Paper as a Colorimetric Biosensing Platform for Tetracyclines Detection in Milk

Tetracyclines are a type of antibiotic that exhibits activity against most gram-positive and gram-negative bacteria. These antibiotics are often added at subtherapeutic levels to feed to act as growth promoters. Due to its low bioavailability, only a fraction of the antibiotic is metabolized in animals, causing waste. These residues can enter human bodies through the food chain and lead to increased antimicrobial resistance, causing allergic or toxic reactions, which led several countries to implement a maximum level of residues for this type of antibiotic. Most methods of detecting TCs are time consuming or inadequate for field analysis. In this way, an inexpensive, easy-to-execute and fast analytical method is required. In this sense, in the present work a colorimetric biosensor was developed in paper for the detection of four type of tetracyclines, presenting an alternative in the performance of point-of-care tests. Paper is low-cost, abundant, biodegradable and easy to dispose of by incineration. The construction of the sensors was performed using Lab-on-Paper technology and is based on the synthesis of gold nanoparticles by reducing a gold salt in which tetracyclines constitute the reducing agent itself. Different concentrations of TCs result in the formation of different colour intensities. Different concentrations of tetracyclines were tested and analysed using ImageJ software, allowing linear calibration lines to be obtained, that relate the concentration of antibiotics in a range between 0.1 and 10 μg/mL and the arithmetic mean of the RGB channels. Validation tests of the sensors developed with TC in milk were also performed. It was observed that it is possible to detect this type of antibiotic in pre-treated milk, and four forms of milk treatment were studied

Paper-Based SERS Platform for One-Step Screening of Tetracycline in Milk

PTDC/CTM-NAN/2912/2014. PTDC/AAG-TEC/5400/2014. POCI-01-0145-FEDER-016637. POCI-01-0145-FEDER-007688. UID/CTM/50025/2019. FCT/MCTES SFRH/BD/115173/2016 and SFRH/BPD/124311/2016 .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.publishersversionpublishe