Electronic Supplementary Material

Journal: Microchimica Acta

Amperometric nitrite biosensor based on cytochrome c immobilized on Nafion and Cu-Mg-Al layered double hydroxide modified gold electrode

Huanshun Yin a,b, Yunlei Zhou a, Shiyun Ai a,*, Lin Cui a, Yanyan Qiu a, Tao Liu a, Lusheng Zhu b,*

a College of Chemistry and Material Science, Shandong Agricultural University, Taian, 271018, Shandong, China

b College of Resources and Environment, Shandong Agricultural University, Taian, 271018, Shandong, China

* Corresponding author.

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1. Characterization of Cu-LDH

Fig. 1S showed the FT-IR spectra of Cu-LDH. The first band was found at 3466 cm-1 and it corresponded to the OH mode, caused by the interlayer water molecules and hydroxyl groups in the brucite-like layers. This band shows a prominent shoulder around 3054 cm-1, which could be ascribed to hydrogen bonding of hydroxyl groups of layered lattice and/or water molecules with interlayer carbonate anions [1]. The weak band observed in the 1633 cm-1 region was due to the H2O from the interlayer water. IR absorptions due to the v2, v3 and v4 stretching vibration of interlayer CO32- ions were recorded around 865 cm-1, 1369 cm-1 and 651 cm-1, This is almost what is observed for every hydroxide irrespective of the nature of the octahedral sheets, suggesting a rather symmetric environment for the interlayer anions. The shoulder at 946 cm-1 has been ascribed to the presence of hydroxyl groups. In the low energy ranges of the spectra, the peaks of 788 cm-1, 554 cm-1 and 448 cm-1 could be attributed to the presence of Mg-O, Al-O and O-M-O bands. No sharp peak was observed at about 1400-1425 cm-1, which demonstrated that the NO3- was successfully exchanged by CO32- [2, 3]. A sharp band at 448 cm-1 was also the characteristics adsorption of skeleton vibration of layered double hydroxide.

Powder X-ray diffraction pattern (XRD) was shown in Fig. 2S. The sharp, intense peaks at low diffraction angles (peaks close to 2θ = 11o, 24o, and 35o) were ascribed to diffraction by basal planes of (003), (006), and (009), respectively. And the broad, less intense peaks at higher angles (peaks close to 2θ = 38o and 46o) were ascribed to the diffraction of (015) and (018) planes, respectively. The doublet close to 61o (2θ) corresponded to diffraction by plane (110) [4]. The results obtained in this work are in accordance with the previous reports [5].

According to the results obtained from FT-IR and XRD, it can be concluded that layered double hydroxide is successfully synthesized.

Fig. 1S. FT-IR spectra of Cu-LDH.

Fig. 2S. Power XRD patterns of Cu-LDH.

2. UV-Vis spectroscopy

As the shape and position of the Soret absorption bands could provide some important information about the denaturation of Cyt c [6], the UV-Vis absorption spectra of Cyt c was recorded in 0.1 M pH 7.0 PBS (Fig. 3S in ESM). The Soret absorption band of Cyt c in Nafion/Cu-LDH located at about 403 nm (curve b), which was close to that of natural Cyt c (407 nm, curve a), while Nafion/Cu-LDH showed no absorption bands in the wavelength range (curve c). It indicates that the physical morphology of Cyt c may keep unchanged and the slight shift can be ascribed to the interaction between Cyt c and Nafion/Cu-LDH. A very small shift suggests that such interaction does not destroy the structure of Cyt c, the microenvironment of Cyt c only changes slightly and Cyt c will still retain its biological activity [7].

Fig. 3S. UV-Vis spectrum of Cyt c (a), Cyt c/Nafion/Cu-LDH (b) and Nafion/Cu-LDH (c).

3. Scan rate

Fig. 4S. Cyclic voltammograms of Cyt c/Nafion/Cu-LDH/Au at different scan rates in 0.1 M pH 7.0 PBS.

Fig. 5S. Cyclic voltammograms of Cyt c/Nafion/Cu-LDH/Au at different scan rates in 0.1 M pH 7.0 PBS.

4. Calibration curves

Fig. 6S. Calibration curve.

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