Background: Anthrax is an acute disease caused by the gram-positive bacterium Bacillus anthracis. Recently, it has been reported that the B. anthracis capsule is composed of poly-γ-D-glutamic acid (PGA), which is closely associated with the pathogenesis of the B. anthracis infection since it protects bacilli from immune surveillance. Consequently, the PGA capsule can be used as a target marker for the detection of B. anthracis.
Methods: We have developed a novel SERS-based magnetic sensor for highly sensitive detection of anthrax biomarker PGA in human serum. For fast, sensitive, and safe detection of such a hazardous material in human serum, we designed and fabricated a solenoid-embedded dual channel microfluidic device to perform the PGA immunoassay in an automated manner.
Results: Quantitative assays for eight different concentrations of PGA trace in serum were performed using the SERS-based microfluidic sensor. Here, PGA and PGA-conjugated AuNPs underwent competitive reaction with anti-PGA-immobilized magnetic beads in the microfluidic channel. Subsequently, magnetic immunocomplexes were trapped by yoke-type solenoids embedded in the channel, and their SERS signals were measured and analyzed. To improve the reliability for SERS measurements, the external standard values for PGA-free serum were measured using the control microfluidic channel. This greatly improved reliability by minimizing the influence of most experimental variables. The LOD determined by the SERS-based magnetic solenoid sensor was estimated to be 100 pg/mL. This low LOD value demonstrated that our SERS-based immunoassay was approximately three orders of magnitude more sensitive than corresponding ELISA-based methods. Accordingly, the proposed SERS-based magnetic solenoid microfluidic sensor technique, which possessed both high sensitivity and selectivity, showed significant potential for the safe, rapid and sensitive detection of hazardous materials in an automated manner.
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