A broad-spectrum quantitative detection method of Gram-positive bacteria was realized based on the competitive binding of Gram-positive bacteria and gold nanoparticles (GNPs) to lysozyme (LZM). LZM and GNPs were incubated under the optimized condition of 15 min, pH 8.0 and room temperature. The Gram-positive bacteria were quantitatively detected by ultraviolet-visible (UV-Vis) spectrum and laser light scattering (DLS). Compared with the UV-Vis spectrum, DLS showed higher sensitivity to particle size changes, and the addition of 0.14 mg/mL LZM solution could be reduced from 40 μL in UV-Vis method to 20 μL in DLS method when the signal intensity reached an acceptable range. Therefore, the limit of quantitation reduced from 1.26×107 CFU/mL to 6.87×105 CFU/mL. Compared with the Gram-negative bacteria, both quantitative methods showed good selectivity for Gram-positive bacteria, and both methods could realize the quantitative bacterial detection in real sample with the average recoveries of 83.0%-87.0% with the relative standard deviation of 2.4%-3.1%. The DLS quantification also showed higher sensitivity. Compared with the UV-Vis method, DLS showed the superiority in this competitive binding detection system, which could improve the sensitivity of detection.
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