In this paper we presented a simple, rapid and label-free surface-enhanced Raman spectroscopy (SERS) based mapping method for the detection and discrimination of Salmonella enterica and Escherichia coli on silver dendrites. The results show the developed mapping method is able to detect single bacterial cells adsorbed on the surface of silver dendrites with a limit of detection as low as 104 CFU/mL, which is two orders of magnitude lower than that of the traditional SERS method under the same experimental condition.
The time needed for collecting a 225 points map was merely 24 minutes. Moreover, the developed SERS mapping method can realize simultaneous detection and identification of Salmonella enterica subsp enterica BAA1045 and Escherichia coli BL21 from a mixture sample.
The surface-enhanced Raman spectroscopy spectrum of an unknown bacterial cell can be used as fingerprints to identify this cell using a prediction model based on principle component analysis results of the standard spectra. The plot of the detected bacterial signal number versus the log value of the bacterial concentration demonstrates the potential quantitative capacity of the developed method at certain range.
To the best of our knowledge, this is the first study that a label-free surface-enhanced Raman spectroscopy mapping method has been developed for simultaneous detection and identification of a bacterial mixture. Our results demonstrate the great potential of the label-free surface-enhanced Raman spectroscopy mapping method to detect, identify and quantify bacteria and bacterial mixtures simultaneously.
Panxue Wang is a visiting PhD student in Dr. Lili He’s Lab (University of Massachusetts, Amherst). Panxue Wang obtained her bachelor’s degree of Food Science and Engineering in 2012 from Northwest A&F University, and she became a master combined with PhD student (Major: Food science; Advisor: Mingtao Fan) of the Northwest A&F University since 2012. She got the scholarship from the China Scholarship Council (CSC) to support her study in the United States and started to work with Dr. Lili He from September 2014. She will finish this program in August 2016. During this time, she focused on developing rapid bacteria detection, identification and characterization methods using an advanced analytical technique, surface enhanced Raman spectroscopy (SERS).
Her research interests comprise many aspects of bacteria, such as rapid detection and identification of food pathogens using SERS mapping, interaction of nanoparticles with bacteria cells, malolactic fermentation process in wine production, and antibiotic resistance in lactic acid bacteria.