Weston Max, Kuchel Rhiannon P, Chandrawati Rona
School of Chemical Engineering and Australian Centre for Nanomedicine (ACN), The University of New South Wales (UNSW Sydney), Sydney, NSW, 2052, Australia.
Electron Microscope Unit, Mark Wainwright Analytical Centre, The University of New South Wales (UNSW Sydney), Sydney, NSW, 2052, Australia.
Anal Chim Acta. 2021 Mar 1;1148:238190. doi: 10.1016/j.aca.2020.12.065. Epub 2021 Jan 5.
The incorporation of colorimetric sensors as quality indicators in food packaging is an exciting new area of research that could improve food management. The standard approach, however, demands a reliable interface between the sensor and the food and risks food contamination which is a significant consumer concern. To overcome this challenge, herein, we develop a polydiacetylene/phospholipid agarose-based sensor that encapsulates milk in the hydrogel matrix during synthesis. The chemical recognition of free fatty acids, a product of microbial spoilage of the encapsulated milk, induces a gradual blue to red color change in the sensor. We demonstrate that the new composite material exhibits the same spoilage kinetics as regular liquid milk (digital colorimetric response 28 ± 1% and 27 ± 3% respectively), indicating the agarose does not preserve the milk ingredients nor inhibit the detection mechanism of the polydiacetylene sensors. As a result, this sensor can be attached to the external surface of food packaging to provide an indirect indication of food quality without the need for contact with the milk product. The quality tags we present can be "switched" on and off using dehydration and rehydration, removing the need for in situ manufacturing and allowing storage before use. We show that the quality tags produce a similar digital colorimetric response of 21 ± 2% to indicate milk spoilage after rehydration. The color change of the quality tags could not be analyzed using absorption spectroscopy, the standard technique for polydiacetylenes, due to the opacity that milk imparts on the sample. To solve this problem, we develop digital colorimetric analysis software using the Python programming language to describe the extent of color change in polydiacetylene materials and develop a new metric termed the Digital Colorimetric Response that describes polydiacetylene response with excellent linearity (R = 0.96). The software is programmed to employ statistical cleaning techniques that automatically remove image noise and outliers based on a pixel's grayscale Z-score. This new approach to sensor design increases practicality and could be extended to the contactless quality monitoring of other foods, medicines and other products whose safety or quality is jeopardized with direct sensor contact.
将比色传感器作为食品包装中的质量指标是一个令人兴奋的新研究领域，有望改善食品管理。然而，标准方法要求传感器与食品之间有可靠的界面，且存在食品污染风险，这是消费者非常关注的问题。为了克服这一挑战，我们在此开发了一种基于聚二乙炔/磷脂琼脂糖的传感器，该传感器在合成过程中将牛奶封装在水凝胶基质中。对封装牛奶微生物腐败产物游离脂肪酸的化学识别会使传感器逐渐发生从蓝色到红色的颜色变化。我们证明，这种新型复合材料与常规液态奶具有相同的腐败动力学（比色响应分别为28±1% 和27±3%），这表明琼脂糖既不会保存牛奶成分，也不会抑制聚二乙炔传感器的检测机制。因此，这种传感器可以附着在食品包装的外表面，无需与奶制品接触就能间接指示食品质量。我们展示的这种质量标签可以通过脱水和再水化来“开启”和“关闭”，无需现场制造，且可在使用前储存。我们发现，再水化后，质量标签会产生类似的21±2% 的比色响应来指示牛奶变质。由于牛奶会使样品产生不透明度，因此无法使用聚二乙炔的标准技术吸收光谱法来分析质量标签的颜色变化。为了解决这个问题，我们使用Python编程语言开发了数字比色分析软件，以描述聚二乙炔材料中的颜色变化程度，并开发了一种新的指标——数字比色响应，该指标能以优异的线性度（R = 0.96）描述聚二乙炔的响应。该软件经过编程，采用统计清理技术，根据像素的灰度Z分数自动去除图像噪声和异常值。这种新型传感器设计方法提高了实用性，并且可以扩展到对其他食品、药品以及其他直接接触传感器会危及安全或质量的产品进行非接触式质量监测。
