Electronic Supplementary Material

Sensing Lorazepam with a glassy carbon electrode coated with an electropolymerized-imprinted polymer modified with multiwalled carbon nanotubes and gold nanoparticles

BehzadRezaei*,[1] • OmidRahmanian • Ali AsgharEnsafi

Department of Chemistry, Isfahan University of Technology, Isfahan 84156−83111 I.R. Iran

Electrochemical impedance spectroscopy measurements

Electrochemical impedance spectroscopy is a useful procedure for probing the features of surface modified electrodes. The impedance spectra including a semicircle part at high frequencies, corresponding to the electron transfer limited process and a linear part at lower frequencies, demonstrating the diffusion-limiting step of the electrochemical process. The semicircle diameter equals to the electron transfer resistance at the electrode surface. Fig.S1 shows the electrochemical impedance spectroscopy for the f−MWCNT/GCE, MIP/f-MWCNT/GCE and AuNP/MIP/f−MWCNT/GCE. In this Figure shows a straight line for f−MWCNT/GCE, which was characteristic of a diffusion-limiting step of the electrochemical process. As predictable, by electropolymerization of ortho-phenylenediamine onto f−MWCNT/GCE, electron transfer resistance was significantly expanded which indicated the polymeric film performs as a definite kinetic barrier for the electron transfer. By formation of Au nanoparticles, electron transfer resistance was decreased that may be due to nanometer-sized gold particles participate a key role similarly to a conducting wire or electron-conducting tunnel and therefore promoting electron-transfer reactions of probe.

Fig. S1.Impedance spectra of 5.0 mMhexacyanoferrate (III) and 0.1 M KCl at: f−MWCNT/GCE; MIP/f−MWCNT/GCE and the AuNP/MIP/f−MWCNT/GCE electrode. Conditions: Potential, 0.20 V; frequency range, 5.0 mHz to 100 kHz; and AC voltage amplitude, 5.0 mV.

Effect of pH

The pH of the solution in adsorption step has important effect on the Lorazepam oxidation at the surface of the sensor. To make the best conformation of Lorazepam, the pH of the sample should be adjusted. For this purpose, a series of phosphate buffer solution were selected in the pH range of 5.0 to 8.0 containing 1.0 µM Lorazepam, using 120 s as an incubation times. As can be seen in Fig. 5, the net current intensity reaches maximum at a pH value of 7.5and decreased as the pH increases further. The reason may be that the Lorazepam was protonated in acidic environment and cannot be fitting into cavities. While, the stability of the imprinted film will be diminished in high alkalinity and the Lorazepam was formed in anionic form. Therefore, pH 7.5 was chosen as the proper pH for further researches.

Fig. S2. Effect of pH of working solution on Lorazepam adsorption in MIP cavities.

(a) (b) (c)

Fig. S3. The chemical structures of (a) Lorazepam, (b) Phenazopyridineand (c)Hydrochlorothiazide.

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