Photonic crystal (PC) cavities, which possess the advantages of compactness, flexible design, and suitability for integration in a lab-on-a-chip system, are able to distinguish slight variations in refractive index with only a small amount of analyte. Combined with the newly proposed optofluidic technology, PC-cavity devices stimulate an emerging class of miniaturized and label-free biochemical sensors. In this review, an overview of optofluidic PC cavities based biochemical sensors is presented. First, the basic properties of the PC, as well as the sensing principle of the PC cavity, are discussed. Second, the applications of the sensors in detecting gas, liquid, and biomolecule concentrations are reviewed, with a focus on their structures, sensing principles, sensing properties, advantages, and disadvantages. Finally, the current challenges and future development directions of optofluidic PC-cavity-based biochemical sensors are discussed.

Optofluidic, as an emerging technology that combines photons and microfluidics, has become a powerful, intelligent, and universal sensing platform in the field of bio-chemical sensing. Optical fiber optofluidic (OFOF), as a branch of optofluidic technology, has stimulated a host of remarkable achievements in the field of bio-chemical sensing due to its superiority of compact structure, immunity to electromagnetic interference, low sample consumption, high sensitivity, and real-time dynamic response. In this paper, an overview of OFOF bio-chemical sensors is presented. The OFOF system architectures are introduced and some advanced functional materials and coating technologies that can be utilized in the OFOF sensing platform to achieve high-performance biochemical sensing are summarized. Research progress and current status of OFOF bio-chemical sensors based on various sensing mechanisms are summarized and analyzed, with emphases on their sensing principles, sensing structures, sensing applications, advantages, and disadvantages. Lastly, the existing challenges and future development trends of OFOF biochemical sensors are briefly discussed.

A multifunction, high-sensitivity, and temperaturecompensated optical fiber DNA hybridization sensor combining surface plasmon resonance (SPR) and Mach−Zehnder interference (MZI) has been designed and implemented. We demonstrate, for the first time to our knowledge, the dual-parameter measurement of temperature and refractive index (RI) by simultaneously using SPR and MZI in a simple single-mode fiber (SMF)−no-core fiber (NCF)−SMF structure. The experimental results show RI sensitivities of 930 and 1899 nm/RIU and temperature sensitivities of 0.4 and −1.4 nm/°C for the MZI and SPR, respectively. We demonstrate a sensitivity matrix used to simultaneously detect both parameters, solving the problem of temperature interference of RI variation-based biosensors. In addition, the sensor can also distinguish biological binding events by detecting the localized RI changes at the fiber's surface. We realize label-free sensing of DNA hybridization detection by immobilizing probe DNA (pDNA) onto the fiber as the probe to capture complementary DNA (cDNA). The experimental results show that the sensor can qualitatively detect cDNA after temperature compensation, and the limit of detection (LOD) of the sensor reaches 80 nM. The proposed sensor has advantages of high sensitivity, real time, low cost, temperature compensation, and low detection limit and is suitable for in situ monitoring, high-precision sensing of DNA molecules, and other related fields, such as gene diagnosis, kinship judgment, environmental monitoring, and so on.

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Highlights Quantitative polymerase chain reaction (qPCR) in an all-fiber all-optical configuration. Thermal cycling and fluorescence detection in a single optical-fiber-integrated device. Advantages of small sample volume, portability and high-speed operation. Potential ability to operate fluorescence-free through direct measurement of refractive index. Target application is disease and pathogen detection in remote communities.