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The pH value plays a vital role in many biological and chemical reactions. In this work, the fiber-optic chemical pH sensors were fabricated based on carboxyl ZnCdSe/ZnS quantum dots (QDs) and tapered optical fiber. The photoluminescence (PL) intensity of QDs is pH-dependence because protonation and deprotonation can affect the process of electron-hole recombination. The evanescent wave of tapered optical fiber was used as excitation source in the process of PL. To obtain higher sensitivity, the end faces of fiber were optimized for cone region. By lengthening the cone region and shrinking the end diameter of optical fiber, evanescent wave was enhanced and the excitation times of QDs were increased, which improved the PL intensity and the sensitivity of the sensor. The sensitivity of sensor can reach as high as 0.139/pH in the range of pH 6.00-9.01. The surface functional modification was adopted to prepare sensing films. The carboxyl groups on the QDs ligands are chemically bonded to the fiber surface, which is good for response time (40 s) and stability (decreased 0.9 % for 5 min). These results demonstrated that ZnCdSe/ZnS QDs-based fiber-optic chemical pH sensors are promising approach in rapid and precise pH detection., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

This work aims to develop the novel TVB-N sensitive film for monitoring food freshness. The film was fabricated based on carboxymethyl starch sodium (CMS)/agar (AG) complex and natural pigment, red radish anthocyanins (RRA). However, RRA is highly unstable under high humid conditions for their hydrophily. To immobilize RRA in AG film, we brought up CMS (negative charge) to immobilize RRA (positive charge) via electrostatic attractions and combined CMS and AG via hydrogen bond self-assembly. Zeta potential, Fourier transforms infrared (FT-IR) spectra, and X-ray diffraction analysis proved the electrostatic interaction and hydrogen bond self-assembly effect, indicating RRA immobilized effectively. Migration evaluation displayed that RRA remained stable in a high humidity environment (from RH 35%-95%). And its color difference is less than 5% in the low-temperature environment (4 °C). The prepared sensing film was found to be applied to detect the freshness of packaged grass carp and shrimp products. Its colors changed from initial orange-red to light red (3rd day) and then purple (4th day) with the increase of volatile amines inside the packaging. These findings suggested the film can be used as a sensing device for intelligent packaging of protein-rich food., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

In this work, a novel 3D graphene framework/Bi nanoparticle (GF/BiNP) film was fabricated with a facile preparation route. 3D graphene framework with porous structures was electrochemically reduced and in situ assembled on the electrode, and BiNPs with tunable morphologies were highly dispersed on the framework by a chemical reduction. Newly-designed 3D GF/BiNP film possessed a significantly large active area, fast electron transfer ability, high mass transfer efficiency, and excellent structure stability and binding strength on electrode. To demonstrate its superior ability, electrochemical sensors for the assay of heavy metal ions were constructed. As a result, a simultaneous assay of Pb 2+ and Cd 2+ with ultralow detection limits (0.02 μg L -1 of Pb 2+ and 0.05 μg L -1 of Cd 2+ , S/N = 3) and a wide linear range from 1 to 120 μg L -1 was achieved. Meanwhile, a separate analysis of Zn 2+ was performed to get optimum responses, in which a low detection limit of 4.0 μg L -1  (S/N = 3) with a linear range from 40 to 300 μg L -1 was observed, confirming the versatility of the GF/BiNP film in the detection of heavy metal ions. Moreover, excellent repeatability, reproducibility and stability, and reliable assays in real water samples were realized with constructed sensors. Due to its convenient preparation, favorable structures and excellent properties, prepared 3D GF/BiNP film will find great potential for advanced applications in environment, biomedicine and energy systems., (Copyright © 2017 Elsevier B.V. All rights reserved.)