Preparation and Characterization of Hydrogel Optical Fiber for Dual Parametric Sensing of Calcium Ions and Dissolved Oxygen

Calcium ions and dissolved oxygen are critical physiological indicators： Calcium ions regulate nerve conduction， muscle contraction， and cardiac function， while dissolved oxygen reflects tissue oxygenation status via blood oxygen partial pressure. Both parameters are implicated in diverse physiological and pathological processes， including respiratory， cardiovascular， and renal disorders.While traditional electrochemical methods can simultaneously detect calcium ions and dissolved oxygen， they have limitations such as the need for blood sampling， high maintenance requirements for electrodes， and long detection cycles. Existing multi-parameter sensing technologies based on fiber optics still have shortcomings in terms of stability and biocompatibility， limiting their application in long-term in vivo monitoring. In contrast， hydrogels， as a novel sensing material， offer the potential for monitoring physiological parameters within the body due to their excellent biocompatibility. Changes in calcium metabolism and oxygenation status interact in many physiological and pathological processes. Therefore， developing a technology capable of simultaneously detecting calcium ions and dissolved oxygen concentrations is crucial for comprehensively understanding an organism's physiological state and disease progression.In response to the above problems， a hydrogel-based dual-parameter fibre-optic fluorescence sensing probe was proposed in this paper based on the principles of fluorescence enhancement and fluorescence quenching. The probe aims to provide an innovative clinical tool for early disease diagnosis， condition monitoring， and treatment evaluation. The probe was made of 80% w/v and 40% w/v polyethylene glycol diacrylate as core and cladding materials， respectively， and the core was doped with calcein and dichlorotris （1，10-phenanthroline） ruthenium （Ⅱ）， which acted as fluorescent indicators for calcium ions and dissolved oxygen， respectively. The preparation process of the dual-parameter sensing probe was optimized， and the sensitivity and accuracy of the probe for the dual-parameter detection were optimal when the concentration of calcein was 0.05 mg/ml， the concentration of dichlorotris （1，10-phenanthroline） ruthenium （Ⅱ） was 2.5 mg/ml， and the pre-soaking time of the probe was 4 h. The double peaks of the probe were obvious in the extreme concentration of the dual-parameter detection.The sensing performance of the probe was investigated experimentally and the results showed that in the range of 0~2 mmol/L for calcium ions， the sensitivity of the system was 0.340 2 （mmol/L）-1 with an R2 of 0.997 8， and the lower limit of detection reached 0.095 mmol/L with a response time of 11 min. In the range of 0~41.6 mg/L for dissolved oxygen， the sensitivity of the system reached 0.020 03 （mg/L）-1 with an R2 of 0.996 82， and the lower limit of detection was 0.44 mg/L， with a response time of 12 min. The stability of this sensing probe was 99.31% and 99.4%， respectively， over a period of 3 days. The reproducibility of the probe reached 98.47% and 99.48%， respectively， after five sets of replicated experiments. Within the physiological temperature range， the probe has reliable detection performance. Compared with other substances in the blood， the probe has high selectivity for calcium ions and dissolved oxygen.The probe takes advantage of the good biocompatibility and flexibility of hydrogel to overcome the rigidity limitations of traditional fiber optic materials and is more suitable for long-term monitoring in vivo. At the same time， the probe can also realize electromagnetic radiation-free detection， featuring a simple preparation process， low cost and high integration. By simultaneously detecting calcium ions and dissolved oxygen concentration， the probe can provide more comprehensive physiological data， overcoming the shortcomings of single-parameter detection. Based on this， the prepared dual parametric hydrogel fiber-optic probe for calcium ions and dissolved oxygen has the advantages of implantability， high sensitivity， and real-time online monitoring， which provides an innovative solution for biomedical detection. Especially in clinical scenarios， it is valuable for early prevention and real-time monitoring of diseases， accurate diagnostic decision-making， treatment planning and efficacy assessment， and other key aspects.