Evaluation of SERS nanoparticles for detection of Bacillus cereus and Bacillus thuringiensis

Authors: HONG, JEEHWA - Us Forest Service (FS); Qin, Jianwei - Tony Qin; Van Kessel, Jo Ann; OH, MIRAE - Us Forest Service (FS); DHAKAL, SAGAR - Us Forest Service (FS); LEE, HOONSOO - Us Forest Service (FS); KIM, DONGHO - Ministry Of Agriculture - Korea; Kim, Moon; CHO, HYUNJEONG - Ministry Of Agriculture - Korea

Submitted to: Biosystems Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/11/2018
Publication Date: 12/1/2018
Citation: Hong, J., Qin, J., Van Kessel, J.S., Oh, M., Dhakal, S., Lee, H., Kim, D., Kim, M.S., Cho, H. 2018. Evaluation of SERS nanoparticles for detection of Bacillus cereus and Bacillus thuringiensis. Biosystems Engineering. 43:394-400. https://doi.org/10.5307/JBE.2018.43.4.394.
DOI: https://doi.org/10.5307/JBE.2018.43.4.394

Interpretive Summary: Outbreaks of foodborne illness due to bacteria in a group known as Bacillus cereus have been identified worldwide, associated with the consumption of contaminated foods including raw vegetables as well as cooked products. Conventional laboratory methods to detect and identify bacterial contamination in foods is time-consuming and labor intensive, often due to the need to sample the bacteria and grow them to detectable levels for conventional tests. This research evaluated five types of metal nanoparticles for potential use for detecting two Bacillus species based on a method of surface-enhanced Raman spectroscopy (SERS). Samples of bacteria mixed with gold- or silver-nanoparticle suspensions were analyzed directly for spectral measurement, without the need to first grow the bacteria to greater volumes before measurement. Analysis of the SERS measurements found that, using three of the five types of nanoparticles with the two Bacillus species, the resulting spectral measurements were similar in character but showed significantly different peak intensities at a particular wavelength that only occurred when bacteria and nanoparticles were combined (not produced for either bacteria or nanoparticles measured separately). These preliminary results suggest that that development of SERS-based detection of these two Bacillus species using gold nanoparticles for practical application has some promise, providing a basis for further research to develop rapid SERS-based Bacillus detection methods that can be used by the food industry to detect contaminated food prior to distribution to consumers.

Technical Abstract: Agricultural products can be contaminated with pathogenic Bacillus species during cultivation and distribution, leading to potential foodborne illness for consumers. Rapid methods to detect and identify such contaminants are critical, particularly for agricultural perishable products subject to short timeframes for distribution and consumption. This research evaluated five types of nanoparticles for developing a surface-enhanced Raman spectroscopy (SERS) method to detect and distinguish two Bacillus species, Bacillus cereus and Bacillus thuringiensis. Bacterial concentrations were adjusted to a constant turbidity and a total of 30 µl of each Bacillus cell suspension was prepared for each nanoparticle. Each sample mixture was placed on a nickel plate for Raman measurement. A point-scan Raman system with 785 nm laser was used to obtain SERS data. There was no qualitative difference in bacterial detection between the SERS data of Bacillus cereus and Bacillus thuringiensis for any of the five nanoparticles. Three gold nanoparticles, stabilized in either citrate buffer or ethanol, showed a Raman intensity difference at 887.7 cm-1 in the two Bacillus species, while a gold nanoparticle stabilized in PBS buffer and a silver nanoparticle stabilized in an aqueous buffer with sodium citrate each showed no SERS effect. For the three gold nanoparticles showing the SERS peak, the % RSD of Bacillus cereus ranged between 1.96 amd 7.49 and that of Bacillus thuringiensis ranged between 6.24 and 12.45. The t-test for Bacillus cereus and Bacillus thuringiensis was significant at the p-value of 0.05. Among the three types of nanoparticles, gold nanoparticle stabilized in citrate buffer showed the least standard deviation, followed by gold nanoparticles stabilized in ethanol. This preliminary result supports the potential use of gold nanoparticles for SERS-based detection of Bacillus cereus and Bacillus thuringiensis.