Synthesis of salt-stable fluorescent nanoparticles (quantum dots) by polyextremophile halophilic bacteria

N Bruna,R Espinoza-Gonzalez,P Caravantes,M Flores,N Díaz-Silva,J P Monrás,A Tello,D Bravo,N Órdenes-Aenishanslins,B Collao,J M Pérez-Donoso

doi:10.1038/s41598-018-38330-8

N Bruna, R Espinoza-Gonzalez + Show 9 more

Open Access

https://doi.org/10.1038/s41598-018-38330-8

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Abstract

Here we report the biological synthesis of CdS fluorescent nanoparticles (Quantum Dots, QDs) by polyextremophile halophilic bacteria isolated from Atacama Salt Flat (Chile), Uyuni Salt Flat (Bolivia) and the Dead Sea (Israel). In particular, a Halobacillus sp. DS2, a strain presenting high resistance to NaCl (3–22%), acidic pH (1–4) and cadmium (CdCl2 MIC: 1,375 mM) was used for QDs biosynthesis studies. Halobacillus sp. synthesize CdS QDs in presence of high NaCl concentrations in a process related with their capacity to generate S2− in these conditions. Biosynthesized QDs were purified, characterized and their stability at different NaCl concentrations determined. Hexagonal nanoparticles with highly defined structures (hexagonal phase), monodisperse size distribution (2–5 nm) and composed by CdS, NaCl and cysteine were determined by TEM, EDX, HRXPS and FTIR. In addition, QDs biosynthesized by Halobacillus sp. DS2 displayed increased tolerance to NaCl when compared to QDs produced chemically or biosynthesized by non-halophilic bacteria. This is the first report of biological synthesis of salt-stable QDs and confirms the potential of using extremophile microorganisms to produce novel nanoparticles. Obtained results constitute a new alternative to improve QDs properties, and as consequence, to increase their industrial and biomedical applications.

Highlights

Semiconductor nanocrystals or Quantum Dots (QDs) exhibit unique optical and electronic properties with fluorescence emission wavelengths depending on nanoparticle (NPs) size and composition[1,2,3]
Bertani (LB) medium supplemented with NaCl 8 or 15% at different temperatures (28 to 37 °C) were obtained from Atacama Salt Flat (ASF), Uyuni Salt Flat (USF) and Dead Sea (DS) samples, as described in methods
All isolates were capable to grow at 28 and 37 °C. These microorganisms can be classified as halophiles

Summary

Introduction

Semiconductor nanocrystals or Quantum Dots (QDs) exhibit unique optical and electronic properties with fluorescence emission wavelengths depending on nanoparticle (NPs) size and composition[1,2,3]. The addition to chemical synthesis procedures of bidentate thiols [e.g. dithiothreitol (DTT), mercaptosuccinic acid (MSA), mercaptopropionic acid (MPA)] and ligands with different functional groups (amino, hydroxyl, carboxylic acid, among others) has been used to improve NPs biocompatibility and stability[12]. These methods produce NPs that still display low biocompatibility, sensitivity to pH and high ionic strength, as well as elevated production costs[11,13,14,15]. Biomimetic procedures have contributed to improve the properties of NPs, being the increase on biocompatibility one of the most significant improvements since it has a direct impact on the range of nanoparticles applications[14,15]

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