**4. Conclusions**

CS/LS nanospheres have been successfully evaluated as a novel biocide for the inhibition of SRB induced biocorrosion. The *Rct* values are approximately doubled in the presence of CS/LS compared with the CS/LS-free media, irrespective of incubation intervals from the electrochemical analysis, with a corrosion inhibition efficiency of 85% at 500 <sup>μ</sup>g·mL−<sup>1</sup> CS/LS. Post-corrosion analysis with SEM and profilometry showed fewer surface defects on the coupon incubated with CS/LS, indicating less corrosion. Two synergic effects can explain the biocidal effect of CS/LS. The hydrophilic CS/LS can readily bind to the bacterial surfaces and thereby damage the bacterial cell wall. Meanwhile, the film forming capability of CS prevents the initial bacterial attachment on the metal surface and thereby leads to a reduction of biofilm formation. In short, due to the biodegradable nature, promising antimicrobial properties of the building blocks, and high biocorrosion inhibition efficiency, the CS/LS nanospheres can present a renewable, cost efficient, and environmentally benign biocide for the inhibition of SRB induced MIC on carbon steel systems.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/1996-1944/13/11/2484/s1, Figure S1: The Nyquist plot of the coupon incubated in the abiotic media (A). The corresponding Bode plots are given in (B) and (C). Figure S2: (A) The Nyquist plot of the coupon incubated with SRB with CS/LS with different concentrations from 0 to 1000 <sup>μ</sup>g·mL−1. The impedance analysis was performed after 10 days of incubation. (B) The *Rct* vs concentration of CS/LS after 10 days of incubation. The error bar indicates the standard deviation from the three independent measurements. Figure S3: The Nyquist plot of the coupon after 7 days of incubation in presence of CS/LS. Figure S4: Nyquist plot of the incubated coupon after 15 days in SRB enriched media with 5% GA. Inset shows the fitting equivalent circuit and the photographs of the incubation mixtures after 15 days of incubation. Figure S5: SEM images of the biofilm grown on the coupon surface after being incubated with SRB enriched media for 4 days without inhibitor (A) and in presence of 500 <sup>μ</sup>g·mL−<sup>1</sup> CS/LS (B). Figure S6: EDS analysis of biofilm incubated in SRB enriched media without CS/LS (A) and with 500 <sup>μ</sup>g·mL−<sup>1</sup> CS/LS (B) after 35 days of incubation. Figure S7: Profilometry of the bare carbon steel coupon surface. (A) 2D and (B) 3D images. Figure S8: Profilometry images (2D and 3D) of the cleaned carbon steel coupon surface after 35 days of incubation in SRB without CS/LS (A and B) and SRB with 500 <sup>μ</sup>g·mL−<sup>1</sup> CS/LS (C and D), respectively. Table S1: Composition of simulated seawater. Table S2. EIS fitting data. Table S3: XRF data of the biofilm incubated in SRB enriched media without CS/LS (A) and with 500 <sup>μ</sup>g·mL−<sup>1</sup> CS/LS (B) after 35 days of incubation.

**Author Contributions:** Conceptualization, P.A.R. and K.A.M.; methodology, P.A.R. and K.A.J.; validation, R.P.P. and K.A.M.; formal analysis, P.A.R. and K.A.J.; investigation, P.A.R.; data curation, P.A.R. and R.P.P.; writing—Original draft preparation, P.A.R. and R.P.P.; writing—Review and editing, A.M.A. and A.S.; visualization, P.A.R.; supervision, K.A.M. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by Qatar National Research Fund QNRF, Qatar Foundation through the NPRP gran<sup>t</sup> # NPRP8-286-2-118. The publication of this article was funded by the Qatar National Library.

**Acknowledgments:** The authors are grateful to V. Madhavan, J. Ponraj, M. Pasha and M. Helal at the Core lab of QEERI/HBKU, Qatar for XPS, TEM and SEM analysis.

**Conflicts of Interest:** The authors declare no conflict of interest.
