In this multidisciplinary project, we aim to develop new techniques and design experiments for the following objectives: <br/>(1) develop new technologies for characterizing fundamental nanoscale processes; (2) construct and characterize self-assembled nanostructures; (3) develop devices and systems incorporating microfabrication and nanotechnology; and (4) develop a framework for economic, environmental and health risk assessment for nanotechnologies applied to food, agriculture and biological systems. Specially, we used new technologies including chemical vapor deposition (CVD) and other microfabrication techniques to develop nanostructures and nanosubstrates for a new biosensor (surface enhanced Raman spectroscopy (SERS)) for detection and characterization of biological and chemical contaminants in food products.
This multidisciplinary project involves using nanotechnology and biosensors to address food safety problems with the aid of some of the latest developments in nanotechnology. New technologies were developed for characterizing nanoscale processes and to fabricate self-assembled nanostructures. SERS method coupled with nanostructures offers an alternative for increasing sample throughput at reduced per sample cost. SERS is a rapid, simple, ultrasensitive, and powerful analytical technique which provides qualitative and quantitative information on trace amounts of food contaminants. Having cost-efficient technologies to quickly and accurately screen foods would be a valuable tool for the US food safety inspectors and the food industry to improve inspection by providing increased capacity for screening a larger number of foods. The results of this project will serve the consumer demand for safe and wholesome foods and increase public confidence in our food supply. In addition, a framework was established for assessing environmental and health risks for nanotechnologies applied to food, agriculture and biological systems.
(1) We used several new technologies including CVD, solution-based crystal growth, and spin coating methods to fabricate SERS-active nanosubstrates. The purpose was to develop a variety of nanosubstrates, test their performance, screen and identify best substrates that show reliable and consistent performance and are suitable for large scale fabrication. CVD is a microfabrication technique used to deposit thin films on wafers. A typical CVD is conducted under vacuum and elevated temperatures (on a heating stage). Thin films (such as Si, SiO2, SiC, etc) and various nanomaterials could uniformly grow on the wafer substrate. Solution-based crystal growth method was also used to prepare uniform ZnO nanostructures.
<br/>(2) We synthesized Au and Ag based nanoparticles, aggregates, and dendrites, and optimize the protocol to improve structural uniformity. Metallic nanoparticles were prepared by a generic chemical reduction method in solution. Different sizes and shapes of nanoparticles were obtained by controlling the reaction temperature, the concentration of precursor solution, the type of reducing agent, and the presence of surfactants as a shaping template. The resulting metallic aggregate were physically stable and optically active.
<br/>(3) Microfabrication and nanotechnology were used in this study to develop devices and systems. Spin coating was used to apply uniform thin films to flat substrates. An excess amount of a solution was placed on a substrate, which was then rotated at a high speed in order to spread the fluid by centrifugal force. When nanomaterials are mixed with the solution, a uniform coating with nanostructures was deposited on wafers. Both CVD and spin coating are microfabrication techniques suitable for making nanostructures in large scale, and these two methods were used in our proposed work.
<br/>(4) We developed a framework and strategies to better assess economic, environmental and health risks for applying nanotechnologies and nanomaterials to food, agriculture and biological systems. We studied the effects of engineered nanoparticles (silver, ZnO) on gut natural microflora, and studied their toxicity using cell cultures such as Caco-2 cell line.
2012/01 TO 2012/12<br/>
OUTPUTS: Outputs during the reporting period include: the study about using a nanotechnology-based sensing and detection technique, surface-enhanced Raman spectroscopy (SERS), to detect and characterize pesticides extracted from fruit surfaces. In this study, gold-coated SERS-active nanosubstrates were used for SERS measurement. Three types of pesticides (carbaryl, phosmet, and azinphos-methyl) widely used in apples and tomatoes were selected. Significantly enhanced Raman signals of pesticides were acquired by SERS from the extract of fruit samples and exhibited characteristic patterns of the analytes. Multivariate statistical methods such as partial least squares (PLS) and principal component analysis (PCA) were used to develop quantitative and qualitative models for detection. SERS was able to detect all three types of pesticides extracted from fruit samples at the ppm level. The study of detection limit demonstrate that at 99.86% confidence interval, SERS can detect carbaryl at 4.51 ppm, phosmet at 6.51 ppm, and azinphos-methyl at 6.66 ppm spiked on apples; and carbaryl at 5.35 ppm, phosmet at 2.91 ppm, and azinphos-methyl at 2.94 ppm on tomatoes. Most of these detection limits meet the maximum residue limits established by FAO/WHO. Satisfactory recoveries (78 to 124%) were achieved for samples with concentrations at and larger than the detection limit.
<br/>PARTICIPANTS: This project has provided training for several doctoral students and Master's students.
<br/>TARGET AUDIENCES: The results of this project were presented at the IFT meeting. Audiences were from academia, the food industry, and government. <br/>PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
IMPACT: Outcomes and impacts of the study include the scientific data and findings that can help address a growing concern in recent years for consumers about contamination of pesticides in fruits due to increasing use of pesticides in agriculture. Today's food safety situation calls for development of rapid, sensitive, and reliable methods that are suitable for on-site detection of food contaminants. Compared with other methods such as chromatogrphy-based techniques, SERS has the following advantages to meet such requirements: simplicity of sample preparation, acceptable accuracy and reliability, and wide applications. In addition, more effective yet simple extraction techniques and better performing substrates will greatly improve the capability of SERS methods. These results demonstrate that SERS coupled with novel SERS-active nanosubstrates is a rapid, sensitive, and reliable method for detection and characterization of chemical contaminants in foods.