Label-free and Aptamer-based Surface Enhanced Raman Spectroscopy for Detection of Food Contaminants

The development of analytical methods to detect food contaminants is a critical step for improving food safety. Surface enhanced Raman spectroscopy (SERS) is an emerging detection technology that has the potential to rapidly, accurately and sensitively detect a wide variety of food contaminants. However, SERS detection becomes a challenge in real complex matrix, such as food, since non-specific matrix signals have the potential to drown out target associated Raman peaks. In this dissertation, we focused on the development and application of label-free, aptamer-based SERS in order to improve the accuracy and specificity of target contaminant detection in food. To accomplish this, different types of aptamer-modified SERS substrates (i.e. thiolated or non-thiolated ssDNA aptamers conjugated onto silver dendrites, gold-coated magnetic nanoparticles, gold nanoparticles and gold nanoparticles coated magnetic nanoparticles) were tested in liquid foods (e.g. apple juice and milk) to detect a variety of food contaminants including pesticides, antibiotics and foodborne pathogens. Next, an integration of aptamer-based SERS and aptamer-assisted colorimetric detection was attempted using gold nanoparticles as the substrate to create a rapid detection-validation protocol. Finally, we attempted to create a simple SELEX method that could be used to design aptamers for food safety applications. Our results demonstrate that aptamer-based SERS is capable of detecting a variety of aptamer-specific food contaminants while drastically reducing Raman signal interference from food matrix. Thus, this method shows great potential as a rapid detection method in food, especially since sample extraction procedure can be simplified. Aptamer-based SERS method can also be used to validate results from the gold nanoparticles based colorimetric assays. It can help us understand the intermolecular interactions that govern the mechanism and successful interpretation of the colorimetric results, which can then reduce false positive and false negative results. Lastly, several breakthroughs were achieved using the developed “gold nanoparticle-assisted SELEX” procedure. This is promising to design a wider variety of target specific aptamers without the need for large, specialized equipment. By advancing the completion of this SELEX method, there is great potential for creating more label-free, aptamer-based SERS methods for food contamination detection and to improve food safety as a whole