Color and distance two-dimensional visual and homogeneous dual fluorescence analysis of pathogenic bacteria in clinical samples

The current study developed a homogeneous dual fluorescence and two-dimensional visualization method for E. coli through the detection of β-glycosidase (β-Gal) using cadmium telluride quantum dots (CdTe QDs) and N-methyl mesoporphyrin IX (NMM) as signal reporters. β-Gal hydrolyzes 4-Aminophenyl β-D-galactopyranoside (PAPG) to form p-aminophenol (PAP) that further reduces Ag+ and Fe3+ to Ag NPs and Fe2+. Ag+/Ag NPs and Fe3+/Fe2+ can then be identified using QDs and NMM, respectively. A visually readable test strip was generated by combining inkjet printing and using QDs as signal readouts. This test strip enabled the detection of E. coli using color and distance. Under optimized conditions, this system could detect E. coli with a limit of detection (LOD) of 0.2 colony-forming units (CFU)/mL using QDs and 0.3 CFU/mL using NMM, respectively. Furthermore, E. coli could be easily identified as low as 10 CFU/mL in the color and distance reading modes. Compared with clinical plate colony counting and mass spectrometry results, this method demonstrated an adequate consistency for the quantification of E. coli in 60 clinical urine samples, including 14 healthy samples, 21 E. coli negative and 25 E. coli positive ones. The distance reading test strip has been successfully applied in clinical urine samples. Quantitative results of positive patients were consistent with clinical data and fluorometer analysis findings. Therefore, our detection system may provide more solutions for point-of-care testing (POCT) analysis of bacteria.