Abstract
Throughout the last decade, the expansion of food testing has been gradually moving towards ordinary high throughput screening methods performed on-site. The demand for point-of-care testing, able to distinguish molecular signatures with high accuracy, sensitivity and specificity has been significantly increasing. This new requirement relies on the on-site detection and monitorization of molecular signatures suitable for the surveillance of food production and processing. The widespread use of antibiotics has contributed to disease control of livestock but has also created problems for the dairy industry and consumers. Its therapeutic and subtherapeutic use has increased the risk of contamination in milk in enough concentrations to cause economic losses to the dairy industry and have a health impact in highly sensitive individuals. This study focuses on the development of a simple Surface-Enhanced Raman Spectroscopy (SERS) method for fast high throughput screening of tetracycline (TET) in milk. For this, we integrate a paper-based low-cost, fully recyclable and highly stable SERS platform, with a minimal sample preparation protocol. A two-microliter sample of milk solutions spiked with TET (from 0.01 to 1000 ppm) is dried on a silver nanoparticle coated cardboard substrate and measured via a Raman spectrophotometer. The SERS substrate showed to be extremely stable with a shelf life of several months. A global spectrum principal component analysis approach was used to test all the detected vibrational modes and their correlation with TET concentration. Peak intensity ratios (455 cm−1/1280 cm−1 and 874 cm−1/1397 cm−1) were found to be correlated with TET concentrations in milk, achieving a sensitivity as low as 0.1 ppm. Results indicate that this SERS method combined with portable Raman spectrometer is a potential tool that can be used on-site for the monitoring of TET residues and other antibiotics.
Highlights
Nowadays, antibiotics are extensively used for the control of diseases and for nutritional purposes of livestock
The most common methods to fabricate these substrates have critical obstacles such as time-consuming complex patterning processes associated with high costs, which limits its extensive use in macroscopic scale systems[15,20,26]
We show the proof-of-concept of using this nanoplasmonic platform for the analysis of antibiotic residues in milk, demonstrating that this one-step thermal evaporation production method combined with an statistical analysis is able to exhibit a very strong SERS signal, with notable stability and shelf-life
Summary
Antibiotics are extensively used for the control of diseases and for nutritional purposes of livestock. The most common methods employed for antibiotics residues monitoring include microbial inhibition tests[7,8], immunoassays[9,10], and chemical-physical methods such as high-performance liquid chromatography[11,12] or mass spectroscopy[13,14] These methods have high operational costs, complex sample. Cellulose based substrates have been developed for several opto-electronic applications due to its unique set of advantages (e.g. 100% recyclable, flexible and low-cost)[21,24,25,26] These exciting applications of paper-based materials for bio-detection, are today presenting several advantages over conventional substrates, due to their inexpensive and easy-to-process nature, achieving high Raman signal enhancements (EF ≈ 105–107) comparable with the commercial counterparts[16,27]. This work reports on highly efficient SERS platforms based on the AgNPs combined with an inexpensive, recyclable and widely used cardboard substrate, commonly used as disposable packaging material, previously fully described in a previous work from our group[21]
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