Luminous Edible Nanoparticles as Sensors of Food Quality and Safety

NON-TECHNICAL SUMMARY: Ensuring and maintaining the overall quality and safety of processed foods during manufacture, shipping, storage, and sale is a constant and everpresent problem in the food industry. This project will develop a novel class of chemical sensors that can be embedded into the foods (they are safe and edible), that can be easily "read" using existing optical scanning devices, and that provide signals to monitor specific physical and microbiological properties of the food.

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APPROACH: This project will develop a novel class of luminescent food sensors based on nanoparticles, colloidal particles with dimensions of ~20-200 nm, fabricated from the food grade hydrocolloids gelatin, chitosan, and starch. These nanoparticles will be doped with luminescent probes, that is molecules with defined fluorescence and phosphorescence properties, that are food compatible, that is, that are either food approved colors (erythrosin; FD& C #3) or molecules found in foods (quinine, flavonols). The resulting nanoparticles will thus potentially qualify as food-grade additives. These nanoparticles, in part due to their small size, will have several advantages for their use as food sensors. They will provide high signal/noise due to the many (>10,000) dyes/particle, be readily dispersable in foods without sedimenting in liquids, provide site specific information, be in close contact with the food matrix, rapidly equilibrate with food properties, be versatile yet selective, and provide a specific readily measured signal detectable with inexpensive, portable, and easily used instruments. These nanoparticle sensors may potentially function in areas of the food industry ranging from fundamental research, to product development, through shipping and storage to point of sale and, perhaps, even home use.
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PROGRESS: 2007/01 TO 2007/12 <BR>
OUTPUTS: This project has developed luminous edible nanoparticles made from gelatin, chitosan, and starch to measure temperature, oxygen, and pH. We have prepared gelatin nanoparticles containing erythrosin B (Ery B; FD&C red #3) that act as temperature and oxygen sensors. Pigskin gelatin (300 Bloom) was labeled with the isothiocyanate derivative of Ery B. Nanoparticles were prepared by adding excess acetone slowly to aqueous solution of labeled gelatin; nanoparticles were then crosslinked with glutaraldehyde and exess excess acetone was removed by evaporation. Both labeled and unlabeled nanoparticles had an effective diameter of ~135 nm as measured by dynamic light scattering. Erythrosin-labeled nanoparticles exhibited delayed luminescence spectra that varied characteristically with temperature over the range from 3 to 60C: the intensity of the phosphorescence band decreases and intensity of the delayed fluorescence band increases with increasing temperature. Analysis of these emission bands provides the peak intensity for phosphorescence (IP) and delayed fluorescence (IDF); this ratio varies characteristically and distinctively with temperature. The erythrosin probe is exquisitely sensitive to oxygen with the phosphorescence lifetime varying directly with the concentration of oxygen in the medium. Ery-labeled nanoparticles will thus also provide a sensitive indicator of oxygen concentration. We have prepared starch nanoparticles containing quinine that act as pH sensors. Starch nanoparticles were made using a microemulsion method, followed by crosslinking with phosphorous tricloride. The nanoemulsion was washed three times with acetone and then ethanol to obtain a precipitate of white solid starch nanoparticles; the solid was freeze-dried to obtain the dry powder. Nanoparticles have a mean diameter of 101 nm and an effective diameter of 235 nm as evaluated by dynamic light scattering; since the size distribution was multi-modal, a population of particles with diameters in excess of ~200 nm diameter was removed by filtration through a 0.2 micron filter. Starch nanoparticles were labeled with quinine by soaking dry starch nanoparticles in solution of quinine. Unbound quinine was then removed by extensive dialysis against distilled water until the dialysis solution exhibited no detectable quinine fluorescence. Quinine-labeled nanoparticles were freeze-dried and stored as dry powder in the dark. Although we have not yet measured the amount of quinine per dry weight of nanoparticles, solutions of nanoparticles at 1 mg/mL gave strong fluorescence signals. The emission spectra were analyzed for peak intensity or integrated and the ratios of the peak intensity or area with excitation at 295 and 345 nm were calculated as a function of solution pH (that is, I345/I295 or A345/A345). The values for quinine standard solutions and for quinine-labeled nanoparticles indicate that both intensity ratios and area ratios are essentially the same in standard solution and nanoparticles, indicating that labeled nanoparticles provide a sensitive indicator of pH over the range from pH 3-5. <BR> PARTICIPANTS: Richard D. Ludescher, Prinicipal Investigator; Melinda Ligneres, graduate assistant; Sanaz Jalalian, graduate assistant; Xiang Zhang, graduate assistant <BR> TARGET AUDIENCES: The target audience of this research is food technologists, food scientists, and the larger food industry. Upon successful generation of various classes of nanoparticles, that is, nanoparticles sensitive to specific food properties, this audience will be informed of sensor properties and utility by means of scientific publications, reports at meetings, and presentations to target audiences.
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IMPACT: 2007/01 TO 2007/12<BR>
We have successfully prepared nanoparticles that are sensitive to temperature, oxygen, and pH from food-grade ingredients (porcine pigskin gelatin, starch, FD&C red #3, quinine). Studies in vitro indicate that these nanoparticles provide sensitive indicators of these solution properties over useful ranges (temperature from 0-60C, pH 3-5). We have thus demonstrated proof of principle of this novel class of edible luminous nanoparticles and developed prototype sensors for three food properties. Future studies will establish the feasibility of using these novel sensors in real food systems.