Study of novel nanoparticle sensors for food pH and water activity:

by Xiang Zhang

Institution: Rutgers University
Department: Food Science
Degree: MS
Year: 2009
Keywords: Nanoparticles; Nanostructured materials; Detectors
Record ID: 1859114
Full text PDF: http://hdl.rutgers.edu/1782.2/rucore10001600001.ETD.000051932


Food sensors, sensitive to food properties, including temperature, oxygen, moisture content and pH, are used in food processing and other food related fields. Recently, applying sensor technology in the food industry has been further emphasized. Nanoparticles, with diameters of tens to hundreds of nanometers, also have generated considerable interest as sensors because of their small size and related novel characters. In this study, we developed fluorescent sensors for food pH based on nanoparticles and investigated water activity probes. The nanoparticles, fabricated from food grade starch and gelatin with dimensions of ~20-50 nm, were doped with three pH-sensitive probes. Quinine and harmane were non-covalently attached onto starch nanoparticles, while gelatin nanoparticles were covalently labeled with fluorescein isothiocyanate (FITC). The study of labeled nanoparticle sensors in buffer solutions of varying pH’s showed the correlation between pH and emission spectra. Quinine labeled starch nanoparticle (QSNP) sensors exhibited blue shifts of emission spectra as pH increased; the ratio of peak intensity or peak area of emission spectra at two different emission wavelengths also decreased dramatically in the range of pH~3.0-5.0. Harmane labeled starch nanoparticle (HSNP) sensors and FITC labeled gelatin nanoparticle (FGNP) sensors did not present any emission spectra shifts. However, the former’s ratio of peak intensity or peak area increased as pH increased in the range of pH~7.0-9.0; the latter’s decreased as pH increased in the range of pH~2.5-7.5. Moreover, FGNP sensors were applied in different real food products. Comparing actual food pH with calculated sensor pH based on a calibration curve suggested that using FGNP sensors to detect food pH is accurate (~1-5% error). Duplicated fluorescent tests of FGNP sensors also showed good reproducibility. These results support a new methodology of using nanoscopic sensors for the measurement of food pH. Study of water activity was focused on charactering the probes Prodan and Laurdan. Prodan was investigated in different saturated salt solutions and water-glycerol solution systems; Laurdan was investigated only in saturated salt solutions. However, these studies did not show any expected correlation between water activity and emission spectra shifts. Therefore, Prodan and Laurdan may not be good indicators of water activity.