**2. Chemical synthesis of magnetic nanoparticles and magnetic-fluorescent nanoparticles**

#### **2.1 Magnetic nanoparticles: synthesis**

In this chapter, we discuss the general and recent progress of different chemical synthetic pathways for IONPs (Fe3O4). Their small and controllable sizes, easily functionalized, as well as the ability to be manipulated by external magnetic forces [15], are all attractive properties for various applications including biomedical pursuits. The properties of MNPs strongly depended on the synthesis route. Consequently, the controllable synthesis of monodispersed IONPs is critical for controlling their size distribution, structural defects, surface chemistry, and magnetic behavior for application in specific biomedical field. The synthesis of shapecontrolled, stable, biocompatible, and monodispersed IONPs have drawn much effort over recent years. IONPs have been produced by various chemical, physical and biological methods which have both advantages and disadvantages (**Table 1**). Chemical synthesis offers significant advantages over other methods, as it is a facile, cost-effective method with ease of control over the NPs characteristics. These methods include thermal decomposition, co-precipitation, microemulsion, hydrothermal synthesis, and sol-gel and polyol methods, also shown in **Table 1** [32]. Of these methods, co-precipitation is the mostly used as it tends to be green, simple and effective with low production cost, high reproducibility and high yields in one synthesis [27]. Hence, it is of interest, and discussed in detail in section below.

#### *2.1.1 Co-precipitation method*

Co-precipitation method is the preferred choice among studied synthetic methods for the preparation of Fe3O4 NPs. It is a simple and classical approach to follow as it is simple, convenient, cheap with high reproducibility, solubility and scalability for large scale production. However, due to the high influence of kinetic factors on the growth of Fe3O4 NPs, such as low reaction temperatures, this resulted

*Mineralogy - Significance and Applications*

cancer treatment are reviewed.

**1.1 Purpose of the study**

multiple imaging is problematic. To improve the versatility and efficiency in numerous technologies, the development of hybrid magnetic nanoparticles combining both fluorescent and magnetic properties magnetic are being developed [13–23]. The combination of MRI and fluorescent spectroscopy in one nanocomposite opens up unique multimodal properties to monitor complementary information in biological applications such as in multimodal biological imaging, drug delivery systems and medical diagnostics. Despite many problems related to the synthesis of hybrid magnetic-fluorescent nanoparticles, major advances in recent years have been made in this field. For the synthesis, both physical and chemical techniques have been used for the synthesis of IONPs; still, the chemical approach are easier to control the NPs, such as the co-precipitation, thermal decomposition, hydrothermal synthesis, microemulsion, and sol-gel and polyol methods. Of all these approaches, the chemical approach, particularly co-precipitation method is discussed in Section 2. As Fe3O4 NPs are the mostly used IONPs, in this section we focus on the chemical synthesis of Fe3O4 NPs. Also, covered in this section is the synthesis of fluorescentmagnetic nanocomposite material, using InP/ZnSe NPs as fluorophore. The syntheses of fluorescent-magnetic nanoparticles are challenging due to chemical stability and the aggregation of the nanoparticles in solution caused by electron transfer interactions between the particles. The main challenge associated is to overcome the quenching of the luminescence of the fluorophore when it is on the particle surface of the magnetic core. This can be due to the electron and energy transfer between the fluorophore and the magnetic nanoparticles [24–26]. The easiest and most commonly used method to overcome this hurdle is to isolate the magnetic core from the fluorescent molecule. This can be achieved by coating the magnetic nanoparticle with a shell before it is attached to the fluorescent structure or by placing a spacer between the two molecules. These solutions lead to most luminescent magnetic nanoparticles to have a core-shell structure [15]. The shell needs to have specific properties namely: non-toxic or harmful to human tissue, should not cause the body to emit an immune response, to avert or reduce agglomeration and reduce nonspecific interactions with proteins, cells and other components of biological media. Hence, Section 3 covers several procedures for the functionalization and formation of the fluorescent-magnetic nanocomposite material to overcome these challenges. In Section 4, the biomedical applications of IONPs including MRI, magnetic hyperthermia, magnetic targeting, and cell tracking, with focus on diagnosis for breast

Nanocomposite material with dual or multiple properties have shown extensive potential to improve the performance of current cancer diagnostic tools and/or therapy, for biosensor applications, *in vivo* optical imaging or drug delivery. The aim of this project is to synthesize a nanohybrid material with luminescent and magnetic properties and having low or no toxicity, to be used for biological studies. In this experiment the synthesis of the multifunctional material will be synthesized via the process seen in **Figure 1**. From the diagram the end product, the nanocomposite material, the QDs are expected to cluster around the MNPs.

In order to synthesize the Fe3O4-InP/ZnSe bifunctional nanocomposite material, the luminescent InP/ZnSe nanocrystals were prepared separately from the Fe3O4 magnetic nanoparticles. Once both the MNPs and QDs nanomaterials are synthesized they are both will be functionalized with a compound containing a thiol group. The MNPs and QDs were functionalized with dimercaptosuccinic acid (DMSA) and mercaptopropionic acid (MPA), respectively. Using thiol chemistry, the QDs will directly combine to the surface of the MNPs (as seen in **Figure 1**).

**136**


#### **Table 1.**

*A comparison of the several synthetic methods of IONPs with advantages and disadvantages.*

in formation of irregularly shaped NPs with broad size distribution. This is the best method for the synthesis of water soluble magnetic nanoparticles. However, it has major drawbacks of broad particle size distribution [27, 33]. In 1982, Rene Massart prepared the first superparamagnetic iron oxide NPs, magnetite (Fe3O4), [17] via an alkaline precipitation of FeCl3 and FeCl2 mixture in a molar ratio of 1:2 [17]. The NPs were some-like spherical shaped, with diameter in broad size range around 8 nm. Hence, a size selection process using NaCl as an extra electrolyte was used to selectively decrease the electrostatic repulsions between NPs. This caused aggregation and formation of larger colloidal particles in the supernatant with a diameter of about 7 nm [18]. Hence, O2-bearing atmospheres is required for subsequent reactions to form maghemite (Fe2O3) or ferric hydroxide (Fe(OH)3) [27, 30, 31], due to the sensitivity and instability of magnetite as it is prone to oxidation [34]. In most cases, the co-precipitation method involves some form of mixing Fe2+/Fe3+ salt solutions in an alkaline medium at standard or elevated temperatures under inert (N2 or Ar) atmospheres to avoid the possible oxidation of Fe2+ into Fe3+ [35]. Most papers apply temperatures between 60 and 80°C, some at even higher temperatures [36]. The alkaline solutions commonly used are sodium hydroxide, potassium hydroxide and ammonium hydroxide. The co-precipitation method consists of two major steps—the first is the occurrence of a short nucleation burst at critical supersaturation is reached, and the second involves the slow nucleation growth via diffusion of the solute to the nanocrystal [15]. To obtain monodispersed Fe3O4 NPs, these two

**139**

**Figure 2.**

*Chemical Synthesis and Characterization of Luminescent Iron Oxide Nanoparticles…*

stages must be kept separate and the Fe2+/Fe3+ must be fixed at 1:2 molar ratio. Large amounts of monodispersed IONPs can be easily synthesized by changing certain reaction parameters for example the pH, temperature, ionic strength, composition of iron salts, ratio of ferrous to ferric iron and the type of the base and salt precursors [27]. Depending on the parameters, the particle size can be tuned in size range of 2–15 nm [27] with superparamagnetic properties. In most cases, the particle size increase as reaction time and temperate increase, the faster reaction rate results in formation of monomeric generation of NPs. Moreover, the pH value has shown an important role in controlling the size and stability [16]. Studies have shown that the pH must be kept in the range of 8–14 for monodispersed IONPs. A decrease in the pH value results in the decrease of the diameter or dissolution of the NPs, while

This can be prevented by using a surfactant on the surface of Fe3O4 NPs which cause repulsive force between radical ions. In addition, the surfactant not only protects the surface of Fe3O4 NPs, but can also control the size of NPs. In a paper Gao et al. synthesized Fe3O4 NPs using an aqueous solution of FeSO4.4H2O, NaNO3, NaOH, and citrate as the surfactant [19]. The diameter range was tuned from 20 to 40 nm by changing Fe2+ concentration. In another paper, Kumar et al. report on an environmentally benign, non-toxic and cost-effective method for the success

Blackberry leaf (ABL) extract is used as capping agent, and added to a solution

of FeSO4.7H2O, using NaOH to adjust the pH to 10–11, the solution was gradually heated between 75 and 80°C. The obtained Fe3O4 NPs had a size range of 54.5 ± 24.6 nm diameter [40]. In our group, Kiplagat et al. synthesized bare and meso-2,3-dimercaptosuccinic acid (DMSA) capped Fe3O4 (as shown in **Figure 2**). We prepared bare iron oxide nanoparticles following a simple co-precipitation method by dissolving salts of Fe3+ and Fe2+ with a molar ratio of 1:2 at the pH of

*TEM and EDX of bare and DMSA capped irregularly spherical shaped Fe3O4 nanoparticles synthesized by* 

*co-precipitation method (insets: histograms showing size distribution).*

*DOI: http://dx.doi.org/10.5772/intechopen.88165*

increase in pH value show NP tendency to oxidate.

synthesis of spherical shaped Fe3O4 NPs.

#### *Chemical Synthesis and Characterization of Luminescent Iron Oxide Nanoparticles… DOI: http://dx.doi.org/10.5772/intechopen.88165*

stages must be kept separate and the Fe2+/Fe3+ must be fixed at 1:2 molar ratio. Large amounts of monodispersed IONPs can be easily synthesized by changing certain reaction parameters for example the pH, temperature, ionic strength, composition of iron salts, ratio of ferrous to ferric iron and the type of the base and salt precursors [27]. Depending on the parameters, the particle size can be tuned in size range of 2–15 nm [27] with superparamagnetic properties. In most cases, the particle size increase as reaction time and temperate increase, the faster reaction rate results in formation of monomeric generation of NPs. Moreover, the pH value has shown an important role in controlling the size and stability [16]. Studies have shown that the pH must be kept in the range of 8–14 for monodispersed IONPs. A decrease in the pH value results in the decrease of the diameter or dissolution of the NPs, while increase in pH value show NP tendency to oxidate.

This can be prevented by using a surfactant on the surface of Fe3O4 NPs which cause repulsive force between radical ions. In addition, the surfactant not only protects the surface of Fe3O4 NPs, but can also control the size of NPs. In a paper Gao et al. synthesized Fe3O4 NPs using an aqueous solution of FeSO4.4H2O, NaNO3, NaOH, and citrate as the surfactant [19]. The diameter range was tuned from 20 to 40 nm by changing Fe2+ concentration. In another paper, Kumar et al. report on an environmentally benign, non-toxic and cost-effective method for the success synthesis of spherical shaped Fe3O4 NPs.

Blackberry leaf (ABL) extract is used as capping agent, and added to a solution of FeSO4.7H2O, using NaOH to adjust the pH to 10–11, the solution was gradually heated between 75 and 80°C. The obtained Fe3O4 NPs had a size range of 54.5 ± 24.6 nm diameter [40]. In our group, Kiplagat et al. synthesized bare and meso-2,3-dimercaptosuccinic acid (DMSA) capped Fe3O4 (as shown in **Figure 2**). We prepared bare iron oxide nanoparticles following a simple co-precipitation method by dissolving salts of Fe3+ and Fe2+ with a molar ratio of 1:2 at the pH of

#### **Figure 2.**

*TEM and EDX of bare and DMSA capped irregularly spherical shaped Fe3O4 nanoparticles synthesized by co-precipitation method (insets: histograms showing size distribution).*

*Mineralogy - Significance and Applications*

Chemical

Electrochemical decomposition

Physical Electron beam lithography

Biological

**Table 1.**

*Data edited from [27–31].*

**Techniques Advantages Drawbacks**

and high surface area-to-volume

cheap, standard ambient conditions

and their internal structure

Good control over inter-particle

Gas phase deposition Easy Poor control over size

Aerosol Relatively narrow size range Complex

scalability, and high yields

*A comparison of the several synthetic methods of IONPs with advantages and disadvantages.*

Sonochemical Easy with narrow size distribution No control over shape and medium

Complex, low yields

shape control

temperature

apparatus

Tedious, laborious

yield

Good control over particle size Very low reproducibility, rough and

Broad size distribution and poor

High pressure and high reaction

Complicated and high pressures

amorphous impurities final product

Only dissolves in non-polar solvents

Costly and use extremely complex

Microemulsion Precise control over shape and size

ratio

Co-precipitation Simple, convenient, very effective,

Hydrothermal Ease of control over size and shape. High efficiency

Polyol and sol-gel Facile with precise control over size

Thermal decomposition Monodispersed NPs, excellent shape and size control

spacing

Bacteria-mediated Cheap, good reproducibility and

in formation of irregularly shaped NPs with broad size distribution. This is the best method for the synthesis of water soluble magnetic nanoparticles. However, it has major drawbacks of broad particle size distribution [27, 33]. In 1982, Rene Massart prepared the first superparamagnetic iron oxide NPs, magnetite (Fe3O4), [17] via an alkaline precipitation of FeCl3 and FeCl2 mixture in a molar ratio of 1:2 [17]. The NPs were some-like spherical shaped, with diameter in broad size range around 8 nm. Hence, a size selection process using NaCl as an extra electrolyte was used to selectively decrease the electrostatic repulsions between NPs. This caused aggregation and formation of larger colloidal particles in the supernatant with a diameter of about 7 nm [18]. Hence, O2-bearing atmospheres is required for subsequent reactions to form maghemite (Fe2O3) or ferric hydroxide (Fe(OH)3) [27, 30, 31], due to the sensitivity and instability of magnetite as it is prone to oxidation [34]. In most cases, the co-precipitation method involves some form of mixing Fe2+/Fe3+ salt solutions in an alkaline medium at standard or elevated temperatures under inert (N2 or Ar) atmospheres to avoid the possible oxidation of Fe2+ into Fe3+ [35]. Most papers apply temperatures between 60 and 80°C, some at even higher temperatures [36]. The alkaline solutions commonly used are sodium hydroxide, potassium hydroxide and ammonium hydroxide. The co-precipitation method consists of two major steps—the first is the occurrence of a short nucleation burst at critical supersaturation is reached, and the second involves the slow nucleation growth via diffusion of the solute to the nanocrystal [15]. To obtain monodispersed Fe3O4 NPs, these two

**138**

12 in ultra-pure water at 50°C [41]. The DMSA capped iron oxide nanoparticles were prepared by dispersing IONPs in toluene and dimethylsulfoxide solution. The diameter of the bare IONPs range from 6 to 13 nm and the average size of 8.5 nm, whereas the DMSA capped IONPs size distribution range from 9 to 16 nm with an average diameter of 10.25 nm as shown histograms in **Figure 2**. The average size of DMSA capped iron oxide nanoparticles increased slightly compared to the bare iron oxide nanoparticles. Consequently, in our study we found that the synthesis of highly crystalline and monodispersed Fe3O4 NPs was not as easy to achieve. The capping of the iron oxide nanoparticles with the DMSA resulted to partial agglomeration as seen **Figure 2(a)** and **(c)**. We speculate that the presence of two thiol functional groups in DMSA lead to coupling the nanoparticles, thus the tendency to agglomerate. Similar observations were made by Kumar et al. [40] where they noted that functionalization with ABL led to partial aggregation and broader particle size distribution of IONPs. The use of suitable capping ligands is a widely used to improve their biocompatibility and stability [27, 44], however various approaches are being employed to avoid aggregation of these magnetic nanoparticles that restricts their applications.

In **Figure 3**, we show the XRD patterns of bare and DMSA capped iron oxide nanoparticles. The XRD pattern was matched with JCPDS no. 00-039-1346 and 00-019-0629 for maghemite (α-Fe2O3) and magnetite (Fe3O4), respectively. Our iron oxide nanoparticles were found to be maghemite. This might be due to the IONPS tendency to undergo oxidation as mentioned earlier [27, 30, 31, 35, 36]. A comparison chart of different coated IONPs and nanocomposites, including their characteristics such as the capping agent, physicochemical and magnetometric properties are shown in **Table 2**. The main of objective was to provide a facile method of preparing Fe3O4 NPs and its corresponding nanocomposites, to overcome the drawbacks of the prior research, particularly a process with less chemical reagents, carried out at standard reaction conditions.

## **2.2 Fluorescent QDs: synthesis**

On the other hand, another class of nanomaterials is quantum dots. Quantum dots (QDs) are inorganic fluorescent semiconductor nanoparticles with dimensions in the range of 1–10 nm. The QDs are usually composed of atoms from groups II–VI, III–V, or IV–VI [45]. The nanometer dimensions of the QDs causes a confinement of electron and hole carriers at dimensions smaller than the bulk Bohr excitation radius; this causes phenomenon, called quantum confinement, to occur in these

**141**

**Type of IONPs**

MnFe

Fe

Fe

Fe

Fe

O3 4 InP-Fe

O3 4 Core-shell

Thermal decomposition,

Cetyltrimethylammonium

bromide (CTAB)

sol-gel and oil-in-water

technique

Co-precipitation

Silica

Irregular nanoflakes;

Ms = 11 emu g−1 (VSM)

98–101 nm

Core-shell structure;

Ms = 37.2 emu g−1 (VSM)

Cytotoxicity

98–101 nm

Fe

SiO @Au 2 FemOn-SiO2 SiO2-FemOn

**Table 2.**

Co-precipitation

*Ms = saturation magnetization; Tb = blocking temperature; Dc = critical size; and Hc = coercivity field.*

*A comparison of several methods of the organic and inorganic coated IONPs, and their corresponding characteristics.*

Silica

O3 @4

Co-precipitation

DMSA

Co-precipitation

O3 4

Green method

Andean blackberry leaf (ABL)

extract

DMSA

O3 4

O3 4

Thermal decomposition of

iron oleate in NaCl

Co-precipitation

DMSA

Nearly spherical,

1.4–6.5 nm

Spherical shape,

54.5 ± 24.6 nm

Spherical shape,

Ms = 43.2 emu/g

(SQUID)

Ms = 6.03 emu/g

Breast cancer treatment

Kiplagat et al.

[41]

Monaco et al.

[42]

(SQUID)

Ms = 50–46 emu/g,

Photoacoustic and

magnetic resonance

imaging detection

Cytotoxicity

Toropova

et al. [43]

Toropova

et al. [43]

Tb = 298 K (SQUID)

9–16 nm

Agglomerated, unable

to obtain particles

Spherical shape,

100–110 nm

O2 4

Thermal decomposition

1,2-Hexadecanediol, dodecanoic

acid, dodecylamine

Oleic acid

Octapodes; 20–30 nm

**Synthetic method**

**Coating**

**Physicochemical properties** Spherical shape; 12 nm

**Magnetometric properties (SQUID)**

**Application**

**Reference**

Ms = 298 K,

Multimode imaging

Lim et al.

[26]

probes

Magnetic resonance

imaging

Lymphoma treatment

Song et al.

[38, 39]

Kumar et al.

[40]

Tb = 43.2 emu/g (SQUID)

Ms = 51–71 emu/g,

Tb = 240–290 K (SQUID)

Ms = 51.7 emu/g,

Tb = 298 K (VSM)

N/A

Degradation of organic

dyes, antioxidant

Breast cancer treatment

Kiplagat et al.

[41]

*Chemical Synthesis and Characterization of Luminescent Iron Oxide Nanoparticles…*

*DOI: http://dx.doi.org/10.5772/intechopen.88165*

Zhao et al.

[37]

**Figure 3.** *XRD pattern for bare and DMSA capped iron oxide nanoparticles.*


#### *Chemical Synthesis and Characterization of Luminescent Iron Oxide Nanoparticles… DOI: http://dx.doi.org/10.5772/intechopen.88165*

**Table 2.**

*A comparison of several methods of the organic and inorganic coated IONPs, and their corresponding characteristics.*

*Mineralogy - Significance and Applications*

restricts their applications.

**2.2 Fluorescent QDs: synthesis**

reagents, carried out at standard reaction conditions.

*XRD pattern for bare and DMSA capped iron oxide nanoparticles.*

12 in ultra-pure water at 50°C [41]. The DMSA capped iron oxide nanoparticles were prepared by dispersing IONPs in toluene and dimethylsulfoxide solution. The diameter of the bare IONPs range from 6 to 13 nm and the average size of 8.5 nm, whereas the DMSA capped IONPs size distribution range from 9 to 16 nm with an average diameter of 10.25 nm as shown histograms in **Figure 2**. The average size of DMSA capped iron oxide nanoparticles increased slightly compared to the bare iron oxide nanoparticles. Consequently, in our study we found that the synthesis of highly crystalline and monodispersed Fe3O4 NPs was not as easy to achieve. The capping of the iron oxide nanoparticles with the DMSA resulted to partial agglomeration as seen **Figure 2(a)** and **(c)**. We speculate that the presence of two thiol functional groups in DMSA lead to coupling the nanoparticles, thus the tendency to agglomerate. Similar observations were made by Kumar et al. [40] where they noted that functionalization with ABL led to partial aggregation and broader particle size distribution of IONPs. The use of suitable capping ligands is a widely used to improve their biocompatibility and stability [27, 44], however various approaches are being employed to avoid aggregation of these magnetic nanoparticles that

In **Figure 3**, we show the XRD patterns of bare and DMSA capped iron oxide nanoparticles. The XRD pattern was matched with JCPDS no. 00-039-1346 and 00-019-0629 for maghemite (α-Fe2O3) and magnetite (Fe3O4), respectively. Our iron oxide nanoparticles were found to be maghemite. This might be due to the IONPS tendency to undergo oxidation as mentioned earlier [27, 30, 31, 35, 36]. A comparison chart of different coated IONPs and nanocomposites, including their characteristics such as the capping agent, physicochemical and magnetometric properties are shown in **Table 2**. The main of objective was to provide a facile method of preparing Fe3O4 NPs and its corresponding nanocomposites, to overcome the drawbacks of the prior research, particularly a process with less chemical

On the other hand, another class of nanomaterials is quantum dots. Quantum dots (QDs) are inorganic fluorescent semiconductor nanoparticles with dimensions in the range of 1–10 nm. The QDs are usually composed of atoms from groups II–VI, III–V, or IV–VI [45]. The nanometer dimensions of the QDs causes a confinement of electron and hole carriers at dimensions smaller than the bulk Bohr excitation radius; this causes phenomenon, called quantum confinement, to occur in these

**140**

**Figure 3.**

nanoparticles. The QDs have tunable energy, optical and electronic properties which are done by either managing the QDs size or composition. QDs may be produced via various methods. These methods include but not limited to colloidal synthesis, plasma synthesis, self-assembly, and electrochemical assembly. However, to be able to tune the QDs to a have desired properties and to produce high quality QDs colloidal synthetic methods are the easiest and the most explored. Since there are several different types of QDs in exists, for simplicities sake this study will focus on InP.

A colloidal synthetic approach to manufacture QDs can either be achieved by a heating-up technique or rapid hot injection method. The heating up method is a batch process and is achieved by adding all the desired chemicals to a reaction vessel at relatively low temperatures or at room temperature, followed by rapidly heating the entire reaction up to a desired temperature that allows for crystal growth to occur. Khanna et al. [46] directly synthesized indium phosphide (InP) nanoparticles by heating a solution of indium powder in n-trioctylphosphine (TOP). The reaction was carried out under an argon atmosphere. The raw materials, the reaction time and temperature were varied to determine which reaction conditions would create the finest results. In addition, their research demonstrated that with high temperatures in conclusion with, short reaction times and a low amount of TOP leads to InP nanoparticles with small particle sizes and less impurity. The formation of the InP is caused by the catalytic activity of indium nanoparticles attempting to reduce C-P bonds found in TOP. The synthesis method is considered to be simple, low cost and avoids the use of hazardous and expensive raw materials.

#### *2.2.1 Hot-injection method*

To obtain QDs via the rapid hot injection technique, a main reaction is heated to a desired temperature and room temperature precursors are added to the reaction by rapidly being injected into the reaction. The quick addition of the precursors causes the reaction to supersaturate thus allowing for nucleation to occur. The reaction temperature when the cooler precursor is added, the addition of the precursor also causes the reaction to become diluted. The lowered temperature and the lowered concentration of the reaction materials prevent further nucleation, but nanocrystal growth still occurs. The work of Lui and co-workers used a reduction colloidal approach Lui and co-workers [47] were able to synthesize high quality InP NCs. The synthesis required the use of octadecene as a solvent and stearic acid as a capping ligand. These were heated in the presence of indium acetate, under an inert atmosphere for 30 min. After being heated a PCl3-precursor was added to the solution at 40°C. The temperature was then elevated to allow the growth of the InP core. By varying the reaction time and the temperature the study showed how the NC growth could be tuned to a desired size and size distribution. Upon further investigation it was demonstrated that, using a HF post-production treatment, the photoluminescence could be vastly enhanced. The research conducted confirms that InP NCs can be synthesized without the use of the hazardous and expensive material P(TMS)3.

#### **2.3 Synthesis of IONPs/QD hybrid nanocomposite**

Creating a complex system like this presents a few complications. The fabrication of such a system would require several synthesis and purifications steps, which is time consuming and expensive. Also having a magnetic element in the presence of a fluorescent compound reduces the photoluminescence and could quench the fluorophore [47–50]. There is currently very little information for possible alternatives to the first problem; the second is usually solved by encasing

**143**

the 3.8 emu g<sup>−</sup><sup>1</sup>

from 54 to 7 emu g<sup>−</sup><sup>1</sup>

was also roughly 7 emu g<sup>−</sup><sup>1</sup>

*Chemical Synthesis and Characterization of Luminescent Iron Oxide Nanoparticles…*

the MNP's in silica or polymer [24]. In the research conducted by Hong et al. [50], the layer-by-layer (LbL) approach was used to synthesize the magnetic-luminescent nanocomposite. LbL approach is based on the electrostatic attraction of oppositely charged species. In this synthesis, MNPs were used as a template for the multiple deposition of CdTe QDs. The MNPs were synthesized using the co-precipitation of ferric chloride and ferrous chloride. While TGA-capped CdTe QDs were prepared by the addition of Cd2+ into a solution of NaHTe in the presence of TGA. Using LbL they were able to fabricate Fe3O4/PEn/CdTe and Fe3O4(PE3/CdTe)n nanocomposite material by varying the number of deposition cycles of polyelectrolyte layers. The polyelectrolyte phases allowed for increased PL intensity while maintaining strong

The synthesis described by Gua et al. [51], demonstrated the synthesis of a multifunctional system by integrated materials, with luminescent and magnetic properties, into microspheres of quantum dots (QD) with a cross-linked polymer shell. They basically synthesized iron oxide magnetic nanoparticles (MNP) via a co-precipitation method and thiol-capped cadmium telluride (CdTe) by hydrothermal route. The MNP were incorporated into a silica sphere via the Stӧber method and the QDs added. These conjugated moieties were capped using a template polymerization. Their technique provides many advantages including the formation of a robust luminescent shell with multicolor bar codes which is generated by the aggregation of the thiol-capped CdTe on the silica particles. The outer shell not only protects the CdTe shells from damage, but also facilitates the covalent bonding of

The synthesis described by Liu et al. [48], demonstrates the synthesis of a magnetic-luminescent MNP-QD nanocomposite via electrostatic interactions. The two major problems that occur is (i) the close interactions of the QDs and MNPs, when they are embedded in a matrix, material causes photobleaching; (ii) while the layer-by-layer process takes an extremely long time and a lot of effort. In this experiment first CdSe QDs are synthesized via the hydrothermal route. While the MNPs are separately prepared using the co-precipitation of Fe2+ and Fe3+ salts, followed by a silica coating by means of the Stӧber method, and finally functionalizing the silica coated MNPs with 3-aminopropyltrimethoxysilane (APTS). The final MNPs were added to a solution of CdSe QDs. The new solution was sonicated and stirred for 6 hours at room temperature. The nanocomposite material was collected and separated by magnetic decantation. The luminescent-magnetic nanomaterial was spherical and had a diameter between 95 and 105 nm. The MNP-QD interactions caused a decrease in the PL intensity. The Ms of the silica-MNPs was 5.4 emu g<sup>−</sup><sup>1</sup>

The increase attention of multifunctional nanomaterial has led Nai-Qiang et al. [52] to develop a method to synthesize a nanocomposite composed of MNPs and QD material. The synthesis started the QDs and MNPs were prepared separately. The Mn-doped ZnS QDs synthesis began with a solution of Zn(NO3)2, manganese acetate and 3-mercaptopropionic acid (MPA) being mixed together. After the mixture undergone a dilution, an adjustment of the pH, and purging the air with N2, NaS2 was injected into the solution. The MNPs were synthesized via the co-precipitation of FeCl3 and FeSO4. The MNPs were then coated with SiO2 using the Stӧber method, finally the coated MNPs were modified with APTS. Using electrostatic interactions, the MNP-QD linkage was able to occur after 6 hours of rapid stirring. The nanocomposite material XRD pattern was a combination of the SiO2-MNP and Mn-doped QD patterns. The TEM results measured the nanocomposite material to be 100–130 nm in size and spherical. The SQUID analysis showed a decrease of

once the MNPs were coated with SiO2 and the nanocomposite

and

*DOI: http://dx.doi.org/10.5772/intechopen.88165*

magnetic properties.

the ligands to the nanoparticles.

for the nanocomposite.

.

*Chemical Synthesis and Characterization of Luminescent Iron Oxide Nanoparticles… DOI: http://dx.doi.org/10.5772/intechopen.88165*

the MNP's in silica or polymer [24]. In the research conducted by Hong et al. [50], the layer-by-layer (LbL) approach was used to synthesize the magnetic-luminescent nanocomposite. LbL approach is based on the electrostatic attraction of oppositely charged species. In this synthesis, MNPs were used as a template for the multiple deposition of CdTe QDs. The MNPs were synthesized using the co-precipitation of ferric chloride and ferrous chloride. While TGA-capped CdTe QDs were prepared by the addition of Cd2+ into a solution of NaHTe in the presence of TGA. Using LbL they were able to fabricate Fe3O4/PEn/CdTe and Fe3O4(PE3/CdTe)n nanocomposite material by varying the number of deposition cycles of polyelectrolyte layers. The polyelectrolyte phases allowed for increased PL intensity while maintaining strong magnetic properties.

The synthesis described by Gua et al. [51], demonstrated the synthesis of a multifunctional system by integrated materials, with luminescent and magnetic properties, into microspheres of quantum dots (QD) with a cross-linked polymer shell. They basically synthesized iron oxide magnetic nanoparticles (MNP) via a co-precipitation method and thiol-capped cadmium telluride (CdTe) by hydrothermal route. The MNP were incorporated into a silica sphere via the Stӧber method and the QDs added. These conjugated moieties were capped using a template polymerization. Their technique provides many advantages including the formation of a robust luminescent shell with multicolor bar codes which is generated by the aggregation of the thiol-capped CdTe on the silica particles. The outer shell not only protects the CdTe shells from damage, but also facilitates the covalent bonding of the ligands to the nanoparticles.

The synthesis described by Liu et al. [48], demonstrates the synthesis of a magnetic-luminescent MNP-QD nanocomposite via electrostatic interactions. The two major problems that occur is (i) the close interactions of the QDs and MNPs, when they are embedded in a matrix, material causes photobleaching; (ii) while the layer-by-layer process takes an extremely long time and a lot of effort. In this experiment first CdSe QDs are synthesized via the hydrothermal route. While the MNPs are separately prepared using the co-precipitation of Fe2+ and Fe3+ salts, followed by a silica coating by means of the Stӧber method, and finally functionalizing the silica coated MNPs with 3-aminopropyltrimethoxysilane (APTS). The final MNPs were added to a solution of CdSe QDs. The new solution was sonicated and stirred for 6 hours at room temperature. The nanocomposite material was collected and separated by magnetic decantation. The luminescent-magnetic nanomaterial was spherical and had a diameter between 95 and 105 nm. The MNP-QD interactions caused a decrease in the PL intensity. The Ms of the silica-MNPs was 5.4 emu g<sup>−</sup><sup>1</sup> and the 3.8 emu g<sup>−</sup><sup>1</sup> for the nanocomposite.

The increase attention of multifunctional nanomaterial has led Nai-Qiang et al. [52] to develop a method to synthesize a nanocomposite composed of MNPs and QD material. The synthesis started the QDs and MNPs were prepared separately. The Mn-doped ZnS QDs synthesis began with a solution of Zn(NO3)2, manganese acetate and 3-mercaptopropionic acid (MPA) being mixed together. After the mixture undergone a dilution, an adjustment of the pH, and purging the air with N2, NaS2 was injected into the solution. The MNPs were synthesized via the co-precipitation of FeCl3 and FeSO4. The MNPs were then coated with SiO2 using the Stӧber method, finally the coated MNPs were modified with APTS. Using electrostatic interactions, the MNP-QD linkage was able to occur after 6 hours of rapid stirring. The nanocomposite material XRD pattern was a combination of the SiO2-MNP and Mn-doped QD patterns. The TEM results measured the nanocomposite material to be 100–130 nm in size and spherical. The SQUID analysis showed a decrease of from 54 to 7 emu g<sup>−</sup><sup>1</sup> once the MNPs were coated with SiO2 and the nanocomposite was also roughly 7 emu g<sup>−</sup><sup>1</sup> .

*Mineralogy - Significance and Applications*

*2.2.1 Hot-injection method*

nanoparticles. The QDs have tunable energy, optical and electronic properties which are done by either managing the QDs size or composition. QDs may be produced via various methods. These methods include but not limited to colloidal synthesis, plasma synthesis, self-assembly, and electrochemical assembly. However, to be able to tune the QDs to a have desired properties and to produce high quality QDs colloidal synthetic methods are the easiest and the most explored. Since there are several different types of QDs in exists, for simplicities sake this study will focus on InP. A colloidal synthetic approach to manufacture QDs can either be achieved by a heating-up technique or rapid hot injection method. The heating up method is a batch process and is achieved by adding all the desired chemicals to a reaction vessel at relatively low temperatures or at room temperature, followed by rapidly heating the entire reaction up to a desired temperature that allows for crystal growth to occur. Khanna et al. [46] directly synthesized indium phosphide (InP) nanoparticles by heating a solution of indium powder in n-trioctylphosphine (TOP). The reaction was carried out under an argon atmosphere. The raw materials, the reaction time and temperature were varied to determine which reaction conditions would create the finest results. In addition, their research demonstrated that with high temperatures in conclusion with, short reaction times and a low amount of TOP leads to InP nanoparticles with small particle sizes and less impurity. The formation of the InP is caused by the catalytic activity of indium nanoparticles attempting to reduce C-P bonds found in TOP. The synthesis method is considered to be simple, low cost and avoids the use of hazardous and expensive raw materials.

To obtain QDs via the rapid hot injection technique, a main reaction is heated to a desired temperature and room temperature precursors are added to the reaction by rapidly being injected into the reaction. The quick addition of the precursors causes the reaction to supersaturate thus allowing for nucleation to occur. The reaction temperature when the cooler precursor is added, the addition of the precursor also causes the reaction to become diluted. The lowered temperature and the lowered concentration of the reaction materials prevent further nucleation, but nanocrystal growth still occurs. The work of Lui and co-workers used a reduction colloidal approach Lui and co-workers [47] were able to synthesize high quality InP NCs. The synthesis required the use of octadecene as a solvent and stearic acid as a capping ligand. These were heated in the presence of indium acetate, under an inert atmosphere for 30 min. After being heated a PCl3-precursor was added to the solution at 40°C. The temperature was then elevated to allow the growth of the InP core. By varying the reaction time and the temperature the study showed how the NC growth could be tuned to a desired size and size distribution. Upon further investigation it was demonstrated that, using a HF post-production treatment, the photoluminescence could be vastly enhanced. The research conducted confirms that InP NCs can be synthesized without the use of the hazardous and expensive

Creating a complex system like this presents a few complications. The fabrication of such a system would require several synthesis and purifications steps, which is time consuming and expensive. Also having a magnetic element in the presence of a fluorescent compound reduces the photoluminescence and could quench the fluorophore [47–50]. There is currently very little information for possible alternatives to the first problem; the second is usually solved by encasing

**142**

material P(TMS)3.

**2.3 Synthesis of IONPs/QD hybrid nanocomposite**

Due to the great potential surrounding multifunctional nanomaterial, there is a desire to create a fast, simple and large-scale synthesis of the nanocomposite material. Microwave irradiation (MWI) been successful in synthesizing various nanostructures that Zedan et al. [53] attempted to use the design to develop a novel synthesis of the magnetic-luminescent nanocomposite material. Using microwave synthesis, the Fe3O4 and CdSe NCs were prepared separately and to create the nanocomposite material a seed-mediated approach was used. The Fe3O4 NCs were used as seeds and CdSe semiconductor material was allowed to grow around the nanoparticle under MWI. The TEM images of the nanocomposite material confirmed that they maintained the core-shell morphology, were spherical and 10–15 nm in size. The XRD pattern of the nanocomposite material showed the material having good crystallinity. The nanocomposite material maintained the same emission and adsorption peaks as the CdSe QDs. Also changing the irradiation time provides the nanocomposite material with tunable optical properties and the ability to control the luminescent shell's thickness.

As mentioned previously the synthesis of such a material is very complex, Cho et al. [54] tried to optimize the synthesis of MNP-QD hybrid system by using a direct nucleation route. The multifunctional nanomaterial was prepared by first synthesizing the iron oxide NCs via the thermal decomposition of FeO(OH) with oleic acid as a surfactant in octadecene. The MNPs which formed were then purified and dispersed in hexane. The synthesis of the complex was created during the synthesis of cadmium selenide (CdSe) QDs via the high temperature decomposition method. Before the nucleation of the CdSe was allowed to take place, a solution of MNPs was injected into the solution, causing the QD to directly bind onto the MNP. The complex was monodispersed, crystalline, with an excitation of 575 nm and emission of 604 nm, and a quantum yield of 5%. The synthesis conditions were then varied in order to optimize the multifunctional nanomaterial produced. By varying the temperatures, injection rate and surfactant composition, created changes in the nanomaterials size, photoluminescence and morphology.

#### **2.4 Experimental details**

For this study magnetic-luminescent multifunctional nanocomposite material was synthesized. Following the work of Wang et al. [55], the QDs and MNPs were prepared separately. For the Fe3O4 MNP synthesis the co-precipitation method was chosen. The QDs were synthesized using the rapid hot injection method, we used InP\ZnSe because the study by Brunetti et al. [56] demonstrated that the In-based core-shell QDs are safer for *in vitro* and *in vivo* analysis than Cd-based QDs. The toxicity assessments found that the Cd-based QDs caused cell membrane damaged genetic material and interferes with Ca2+ homeostasis. The QDs were synthesized using the rapid hot injection technique and then a ligand exchange was performed on them and the resultant QDs were capped with 3-mercaptopropionic acid (MPA). The MNPs were functionalized with meso-2,3-dimercaptosuccinic acid (DMSA). This functionalization was achieved by creating a solution of 30 mM of DMSA in dimethyl sulfoxide (DMSO). This solution was added to a 40 mM of MNPs in toluene, at a 1:1 volume ratio. The resultant solution was stirred until it was observed that a black precipitate was forming. This black precipitate is the newly thiol-capped MNPs. These MNPs were removed from the solution with a magnet, washed with PBS, and dried in an oven. Using thiol chemistry, the QDs will be allowed to bond to the surface of the MNPs. Jeong et al. [57] was able to prepare multifunctional material using a similar synthesis method. The synthesis between the QDs and MNPs was accomplished through a partial ligand exchange reaction.

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**Figure 4.**

*MNPs-QDs nanocomposite.*

less toxic.

*Chemical Synthesis and Characterization of Luminescent Iron Oxide Nanoparticles…*

The synthesized iron oxide magnetic-luminescent nanocomposite, was characterized using high resolution transmission electron microscopy (HR-TEM), photoluminescence (PL), and superconducting quantum interference device (SQUID)

The multifunctional nanocomposite material was synthesized using a partial ligand exchange. Using the partial ligand exchange method multifunction nanoclusters are formed; this occurred due to using InP\ZnSe in excess. The choice to use excess QDs was an attempt to reduce the quenching of fluoresce quantum dots caused by the MNPs. As seen by the HR-TEM image (**Figure 3**) the use of the InP/ ZnSe in large excess compared to a number of MNPs led to enormous particle crowding. This crowding scenario makes it difficult to determine the average size of nanocomposite particles since the quantum dots filled the spaces between the MNPs. The PL spectrum the MNP-QD nanocomposite confirms that the composite was successfully formed. In this study, it was discovered that in spite of the high ratio of the QDs to MNPs, the black MNPs quenched the fluorescing capability of the QDs, the lowered intensity is observed in the PL spectrum (**Figure 4**). The quenching could be possibly due to energy transfer process resulting from contact between the

It is also clear that the absorption peak red shifted to 676 nm. This observation was also sufficient evidence for the successful formation of the nanocomposite, as the red shift emission observed in this study is most likely caused by the modification at the surface of the QDs brought by hydrophilic ligands and also immobiliza-

The nanocomposite material maintained its magnetic properties after the MNPs were conjugated to the QDs as shown by, **Figure 6**, the magnetization curve. Saturation magnetization of Fe3O4-InP/ZnSe core-shell nanocomposite ∼5.7 emu/g. After the MNP's were conjugated to the QD's the saturation magnetization is now a

cytotoxicity of the nanocomposite is presented in **Figure 7** below.

The nanocomposites were exposed to both MCF-12A and KMST 6 cell lines. The

As shown by the **Figure 7** the cell viability was greater than 90% for all concentrations of the nanocomposite. The findings suggest that the nanocomposites are

*DOI: http://dx.doi.org/10.5772/intechopen.88165*

quantum dots and the surface of the iron oxide particles.

tion of the MNPs (**Figure 5**).

10% fraction of the original MNPs.

**3. Characterization**

analysis.

*Chemical Synthesis and Characterization of Luminescent Iron Oxide Nanoparticles… DOI: http://dx.doi.org/10.5772/intechopen.88165*
