Comparative Evaluation of Aptamer- and Antibody-Functionalized Gold Surfaces for Bacillus Cereus Spore Capture

The development of an effective recognition interface is a critical step in biosensor design. In this study, aptamer- and antibody-functionalized gold surfaces were compared as capture interfaces for Bacillus cereus spores. Two aptamer sequences and different antibody immobilization approaches, including random and oriented immobilization, were investigated. Spore capture was evaluated by fluorescence imaging using either an aptamer–antibody sandwich assay or direct SYTO®9 staining, with Raman spectroscopy employed as a complementary characterization method. At the fixed spore concentration investigated, the aptamer-functionalized surfaces produced higher fluorescence responses than the antibody-functionalized surfaces under the tested experimental conditions. Raman bands associated with calcium dipicolinate provide additional evidence consistent with the presence of captured endospores. An opal/gold hybrid structure was also examined as a preliminary optical transduction platform. The immobilization of two distinct molecular recognition elements (MREs) was performed via spotter deposition, thus enhancing the signal-to-noise ratio. Our findings suggest that, in this configuration, aptamers outperform antibodies in capturing B. cereus spores and, therefore, are identified as the most useful MRE to be implemented in future biosensors. Furthermore, an easy method for the fluorescence labeling of spores, i.e., via SYTO®9, is proposed as an effective way to directly detect spore presence.