Twisted Optical Micro/Nanofibers Enabled Detection of Subtle Temperature Variation.

The detection of subtle temperature variation plays an important role in many applications, including proximity sensing in robotics, temperature measurements in microfluidics, and tumor monitoring in healthcare. Herein, a flexible miniaturized optical temperature sensor is fabricated by embedding twisted micro/nanofibers in a thin layer of polydimethylsiloxane. Enabled by the dramatic change of the coupling ratio under subtle temperature variation, the sensor exhibits an ultrahigh sensitivity (-30 nm/°C) and high resolution (0.0012 °C). As a proof-of-concept demonstration, a robotic arm equipped with our sensor can avoid undesired collisions by detecting the subtle temperature variation caused by the existence of a human. Moreover, benefiting from the miniaturized and engineerable sensing structure, real-time measurement of subtle temperature variation in microfluidic chips is realized. These initial results pave the way toward a category of optical sensing devices ranging from robotic skin to human-machine interfaces and implantable healthcare sensors.

Optical Microfibers for Sensing Proximity and Contact in Human-Machine Interfaces.

The monitoring of proximity-contact events is essential for human-machine interactions, intelligent robots, and healthcare monitoring. We report a dual-modal sensor made with two functionalized optical microfibers (MFs), which is inspired by the somatosensory system of human skin. The integrated sensor with a hierarchical structure gradationally detects finger approaching and touching by measuring the relative humidity (RH) and force-triggered light intensity variations. Specifically, the RH sensory part shows enhanced evanescent absorption, achieving a sensitive RH measurement with a fast response (110 ms), a high resolution (0.11%RH), and a wide working range (10-100%RH). Enabled by the transition from guided modes into radiation modes of the waveguiding MF, the force sensory part exhibits a high sensitivity (6.2%/kPa) and a fast response (up to 1.5 kHz). By using a real-time data processing unit, the proximity-contact sensor (PCS) achieves continuous detection of the full-contact events, including finger approaching, contacting, pressing, releasing, and leaving. As a proof of concept, the electromagnetic-interference-free PCS enables a smart switch system to recognize the proximity and contact of bare/gloved fingers. Moreover, skin humidity detection and respiration monitoring are realized. These initial results pave the way toward a category of optical collaborative devices ranging from human-machine interfaces to multifunctional on-skin healthcare sensors.

Ultra-sensitive capillary immunosensor combining porous-layer surface modification and biotin-streptavidin nano-complex signal amplification: Application for sensing of procalcitonin in serum.

We propose a promising capillary immunosensor by combining porous-layer surface modification of an open-tubular capillary and streptavidin-biotin-peroxidase nano-complex signal amplification of chemiluminescence read-out. The immunosensor, namely Porous Layer Open Tubular-Signal Amplification (PLOT-SA) sensor, is successfully applied for ultra-sensitive sensing of procalcitonin (PCT) in human serum samples. The results show the PLOT-SA sensor exhibits essential features for PCT determination, including a wide linear detection range of 0.1 pg/mL-100 ng/mL, an extremely low limit-of-quantitation of 0.01 pg/mL, excellent intra-day and inter-day stability and reproducibility with RSDs less than 4.5%. Our study provides a reliable and robust approach for developing capillary sensors that can be used in analysis of complex biologic samples.

Multiplex immunoassays using surface modification-mediated porous layer open tubular capillary.

We proposed an innovative surface modification-mediated porous layer open tubular (PLOT) capillary, which was modified via an in situ biphasic reaction. This capillary comprised three-dimensional homogeneous and porous structures, which could increase the surface-area-to-volume ratio for antibody immobilization. The PLOT capillary was shown as an ideal immunoreaction base to enhance the sensitivity of immunoassays and shorten analysis time. By connecting two separate PLOT capillaries using a suitable sleeve tube, we can perform multiplex targets detection in the same sample. We developed a sensitive, rapid, and multiplex PLOT capillary-mediated immunosensor for the simultaneous identification of alpha fetoprotein (AFP) and carcinoembryonic antigen (CEA) in clinical serum samples with good accuracy. The detection sensitivity of the PLOT immunosensor improved by 10-fold compared with that of bare-capillary sensor, and the whole analysis could be completed within 1 h. This work suggest that suitable surface modification strategy is an effective tool to improve the analytical performance of conventional immunoassay and our study provided a feasible, sensitive, and multi-target assay for the detection of cancer biomarkers, which would be of valuable application in clinical diagnosis.

Photonic crystal fiber-based immunosensor for high-performance detection of alpha fetoprotein.

We have developed a sensitive photonic crystal fiber (PCF)-based immunosensor for detection of alpha fetoprotein (AFP). The unique PCF possesses a morphology characterized by numerous pore structures and a large surface area-to-volume ratio, which can be used as an immune-reaction carrier to improve the sensitivity and reaction speed of AFP detection. The PCF-based immunosensor possesses a low limit of detection of 0.1ng/mL, which is five times lower than that of the capillary-based sensor and 35 times lower than that of the traditional enzyme-linked immunosorbent assay. The wide linear dynamic range of 0.1-150ng/mL makes the developed immunosensor suitable for clinical practice. The proposed method was successfully applied to AFP detection in a clinical serum sample with acceptable precision. It is indicated that the present PCF-based immunosensor could be used as an attractive analytical platform for sensitive and specific detection of cancer biomarkers.