A simple surface-enhanced Raman spectroscopic method for on-site screening of tetracycline residue in whole milk

Authors: DHAKAL, SAGAR - Forest Service (FS); Chao, Kuanglin - Kevin Chao; HUANG, QIN - Chinese Academy Of Sciences; Kim, Moon; Schmidt, Walter; Qin, Jianwei - Tony Qin; Broadhurst, C

Submitted to: Sensors
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/29/2018
Publication Date: 2/1/2018
Citation: Dhakal, S., Chao, K., Huang, Q., Kim, M.S., Schmidt, W.F., Qin, J., Broadhurst, C.L. 2018. A simple surface-enhanced Raman spectroscopic method for on-site screening of tetracycline residue in whole milk. Sensors. 18(2):424.

Interpretive Summary: The residual presence of veterinary drugs in animal food products is a major concern due to risks in the areas of public health and food safety, animal health, antimicrobial resistance, and environmental contamination. This study demonstrates a simple, on-site sensing method to detect tetracycline residue in cow milk. A customized portable 785 nm Raman spectroscopic system was used to detect tetracycline in milk. The spectral peak of tetracycline at 1317 wavenumber in water-tetracycline solution and 1322 wavenumber in milk-tetracycline solution was used to detect tetracycline residue. The method could detect tetracycline residue in milk and water at concentrations as low as 0.01 ppm; this is on the same level as industry regulatory standards. The peak intensities of 1317 and 1322 wavenumbers were linearly correlated to the concentrations with correlation coefficients of 0.92 for water and 0.88 for milk. The results of this study will serve as a foundation for further research to adapt the method for screening other possible veterinary drugs in animal products.

Technical Abstract: Therapeutic and sub-therapeutic use of veterinary drugs has increased the risk of residue contamination in animal food products. Antibiotics such as tetracycline are used for mastitis treatment of lactating cows. Milk expressed from treated cows before the withdrawal period has elapsed may contain tetracycline residue. This study developed a simple surface-enhanced Raman spectroscopic (SERS) method for on-site screening of tetracycline residue in milk and water. Six batches of silver colloid nanoparticles were prepared for surface enhancement measurement. Milk-tetracycline and water-tetracycline solutions were prepared at seven concentration levels (1000, 500, 100, 10, 1, 0.1, and 0.01 ppm) and spiked with silver colloid nanoparticles. A 785 nm Raman spectroscopic system was used for spectral measurement. Tetracycline vibrational modes were observed at 1285, 1317 and 1632 cm-1 in water-tetracycline solutions and 1322 and 1621 cm-1 (shifted from 1317 and 1632 cm-1, respectively) in milk-tetracycline solutions. The peak intensities at 1285 and 1322 cm-1 were used to estimate the tetracycline concentrations in water and milk with correlation coefficients of 0.92 for water and 0.88 for milk. Results indicate that this SERS method is a potential tool that can be used on-site at field production for qualitative and quantitative detection of tetracycline residues.