Poly(ethylene terephthalate) (PET) is one of the most popular thermoplastics for daily use and finds application in packaging products for food and beverage storage, as well as textile materials for clothing. 1 The important features of PET, such as shatterproof nature, high strength to weight ratio, low cost, and recyclability make it feasible for use at the industrial scale for the aforementioned products. 2,3 In addition, PET shows flexible processability as well as moderate mechanical durance and physicochemical stability when in direct contact with body fluids; hence, it is a promising biomaterial for the development of medical products, including implantable devices, vascular grafts, and biosensors. 4,5 However, PET has poor biocompatibility, which results from non-specific binding to proteins because of its inherent hydrophobicity. 6 For example, non-specific protein adsorption onto a sensing platform would decrease the signal-to-noise ratio and reduce the sensitivity for target detection. 7 In the case of medical implants, adsorption of fibrinogen and platelet adhesion can cause immune responses, limiting their applications. 8 The most effective and general approach to reduce non-specific binding of proteins in the coating method is to form a hydrophilic polymer brush onto the surface of interest via a two-step process: functionalization of the initiator onto the target surface, and then, polymer brush formation by surface-initiated atom transfer radical polymerization (SI-ATRP) under airtight conditions. 9 However, there are several concerns regarding the use of the conventional protocol on PET substrates in biomedical applications. First, chemical inertness of PET is relatively difficult to be functionalized by initiators compared to other well-known surface chemistry, such as thiols on golds and silanes on oxides. 10 Second, the substrates for PET-based biomedical devices are not limited to small planar ones, but vary in size, shape, and curvature. This makes deoxygenation in the conventional SI-ATRP process difficult, where the presence of air can lead to early radical termination. Therefore, an alternative strategy is required to realize PET substrates with non-fouling properties for biomedical applications.In this work, we report aryl azide-based photochemical methods to immobilize the initiator, followed by activators regenerated by electron transfer (ARGET) for ATRP that Communication