Cyclopropylamine plasma polymer surfaces for label-free SPR and QCM immunosensing of Salmonella

We report on the first successful application of nitrogen-containing functional surfaces prepared by plasma polymerization in surface plasmon resonance (SPR) immunosensing. The plasma polymers (PPs) were deposited from cyclopropylamine (CPA) vapors onto gold surfaces of SPR and quartz crystal microbalance (QCM) sensors. It provided an excellent platform for a stable immobilization of antibodies using glutaraldehyde (GA) activation. The performance of the SPR immunosensor was proven by a model pair of monoclonal antibody (Ab) AL-01 and human serum albumin as well as by the selective detection of bacterial pathogen Salmonella Typhimurium using the immobilized anti-Salmonella Ab. A baseline drift of the measured SPR signal, caused by the long-term reactivity of CPA plasma polymers, was well stabilized by 18 h immersion in phosphate buffered saline prior to the GA activation. The immunosensors can be successfully regenerated several times using 10 mM NaOH. The limit of detection of 105 CFU/mL and a wide linear response were achieved for Salmonella. The assay parameters are comparable to the conventional label-free methods. However, the replacement of conventional immobilization matrix with the CPA PPs offers an advantage of excellent adhesion to gold QCM and SPR surfaces achieved by fast and eco-friendly procedure compatible with the vacuum deposition of gold.