Qdot-peptide conjugate probe testing. (A) Tryptophan fluorescence emission spectra of S1 in buffer (dotted line), bound to Qdots (dashed line) or bound to Qdots in POPS (solid line). The samples contained either only 500 nM peptide or 500 nM Qdot-peptide conjugates with or without 25 μM POPS. (B) Lipopolysaccharide (LPS) neutralization assay. Recombinant Factor C activation assay of unlabeled S1 (open circle) or as a Qdot conjugate (open triangle). The activation of Factor C without LPS binding peptide is displayed with a solid square. The samples contained 125 nM S1 or S1-Qdot conjugate (1:1 ratio) or no peptide. Non-conjugated Qdot as well as negS1 showed no neutralization ability in this assay. (C) Flow cytometry histogram of Qdot-labeled Escherichia coli. Biotin-Qdot (black line) shows very little fluorescence similar to the E. coli auto-fluorescence (blue line). The Qdot-negS1 labeled E. coli cells show minor fluorescence (green line). The mean fluorescent intensity for Qdot-S1 labeled cells is clearly separated and indicates the specific staining of the cells by the probe (red). Settings: Excitation 488 nm, emission 675 nm, counted cells 100,000. (D) Staining of E. coli with Qdot-S1 conjugate. Overlay of light microscopy and fluorescence images. Intense staining is observed by using Qdots-S1 peptide (left). The controls with biotin (upper right) or negS1 (lower right) show that the unspecific binding was minimal. Total magnification: 400×.