A Simple Colorimetric Detection of Haemophilus parasuis Based on Aptamer-Functionalized Gold Nanoparticles

Porcine Haemophilus parasuis disease, also known as Graze's disease, is the leading bacterial infectious disease caused by H. parasuis in modern pig farms. Due to the high nutritional requirement of H. parasuis, it usually gets a false positive result through the traditional methods of plate culture. Therefore, it is necessary to establish a simple and fast detection method for this pathogen identification. This work aimed to develop a colorimetric probe using aptamer-functionalized gold nanoparticles for identifying H. parasuis. The detection mechanism is based on the color change of gold nanoparticles (AuNPs) from red to blue-purple through NaCl induction after bacteria incubation and aptamer-target binding. First, aptamer-functionalized gold nanoparticles were synthesized and characterized. Then, the best concentration of aptamers and NaCl for detection was optimized at 80 pM and 0.25 M. Under the above optimized conditions, a good linear relationship between the absorbance ratio A678/521 and H. parasuis over the range from 103 to 109 CFU/mL. The limit of detection (LOD) is 12 CFU/mL. This method is simple and rapid, results in high sensitivity and specificity, and can be used to detect actual samples.