Herein we report a novel strategy for the detection of bacteria using unfunctionalized gold nanoparticles (AuNPs), which was utilized as a colorimetric sensor. The UV–vis absorbance of AuNPs showed red shift due to the interactions between bacteria and AuNPs in the high acidic environment, producing a distinct color change which can be visually detected by naked-eye. The proposed low pH-based colorimetric assay was studied with seven types of foodborne bacteria, and the detection limit was found to be 1.6 × 10⁷ CFU/mL, 3.3 × 10⁵ CFU/mL, 4.5 × 10⁶ CFU/mL, 5.8 × 10⁶ CFU/mL, 2.8 × 10⁵ CFU/mL, 4.4 × 10⁷ CFU/mL and 6.6 × 10⁶ CFU/mL for strains Staphylococcus aureus, Shigella flexneri, Pseudomonas aeruginosa, Vibrio parahaemolyticus, Bacillus subtilis, Escherichia coli O157:H7, and Salmonella typhimurium respectively. The result can be observed by naked-eye within 5 min, the color changed from red to purple, blue and colorless with increasing the concentration of the bacteria, indicated the assay have the ability to differentiate bacteria of different concentrations. This work demonstrates that low pH-based colorimetric assay using unfunctionalized AuNPs for the directly detection of untreated bacteria is fast, simple and visual, has the potential for applications in bacterial diagnostics, especially the detection of pathogenic bacteria in food.

在此，我们报告了一种使用未功能化的金纳米粒子 (AuNPs) 检测细菌的新策略，该策略用作比色传感器。由于细菌和 AuNPs 在高酸性环境中的相互作用，AuNPs 的 UV-vis 吸光度显示红移，产生明显的颜色变化，可以用肉眼观察。所提出的基于低 pH 值的比色法对七种食源性细菌进行了研究，发现检测限为 1.6 × 10 ⁷  CFU/mL、3.3 × 10 ⁵  CFU/mL、4.5 × 10 ⁶  CFU/mL、5.8 × 10 ⁶  CFU/mL、2.8 × 10 ⁵  CFU/mL、4.4 × 10 ⁷  CFU/mL 和 6.6 × 10 ⁶  CFU/mL 菌株金黄色葡萄球菌、弗氏志贺氏菌、铜绿假单胞菌、副溶血性弧菌、枯草芽孢杆菌、大肠杆菌O157:H7和鼠伤寒沙门氏菌分别。5 min内肉眼观察结果，随着细菌浓度的增加，颜色由红色变为紫色、蓝色和无色，表明该测定具有区分不同浓度细菌的能力。这项工作表明，使用非官能化 AuNP 直接检测未处理细菌的基于低 pH 值的比色法快速、简单且直观，具有在细菌诊断中的应用潜力，尤其是检测食品中的致病菌。