Photonic crystal fibers for food quality analysis

1. A.V. Malinin1,2, A.A. Zanishevskaya1, Yu. S. Skibina1,2, V.V. Tuchin1,3, I. Yu. Silokhin2, 1Saratov State University, 83, Astrakhanskaja str., Saratov, 410012 Russia; 2SPE Nanostructured Glass Technology, 101, 50 let Oktjabrja ave., Saratov, 410033 Russia; 3Institute of Precise Mechanics and Control RAS, 24 Rabochaya str., Saratov, 410028 Russia; Hollow core photonic crystal fibers provide high sensitivity to the optical parameters of a medium, filling up a hollow core of the fiber, e.g. refractive index and absorption coefficient. By making only one measurement one can obtain both, optical density value (in determined spectral range) and refractive index of a tested liquid. In a purpose of providing precise analysis of multicomponent liquid solutions, photonic crystal fiber may become a tool of a big efficiency. One of the possible applications of PCF-based optical sensors is considered in this work. The use of photonic crystal fibers allows one to make a complex analysis of different drinks like juices, vines, etc. In our investigation we considered the influence of sugar and iron, which are the most important components of an apple juice, to spectral properties of hollow core PCFs. Thus, we considered an ability of application of hollow core photonic crystal fibers in food quality analysis. Photonic crystal fibers for food quality analysis Spectrum of optical radiation from light source transforms after propagation through the PCF sample. Spectral characteristics of output signal depend on both, internal geometry of the fiber and optical properties of a medium, filling up the hollow core. Transmission properties of PCF are extremely sensitive to fluctuations of absorption coefficient or refractive index of a liquid, injected into fiber’s structure. The scheme of the experimental setup. Iron and sugar are the important components of the apple juice and both determine its optical properties. Appearance of the iron in the apple juice is the reason of its light-brown color. Concentration of this valuable component may be determined simultaneously with sugar concentration using samples of hollow core photonic crystal fibers for analysis. Transmission spectrum of iron hydrate, dissolved in water, is depicted on fig. 1. After injection of the solution into hollow core of PCF sample, the influence of strong light absorption to spectral characteristics of the PCF manifested itself as attenuation of intensity peak (465 nm) in transmission spectrum of the fiber (see fig. 2). In accordance with Bouguer-Lambert-Beer law, this peak attenuates exponentially. Using curve from graph 3 as a calibration curve one can obtain iron concentration value. In the same time, using only one measurement, a concentration of sugar can be determined. The concentration of sugar mostly determines a refractive index of the apple juice. Hollow core PCF’s spectral properties are very sensitive to refractive index change. Graph 4 delivers transformations of PCF’s transmission spectrum after filling up its core with water solutions of glucose. One can see, that with the increasing of glucose concentration and refractive index of the solution respectively, transmission bands of PCF sample shift to shorter wavelength region. There is an accurate experimentally obtained dependence of definite transmission band location on refractive index (fig. 5) and glucose concentration (fig. 6) in solution. On the graph 5 and 6 experimentally determine values for real apple juice (fig. 7) are indicated with red color. Using model liquids, which cause similar influence on photonic crystal fiber’s spectral characteristics as the apple juice does, we experimentally obtained the evidence of an ability of using PCFs in food quality analysis. Small sample volume (~10 µL), instantaneous response and ability for simultaneous determination of a few optical parameters of an analyzed liquid make hollow core photonic crystal fibers universal and powerful instrument. The techniques and PCF configurations for quality analysis of juices, oils, vines and other products of food industry may be designed and realized in order to improve and simplify evaluation of food quality.