Ultrasensitive and Multiple Biomarker Discrimination for Alzheimer's Disease via Plasmonic & Microfluidic Sensing Technologies.

As the population ages, the worldwide prevalence of Alzheimer's disease (AD) as the most common dementia in the elderly is increasing dramatically. However, a long-term challenge is to achieve rapid and accurate early diagnosis of AD by detecting hallmarks such as amyloid beta (Aß42). Here, a multi-channel microfluidic-based plasmonic fiber-optic biosensing platform is established for simultaneous detection and differentiation of multiple AD biomarkers. The platform is based on a gold-coated, highly-tilted fiber Bragg grating (TFBG) and a custom-developed microfluidics. TFBG excites a high-density, narrow-cladding-mode spectral comb that overlaps with the broad absorption of surface plasmons for high-precision interrogation, enabling ultrasensitive monitoring of analytes. In situ detection and in-parallel discrimination of different forms of Aß42 in cerebrospinal fluid (CSF) are successfully demonstrated with a detection of limit in the range of ≈30-170 pg mL-1, which is one order of magnitude below the clinical cut-off level in AD onset, providing high detection sensitivity for early diagnosis of AD. The integration of the TFBG sensor with multi-channel microfluidics enables simultaneous detection of multiple biomarkers using sub-µL sample volumes, as well as combining initial binding rate and real-time response time to differentiate between multiple biomarkers in terms of binding kinetics. With the advantages of multi-parameter, low consumption, and highly sensitive detection, the sensor represents an urgently needed potentials for large-scale diagnosis of diseases at early stage.

In situ surface turbidity sensor based on localized light scattering from tilted fiber Bragg gratings.

We propose a compact fiber-optic sensor for in situ and continuous turbidity monitoring, based on surface optical scattering of polarized evanescent waves from targeted particles. The sensor is composed of a tilted fiber Bragg grating (TFBG) packaged inside a microfluidic capillary. The transmission spectrum of the TFBG provides a fine comb of narrow cladding resonances that are highly sensitive to the turbidity due to the localized light scattering of polarized evanescent waves from the microparticles near the fiber surface (as opposed to traditional bulk/volumetric turbidity measurement). We also propose a transmission spectral area interrogation method and quantify the repeatable correlation between the surface turbidity and the optical spectral area response. We show that the maximum sensitive turbidity response is achieved when the wavelength of the sensing cladding resonance matches the size of surrounding solid particles.

Simultaneous measurement of the BOD concentration and temperature based on a tapered microfiber for water pollution monitoring.

An optical sensor that simultaneously measures the concentration of the biochemical oxygen demand (BOD) and temperature in water based on a tapered microfiber is proposed for environmental monitoring. The sensor is characterized by a strong evanescent field, which is more sensitive to liquids with a low refractive index and a low transmission loss. The results show that as the BOD concentration increases, the interference spectrum shifts toward longer wavelengths, the spectral loss decreases, and the sensitivities of the BOD are 12.17 nm/mg/mL and -2.387dB/mg/mL in the range of 0.25-1 mg/mL, which indicates the extent of the water pollution. The detection limit for the BOD concentration is as low as 0.0016 mg/mL. As the ambient temperature increases, the interference spectrum shifts toward shorter wavelengths, the spectral loss decreases, and the temperature sensitivities are -0.339nm/∘C and -0.031dB/∘C in the range of 30°C-60°C. The matrix method can be used to achieve the simultaneous measurement of the BOD concentration and environmental temperature because the spectral interference peaks have different responses to these two parameters. The sensor can not only be used for detecting water pollution in rivers, drinking water, and groundwater but can also be utilized for other types of environmental monitoring. This sensor has great potential to act as a basic sensing unit in fiber-optic sensor networks for multiparameter measurements and intelligent monitoring.

Microfiber coupler with a Sagnac loop for water pollution detection.

The measurement of chloride ion concentrations has been studied for the purpose of monitoring the quality of water resources. In this paper, a chloride ion sensor based on a microfiber coupler with a Sagnac loop is proposed. The microfiber coupler, which acts as the sensing unit and has a diameter of 10 µm and a length of 1 mm, is fabricated using the flame-brushing technique, and the two ends are connected to form a Sagnac loop, which acts as a reflector to enhance the reflection in the structure. Experimental results show that the sensitivity reaches a maximum of 423 pm/‰ and that the detection limit for the chloride ion concentration is 0.447‰ at a wavelength of 1595 nm. The proposed sensor is characterized by a simple and easy manufacturing process, compact structure, and low cost; further, this sensing unit has great potential for applications in marine chloride detection and environmental safety monitoring, especially for monitoring building corrosion and water pollution.