Kaushik Siddharth, Tiwari Umesh, Prashar Shivendu, Das Bhargab, Sinha Ravindra K
Advanced Materials and Sensors (V 4), Central Scientific Instruments Organization, Chandigarh 160030, India.
Department of Statistics, Manipal Academy of Higher Education, Manipal 576104, India.
Rev Sci Instrum. 2019 Feb;90(2):025003. doi: 10.1063/1.5036693.
An optical fiber based immunosensing platform formed by two identical chirped long period gratings (CLPGs) for sensitive and label-free detection of Escherichia coli (E. coli) is presented. The proposed immunosensor having two CLPGs with an inter-grating space (IGS) works like a Mach-Zehnder interferometer. The important feature of this sensor is that by changing the refractive index (RI) induced phase at the IGS region, a corresponding shift in resonance wavelength can be realized without affecting the actual grating region. Additionally, the confining bandwidth of the interference fringes promotes greater resolution in the resonance wavelength analysis of the transmission spectrum. The main aim of this study was the specific and rapid detection of the E. coli bacteria in phosphate buffer saline (detection range: 10 cfu/ml to 60 cfu/ml) by using the bio-functionalized IGS region as a sensing probe of the dual CLPG structure. The observed detection limit was 7 cfu/ml. For specificity analysis, Salmonella typhimurium and Staphylococcus aureus were tested and no significant shift in resonance wavelength was observed. In addition, the proposed immunosensor has the ability to selectively detect E. coli in real samples including lake water. The high specificity, good sensitivity to ambient RI, and robustness of the developed sensing platform will open a new avenue in optical immunosensing technology, and cascaded long CLPG sensors can contribute significantly to the detection of pathogenic bacteria in water and food samples.
本文提出了一种基于光纤的免疫传感平台，该平台由两个相同的啁啾长周期光栅（CLPG）组成，用于灵敏且无标记地检测大肠杆菌（E. coli）。所提出的具有两个CLPG且光栅间距（IGS）的免疫传感器的工作原理类似于马赫-曾德尔干涉仪。该传感器的重要特性在于，通过改变IGS区域的折射率（RI）诱导相位，可实现共振波长的相应偏移，而不会影响实际的光栅区域。此外，干涉条纹的限制带宽在透射光谱的共振波长分析中提高了分辨率。本研究的主要目的是利用生物功能化的IGS区域作为双CLPG结构的传感探针，特异性且快速地检测磷酸盐缓冲盐水中的大肠杆菌（检测范围：10 cfu/ml至60 cfu/ml）。观察到的检测限为7 cfu/ml。为了进行特异性分析，对鼠伤寒沙门氏菌和金黄色葡萄球菌进行了测试，未观察到共振波长有明显偏移。此外，所提出的免疫传感器能够选择性地检测包括湖水在内的实际样品中的大肠杆菌。所开发传感平台的高特异性、对环境RI的良好敏感性以及稳健性将为光学免疫传感技术开辟一条新途径，并且级联长CLPG传感器可为水和食品样品中病原菌的检测做出重大贡献。
