# Gold Nanoparticles for Drug Delivery and Cancer Therapy
## 4 Gold Nanoparticle-Based Drug Delivery  
Nanomedicine demonstrates excellent clinical performance with good therapeutic effectiveness and less healthy tissue toxicity. Au NP-based drug delivery has gained considerable attention because of its prominent performance. Although no pharmaceutical approval of Au NPs regarding nano-drugs is officially marketed, many studies on this aspect are being carried out. A number of Au NP-based nano-drugs combined with other biomedical applications, including drug-conjugated Au NPs prepared for cancer therapy and tumor-targeting, are being studied [59]. Au NPs are known to be an effective nano-carrier for various drugs, such as peptides, plasmid deoxynucleic acids (pDNAs), proteins, small interfering ribonucleic acids (siRNAs), and chemo-therapeutic agents. In most cases, the surface area of Au NPs is modified with a cationic polymer or functional group such as carboxyl, amine and thiol groups to increase the surface area or surface-to-volume ratio for carrying the drug. The engineered surface area allows the stable and effective immobilization of the drug on to the Au NPs. The drug encapsulated in the Au NP complexes is protected from enzyme degradation by serum proteins in the blood stream. Cell-specific targeting molecules can also be attached to the drug-Au NP complexes and deliver the drug to specific target cells [60]. Fucoidan is an immune-therapeutic function polymer and is mainly used in pharmaceutical applications. It has a wide range of biological activities, such as anticoagulant, antibacterial, antiviral, immunomodulatory, anti-tumor, anti-inflammatory, and antithrombotic effects. The Au NPs are synthesized using fucoidan, which has increased biocompatibility and nontoxicity more than regular methods using naturally occurring marine polymers such as chitosan and porphyrin [61]. The synthesis of anticancer particle aptamers and Au NP-modified Morin pH-sensitive liposome with targeting properties was studied. Tumors with a pH lower than the normal tissue reduces the effectiveness of the drug. Au NPs can be used to deliver pH-responsive drugs such as Morin safely to the target for high effectiveness. In vivo results show that Au NP-encapsulated Morin can inhibit tumor growth in xenograft mouse models and promote tumor apoptosis. Blood biochemistry test shows these materials exhibit acute toxicity [62]. Bacterial infection is still one of the major causes of morbidity and mortality. In the case of Staphylococcus infection, the antimicrobial activity of antibiotics against microbes is severely limited by poor membrane transport ability [63]. Other challenges that need to be overcome when administering antimicrobial drugs are their low water solubility, clearance in blood stream, rapid degradation and cytotoxicity to healthy tissues. Au NPs are used in diagnosis and for therapeutic purposes for this case because of their specific properties--such as their large surface-to-volume ratio, small size, stability over high temperatures and high reactivity to living cells. Gentamicin sulfate is an aminoglycoside and has a board range of antibacterial activities. However, gentamicin sulfate has some serious side effects such as ototoxicity and nephrotoxicity, which restrict its usage. It also does not make cell membrane efficiently and is highly soluble to water. Gentamicin can be used for the treatment of serious microbial infection when it is conjugated to Au NPs [64]. A new delivery system was developed where each Au NP is surrounded by many drug moieties, acting as an individual group against the microbial organisms and able to penetrate cell wall effectively. This ability allows Au NPs to deliver a large number of antibiotic molecules into cells at a highly localized volume [65]. In Bronchiolitis obliterans syndrome, mesenchymal cells are primarily responsible for the fibro obliteration of small airways. An engineered Au NP with everolimus is very effective at inhibiting the proliferation and increasing the apoptosis of mesenchymal cells [66].