Electrically Active Magnetic Nanoparticles for Concentrating and Detecting Bacillus anthracis Spores in a Direct-Charge Transfer Biosensor

Bacillus anthracis, the causative agent of anthrax, is considered as one of the most important pathogens in the list of bioterrorism threats. This paper describes the synthesis of electrically active magnetic (EAM) nanoparticles and their application in a direct-charge transfer biosensor for detecting B. anthracis Sterne endospores. These EAM nanoparticles were synthesized from aniline monomer made electrically active by acid doping and gamma iron (III) oxide nanoparticles resulting in nanomaterials with diameters ranging from 50 to 200 nm. Room temperature hysteresis measurements of the synthesized nanomaterials using a quantum design MPMS SQUID magnetometer showed that their saturation magnetization values were between 61.1 and 33.5 emu/gm. The structural morphology of the nanomaterial was studied using transmission electron microscopy and the electronic diffraction patterns were observed to determine their crystalline nature. The EAM nanoparticles were coated with antibodies specific to B. anthracis Sterne endospores and used to capture the target antigen from varying spore concentrations ( to ) by applying a magnetic field. The immunomagnetically captured spores were then applied to a direct-charge transfer biosensor having a dimension of 5 mm 60 mm. The detection of the spores was based on the capillary flow of the captured spores aided by a direct-charge transfer of the EAM nanoparticle. The electric signal generated was recorded for 6 min in a reagentless process. The biosensor was able to detect the presence of B. anthracis spores at a concentration of 4.2. Specificity studies were also carried out to determine the biosensor responses in the presence of nontarget antigens. This study shows the novel application of EAM nanoparticles both as an immunomagnetic concentrator and a transducer in a portable, easy to use, biosensor that has the potential to be used as a rapid detection device for defense and biosecurity.