Parylenes in bioanalytical and cell culture applications

Parylenes are a family of polymers derived from poly(p-xylylene). The most commonly used member of this family is parylene C, which contains one chlorine substituent per monomer unit. It is used as a passivation layer in bioanalytical devices, among other applications. However, parylene C is chemically inert. This limits its use in bioanalytical applications and other fields that require chemical functionalization of the surface. Therefore, various methods have been developed to functionalize parylene C surfaces. Other approaches have aimed to develop parylenes with other moieties that are easier to functionalize. Depending on their functional group, parylenes have different characteristics, fields of application, and adjustment possibilities. In this work, four groups of parylenes are discussed: (1) parylene C and parylene N (poly(p-xylylene)) as the most common representatives of this polymer family, (2) heat-resistant parylenes, which include fluorinated parylenes, (3) parylenes with functional groups for protein coupling, such as amino groups and formyl groups, and (4) parylenes with moieties for click chemistry, allowing for a wide variety of functionalization and application. Applications include cell culture, biosensors, immunoassays, and enzyme assays, among others. A comparison of the performance of the respective parylenes is made, if possible, with regard to a specific analytical task. Though many tasks have been accomplished with available parylenes, limitations regarding functional groups, including the ability to undergo functionalization, still exist. This paves the way for new parylenes or new methods of surface modification that have not yet been widely adopted and are ready to be investigated.