**2. Experimental procedure**

### **2.1 Reagents**

The triflato iron porphyrin (Fe(III)TMPP) has been synthesized and characterized by proton NMR and FTIR according to the previously reported procedure [26]. The reduced graphene oxide (RGO) has been synthesized and characterized by FTIR and XPS as described previously [27]. Carbon nanotubes (MWCNTs) used in this study, have been obtained commercially from Baytubes, and produced in a high-yield catalytic process based on chemical vapor deposition (CVD). The diameter of these MWCNTs varies between 5 and 20 nm with a length of over 1 mm. Gold transducer (bare Au), indium tin oxide (ITO), phosphate-buffered saline tablets (PBS, pH = 7.4), acetone (≥99.5%), dimethylformamide (DMF, 99.8%), ethanol (≥99.9%), bisphenol A (BPA, ≥99%), catechol (≥99%) and 2,2<sup>0</sup> -biphenol (99%) were purchased from Sigma Aldrich (France).

### **2.2 Instruments and characterization methods**

Electrochemical measurements were performed using an AUTOLAB PGSTAT 100 (supported by "FRA 4.9" software (Methrom)) coupled to a computer and an electrochemical cell (**Figure 1**). The electrochemical measurements were carried out in an electrochemical cell involving a three electrodes system purchased from BASi: bare Au (surface 2.01 � <sup>10</sup>�<sup>2</sup> cm2 ) or modified Au with Fe(III)TMPP or RGO/ Fe(III)TMPP membranes as the working electrode, Ag/AgCl (3 M KCl) as the reference electrode and platinum wire as the counter electrode. The analyses were performed by electrochemical impedance spectroscopy (EIS). The modified Au transducer is normally placed in a 0.1 M phosphate buffer solution (PBS (0.1 M), pH = 7) containing target species such as bisphenol A, 2,2<sup>0</sup> -biphenol and catechol

### **Figure 1.**

*Experimental electrochemical measurement device composed by electrochemical cell (place of electrochemical reactions between analytes and the sensitive membrane), potentiostat (electrochemical analysis system) and computer (electrochemical response display).*

and then simply followed by fixing the potential. All experiments were conducted at ambient temperature (25°C).

EIS was measured at 0.9 V using an alternating potential of 10 mV amplitude in the frequency range from 100 kHz to 30 mHz.

The UV–vis spectra have been recorded with a Win ASPECT PLUS (validation for SPECORD PLUS version 4.2) spectrometer using a 100 μl quartz cell.

### **2.3 Preparation and measurement of electrochemical sensor**

The used gold electrodes in this work have a dimension of 1 cm 1 cm, where the thickness of the gold deposited by evaporation on Si/SiO2 substrates is of the order of 50 nm [28]. Before the analysis, in order to improve the adhesion of the sensitive membrane on the electrode surface, the gold substrates were cleaned with acetone in an ultrasonic bath for 10 min and dried under nitrogen flow. Then, the gold substrate has been cleaned in piranha solution (1/3 H2O2 + 2/3 H2SO4) for about 2 min to activate the surface [29], after this treatment, the gold substrates were rinsed with ultra-pure water and dried under nitrogen flow.

For the preparation of Au/Fe(III)TMPP sensor, the pretreated gold was dropcasted by 20 μL of Fe(III)TMPP solution (4.7 mg in 500 μl DMF) and dried at 80°C in an oven for 1 h to evaporate residual solvent. The obtained modified electrode was then rinsed with distilled water to remove the non- attached Fe(III)TMPP and dried under nitrogen flow.

The nanocomposites 2%CNTs/Fe(III)TMPP and 4%CNTs/Fe(III)TMPP were prepared by mixing 4.7 mg of Fe(III)TMPP and different weight proportions of CNTs (2% and 4%) in 500 μl of DMF followed by sonication in an ultrasonic bath for 2 hours. Then, 20 μl of each nanocomposite solution was dropped onto the Au electrode, dried at 80°C in an oven for 1 h and rinsed with distilled water prior to electrochemical measurements.

For the construction of Au/RGO/Fe(III)TMPP sensor, the preparation was divided into two steps. In the first step, the pretreated gold was drop-casted by 20 μL of RGO solution (1 mg in 1 ml DMF) and dried at 80°C in an oven for 1 h. The obtained Au/RGO nanocarbon transducer electrode was rinsed with distilled water to remove the non-adsorbed materials. In the second step, 20 μl of Fe(III)TMPP solution was deposited onto the Au/RGO electrode by drop-casted method. After being dried and washed, the Au/RGO/Fe(III)TMPP modified electrode was ready to be used for electrochemical measurements.

ITO/Fe(III)TMPP and ITO/RGO/Fe(III)TMPP electrodes were prepared using the same procedure for Au/Fe(III)TMPP and Au/RGO/Fe(III)TMPP sensors preparations respectively.
