An electrochemical surface-enhanced Raman spectroscopy approach to anthrax detection

Metal film over nanosphere (MFON) electrodes are excellent substrates for surface-enhanced Raman scattering (SERS) spectroscopy. These surfaces are produced by vapor deposition of a metal film over nanospheres that are assembled in a hexagonally close packed arrangement. The efficiency and reproducibility of AgFON electrode as SERS substrates are confirmed by the repeatability of the electrochemical surface enhanced Raman scattering spectra of pyridine and the Ru(bpy)(3)(3+)/Ru(bpY)(3)(2+) complexes adsorbed on AgFON electrodes. The Raman signal for AgFON electrodes is observed to be extremely stable even at extremely negative potentials in both aqueous and nonaqueous electrolytes. Recent reports have indicated that SERS enhancement factors of up to 14 orders of magnitude can be achieved, providing the sensitivity requisite for ultra trace level detection of target analytes. For this reason, we are developing a method for bacterial endospore SERS detection based on the endospores marker -- dipicolinic acid (DPA). The SERS spectra of dipicolinic acid in aqueous solutions are reported. The dipicolinate vibrational features could be observed in the SERS spectra at the concentration as low as 8 x 10(-5) M in 5 minutes. These limits of detection are entirely controlled by the thermodynamics and kinetics of DPA binding to the AgFON surface.