A Computational and Mathematical Approach towards the Design and Synthesis of Uniform Au Seed Decorated Fe3O4 Nanoparticle for Potential Bio-application

Procedia Technology 10 ( 2013 ) 457 – 463

2212-0173 © 2013 The Authors. Published by Elsevier Ltd.Selection and peer-review under responsibility of the University of Kalyani, Department of Computer Science & Engineeringdoi: 10.1016/j.protcy.2013.12.383

ScienceDirect

International Conference on Computational Intelligence: Modeling Techniques and Applications (CIMTA) 2013

A Computational and Mathematical Approach towards the Design and Synthesis of Uniform Au seed decorated Fe3O4 Nanoparticle for

Potential Bio-application

Saptarshi Chatterjeea, Keka Sarkarb* aDepartment of Microbiology, University of Kalyani, West Bengal. Pin-741235, India bDepartment of Microbiology, University of Kalyani, West Bengal. Pin-741235, India

Abstract

Abstract

In recent years, superparamagnetic iron oxide nanoparticles (SPION) with appropriate surface chemistry have been

widely used. Au coated form of SPION or bimetallic nanocomposite have also gained considerable interest of

scientists because of their unique and tunable properties. In this study we attempt to design a uniform gold nano seed

decorated SPION having affinity towards biomolecular attachment. The design has been optimized to estimate the

number of gold nano-seeds by various mathematical models to cover up the magnetic core with uniform

distribution. Computational modeling has also been used in the design. The process of wet lab synthesis of the

designed nanocomposite has also been developed. Finally the characterization proves the successful design and

synthesis of the desired nanocomposite. Provision of biomolecular attachment onto the nanocomposite serves as a

possible diverse application of this nanocomposite in various biological systems.

* Corresponding author. Tel.:+91-9432191495; fax: +033-2582-8282 E-mail address: [email protected].

Available online at www.sciencedirect.com

458 Saptarshi Chatterjee and Keka Sarkar / Procedia Technology 10 ( 2013 ) 457 – 463

© 2013 The Authors. Published by Elsevier Ltd. Selection and peer-review under responsibility of the University of Kalyani, Department of Computer Science & Engineering.

Keywords: Super paramagnetic iron oxide nanoparticle (SPION); Gold Nanoparticle; Computational and

Mathematical model; Bio-application

1. Introduction

Super paramagnetic Iron oxide nanoparticles (SPION) have been the focus of extensive investigation over the past

decade [1-2]. Fe3O4 possesses inherent magnetic properties which are desirable for a large range of biomedical

applications including cellular sorting [3], targeted drug delivery [4], tissue engineering [5] and as MRI contrast

agents [6-7]. Bimetallic nanoparticles are promising in the field of biomedical sciences [8] for various desirable

properties [9].

The synthesis of Fe3O4/Au core-shell nanoparticles is challenging given the difference in surface energies of the two

materials [10]. Consequently, gold metals tend to nucleate rapidly forming discrete nanoparticle in solution without

coating the surface of magnetite.

The gold shell forms a poor diffusion barrier because of the high density of the grain boundaries at the gold surface

which itself is a challenge during such synthesis [11-12]. Moreover it is somewhat difficult to control the uniformity

and thickness of the metal coating [13].

Here we make an attempt to design a uniform gold seed decorated SPION. The design has been done based on the

wet lab synthesis and characterization of the individual components of the nanocomposite. The synthesized

nanocomposite was capable of biomolecular attachment on to the gold seed. Thus the Au seeded SPION

nanocomposite makes the newly designed nano material to be suitable for various biological applications [14].

2. Materials and Method

2.1 Materials

Various software (Autodesk: CAD, Maya) were used in developing the design of the nanocomposite. Mathematical

modeling has also been done in estimating the number of gold seed. For wet lab synthesis chemicals such as

Glutathione, HauCl4, NaBH4 etc have been bought from Sigma Aldrich, USA. Double distilled water filtered by

0.22μm filter (Merck, Millipore, USA) is used through out the study.

© 2013 The Authors. Published by Elsevier Ltd.Selection and peer-review under responsibility of the University of Kalyani, Department of Computer Science & Engineering


2.2 Design and model

The design of the nanocomposite has been done based on the characters (size, shape, dispersity etc) of the individual

nanoparticles (i.e. gold seed and Fe3O4 nanoparticle). A CAD image (2D) of the proposed nanoparticle is done. 3D

model is also developed that explains the arrangement and nature of the nanocomposite. The dimension of the

nanoparticles as well as nanocomposite has been obtained by Autodesk AutoCAD design suit and the images (2D

and 3D) are developed accordingly using Autodesk Maya software.

2.3 Synthesis

The synthesis of the gold seeded iron oxide nanocomposite is divided into three steps. In the first step Glutathione

functionalized gold nanoparticle (seed) is synthesized, followed by the synthesis of glutathione functionalized iron

oxide nanoparticle (core) in the second step. The final step involves the arrangement of Au seeds on to the core

magnetic nanoparticle.

GNPs are the colloidal suspension of gold particles of nanometer sizes. GNPs have been synthesized by an array of

methods which mainly are based on the reduction of chloroauric acid in the presence of a stabilizing agent. Here we

have synthesized the Au nanoparticle by the reduction of AuCl3 by NabH4 using standard method [15] followed by

GSH coating with some modifications [16].

The second step that involve the synthesis of glutathione functionalized Fe3O4 nanoparticle is prepared by the

addition of 25μm of glutathione into the water dispersed Fe3O4 nanoparticles synthesized by method of chemical

co-precipitation [17].

Mixing of the excess of glutathione functionalized Au seed with the surface functionalized Fe3O4 nanoparticles

under constant sonication at 60 MHz synthesizes the Au gold seed coated Fe3O4 nanoparticle. This is followed by

several round of washing and magnetic separation to separate the Au Seed decorated magnetic nanocomposite from

the excess Au seed and other impurities.

2.4 Characterization

Size of the synthesized gold seed, magnetic core (SPION) and gold seed decorated SPION were characterized using

transmission electron microscopy (TEM; Tecnai S-Twin, FEI, Hillsboro, OR, USA). The X-ray diffraction on dried

nanocomposite powder was performed (D500, Siemens, Berlin, Germany) within a 2θ range of 20–80◦ using Cu Kα

radiation. SQUID data of the gold seeded magnetic nanocomposite was also obtained (MPMS, Quantum Design

Inc., San Diego, CA, USA), which revealed its magnetic property.


3. Result and Discussion

3.1 Characterization

From the TEM study the size of the glutathione functionalized gold seed, Fe3O4 nanoparticle and Au seeded Fe3O4

nanoparticle was found to be 2nm, 8nm and 12 nm respectively (Fig.1). The XRD data confirmed the coexistence

of Au as well as Fe3O4 and their diffraction peaks at 2θ can be indexed to (220), (311), (111), (400), (200), (511) and

(440) planes as shown in Fig.2. The SQUID data (Fig. 3) demonstrates the magnetic strength of the nanocomposite

(Au seeded Fe3O4) even after the attachment of Au seeds over the magnetic core, yielding a gold seeded SPION.

Fig 1: TEM image of the Au seeded Fe3O4 nanocomposite Fig 2: XRD of the Au seeded Fe3O4 nanocomposite

Fig 3 SQUID data of nanocomposite showing Fig 4: 2D CAD image of the nanocomposite

magnetic momentum. with accurate dimentions


3.2 Model

The model of the gold seed decorated magnetic nanocomposite has been done based on the practical data obtained

from the characterization of the designed and synthesized nanocomposite. Fig. 4 is a two dimensional CAD diagram

of the proposed nanocomposite. The distribution of the 2nm Au seeds over the 8nm Fe3O4 core is shown here. The

concept of kissing number [18] has been considered during the study but the difference of sizes among the larger

inner core and the smaller Au seed makes the calculation different from the conventional. The 3D image as shown in

Fig.5 is based on the actual size on the nanocomposite.

Fig: 5: 3D representation of the synthesized nanocomposite by Auto CAD Maya software

3.3 Mathematical calculation on the number of Au seeds

Mathematical attempts have been made to count the possible number of Au seeds over the entire surface of Fe3O4

nanoparticle (core) in a 3D model.

The attempt can be named as: By surface area approximation.

1. By Surface area approximation:

Considering the two dimensional figure of the two spheres (Au and Fe3O4 nanoparticles) as two circles: OA is the tangent to the smaller particle (Au) at point A. Since, tangent is perpendicular to the radius at the point of contact therefore

OAX=90°

In Right Angled Triangle OAX, sin AOX= XA/OX = 1/5 = 0.5

AOX= sin-1 0.2 = 11.53°


Therefore, total two dimensional angle subtended at the centre ‘O’ by the smaller ball = θ =2 * AOX = 2 X 11.53°

= 23.073°

Now, It is known that S = r θ where S= length of arc, r = radius and θ = angle DOE = (Π X 23.073) / 180 radian =

0.4026 radian.

By the formula S = r θ , The value of S = 4 X 0.4026 = 1.6107 nm

Now let us approximate DE into one side of a square as D’E’ and form a square D’E’F’G’

Area of D’E’F’G’ = (1.6107nm) 2

The total surface area of the Fe3O4 nanoparticle = 4 Π r2 = 4 * Π * 42

Therefore, the number of Au nano seeds (2 nm dia) that can accommodate over the entire surface of Fe3O4

nanoparticle (8 nm dia) = Total surface area of the Fe3O4 nanoparticle / Approximate area covered by each Au seed

on the surface of Fe3O4 nanoparticle. = 4 * Π * 42 / (1.6107) 2 = 77.49 approx

The maximum number of Au seed that can accommodate over the surface of Fe3O4 nanoparticle is 77 (approx).

This value enables the quantitative approach of the nanocomposite, which now possess a maximum of 77 Au seeds

and thus possess 77 active sites for attachment of desired molecules.

4. Bio-molecular attachment and potential application

The attachment of biological molecules specially the DNA creates huge scope for the generation of biological nano-

devise in the form of sensing. Thus the provision of DNA attachment in the nanosystem is a critical phenomenon

governs the use of such systems in biological applications. Several studies have reported DNA self assembled

monolayer on gold surface using thiolated DNA molecules [19, 20] however the development of highly ordered

system remains a challenge. Hence, this approach is aimed to successfully create the organized nanosystem for bio-

molecular attachment that can be applied as a universal sensing devise both qualitative and quantitatively. Distinct

number of surface functionalized gold seed can provide a quantitative bio-molecular (eg. thiolated ssDNA)

attachment, whereas the magnetic core serves as an anchor for easy separation from liquid system.

5. Conclusion

The design of the Au seed decorated magnetic nanoparticle is aimed to produce a defined and highly organized

nanosystem that would be capable of bio-molecular applications. The wet lab synthesis is a combination of different

available method which has been characterized for its physical properties. These data has been utilized in designing

the model of the nanocomposite using mathematical modeling and computational aids. Thus the computational and

mathematical approach provides a clear idea of the synthesized nanocomposite which is essential in utilizing the Au

seed decorated nanocomposite for further biological applications. Provision for specific bio-molecular attachment

based on already developed and established protocol helps in applying this system as a universal tool that may be

modulated for diverse application based on need. Moreover the critical problem of optimization of the material has


been solved using computational and mathematical approach. Further research would definitely be required for

applying the system for various biological processes considering the background and design of the system has been

already done in this work.

Acknowledgements

This research work has been carried out with the financial support of Dept. of Science & Technology, Govt. of India

(Project-Nanomission: SR/NM/NS-48/2009) and University of Kalyani, Nadia, West Bengal. The authors also

acknowledge the help of Mr. Utpal Dey (M.Tech student of IIT Roorkie, India) for his useful contribution in

developing the mathematical model.

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A Computational and Mathematical Approach towards the Design and Synthesis of Uniform Au Seed Decorated Fe3O4 Nanoparticle for Potential Bio-application