Engineering the Multifunctional Surface on Magnetic Nanoparticles for Targeted Biomedical Applications

A Chemical Approach

Humphrey H P Yiu

Nanomedicine. 2011;6(8):1429-1446.

Conclusion

Magnetic nanoparticles can be functionalized to carry out specific tasks in nanomedicines via surface functionalization. However, when a multitasking property of these MNPs is desired, a multifunctional surface has to be designed to match such requirements. Chemical principles for assembling these multifunctional surfaces have been introduced in this article and they are critical to the successful synthesis and the subsequent stability of the materials. Thorough understanding of these chemistries can allow optimization of the resultant nanomaterials. As such the physiological behavior of these materials will be more predictable and improvements in their properties (including toxicity and stability) will be made more systematically. This is also vital for any leap from a bifunctional to tri-functional, and beyond, surface as the chemistry is getting more and more complicated and the opportunity for potential interference between functionality is getting higher.

In this article, we have introduced four main routes for the assembly of a multifunctional surface on a MNP. As the demand for a complex functional surface increases, these routes may not meet such needs. A combination of these methods might be required. The introduced silanization methods (both cocondensation and secondary reaction) open some new directions as the readily bifunctional surface can afford binding of various functional polymer chains, and some rather complex structures can then be constructed. With these technologies in place, MNP systems of higher complexity and more interesting properties will soon be made available for advanced biomedical uses. The situation is improving and this can only get better with increasing communication between scientists from different backgrounds.

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Cite this: Engineering the Multifunctional Surface on Magnetic Nanoparticles for Targeted Biomedical Applications - Medscape - Oct 01, 2011.

Table 1. A list of chemical functional groups for binding commonly used bioactive molecules, with suggested binding methods and other functional groups possibly causing interference in chemistry
Functionalities	Organic groups for binding	Binding method	Possible interference with
Antibodies, proteins, streptavidin, enzymes	-COOH -CH=O (aldehyde) -SH	EDC/NHS Direct interaction Direct interaction Direct interaction	-NH₂ -NH₂ -NH_2, -OH, -COOH -Br, -I
DNA	-NH₂ -NHR, -NR₂	Electrostatic Electrostatic	-CH=O (aldehyde), epoxy -Br, -I, -Cl -Br, -I, -Cl
Folic acid/folate	-NH₂	EDC/NHS	-COOH -CH=O (aldehyde), epoxy -Br, -I, -Cl
FITC, RITC, TRITC (any isothiocyanated fluorophores)	-NH₂	Direct interaction	-CH=O (aldehyde) epoxy -Br, -I, -Cl
Drugs (negatively charged)	-NH₂ -NHR, -NR₂	Electrostatic Electrostatic	-CH=O (aldehyde) epoxy -Br, -I, -Cl -Br, -I, -Cl
Drugs (positively charged)	-COOH	Electrostatic	epoxy
Cholic acid	-NH₂	EDC/NHS	-COOH, -CH=O (aldehyde), epoxy -Br, -I, -Cl

EDC: 1-Ethyl-3-(3-dimethylaminopropyl)carbodiimide; NHS: N-hydroxysuccinimide

Table 2. Examples of functionalized magnetic nanoparticles with first coating layer and, in some cases, the bioactive species for biomedical applications.
Coating materials	MNP types	Specific functional molecules	Applications	Ref.
Dextran	Fe₃O₄	Transferrin	Targeted MRI	[37]
	g-Fe₂O₃ (10 nm)	Folic acid	Magnetic hyperthermia	[80]
	Fe₃O₄ (5 nm)	¹⁸F	PET-CT scan	[81]
	Fe₃O₄ (8 nm)	⁶⁴Cu	PET-MRI scan	[82]
Chitosan	Fe₃O₄ (20 nm)	–	MRI	[83]
	Fe₃O₄ (8–11 nm)	Papain	Biocatalysis	[84]
	Fe₃O₄ (10–11 nm)	–	Magnetic hyperthermia	[85]
	Fe₃O₄ (10–16 nm)	FITC	Fluorescence imaging	[86]
Starch	Fe₃O₄ (6 nm)	–	MRI	[87]
	Fe₃O₄ (8 nm)	AGKGTPSLETTP peptide (A54) and doxorubicin	Drug delivery (doxorubicin)	[88]
	Fe₃O₄ (10–11 nm)	–	Magnetic hyperthermia	[85]
Polylysine	Fe₃O₄ (35 nm)	–	Cell labeling	[89]
Polylysine	Fe₃O₄	–	Gene delivery	[90]
Polyethylene glycol	Fe₃O₄ (10 nm)	Chlorotoxin and Cy5.5	MRI and fluorescence imaging	[41]
	Fe₃O₄ (10 nm)	Methotrexate	MRI and drug delivery	[42]
	Fe₃O₄ (10 nm)	Folic acid	MRI	[43]
Polylactic acid	Fe₃O₄ (5–10 nm)	Noscapine	Drug delivery	[44]
Polyglycolic acid	Fe₃O₄ (5–10 nm)	Noscapine	Drug delivery	[44]
Poly(lactide-co-glycolide)	Fe₃O₄ (10–15 nm) FeCo (7–23 nm)	HER antibody and doxorubicin –	Drug delivery (doxorubicin) MRI	[91] [92]
Polycaprolactone	Fe₃O₄ (5–15 nm)	Cisplatin and gemcitabine	Drug delivery	[46]
Polyvinyl alcohol	Fe₃O₄	Cy3.5, Texas Red	Cell labeling	[45]
Polyethyleneimine	Fe₃O₄ (11–25 nm)	–	Gene delivery	[93]
Polyethyleneimine	Fe₃O₄ (5–10 nm)	–	Gene delivery	[94]
Gold	Fe (19 nm)	–	MRI	[95]
Silica	Fe₃O₄ (10 nm) [97]
Aminopropyl silica	Fe₃O4 (15 nm)	¹⁸⁸Re	Radiotherapy	[52]
Aminopropyl silica	Fe₃O4 (10 nm)	Bovine serum albumin	Magnetic hyperthermia	[98]
Meso-2,3- dimercaptosuccinic acid	g-Fe2O₃ (3–15 nm)	Bovine serum albumin	Cell labeling	[99]

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