There has been intensive research on nanoparticles (NPs) of biodegradable

polymers for controlled drug delivery to improve the therapeutic effects and

reduce the side effects of the formulated drug [1-4]. However, lack of selectivity

of the NPs between cancerous and healthy cells is a main disadvantage. Although

passive targeting of the NPs to solid tumors can be realized through the enhanced

permeability and retention (EPR) effect of the tumor vessels, the majority of the

NPs would still be cleared by the reticuloendothelial system (RES) [5-8]. Active

targeting can achieve specific effect and high uptake of the NPs in the tumor cells,

and leave the healthy cells untouched, which further improves the therapeutic

efficacy and reduces the side effects of chemotherapy. To achieve active targeting,

the NPs should be equipped with functional molecules, which can recognize and

adhere to the biomarkers on the surface of the corresponding cancer cells. The

targeting molecules employed in the literature include small organic molecules

such as folic acid [9-12], peptide such as cRGD peptide [13], carbohydrates such

as galactose and lactose [14-18], monoclonal antibodies such as anti-GFA Ab [19]

and mAb 2C5 or mAb 2G4 [20], and aptamers such as anti-PSMA aptamer [21,

22]. Among them folic acid is used most often for breast cancer targeting.