Protective antigen detection using horizontally stacked hexagonal ZnO platelets.

Anthrax toxin detection before bacteremia, when toxin concentration is low, improves the chances of efficient treatment and cure. We present a novel technique for ultrasensitive detection of a protective antigen (PA(83)) of anthrax using an array of zinc oxide nanorods in conjunction with a FITC-labeled PA affinity peptide. The nanorods are composed of horizontally stacked hexagonal platelets which are uniformly spaced and grown unidirectionally upon a glass substrate via a new and simple technique. Images taken under UV emission demonstrate fluorescence sensitivity to PA as a function of antigen concentration, and a negative control using bovine serum albumin produced no fluorescence signal. The fluorescence signal of the PA-peptide complex is also significantly reduced in the absence of the nanorods, suggesting that the presence of ZnO nanorods inhibits the self-quenching properties of the fluorophore. A lower limit of detection for the assay system for PA is estimated at 150 aM, which demonstrates the possibility of using ZnO nanorods in biological sensor systems.