Elsevier

Materials Research Bulletin

Volume 50, February 2014, Pages 348-353
Materials Research Bulletin

A biotemplated nickel nanostructure: Synthesis, characterization and antibacterial activity

https://doi.org/10.1016/j.materresbull.2013.09.055Get rights and content

Highlights

  • Nickel nanostructure-encapsulated bacteria were prepared using electroless deposition.

  • Bacterium surface was activated by red-ox reaction of its surface amino acids.

  • Interfacial changes at cell surfaces were investigated using fluorescence spectroscopy.

  • TEM and AFM depicted morphological changes.

  • Antibacterial activity of nanostructure was examined against different bacteria strains.

Abstract

Nickel nanostructure-encapsulated bacteria were prepared using the electroless deposition procedure and activation of bacterium cell surface by red-ox reaction of surface amino acids. The electroless deposition step occurred in the presence of Ni(II) and dimethyl amine boran (DMAB). Interfacial changes at bacteria cell surfaces during the coating process were investigated using fluorescence spectroscopy. Fluorescence of tryptophan residues was completely quenched after the deposition of nickel onto bacteria surfaces. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) depicted morphological changes on the surface of the bacterium. It was found that the Ni coated nanostructure was mechanically stable after ultrasonication for 20 min. Significant increase in surface roughness of bacteria was also observed after deposition of Ni clusters. The amount of coated Ni on the bacteria surface was calculated as 36% w/w. The antibacterial activity of fabricated nanostructure in culture media was examined against three different bacteria strains; Escherichia coli, Bacillus subtilis and Xantomonas campestris. The minimum inhibitory concentrations (MIC) were determined as 500 mg/L, 350 mg/L and 200 mg/L against bacteria, respectively.

Introduction

During the past decade, the application of biological templates to fabricate nanostructures with well-defined architectures has gained significant interest as a subfield in nanotechnology researches [1]. Biological materials display vast morphological variety with suitable surface functionalities and many of them can be produced in large scale, using inexpensive and environmentally green procedures. There are few reports about the fabrication of nanomaterials using several kinds of biotemplates with different sizes and shapes, such as proteins [2], [3], [4], [5], DNA [6], [7], viruses [8], [9], [10], bamboo [11], pollen grains [12], [13], [14], diatoms [15], bacteria [16], [17], [18], [19] and yeasts [21], [22], [23]. Biotemplated nanostructures can be used in fluidis, injection and optical systems [1], [16].

Bacteria are commercially available and flexible for genetic manipulation, having variety of well-established morphologies and long lifetimes. There are two approaches for bonding of a metal nanostructure onto the bacterial cell surfaces; in situ deposition from solution of metal ions and adsorption of pre-synthesized metal nanoparticles. Amino acids such as cysteine, glutamic acid, and aspartic acid and different functional groups such as carboxyls, amines, hydroxyls and phosphoryl in specific locations on the bacterial cell surfaces provide a variety of binding sites toward metal ions and metal nanoparticles [2], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25]. Selective deposition of Au nanoparticles has been reported on live gram-positive Bacillus cereus bacterial cell surface [17]. ZnO hollow spheres have been synthesized using Streptococcus thermophilus as a biological template [18]. Also monomeric magnetic nickel microstructures have been prepared using Deinococcus radiodurans, elongated Escherichia coli and Rhodospirillum rubrum [14]. Recently, the controlled assembly of metal chalcogenide nanoparticles into biomorphic porous hollow nanostructures was reported by two species of bacteria [26].

Besides various metal nanoparticles such as Ag, Cu, Mg, Zn [27], [28], [29], antibacterial activity has been reported for Ni nanoparticles [30]. This activity is attributed to high surface area of nanoparticles toward bacterial surfaces. The antibacterial activity of smaller nanoparticles is higher than larger ones [31]. Nanoparticles applied in various fields such as food processing, food packaging systems, water treatment and medical instruments.

In this paper, we report fabrication of a nickel nanostructured shell on the gram-positive Bacillus subtilis bacterium cell as a biological template through in situ electroless deposition procedure as already described by Mertig et al. [2]. In this procedure, the bacterium cell surface was first activated using a nobel metal and then coating process was carried out in electroless metal deposition bath. The fluorescence spectroscopic measurements of the activated and metalized bacteria solutions were used to reveal interfacial changes in bacterial cell surface during activating and coating processes. The synthesized Ni encapsulated bacteria were characterized by transmission electron microscopy (TEM), energy-dispersive X-ray (EDS), atomic force microscopy (AFM), Fourier transforms infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and thermogravimetric analysis (TGA/DSC). The antibacterial activity of the nanostructure was investigated against three bacteria strains.

Section snippets

Materials

Nikel sulfate hexahydrate (NiSO4·6H2O) and 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) were supplied by ACROS (Newjersey, USA) and USB (Cleveland, OH, USA), respectively. K2PtCl4 was purchased from Aldrich (St. Louis, MO, USA) and dimethyl amine boran (DMAB) was supplied from Merck (Hohenbrunn, Germany). B. subtilis 1A772 was provided by Bacillus Genetic Stock Center. All the aqueous solutions were prepared with double-distilled water.

Methods

In this work, gram-positive bacterium of B.

Mechanism of metal deposition on the bacterium surface

One of the most established procedures for coating of metal nanostructures on the surface of biological templates via in situ deposition approach is deposition of metal ions by surface-catalyzed reactions [2]. In this procedure, deposition reactions are conducted on catalyzing sites immobilized onto the biotemplate surface. Immobilization of catalyzing sites, consisting of noble metal clusters, on the surface of biotemplate is called surface activation. The surface activation can be performed

Conclusions

In conclusion, the results presented here demonstrate the efficiency of the “in situ electroless deposition” procedure for generating nickel nanostructure-coated bacteria through surface-catalyzed reactions. The use of immobilized catalyzing sites provided controllable conditions for the deposition process. Gram-positive B. subtilis bacteria cells were successfully used as biological templates. The bacterium cell was stable and retained its original 3D shape during successive steps of coating.

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