Oxidation of virus proteins during UV(254) and singlet oxygen mediated inactivation.

Despite the widespread use of UV(254) irradiation and solar disinfection for water treatment, little is known about the photochemical pathways that lead to virus inactivation by these treatments. The goal of this study was to identify reactions that occur in virus capsid proteins upon treatment by UV(254) irradiation and (1)O(2), an important oxidant involved in sunlight-mediated disinfection. Bacteriophage MS2 was inactivated via UV(254) irradiation and exposure to (1)O(2) in buffered water, and their capsid proteins were then analyzed with MALDI-TOF-TOF and ESI-TOF before and after digestion with protease enzymes. The results demonstrate that chemical modifications occur in the MS2 major capsid protein with both treatments. One oxidation event was detected following (1)O(2) treatment in an amino acid residue located on the capsid outer surface. UV(254) treatment caused three chemical reactions in the capsid proteins, two of which were oxidation reactions with residues on the capsid outer surface. A site-specific cleavage also occurred with UV(254) irradiation at a protein chain location on the inside face of the capsid shell. We attribute this UV(254) induced protein scission, which is nearly unprecedented in the literature, to a close association between the affected residues and viral RNA, an efficient UV(254) absorber. These results suggest that viral protein oxidation by UV(254) and (1)O(2) may play a role in virus inactivation and that viral inactivation may be tracked with mass spectrometric measurements.

Gold-coated polycarbonate membrane filter for pathogen concentration and SERS-based detection.

A SERS-based method for the concentration and detection of Giardia lamblia cysts in finished drinking water is reported. In this method, samples are concentrated with a membrane filter and then cysts captured on the filter surface are labeled with immunogold SERS labels and quantified via Raman spectroscopy. Anodisc((R)) membrane filters, silver membrane filters, and electroless gold-coated polycarbonate track etched (PCTE) membrane filters were investigated for their compatibility with the SERS based detection strategy. The largest pore size Anodisc((R)) membrane commercially available was too small for the proposed method because they led to physical retention of immunogold. When silver membrane filters were employed, cysts were difficult to distinguish from nonspecifically bound labels and cyst recovery from distilled water samples was only approximately 12.3%. With gold-coated PCTE membranes, however, cysts were readily detectable and cyst recovery was approximately 95%. This Raman based method simplifies Giardia detection and has potential to be extended to the simultaneous detection of numerous pathogenic organisms. To our knowledge, this is the first report coupling the use of membrane filters for the concentration and detection of organisms from water samples with a SERS based detection strategy.