Ultrasensitive on-chip biosensing of MUC1 enabled by LSPR-enhanced two-channel optofluidic lab-in-fiber platform

For efficiently diagnosing early-stage breast cancer, current existing MUC1 biomarker detection methods suffer from common issues of low sensing sensitivities. In this study, a single-core two-channel optical fiber optofluidic on-chip sensor is employed to high-sensitivity detect breast cancer biomarker MUC1 protein, where a Mach-Zehnder interferometer (MZI) waveguide and a fiber Bragg grating (FBG) inscribed into the device by using a femtosecond laser direct writing technique. To improve the device's sensitivity, two microfluidic channels are etched using hydrofluoric (HF) solution, and Au nanobipyramids (Au NBPs) material on an optical fiber is used to excite and realize the localized surface plasmon resonance (LSPR) enhancement. Thus, the device's refractive index (RI) sensitivity increases from 25.07 to 580.22 nm/RIU. FBG compensates the device's temperature sensitivity, achieving at -0.139 nm/℃. On the basis of the advanced LSPR enhancement strategy, the sensor can not only specifically sense MUC1 protein with an ultra-low limit of detection (LOD) of 20.74 aM, it can also detect MUC1 protein in real serum background with a LOD of 42.07 aM. The obtained ultra-low LOD is lower than most existing state-of-the-art MUC1 detection technologies. This study paves what we believe to be a new universal way for developing advanced high-sensitivity lab-in-fiber optofluidic sensing strategy.