Electronic Supplementary Material

Amperometric enzymatic determination of bisphenol A using an ITO electrode modified with reduced graphene oxide and Mn3O4 nanoparticles in a chitosan matrix

K. Kamil Rezaa*, Md. Azahar Alib, Manish Kumar Singhc, Ved Varun Agrawala and A. M. Biradara

aBiomedical Instrumentation Section, National Physical Laboratory(CSIR) , Dr. K.S. Krishnan Marg, New Delhi 110012, India.

bDepartment of Electrical and Computer Engineering, Iowa State University, Ames, Iowa, 50011 USA

cDepartment of Physics, The LNM Institute of Information Technology, Jaipur-302031 India

*Corresponding author:E-mail address: , Tel/Fax: +91-1145609152.

TEM image (figure S1b) shows the solution made out of chitosan, rGO and Mn3O4 dissolved in acetic acid has been optimized in order to make a fine nano hybrid so that nanoparticles less agglomerate and remain active for electrode formation. Further it confirms chitosan bonded rGO/Mn3O4 nano hybrid are well dispersed making a suitable nanosheet surface for biomolecule attachment. A FESEM image shows rGO/Mn3O4 hybrid nanosheet [figure S1(b).]. The nano hybrid formation is evident from the figure 1 which show the change in the morphology after the nano hybrid formation. The rGO sheets have been coated with Mn3O4 in presence of chitosan. The stark differences in the nanosheet structure before and after the hybrid formation are visible. Another SEM image (magnified) provide evidence of metal oxide sheet nano hybrid formation onto the ITO substrate (figure S1c). A high magnification SEM image (figure S1d) depicts the three dimensional single folded rGO sheet.

Figure S1. (a) HRTEM image of Mn3O4 nanoparticles (b) FESEM image of rGO/Mn3O4 nano hybrid sheets (c) SEM image of hybrid rGO/Mn3O4 electrode. (d) SEM image shows a three dimensional single folded rGO sheet.

Figure S2: XRD of rGO electrode, Mn3O4 and rGO/Mn3O4 hybrid electrode.

The spectroscopic studies of the thin films have been investigated by FTIR. The characteristics typical peaks of rGO/Mn3O4/ITO and Tyrs-rGO/Mn3O4/ITO spectra can be seen in figure S3 (curve a & b respectively). After enzyme immobilization, prominent peaks were observed due to bonding between Tyrs and nano hybrid electrode. The following peaks were observed at 1646 cm−1 due to amide I group (C–O stretching along with N–H deformation mode), 1541 cm−1 peak is attributed to NH2 group due to N–H deformation, 1247 cm−1 peak belong to C-N aromatic chain and 1053 cm−1 is attributed to the stretching vibration mode of the hydroxyl group. The characteristic absorption band appears at 3100–3400 cm−1 due to the stretching vibration mode of OH and NH2 groups. Moreover, the peaks at 1076 cm-1 and 3348 cm-1 in rGO spectra may be due to the –C–O–C– vibration and O–H stretching, respectively, has been shifted due to Cn and Tyrs interactions.

Figure S3: FTIR of rGO/Mn3O4 and Tyrs-rGO/Mn3O4 electrodes.

Figure S4: (a) Stability of the Tyrs-rGO/Mn3O4 bioelectrode (b) Reproducility study of the sensor Tyrs-rGO/Mn3O4