In recent years, detecting and quantifying multiple gases have garnered widespread attention across various fields, particularly in volatile organic compound (VOC) detection, which holds significant importance for ecosystems and the medical field. The Raman spectroscopy has been widely used in multi-gas detection due to its advantages in fast response speed and non-destructive detection. This paper reviews the latest research progress of the multi-gas sensing technology in the Raman spectroscopy, focusing on using the hollow-core fiber to enhance the gas signal intensity. The basic principles of the fiber-enhanced Raman spectroscopy are introduced. The detailed discussion includes the system architecture, parameter configuration, and experimental results. Then, the latest advances in the coherent anti-Stokes Raman scattering multi-gas detection technology are reviewed. Finally, the challenges faced by the hollow-core fiber in practical applications are discussed.
A new type of human immunoglobulin G (IgG) sensors based on the surface plasmon resonance (SPR) in the low refractive index (RI) plastic optical fiber (POF) and an antibody immobilization method is presented. A 50-nm-thick gold film was formed on the polished D-shaped fiber surface by magnetron sputtering. The RI response of the POF sensor is 30 049.61 nm/RIU, which is 26.5 times higher than that of single mode fiber (SMF) SPR sensors. The proposed SPR biosensor can be developed by simple and rapid modification of the gold film with 11-mercapto undecanoic acid (MUA). Upon immobilization of the goat anti-human IgG antibody, the resonance wavelength shifts by 11.2 nm. The sensor can be used to specifically detect and quantify the human IgG at concentrations down to 245.4 ng/mL with the sensitivity of 1.327 7 nm per µg/mL, which offers an enhancement of 12.5-fold compared to that of the conventional SMF based SPR sensors. The proposed device may find the potential applications in the case of use at the point of care.
Fabry-Pérot (FP) microcavities have attracted tremendous attention in recent years due to their favorable optical characteristics of the high quality (Q) factor and small mode volume. In this work, we presented a novel approach that utilized the soft lithography and imprinting technology to incorporate the convex micro-lens array structure into the FP (FP-lens) cavity. A strong mode-profile restriction of the micro-lens simultaneously reduced the mode volume and enhanced the Q factor, exhibiting high tolerance to non-parallelism of mirrors compared with that of the plane-plane FP (PP-FP) microcavities. In the experiment, the Q factor of the FP-lens cavity was measured to be 8.145×104, which exhibited a 5.6-fold increase than that of the PP-FP cavity. Furthermore, we experimentally measured the refractive index sensing performance of the FP-lens cavity with the sensitivity of 594.7 nm/RIU and a detection limit of 4.26×10−7 RIU. On the basis of this superior sensing performance, the FP-lens cavity has the great potential for applications in biosensors.
Cancer has been one of the most serious diseases, resulting in more than 10 million deaths every year. Fiber-optic sensors have great potential for diagnosing and treating cancer due to their flexibility, precise positioning, real-time monitoring, and minimally invasive characteristics. Compared to traditional central laboratory examination, fiber-optic biosensors can provide high sensitivity, miniaturization, and versatility, which feature the point-of-care diagnostic capability. Herein, we focus on recent advances in fiber-optic biosensors for cancer theranostics. It is primarily concerned with advancements in the design of various fiber sensing approaches, fiber cancer sensing, and therapy sensors. With fiber-optic biosensors, cancer marker detection, cancerous cell differentiation, ex vivo tumor model validation, and in vivo tumor detection can be achieved. And the medical fiber also can be used to provide photothermal therapy, photodynamic therapy, and combination therapy for solid tumors. Additionally, cancer sensing and therapy can be integrated into the fiber, which demonstrates the multiplexing capabilities of fiber-optic biosensors. Lastly, we systematically summarize the fiber biosensor applications from in vitro to in vivo, and conclude with the challenges in development and prospects.
An acidic gas is an important basic chemical raw material used for synthesizing fertilizers, insecticides, explosives, dyes, and salts. Alternatively, inorganic acidic gases that leak into the air have harmful effects on the human health, infrastructure, and cultural relics. Therefore, the demand for inorganic acidic gas sensors for air quality monitoring and management has continuously increased, enabling the development of various sensing technologies. Among them, fiber-optic sensors are promising for acidic gas detection because of their excellent in-situ measurement, resistance to corrosion, anti-electromagnetic interference, long service life, and smart structure. In particular, fiber-optic sensors have proven to be very useful for the in-situ detection and distributed monitoring of multiple gas parameters. However, the sensitivity, selectivity, repeatability, and limits of detection of these sensors can be improved to achieve acceptable performance levels for practical applications. In this review, we introduce fiber-optic sensors based on structured optical fibers and fiber gratings for detecting H 2S, SO 2, NO 2, CO 2, and N 2O. The structures of the sensing regions, gas-sensitive materials, and measurement principles of these sensors are presented. The sensitivity, selectivity, limit of detection, and response time of the sensors are summarized. Finally, the future of fiber-optic sensors for the detection of inorganic acidic gases is discussed.