Abstract
We propose and experimentally verify an innovative label-free optical fiber biosensor based on a Mach-Zehnder interferometer for bovine serum albumin (BSA) concentration detection. The proposed fiber biosensor utilized a micro-cavity within a single-mode fiber to induce Mach-Zehnder interference. A remarkable feature of this biosensor is that external media can directly interact with the fiber core signal through microfluidic channels connected to the micro-cavity and sensor surface. The device was fabricated by means of femtosecond laser micromachining and chemical etching. A fiber interferometer of this type exhibits an ultrahigh refractive index sensitivity of -10,055 nm/RIU and a detection limit of 3.5 × 10-5 RIU. Different concentrations of BSA with an infinitesimally small refractive index difference can be clearly differentiated in situ by the interferential spectra of the structure. Experiments demonstrated the biosensor exhibited a BSA solution concentration sensitivity of -38.9 nm/(mg/mL) and a detection limit of 2.57 × 10-4 mg/mL, respectively. Moreover, this biosensor is a sub-microliter dose and ultrasensitive at the low concentrations detected in BSA, which make it a promising for biochemical applications such as DNA hybridization, cancer screenings, medicine examination and environmental engineering, etc.
Highlights
Over the past decade, the in situ detection of proteins has been extensively investigated as the analysis of proteins is of significant importance to disease and drug research, as well as biological engineering
tilted fiber Bragg gratings (TFBGs) operates in an evanescent cladding mode which is sensitive to the surrounding refractive index (RI)
The Mach-Zehnder interferometers (MZIs)-based biosensor was immersed in a series of RI liquids (Cargille Labs, http://www.cargille.com) in an RI ranging from 1.300 to 1.330 in intervals of 0.005 at room temperature
Summary
The in situ detection of proteins has been extensively investigated as the analysis of proteins is of significant importance to disease and drug research, as well as biological engineering. As a widely-used photonic device, tilted fiber Bragg gratings (TFBGs) have several advantages, including highsensitivity wavelength response, narrow line width, reflective measurement. These properties make it an excellent biosensor. An etched FBG coated with an anti-C-reactive protein antibody graphene-oxide complex was used to detect C-reactive proteins with a DL of 0.01mg/L [3]. Another approach uses surface plasmon resonance (SPR) technology to observe and characterize protein behavior. Like SPR sensors, tapered fiber-based devices respond to variations in the evanescent field, arising from alterations in the outside RI. For SPR sensors, film coating increases the difficulty of device fabrication and the coated film drops out during the measurement
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