Quantification Detection of Probiotic Bacteria Based on Plasmonic Gold-Nanoparticle Sensors

Probiotic products are of significant research interest in recent years due to their powerful health benefits. One of the most popular commercial probiotic products is probiotic milk drinks containing Lactobacillus bacteria. The quality and effectiveness of such drinks are highly dependent on their bacterial content. However, such information is only available in producers’ advertisements—which may be misleading, and there are few studies done on the true bacterial content of these drinks. More significantly, conventional methods of measuring Lactobacillus bacterial content are laborious and time-consuming. Hence, this research aims to develop a fast and easy test that shows visible results rapidly and can be applied to other Lactobacillus-containing products. Recent developments have presented gold nanoparticles as a strong candidate for various applications in chemistry, physics, and biology for their unique optical properties. One essential optical property of gold nanoparticles is their red or blue color due to plasmon resonance. In this research, strong potential for this property of gold nanoparticles is recognised in a novel method of measuring the bacterial CFU in probiotic milk drinks. Gold nanoparticles function as the key material and indicator in this method as they are found capable of adhering to the Lactobacillus bacteria. The bacterial CFU can then be determined from the amount of gold nanoparticles attached to the bacteria. The eventual measuring scheme established enables fast (15 - 16 times faster than colony counting) and convenient (a sterile environment is not necessary) tests of the bacterial CFU in different probiotic milk drinks and has great potential in other related applications.