry “Ilie Murgulescu” of the Romanian Academy, 202 Splaiul

Independentei, 060021 Bucharest, Romania

2 Department of Inorganic Chemistry, Physical Chemistry and Electrochemistry, Faculty of

Applied Chemistry and Materials Science, University Politehnica of Bucharest, 1-7 Polizu Street,

011061 Bucharest, Romania

3 Department of Analytical Chemistry and Environmental Engineering, Faculty of Applied

Chemistry and Materials Science, University Politehnica of Bucharest, 1-7 Polizu Street, 011061

Bucharest, Romania

The cyclic voltammogram of the PEDOT coating recorded in phosphate buffer solution displays the well known capacitive shape. On contrary, the CV of the PEDOT-Ty coating displays a lower background current which is due to the presence of the enzyme in the deposition solution.

The PEDOT-Ty coating shall display a different CV response in buffer solution because the

PEDOT is doped with tyrosinase. The enzyme incorporation within the PEDOT layer is based on

1 We wish to Professor George Inzelt happiness, good health, and success on the occasion of its 70th birthday.  Corresponding author. Phone: +40 21 4023886; fax: +40 21 3111796 (S. Lupu). E-mail address: [email protected] (S. Lupu).

1 the electrostatic interactions between the polarons present on the polymer backbone and the negatively charged enzyme, resulting in the doping of the polymer. The lower background current in the CV trace of the PEDOT-Ty modified electrode attests a higher conductivity of the doped polymer.

-4 4.0x10 PEDOT coating PEDOT-Ty coating

2.0x10-4 A

-2.0x10-4

-0.8 -0.4 0.0 0.4 0.8 E / V

Fig. 1s Cyclic voltammograms recorded at Au-QCM/PEDOT and Au-QCM/PEDOT-Ty modified electrodes, prepared at 0.6 V d.c. potential for 5 min deposition time using a SV signal with 50 mHz frequency and 0.35 V amplitude, in an aqueous solution of 0.1 M phosphate buffer of pH 7; potential scan rate of 0.05 V s−1

The electrochemical behavior of hydroquinone was investigated by using cyclic voltammetry.

The reaction is a diffusion controlled process as demonstrated by the value of the slope of the log

(I) vs. log (v) plot over a wide potential scan rate (v) range (see Fig. 2s). The data are related to the electrochemical behavior of 700 μM hydroquinone at the PEDOT-Ty based biosensor

2 prepared at 0.6 V d.c. potential value with SV of 50 mHz frequency and 0.35 V amplitude for 5 min. deposition time. The value of the slope is ca. 0.5, attesting the diffusion controlled process.

0.0 (Ia) (Ic)

) -0.2 A m

I ( -0.4 g o l log(Ia)= -1.37 + 0.5 log(v) log(Ic)= -1.4 + 0.48 log(v) -0.6 1.6 1.8 2.0 2.2 2.4 2.6 2.8 log (v / mV s-1)

Fig. 2s Log (I) vs log (v) plot for of 700 μM hydroquinone at the PEDOT-Ty based biosensor prepared at 0.6 V d.c. potential value with SV of 50 mHz frequency and 0.35 V amplitude for 5 min. deposition time.