This article reports on a fiber‐based ratiometric optical pH sensor for use in real‐time and continuous in vivo pH monitoring in human tissue. Stable hybrid sol–gel‐based pH sensing material is deposited on a highly flexible plastic optical fiber tip and integrated with excitation and detection electronics. The sensor is extensively tested in a laboratory environment before it is applied in vivo in a human model. The pH sensor performance in the laboratory environment outperforms the state‐of‐the‐art reported in the current literature. It exhibits the highest sensitivity in the physiological pH range, resolution of 0.0013 pH units, excellent sensor to sensor reproducibility, long‐term stability, short response time of <2 min, and drift of 0.003 pH units per 22 h. The sensor also exhibits promising performance in in vitro whole blood samples. In addition, human evaluations conducted under this project demonstrate successful short‐term deployment of this sensor in vivo.
functional materials for tackling challenging material-related problems in diverse areas such as medicine, pharmacy, mechanics, electronics, chemistry and others. [1][2][3][4][5] One of the most popular and successful applications of the hybrid sol-gel technology is the development of multifunctional coatings for the protection of metal surfaces against corrosion and environmental degradations. [6] Other promising applications include photoreactive hybrid sol-gel coatings for the fabrication of microstructured components such as optical waveguides, [7] photonic crystals [8] and microfluidic devices. [9] The main advantage of the hybrid sol-gel technology, in comparison to conventional organic or inorganic chemistries, is its flexibility which allows for a combination of both organic and inorganic functional chemistries that facilitates low temperature preparation, generally at room temperature. [5] As a result, structural properties of thermo-sensitive organic groups are maintained and remain available for further exploitation as network modifiers in the inorganic structure and in the microstructuring processes used to fabricate miniature devices. Among the many applications of the sol-gel technology, the preparation of photopolymerizable glasses for holographic applications is of particular interest. The concept of sol-gel preparation of hybrid organic-inorganic materials by the Advancements in hybrid sol-gel technology have provided a new class of holographic materials as photopolymerizable glasses. Recently, a number of photosensitive glass compositions with high dynamic range and high spatial resolution have been reported and their excellent capability for volume holography has been demonstrated. Nevertheless, challenges remain, particularly in relation to the processing time and environmental stability of these materials, that strongly affect the performance and durability of the fabricated holograms. State-of-the-art photopolymerizable glasses possess long curing times (few days) required to achieve thick films, thus limiting the industrial implementation of this technology and its commercial viability. This article presents a novel, fast curing, water-resistant, photopolymerizable hybrid sol-gel (PHSG) for holographic applications. Due to introducing an amine-based modifier that increases the condensation ability of the sol-gel network, this PHSG overcomes the problem of long curing time and can readily produce thick (up to a few hundred micrometers) layers without cracking and breaking. In addition, this PHSG exhibits excellent water-resistance, providing stable performance of holographic gratings for up to 400 h of immersion in water. This finding moves photopolymerizable glasses to the next development stage and renders the technology attractive for the mass production of holographic optical elements and their use across a wide number of outdoor applications.
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