Fig. 4. (a) Photographs (i) and fluorescence pictures (ii) of the SiO2@PEI-QD-based fluorescent LFA strip used for detecting S. typhi. (b) Corresponding test line intensities and calibration curve as a sigmoidal function of the concentration of S. typhi within the range 107 to 0 cells per mL. The inset shows the linear relationship of the data in the low-concentration range.
