Tapered Microfiber MZI Biosensor for Highly Sensitive Detection of <i>Staphylococcus</i> Aureus
Hou-Chang Li, Yuankui Leng, Yun-Cheng Liao, Bin Liu, Wei Luo, Juan Liu, Jiulin Shi, Jinhui Yuan, Hengyi Xu, Yonghua Xiong, Xingdao He, Qiang Wu
Abstract
A new double-taper microfiber Mach-Zehnder interferometer (MZI) biosensor is applied for <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Staphylococcus aureus</i> ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S. aureus</i> ) detection. The microfiber MZI structure is fabricated by creating two tapers along a traditional single mode fiber (SMF) firstly and tapering the SMF sandwiched between two tapers into very small diameter (in the order of micrometers). The measured refractive index (RI) sensitivity of the microfiber MZI is up to 2731.1 nm/RIU in the RI range of 1.34 when the taper waist diameter was <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10.2 ~\mu \text{m}$ </tex-math></inline-formula> , which is in good agreement with numerical simulation results by using the beam propagation method (BPM). The microfiber MZI functionalized with pig immunoglobulin (pig IgG) could be used to specifically binding to <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S. aureus</i> . In experiment, the maximum wavelength shift of 1.408 nm was achieved when the microfiber biosensors were immersed into <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S. aureus</i> with concentration of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$7\times 10^{1}$ </tex-math></inline-formula> CFU/mL. The limit of detection (LoD) of the microfiber biosensor for <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S. aureus</i> is calculated as low as 11 CFU/mL. The proposed microfiber MZI biosensor has advantages of simple structure configuration, high sensitivity, good repeatability and specificity, wide detection range and fast detection response time (< 30 minutes) and thus was demonstrated a good application prospect in food safety inspection, biochemical sensing, diseases and medical diagnostics.