Development of effective QCM biosensors by cyclopropylamine plasma polymerization and antibody immobilization using cross-linking reactions

• Plasma polymerized cyclopropylamine can be used in effective immunosensors.
• Films with similar amount of NH2 but different stability show different performance.
• Three different antibody immobilization methods were explored.
• GA and sulfo-SMCC methods provide stable baseline, selective and high response.

Biosensors have been extensively developed and applied for biomedical and environmental studies. Although there are many different types of biosensing techniques, immobilization of the biorecognition biomolecules onto the sensor surface is always required. Cyclopropylamine pulsed plasma polymerization in radio frequency (RF) capacitive discharges was employed to deposit amine thin films on the gold electrode of quartz crystal microbalance (QCM) biosensors and the monoclonal antibody AL-01, specific to human serum albumin (HSA), was immobilized onto the plasma polymer surface. Two different amine plasma polymers were studied. They had a similar amount of primary amine groups, 1.3–1.5 at.%, as determined by chemical derivatization but their stability in water was different. The 1st type, deposited at the floating potential and 120 Pa, exhibited 16% thickness loss after 24 h in water whereas the 2nd type deposited at RF electrode and 50 Pa was completely stable (2% thickness loss). Glutaraldehyde (GA) coupling of AL-01 was employed for both types of the amine films and the performance of QCM immunosensors was evaluated by the immunoassay flow test. A high-stability of the frequency signal was obtained in both the cases but the 2nd type of the film provided low response to HSA. It was explained by its highly cross-linked structure and steric hindrance of active sites. Three different antibody immobilization methods were explored for the 1st type of the film. Stable baseline, selective and high response were recorded for GA and sulfo-SMCC methods. The results confirmed that the presented methodologies for the grafting of biomolecules on the gold are highly efficient and very promising for future use in biosensing.