Manufacture and utilization of a biodegradable sensor platform from gold coated zein nanophotonic films to detect acrylamide and Ara-h1 using SERS
With the current developments in biosensor and nanotechnology, detection of analyses that are important to food industry are becoming more commonplace. One of the strong tools that nanotechnology enabled is Surface Enhanced Raman Spectroscopy (SERS). SERS is a highly sensitive and specific technique which provides molecular fingerprinting, with the enhancement effect as a result of roughened noble metal surfaces. The platform for these surfaces are generally made out of non-biodegradable, plastic materials. As the one-time use, large scale applications are needed for many fields such as medical, forensic and food industry, disposability of these sensors will pose a problem in the future. In the scope of this dissertation, we investigated the feasibility of a biodegradable sensor platform that is made of zein, a corn protein, utilized in SERS measurements of food analytes. First, the effect of parent substrate (the surface, which zein was cast on) and plasticizer, oleic acid content, on the surface hydrophilicity of resulting zein films was analyzed. It was found that the surface chemistry of the parent substrate was more important than the topography of the parent substrate. Oxygen plasma was used to make the polydimethylsilohexane (PDMS) surfaces more hydrophilic and it was found that zein film surfaces that were in contact with PDMS also had more hydrophilic surfaces, compared to regular PDMS, which is a hydrophobic material. Water contact angle (WCA) method was used to quantify the hydrophilicity of zein films. WCA reached values as low as 20 degrees with a high oleic acid content. Increase in oleic acid content in the formulation of zein films as well as the parent substrate chemistry was found to influence the water affnity of zein films. In the development of the fabrication method of nanopatterned and gold coated zein surfaces, a simultaneous three-dimensional transfer was used. Four different nanopatterns, namely positive pyramids, inverted pyramids, nano pillars and nano pores were transferred onto zein films along with either 80 or 200 nm gold coating by using solvent casting technique. Scanning microscopy images showed that the patterns were transferred onto zein films with high fidelity and success. The enhancement effect of these SERS substrates were tested by using a model molecule, Rhodamine 6G. It was found that the best enhancement effect was provided by inverse-pyramid structures coated with 200 nm gold. For the rest of the study, these structures were used. Zein-SERS substrates were utilized in two different food analyte detection purpose, acrylamide and peanut allergen protein Ara h1. Acrylamide is a potential carcinogenic compound that is formed during high temperature food processing. French fries, potato chips, bread and coffee are some of the food products that may contain high amounts of acrylamide. Since Food and Drug Administration released a draft advisory for mitigation strategies for acrylamide content in foods, there is a need for routine testing technique of acrylamide in food products. In this research, acrylamide was detected by using zein-SERS substrates as a proof of concept. Limit of detection was found to be 10 micrograms/milliliter. Calibration curve was obtained with an R2 value of 0.93 and 0.97 for log-log version. Peanut allergies are among the most common food allergies, and they can result in life-threatening reactions in allergic patients. For this reason, it is extremely important to monitor the presence or cross-contamination of peanuts into food products. There are 8 identified peanut allergen proteins and Ara h1, consists of the largest percentage of protein content, in addition to causing reactions in almost 100 % of the patients. Zein-SERS substrates were utilized in detection of Ara h1. With the use of statistical clustering technique called principal component analysis (PCA), it was possible detect and quantify Ara h1 protein. Limit of detection was found to be 0.14 mg/ml. The surface of the zein-SERS substrates were functionalized with monoclonal antibody and tested for capturing Ara h1 as a proof-of-concept. With this research, utilizing zein as a biodegradable sensor platform for SERS measurements were investigated for the first time. It was shown that detection of both acrylamide and Ara h1, peanut protein, was possible. The methods developed in this study for controlling the surface hydrophilicity of zein films and direct transfer of both micro and nano-scale patterns onto zein along with noble metals can be employed in other biosensor and biopolymer applications as well in the future. This kind of biodegradable platforms might be an alternative solution for environmentally friendly and large scale sensor applications.
Zein, biosensor, Surface Enhanced Raman Spectroscopy (SERS), Raman, acrylamide, peanut allergen, detection, surface
University of Illinois - Urbana-Champaign
Networked Digital Library of Theses and Dissertations
University of Illinois at Urbana-Champaign