Electrochemical detection of L-Dopa using crude Polyphenol oxidase enzyme

immobilized on electrochemically reduced RGO-Ag nanocomposite modified

graphite electrode.Shadakshari Sandeep 1, Arehalli S Santhosh1, Ningappa Kumara Swamy1, 2*, Gurukar S

Suresh3, Jose S Melo4, Kundachira S Nithin5

1Department of Chemistry, Sri Jayachamarajendra College of Engineering, Mysuru-570006, India.2JSS Research Foundation, Sri Jayachamarajendra College of Engineering Campus, Mysuru-570006, India.3Department of Chemistry and Research Centre, NMKRV College for Women, Jayanagar, Banglore-560011, India.4 Nuclear Agriculture and Biotechnology Division, Bhabha Atomic Research Centre, Mumbai 400 085, India.

5Department of Chemistry, National Institute of Engineering, Mysuru – 570008, India.

* E-mail: kumaryagati@gmail.com

Supplementary files

Figure S1

Fig S1 EDS spectra of (A) GO-Ag, (B) RGO-Ag nanocomposite

The successful electrochemical reduction of GO-Ag to RGO-Ag was established by EDS

analysis (Fig S1). As can be seen, Fig S1(A) exhibits EDS characteristic peaks corresponding to

binding energy of C, O and Ag, thereby substantiating the presence of GO-Ag nanocomposites

[1, 2]. Nevertheless, Fig S1 (B) supports the successful electrochemical reduction with peak

intensity corresponding to elemental O showing an appreciable decline (decrease upon

reduction). Additionally, there also occurred a substantial increase in peak intensity at 3 keV

which supports the presence of AgNPs [3,4].

Figure S2

Fig S2 FTIR spectrum of GO-Ag (A), RGO-Ag (B) and RGO-Ag/PPO (C)

The FTIR spectra of GO-Ag, RGO-Ag, RGO-Ag/PPO modified electrodes are shown in Fig S2.

As illustrated in Fig S2 (A), the absorption bands of GO-Ag nanocomposite observed at 3410,

1735 and 1040 cm-1 corresponding to the stretching vibration of O-H, C=O and C-O-C

respectively [5]. The peaks at 1395 and 1210 cm-1 are attributed to the vibrations of carboxyl

groups [6, 7]. In addition, the peak at 1615 cm-1 (C=C) is assigned to the contribution from

skeletal vibration of the graphitic domains [8]. After electrochemical reduction of GO-Ag to

RGO-Ag nano composite the absorption bands corresponding to the oxygen functionalities (O-H,

C=O and C-O-C) disappears (Fig S2 B) and only the peak at 1615 cm-1 remains which confirms

the successful electrochemical reduction of GO-Ag to RGO-Ag nano composite [9]. Finally the

RGO-Ag/PPO modified electrode (Fig S2 C) exhibited the absorption peak at 534, 1520 cm-1

which can be attributed to the vibration of Cu-N and amide groups of PPO enzyme respectively

[10].

Figure S3

Fig S3 (A) Repeatability analysis of developed sensor in presence of L-dopa (0.05 mM) for 15 consecutive CV

measurements. (B) The current response of biosensor depicting the stability of biosensor in a duration of a week.

Figure S4

Fig S4 DPV curve showing real sample analysis of urine for spiked L-dopa concentrations of 30, 50 and 100 µM.

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