Photodynamic therapy (PDT) utilizes photosensitizers (PSs) to produce reactive oxygen species (RO... more Photodynamic therapy (PDT) utilizes photosensitizers (PSs) to produce reactive oxygen species (ROSs) upon irradiation, which causes the shutdown of vessels and deprives the tumor of nutrients and oxygen, and in turn induces adverse effects on the immune system. However, significant efforts are needed to increase the efficiency in PDT in terms of light delivery to specific PSs for the clinical treatment of tumors located deep under the skin. Even though PDT offers a disease site-specific treatment modality, current efforts are directed to improve the solubility (in body fluids and injectable solvents), photostability, amphiphilicity (for tissue penetration), elimination, and systemic toxicity of traditional PSs based on porphyrin derivatives. Nanostructured materials show promising features to achieve most of such combined efforts. They can be artificially engineered to carry multiple theranostic agents onto targeted tumor sites. However, recent studies on photosensitive Cd-based nan...
the engineering of materials with controlled magnetic properties by means other than a magnetic f... more the engineering of materials with controlled magnetic properties by means other than a magnetic field is of great interest in nanotechnology. In this study, we report engineered magnetic graphene oxide (MGO) in the nanocomposite form of iron oxide nanoparticles (IO)-graphene oxide (GO) with tunable core magnetism and magnetic resonance transverse relaxivity (r 2). These tunable properties are obtained by varying the IO content on GO. The MGO series exhibits r 2 values analogous to those observed in conventional single core and cluster forms of IO in different size regimes-motional averaging regime (MAR), static dephasing regime (SDR), and echo-limiting regime (ELR) or slow motion regime (SMR). The maximum r 2 of 162 ± 5.703 mM −1 s −1 is attained for MGO with 28 weight percent (wt%) content of IO on GO and hydrodynamic diameter of 414 nm, which is associated with the SDR. These findings demonstrate the clear potential of magnetic graphene oxide for magnetic resonance imaging (MRI) applications. Magnetic materials such as superparamagnetic iron oxide nanoparticles (IO) have attracted mounting interest for a wide range of applications in nanomedicine 1-4 , magneto-mechanical actuation 5 , energy storage 6-8 , optoelectronics 9,10 , and environmental remediation 11-15 due to their biocompatibility, hydrophilicity, distinct morphology, and unique magnetic and electric properties. In medical diagnostics, the MRI applications of such materials are of paramount interest, and they are widely used as MRI negative contrast agents (CAs) 16,17 due to their hallmark characteristics of spin-spin or transverse relaxation enhancement. In pursuit of high-performance MRI CAs, the surface modification of IO is mostly executed in the form of core-shell 18,19 and Janus structure 20 using polymer stabilizers along with their controlled shape and size. In addition, with the advances in the research of graphene-based materials, GO has been utilized for surface modification of IO owing to its oxygenated functionalities, i.e., epoxide, hydroxyl, carbonyl, and carboxyl moieties 21,22 and biocompatibility 23,24. These functionalities can serve as the conjugation sites for IO to form GO-based nanocomposites, and in particular, magnetic graphene oxide (MGO). Recently, IO/GO-based nanocomposites have been proposed as T 1 25 and T 2 CAs 4,26,27 for MRI. However, no systematic studies on the tunable magnetic behavior and magnetic resonance (MR) relaxivity of such materials have been reported, and its corresponding size regime correlation remains unsettled. Some groups have recently explored the tunability of magnetic resonance transverse relaxivity (r 2) in single core or cluster forms of IO in the PEGylated core-shell nanostructures. The distinct r 2 values of IO with size range ~5-14 nm were reported via optimization of the coating thickness using PEG with molecular weights of 550, 750, 1000, 2000 and 5000 Da 28. Similarly, the PEGylated raspberry-like nanoclusters of superparamagnetic IO nanocrystals with a diameter range of 30 to 200 nm were reported with distinct r 2 values associated with three size
MBE Grown In x Ga1−x N Thin Films with Bright Visible Emission Centered at 550 nm
Journal of Electronic Materials
The InxGa1−xN thin films with indium content of x = 14–18 at.% were successfully grown by using m... more The InxGa1−xN thin films with indium content of x = 14–18 at.% were successfully grown by using molecular beam epitaxy (MBE) at high growth temperatures from 650°C to 800°C. In situ reflection high-energy electron diffraction (RHEED) of the InxGa1−xN films confirmed the Stranski–Krastanov growth mode. X-ray diffraction (XRD) of the films confirmed their highly crystalline nature having c-axis orientation with a small fraction of secondary InN phase admixture. High-resolution cross-sectional scanning electron microscopy images showed two-dimensional epilayers growth with thickness of about ∼260 nm. The high growth temperature of InxGa1−xN epilayers is found to be favorable to facilitate more GaN phase than InN phase. All the fundamental electronic states of In, Ga, and N were identified by x-ray photoelectron spectroscopy (XPS) and the indium composition has been calculated from the obtained XPS spectra with CASAXPS software. The composition calculations from XRD, XPS and photoluminescence closely match each other. The biaxial strain has been calculated and found to be increasing with the In content. Growing InxGa1−xN at high temperatures resulted in the reduction in stress/strain which affects the radiative electron–hole pair recombination. The InxGa1−xN film with lesser strain showed a brighter and stronger green emission than films with the larger built-in strain. A weak S-shaped near band edge emission profile confirms the relatively homogeneous distribution of indium.
We investigated the magnetic control of the Mn photoluminescence (PL) in iron oxide/L-cysteine-ca... more We investigated the magnetic control of the Mn photoluminescence (PL) in iron oxide/L-cysteine-capped zinc sulfide (Fe 3 O 4 /L-cys ZnS:Mn) nanocomposites via temperatureand field-dependent PL intensity studies. Fe 3 O 4 /L-cys ZnS:Mn was synthesized following a wet chemical deposition route and then its physicochemical, morphological, and magnetic properties were characterized. X-ray diffraction analysis indicates the formation of a semiconducting composite material with coexisting phases with high crystalline quality and purity. Electron microscopy reveals that the surfaces of the nanoparticles are clean and smooth, sized between 15 and 30 nm, without any sheathed amorphous phase. Vibrating sample magnetometry and UV light excitation show a clear superparamagnetic behavior and an optical response of Fe 3 O 4 /L-cys ZnS:Mn, which revealed its bifunctional nature. Magnetoluminescent coupling at 1.0 T is seen in the form of PL suppression in Fe 3 O 4 /L-cys ZnS:Mn from low temperature (10 K) to room temperature, with a PL intensity drop of ∼5% at 10 K and a maximum drop of 10% at room temperature. This observation can be explained by restriction of the energy transfer to Mn orbitals through magnetic ordering and Jahn−Teller distortions. Fe 3 O 4 / L-cys ZnS:Mn shows promise as a bifunctional biocompatible compound that can be applied as a theranostic agent and a quantum computational element. A deeper understanding behind the magnetic control of the optical response in bifunctional materials brings forth new arenas in diagnostics and drug delivery.
{"__content__"=>"T- and T-weighted Magnetic Resonance Dual Contrast by Single Core Truncated Cubic Iron Oxide Nanoparticles with Abrupt Cellular Internalization and Immune Evasion.", "sub"=>[{"__content__"=>"1"}, {"__content__"=>"2"}]}
ACS applied bio materials, Jan 16, 2018
Conventional T- or T-weighted single mode contrast-enhanced magnetic resonance imaging (MRI) may ... more Conventional T- or T-weighted single mode contrast-enhanced magnetic resonance imaging (MRI) may produce false results. Thereby, there is a need to develop dual contrast agents, T- and T-weighted, for more accurate MRI imaging. The dual contrast agents should possess high magnetic resonance (MR) relaxivities, targeted tumor linking, and minimum recognition by the immune system. We have developed nitrodopamine-PEG grafted single core truncated cubic iron oxide nanoparticles (ND-PEG-tNCIOs) capable of producing marked dual contrasts in MRI with enhanced longitudinal and transverse relaxivities of 32 ± 1.29 and 791 ± 38.39 mM s, respectively. Furthermore, the ND-PEG-tNCIOs show excellent colloidal stability in physiological buffers and higher cellular internalization in cancerous cells than in phagocytic cells, indicating the immune evasive capability of the nanoparticles. These findings indicate that tNCIOs are strong candidates for dual contrast MRI imaging, which is vital for noninv...
Biodiesel Brown grease Candida rugosa lipase Crosslinked lipase nanoparticles Conjugated lipase n... more Biodiesel Brown grease Candida rugosa lipase Crosslinked lipase nanoparticles Conjugated lipase nanoparticles Used cooking oil Inexpensive but resourceful sources of lipids, for example, used cooking oil (UCO) and brown grease (BG), which often contain large amounts of free fatty acids (FFA), are difficult to convert into biodiesel economically and in good yield. Candida rugosa lipase nanoparticles (cNP) were formed first and subsequently cross-linked nanoparticles (CLNP) were obtained by crosslinking of them. Alternatively, cNP were conjugated to magnetic nanoparticles (mNP) to achieve a cNP-mNP conjugate. All three formulations were employed in three different organic solvents (n-heptane, 1,4-dioxane, and t-butanol) to produce biodiesel using BG and UCO in the transesterification reaction with ethanol and methanol. The radii of nanoparticles (NP) were 5.5, 75, 100, 85 nm for mNP, cNP, CLNP, and cNP-mNP, respectively, as measured by scanning/transmission electron microscopy and dynamic light scattering. The catalytic efficiency (Kcat/KM) of cNP, CLNP, and cNP-mNP was increased ca.-25,-68,-176 folds in n-heptane and-35,-131,-262 folds in 1,4-dioxane compared to the lyophilized lipase in the model transesterification reaction of p-nitrophenyl palmitate (PNPP) with ethanol. In biodiesel formation, the best performance with 100% conversion of BG was achieved under optimum conditions with cNP-mNP, ethanol at a 1:3 molar ratio of lipid-to-alcohol, NP at a 1:0.1 weight ratio of lipid-to-enzyme, and water at a 1:0.04 weight ratio of enzyme-to-water at 30 o C for 35 h. The operational stability of the CLNP and cNP-mNP was sustained even after five consequent biodiesel batch conversions while 50% and 82% residual activity (storage stability) were retained after 40 d.
The engineering of materials with controlled magnetic properties by means other than a magnetic f... more The engineering of materials with controlled magnetic properties by means other than a magnetic field is of great interest in nanotechnology. In this study, we report engineered magnetic graphene oxide (MGO) in the nanocomposite form of iron oxide nanoparticles (IO)-graphene oxide (GO) with tunable core magnetism and magnetic resonance transverse relaxivity (r 2). These tunable properties are obtained by varying the IO content on GO. The MGO series exhibits r 2 values analogous to those observed in conventional single core and cluster forms of IO in different size regimes-motional averaging regime (MAR), static dephasing regime (SDR), and echo-limiting regime (ELR) or slow motion regime (SMR). The maximum r 2 of 162 ± 5.703 mM −1 s −1 is attained for MGO with 28 weight percent (wt%) content of IO on GO and hydrodynamic diameter of 414 nm, which is associated with the SDR. These findings demonstrate the clear potential of magnetic graphene oxide for magnetic resonance imaging (MRI) applications. Magnetic materials such as superparamagnetic iron oxide nanoparticles (IO) have attracted mounting interest for a wide range of applications in nanomedicine 1-4 , magneto-mechanical actuation 5 , energy storage 6-8 , optoelec-tronics 9,10 , and environmental remediation 11-15 due to their biocompatibility, hydrophilicity, distinct morphology, and unique magnetic and electric properties. In medical diagnostics, the MRI applications of such materials are of paramount interest, and they are widely used as MRI negative contrast agents (CAs) 16,17 due to their hallmark characteristics of spin-spin or transverse relaxation enhancement. In pursuit of high-performance MRI CAs, the surface modification of IO is mostly executed in the form of core-shell 18,19 and Janus structure 20 using polymer stabilizers along with their controlled shape and size. In addition, with the advances in the research of graphene-based materials, GO has been utilized for surface modification of IO owing to its oxygenated functionalities, i.e., epoxide, hydroxyl, carbonyl, and carboxyl moieties 21,22 and biocompatibility 23,24. These functionalities can serve as the conjugation sites for IO to form GO-based nano-composites, and in particular, magnetic graphene oxide (MGO). Recently, IO/GO-based nanocomposites have been proposed as T 1 25 and T 2 CAs 4,26,27 for MRI. However, no systematic studies on the tunable magnetic behavior and magnetic resonance (MR) relaxivity of such materials have been reported, and its corresponding size regime correlation remains unsettled. Some groups have recently explored the tunability of magnetic resonance transverse relaxivity (r 2) in single core or cluster forms of IO in the PEGylated core-shell nanostructures. The distinct r 2 values of IO with size range ~5-14 nm were reported via optimization of the coating thickness using PEG with molecular weights of 550, 750, 1000, 2000 and 5000 Da 28. Similarly, the PEGylated raspberry-like nanoclusters of superparamagnetic IO nanocrystals with a diameter range of 30 to 200 nm were reported with distinct r 2 values associated with three size
Photodynamic therapy (PDT) utilizes photosensitizers (PSs) to produce reactive oxygen species (RO... more Photodynamic therapy (PDT) utilizes photosensitizers (PSs) to produce reactive oxygen species (ROSs) upon irradiation, which causes the shutdown of vessels and deprives the tumor of nutrients and oxygen, and in turn induces adverse effects on the immune system. However, significant efforts are needed to increase the efficiency in PDT in terms of light delivery to specific PSs for the clinical treatment of tumors located deep under the skin. Even though PDT offers a disease site-specific treatment modality, current efforts are directed to improve the solubility (in body fluids and injectable solvents), photostability, amphiphilicity (for tissue penetration), elimination, and systemic toxicity of traditional PSs based on porphyrin derivatives. Nanostructured materials show promising features to achieve most of such combined efforts. They can be artificially engineered to carry multiple theranostic agents onto targeted tumor sites. However, recent studies on photosensitive Cd-based nan...
the engineering of materials with controlled magnetic properties by means other than a magnetic f... more the engineering of materials with controlled magnetic properties by means other than a magnetic field is of great interest in nanotechnology. In this study, we report engineered magnetic graphene oxide (MGO) in the nanocomposite form of iron oxide nanoparticles (IO)-graphene oxide (GO) with tunable core magnetism and magnetic resonance transverse relaxivity (r 2). These tunable properties are obtained by varying the IO content on GO. The MGO series exhibits r 2 values analogous to those observed in conventional single core and cluster forms of IO in different size regimes-motional averaging regime (MAR), static dephasing regime (SDR), and echo-limiting regime (ELR) or slow motion regime (SMR). The maximum r 2 of 162 ± 5.703 mM −1 s −1 is attained for MGO with 28 weight percent (wt%) content of IO on GO and hydrodynamic diameter of 414 nm, which is associated with the SDR. These findings demonstrate the clear potential of magnetic graphene oxide for magnetic resonance imaging (MRI) applications. Magnetic materials such as superparamagnetic iron oxide nanoparticles (IO) have attracted mounting interest for a wide range of applications in nanomedicine 1-4 , magneto-mechanical actuation 5 , energy storage 6-8 , optoelectronics 9,10 , and environmental remediation 11-15 due to their biocompatibility, hydrophilicity, distinct morphology, and unique magnetic and electric properties. In medical diagnostics, the MRI applications of such materials are of paramount interest, and they are widely used as MRI negative contrast agents (CAs) 16,17 due to their hallmark characteristics of spin-spin or transverse relaxation enhancement. In pursuit of high-performance MRI CAs, the surface modification of IO is mostly executed in the form of core-shell 18,19 and Janus structure 20 using polymer stabilizers along with their controlled shape and size. In addition, with the advances in the research of graphene-based materials, GO has been utilized for surface modification of IO owing to its oxygenated functionalities, i.e., epoxide, hydroxyl, carbonyl, and carboxyl moieties 21,22 and biocompatibility 23,24. These functionalities can serve as the conjugation sites for IO to form GO-based nanocomposites, and in particular, magnetic graphene oxide (MGO). Recently, IO/GO-based nanocomposites have been proposed as T 1 25 and T 2 CAs 4,26,27 for MRI. However, no systematic studies on the tunable magnetic behavior and magnetic resonance (MR) relaxivity of such materials have been reported, and its corresponding size regime correlation remains unsettled. Some groups have recently explored the tunability of magnetic resonance transverse relaxivity (r 2) in single core or cluster forms of IO in the PEGylated core-shell nanostructures. The distinct r 2 values of IO with size range ~5-14 nm were reported via optimization of the coating thickness using PEG with molecular weights of 550, 750, 1000, 2000 and 5000 Da 28. Similarly, the PEGylated raspberry-like nanoclusters of superparamagnetic IO nanocrystals with a diameter range of 30 to 200 nm were reported with distinct r 2 values associated with three size
MBE Grown In x Ga1−x N Thin Films with Bright Visible Emission Centered at 550 nm
Journal of Electronic Materials
The InxGa1−xN thin films with indium content of x = 14–18 at.% were successfully grown by using m... more The InxGa1−xN thin films with indium content of x = 14–18 at.% were successfully grown by using molecular beam epitaxy (MBE) at high growth temperatures from 650°C to 800°C. In situ reflection high-energy electron diffraction (RHEED) of the InxGa1−xN films confirmed the Stranski–Krastanov growth mode. X-ray diffraction (XRD) of the films confirmed their highly crystalline nature having c-axis orientation with a small fraction of secondary InN phase admixture. High-resolution cross-sectional scanning electron microscopy images showed two-dimensional epilayers growth with thickness of about ∼260 nm. The high growth temperature of InxGa1−xN epilayers is found to be favorable to facilitate more GaN phase than InN phase. All the fundamental electronic states of In, Ga, and N were identified by x-ray photoelectron spectroscopy (XPS) and the indium composition has been calculated from the obtained XPS spectra with CASAXPS software. The composition calculations from XRD, XPS and photoluminescence closely match each other. The biaxial strain has been calculated and found to be increasing with the In content. Growing InxGa1−xN at high temperatures resulted in the reduction in stress/strain which affects the radiative electron–hole pair recombination. The InxGa1−xN film with lesser strain showed a brighter and stronger green emission than films with the larger built-in strain. A weak S-shaped near band edge emission profile confirms the relatively homogeneous distribution of indium.
We investigated the magnetic control of the Mn photoluminescence (PL) in iron oxide/L-cysteine-ca... more We investigated the magnetic control of the Mn photoluminescence (PL) in iron oxide/L-cysteine-capped zinc sulfide (Fe 3 O 4 /L-cys ZnS:Mn) nanocomposites via temperatureand field-dependent PL intensity studies. Fe 3 O 4 /L-cys ZnS:Mn was synthesized following a wet chemical deposition route and then its physicochemical, morphological, and magnetic properties were characterized. X-ray diffraction analysis indicates the formation of a semiconducting composite material with coexisting phases with high crystalline quality and purity. Electron microscopy reveals that the surfaces of the nanoparticles are clean and smooth, sized between 15 and 30 nm, without any sheathed amorphous phase. Vibrating sample magnetometry and UV light excitation show a clear superparamagnetic behavior and an optical response of Fe 3 O 4 /L-cys ZnS:Mn, which revealed its bifunctional nature. Magnetoluminescent coupling at 1.0 T is seen in the form of PL suppression in Fe 3 O 4 /L-cys ZnS:Mn from low temperature (10 K) to room temperature, with a PL intensity drop of ∼5% at 10 K and a maximum drop of 10% at room temperature. This observation can be explained by restriction of the energy transfer to Mn orbitals through magnetic ordering and Jahn−Teller distortions. Fe 3 O 4 / L-cys ZnS:Mn shows promise as a bifunctional biocompatible compound that can be applied as a theranostic agent and a quantum computational element. A deeper understanding behind the magnetic control of the optical response in bifunctional materials brings forth new arenas in diagnostics and drug delivery.
{"__content__"=>"T- and T-weighted Magnetic Resonance Dual Contrast by Single Core Truncated Cubic Iron Oxide Nanoparticles with Abrupt Cellular Internalization and Immune Evasion.", "sub"=>[{"__content__"=>"1"}, {"__content__"=>"2"}]}
ACS applied bio materials, Jan 16, 2018
Conventional T- or T-weighted single mode contrast-enhanced magnetic resonance imaging (MRI) may ... more Conventional T- or T-weighted single mode contrast-enhanced magnetic resonance imaging (MRI) may produce false results. Thereby, there is a need to develop dual contrast agents, T- and T-weighted, for more accurate MRI imaging. The dual contrast agents should possess high magnetic resonance (MR) relaxivities, targeted tumor linking, and minimum recognition by the immune system. We have developed nitrodopamine-PEG grafted single core truncated cubic iron oxide nanoparticles (ND-PEG-tNCIOs) capable of producing marked dual contrasts in MRI with enhanced longitudinal and transverse relaxivities of 32 ± 1.29 and 791 ± 38.39 mM s, respectively. Furthermore, the ND-PEG-tNCIOs show excellent colloidal stability in physiological buffers and higher cellular internalization in cancerous cells than in phagocytic cells, indicating the immune evasive capability of the nanoparticles. These findings indicate that tNCIOs are strong candidates for dual contrast MRI imaging, which is vital for noninv...
Biodiesel Brown grease Candida rugosa lipase Crosslinked lipase nanoparticles Conjugated lipase n... more Biodiesel Brown grease Candida rugosa lipase Crosslinked lipase nanoparticles Conjugated lipase nanoparticles Used cooking oil Inexpensive but resourceful sources of lipids, for example, used cooking oil (UCO) and brown grease (BG), which often contain large amounts of free fatty acids (FFA), are difficult to convert into biodiesel economically and in good yield. Candida rugosa lipase nanoparticles (cNP) were formed first and subsequently cross-linked nanoparticles (CLNP) were obtained by crosslinking of them. Alternatively, cNP were conjugated to magnetic nanoparticles (mNP) to achieve a cNP-mNP conjugate. All three formulations were employed in three different organic solvents (n-heptane, 1,4-dioxane, and t-butanol) to produce biodiesel using BG and UCO in the transesterification reaction with ethanol and methanol. The radii of nanoparticles (NP) were 5.5, 75, 100, 85 nm for mNP, cNP, CLNP, and cNP-mNP, respectively, as measured by scanning/transmission electron microscopy and dynamic light scattering. The catalytic efficiency (Kcat/KM) of cNP, CLNP, and cNP-mNP was increased ca.-25,-68,-176 folds in n-heptane and-35,-131,-262 folds in 1,4-dioxane compared to the lyophilized lipase in the model transesterification reaction of p-nitrophenyl palmitate (PNPP) with ethanol. In biodiesel formation, the best performance with 100% conversion of BG was achieved under optimum conditions with cNP-mNP, ethanol at a 1:3 molar ratio of lipid-to-alcohol, NP at a 1:0.1 weight ratio of lipid-to-enzyme, and water at a 1:0.04 weight ratio of enzyme-to-water at 30 o C for 35 h. The operational stability of the CLNP and cNP-mNP was sustained even after five consequent biodiesel batch conversions while 50% and 82% residual activity (storage stability) were retained after 40 d.
The engineering of materials with controlled magnetic properties by means other than a magnetic f... more The engineering of materials with controlled magnetic properties by means other than a magnetic field is of great interest in nanotechnology. In this study, we report engineered magnetic graphene oxide (MGO) in the nanocomposite form of iron oxide nanoparticles (IO)-graphene oxide (GO) with tunable core magnetism and magnetic resonance transverse relaxivity (r 2). These tunable properties are obtained by varying the IO content on GO. The MGO series exhibits r 2 values analogous to those observed in conventional single core and cluster forms of IO in different size regimes-motional averaging regime (MAR), static dephasing regime (SDR), and echo-limiting regime (ELR) or slow motion regime (SMR). The maximum r 2 of 162 ± 5.703 mM −1 s −1 is attained for MGO with 28 weight percent (wt%) content of IO on GO and hydrodynamic diameter of 414 nm, which is associated with the SDR. These findings demonstrate the clear potential of magnetic graphene oxide for magnetic resonance imaging (MRI) applications. Magnetic materials such as superparamagnetic iron oxide nanoparticles (IO) have attracted mounting interest for a wide range of applications in nanomedicine 1-4 , magneto-mechanical actuation 5 , energy storage 6-8 , optoelec-tronics 9,10 , and environmental remediation 11-15 due to their biocompatibility, hydrophilicity, distinct morphology, and unique magnetic and electric properties. In medical diagnostics, the MRI applications of such materials are of paramount interest, and they are widely used as MRI negative contrast agents (CAs) 16,17 due to their hallmark characteristics of spin-spin or transverse relaxation enhancement. In pursuit of high-performance MRI CAs, the surface modification of IO is mostly executed in the form of core-shell 18,19 and Janus structure 20 using polymer stabilizers along with their controlled shape and size. In addition, with the advances in the research of graphene-based materials, GO has been utilized for surface modification of IO owing to its oxygenated functionalities, i.e., epoxide, hydroxyl, carbonyl, and carboxyl moieties 21,22 and biocompatibility 23,24. These functionalities can serve as the conjugation sites for IO to form GO-based nano-composites, and in particular, magnetic graphene oxide (MGO). Recently, IO/GO-based nanocomposites have been proposed as T 1 25 and T 2 CAs 4,26,27 for MRI. However, no systematic studies on the tunable magnetic behavior and magnetic resonance (MR) relaxivity of such materials have been reported, and its corresponding size regime correlation remains unsettled. Some groups have recently explored the tunability of magnetic resonance transverse relaxivity (r 2) in single core or cluster forms of IO in the PEGylated core-shell nanostructures. The distinct r 2 values of IO with size range ~5-14 nm were reported via optimization of the coating thickness using PEG with molecular weights of 550, 750, 1000, 2000 and 5000 Da 28. Similarly, the PEGylated raspberry-like nanoclusters of superparamagnetic IO nanocrystals with a diameter range of 30 to 200 nm were reported with distinct r 2 values associated with three size
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