A compact optical fiber sensor based on a no-core fiber (NCF) segment functionalized with a Cu²⁺-imprinted chitosan/polyvinyl alcohol (CS/PVA) film was developed to enable operando on-line monitoring of Cu²⁺ with high selectivity and sensitivity in complex environmental water matrices. The optimal length of the NCF segment was determined to be 1 cm based on simulation and experimental evaluation, under which the highest sensitivity was achieved. The pseudo-second-order kinetic behavior of Cu²⁺ adsorption was first validated by analyzing the time-dependent shift of the interference valley, providing direct spectral evidence of a chemisorption-driven mechanism. A sensitivity of 0.0768 nm/μM and a detection limit of 0.1245 μM were obtained. A rapid response time of less than 20 s and excellent measurement repeatability, with strong specificity toward the target ion and relative standard deviation below 5 percent over five regeneration cycles, were also demonstrated. The sensor was further applied to spiked water samples from the Yangtze River and tap water. By integrating ion-imprinting technology with an optimized NCF-based fiber structure, a portable, cost-effective, and interference-resistant platform has been established for real-time and on-site monitoring of heavy metal ions in complex aquatic environments.
This study aims to develop an advanced glucose sensor based on Single-mode fiber - No-core fiber -Single-mode fiber (SMF-NCF-SMF) microfibers modified with glucose oxidase (GOD) for accurate and simultaneous measurement of glucose concentration and temperature, which could significantly enhance diagnostic capabilities in medical and biological applications. The sensor utilizes the evanescent wave principle to detect glucose concentration and the thermal optical effect to measure temperature. Experimental results demonstrate a concentration sensitivity of 2.07 nm/(mg/mL) within the range of 0-3 mg/mL and a temperature sensitivity of -0.35 nm/°C within the range of 25-50°C. These findings highlight the distinct impacts of concentration and temperature on the interference wavelength. By establishing a demodulation matrix, the sensitivities for both concentration and temperature can be separately determined. In-situ temperature monitoring not only eliminates temperature interference but also ensures that GOD remains at its optimal temperature for maximum activity, thereby enhancing the sensitivity and accuracy of glucose concentration detection. Given its high sensitivity, accuracy, and simplicity, this sensor shows promising potential for widespread use in disease diagnosis and biological detection, paving the way for more advanced diagnostic technologies.
A carbon monoxide (CO) sensor based on a Michelson interferometer combined with α-Fe2O3/reduced graphene oxide quantum dots (rGOQDs) composite film is proposed and fabricated. First, a waist-enlarged taper is formed between the single-mode fiber (SMF) and the no-core fiber (NCF), then the other end of the NCF is spliced with a section of thin-core fiber (TCF). The end of the TCF is coated with a layer of silver film to enhance the reflection. Thus, a Michelson interferometer comprising SMF–NCF–TCF is formed. The α-Fe2O3/rGOQDs composite film is deposited on the outside surface of the TCF. The specific adsorption of CO by the composite film leads to a change in the sensor's effective refractive index, realizing the detection of CO. The results show that the interference intensity of the monitoring valley decreases with increase in the concentration of CO. The sensitivity of the sensor is 0.057 dBm ppm−1, the detection limit of the sensor is 105 ppb and the response time and recovery time are 70 s and 100 s, respectively. The sensor has the advantages of high sensitivity, high selectivity and simple structure, and it is expected to be used for the detection of low concentrations of CO gas.
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