Fiber-optic sensor for bacteria detection based on intensity-modulated SPR by monochromatic excitation

A. da Silva Arcas, F. da Silva Dutra, R.C.S. Barros Allil, M.M. Werneck
Federal University of Rio de Janeiro,

Keywords: fiber-optic sensor, POF sensor, bacteria sensor, SPR fiber-optic sensor


The Escherichia coli (E. coli) O157:H7 is a human pathogen of animal origin that can cause serious illness if ingested. The most common routes of E. coli contamination are drinking water, vegetables, undercooked meat, unpasteurized milk and by bathing in polluted rivers and seas. Its importance as a public health was observed in the United States outbreak occurred in 1982 on which 171 people have been infected. Besides the public health problem, an E. coli outbreak may result in financial losses to the industry and agriculture, as occurred in Germany in 2011, which caused $ 1.3 million in losses to farmers and industries. Therefore, the food quality is an issue of global importance that must be ensured by constant monitoring. In order to predict and prevent further outbreaks, fast and reliable detection methods are crucial. Yet conventional detection methods such as the culture-based are far from being rapid and reliable. An alternative method to culturing is the polymerase chain reaction (PCR). The analysis time of a PCR-based biosensor is much shorter (∼3 h). However, PCR cannot differentiate between live and dead cells. In addition, a certain time for samples preparation are required prior to analysis. Biological detection through RI measurements can be performed in several ways by the use of optical fiber sensors. Surface Plasmon Resonance (SPR) is one of these methods and is used widely as a detection principle in different fields. SPR is very attractive because it can attain resolutions as high as 10-7 RIU. This study focuses on the developing a biosensor based on intensity-modulated SPR excited by monochromatic light. The sensor is made of a U-shaped plastic optical fiber (POF) for having greater sensitivity than the straight ones. The sensor is coated with a gold thin film immobilized with E. coli antibodies for specific bacteria detection. To the best of our knowledge, this is the first biosensor for E. coli detection that uses this technique. Preferred use of gold instead of silver or copper is due to its high chemical stability. This scheme reduces the cost because it requires no optical spectrum analyzer (OSA) to measure the output spectrum of the transmitted light which goes through the U-shaped probe. With a simple and easy-to-fabricate detection system, this scheme has a larger possibility of ending up in a commercial and large-scale production. The U-shaped POF probes were coated with gold thin film by a RF magnetron sputtering with a 3.5 nm/min deposition rate. Probes coated with 50, 70 and 100 nanometer thickness of gold were produced. Then E. coli antibodies were directly immobilizated on the surface of gold deposited over the fiber. Tests with bacteria solutions were carried out and the sensors were able to detect E. coli concentration of 104 CFU/mL.