Submitted to: Symposium Proceedings of Nanotechnology Conference 2003
Publication Type: Proceedings
Publication Acceptance Date: 3/20/2007
Publication Date: 7/1/2007
Citation: Chen, Y., Liu, Y., Nou, X., Chao, K. Development of SERS spectroscopy for routine and rapid identification of escherichia coli and listeria monocytogenes on silver colloidal nanoparticles. Proceedings of Annual NSTI Nanotech Conference, Santa Clara, CA, May 20-24, 2007. 2(6)549-552, CDROM. Interpretive Summary: Rapid and routine methods for the identification of foodborne bacteria are increasingly important, because of not only the threat of bio-/agro-terrorism but also the public health concern and economic loss that are presented unexpectedly by outbreaks of foodborne illness. Traditional, antibody labeling, and immunoassays are generally multi-step procedures requiring significant volumes of chemical reagents, labor-intensive, and prone to operator-to-operator’s variation. Rapid microbial detection requires minimal sample preparation, permits routine analysis of a number of samples with low reagent costs, and must be easy to operate. To limit the probability of bacterial cross-contamination, reducing bacterial exposure to the environment is also desirable. Silver colloidal nanoparticle-based surface-enhanced Raman scattering (SERS) technique is an alternative approach that offers highly structural information and lacks interference from water. In this study, we first determined the characteristic and unique bands from SERS spectra of E. coli and L. monocytogenes cultures, and then developed simple algorithms for their identification with a 100% success rate. The findings demonstrate the potential of SERS in routine and rapid detection and screening of bacteria, because of the following advantages: (1) incubated bacterial culture was directly analyzed and procedures of centrifuging/washing/drying were not involved, (2) bacteria were always retained in suspensions and cross-contamination was avoided, (3) much lower volumes of chemical reagents were used compared to the requirements of current traditional methods, (4) the technique required only a short time (about 15-20 min) to complete a test, (5) both the step of mixing bacterial/silver nanoparticle suspensions and 25 mL culture volumes allowed the analysis of samples on a large scale, and(6) silver nanoparticle colloids were easy and inexpensive to fabricate and demonstrated good binding effect over storage periods of at least thirteen-weeks. This result provides agricultural/medical engineers and researchers a new insight in applying both nanotechnology and Raman spectroscopy for rapid, specific, and routine bacterial identification in processing of raw materials and ready-to-eat food products, in manufacturing process control, and in monitoring of cleaning and hygiene practices.
Technical Abstract: SERS spectra were collected to explore its potential for rapid and routine identification of E. coli and L. monocytogenes cultures. Ratios of SERS peaks from K3PO4 were used to evaluate the reproducibility, stability, and binding effectiveness of citrate-reduced silver colloids over batch and storage process. Notably, lifetime of silver colloidal nanoparticles was much longer than that of silver nanoparticle island films. Mixtures of different batches of bacterial cultures with colloids revealed that, despite large variations in relative intensities and positions of SERS bands, intense and unique bands at 712 and 390 cm-1 were consistently observed in E. coli and L. monocytogenes cultures, respectively. Two specific bands were then used to develop simple algorithms for identification, with a 100% success. As scanning one spectrum took 5~6 min and a minimum of 50 mL colloid/culture mixture was used, silver colloidal nanoparticle based SERS could be used in routine and rapid screening of bacteria in a large scale.