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Concern about food safety triggers demand on rapid, accurate and on-site detection of foodborne pathogens. Among various fluorescent probes for detection, carbon dots (CDs) prepared by carbonization of carbon-rich raw materials show extraordinary performance for their excellent and tailorable photoluminescence property, as well as their facilely gained specificity by surface customization and modification. CDs-based fluorescent probes play a crucial role in many pathogenic bacteria sensing systems. In addition, microfluidic technology with characteristics of portability and functional integration is expected to combine with CDs-based fluorescent probes for point-of-care testing (POCT), which can further enhance the detection property of CDs-based fluorescent probes. Here, this paper reviews CDs-based bacterial detection methods and systems, including the structural modulation of fluorescent probes and pathogenic bacteria detection mechanisms, and describes the potential of combining CDs with microfluidic technology, providing reference for the development of novel rapid detection technology for pathogenic bacteria in 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 © 2024 Elsevier Ltd. All rights reserved.)

N 2 H 4 is a common raw material used in the production of pesticides and has good water solubility, so it may contaminate water sources and eventually enter living organisms, causing serious health problems. Viscosity is an important indicator of the cellular microenvironment and an early warning signal for many diseases. The high reactivity of hydrazine depletes glutathione (GSH) in hepatocytes, causing oxidative stress ultimately leading to significant changes in intracellular viscosity and even death. Therefore, it is particularly important to develop an effective method to detect N 2 H 4 and viscosity in environmental and biological systems. On this basis, we developed two fluorescent probes, BDD and BHD, based on xanthene and 2-benzothiazole acetonitrile. The experimental results show that BHD and BDD have good imaging capabilities for N 2 H 4 in cells, zebrafish and Arabidopsis. BHD and BDD also showed sensitive detection and fluorescence enhancement in the near-infrared region when the intracellular viscosity was changed. Notably, the probe BDD has also successfully imaged N 2 H 4 in a variety of real water samples., 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.)

Hydrogen peroxide (H 2 O 2 ) is a reactive oxygen species (ROS) that can be used as a marker for the occurrence of oxidative stress in the organism. Lysosomes serve as intracellular digestive sites, and when the concentration of H 2 O 2 in them is abnormal, lysosomal function is often impaired, leading to the development of diseases. Hydrogen sulfide (H 2 S) acts as a gaseous signaling molecule that scavenges H 2 O 2 from cells and tissues, thereby maintaining the redox environment of the body. However, most of the reported hydrogen peroxide fluorescent probes so far can only detect H 2 O 2 , but cannot maintain the intracellular redox environment. In this paper, an H 2 O 2 fluorescent probe LN-HOD with lysosomal targeting properties was designed and synthesized by combining the H 2 O 2 recognition site with a naphthylamine fluorophore via a thiocarbamate moiety. The probe has the advantages of large Stokes shift (110 nm), high sensitivity and good H 2 S release capability. The probe LN-HOD can be used to detect H 2 O 2 in cells, zebrafish and plant roots. In addition, LN-HOD detects changes in the concentration of H 2 O 2 in plant roots when Arabidopsis is stressed by cadmium ion (Cd 2+ ). And through its ability to release H 2 S, it can help to remove excess H 2 O 2 and maintain the redox environment in cells, zebrafish and plant roots. The present work provides new ideas for the detection and assisted removal of H 2 O 2 , which contributes to the in-depth study of the cellular microenvironment in organisms., 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.)

A series of fluorescent dyes (NapPAs) based on 4-phenylacetylene-1,8-naphthalimide were synthesized and characterized, whose conjugated structures were extended by the introduction of phenylethynyl. Furthermore, changes in the photophysical properties of the dyes when substituents with varying electron richness were introduced at the p-position of phenylacetylene were studied. The theoretical calculation of the dye molecules was carried out by B3LYP functional and 6-31G(d,p) basis set, and the effects of different substituents at the p-position of phenylacetylene on the electronic structure and photophysical properties of the dyes were studied by theoretical calculation results. Theoretical calculations provided a reliable means of predicting the properties of dyes, which could help in the design of more efficient and novel dyes. To verify the practicability of the dyes, two dyes with excellent photophysical properties (large Stokes shift, high polarity-viscosity sensitivity, good biocompatibility) were selected as fluorescent probes for visualization of LDs and two-color imaging of LDs and lysosomes. Cell imaging showed that NapPA-LDs and NapPA-LDs-Lyso serve as excellent imaging tools to monitor the dynamic changes, movements, and behaviors of LDs and lysosomes in real time. Notably, NapPA-LDs-Lyso held promise as a potential tool to study the interaction between LDs and lysosomes., 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 © 2023 Elsevier B.V. All rights reserved.)

Hydrazine (N 2 H 4 ) plays an important role in industrial production, but it is highly toxic, leaking or exposing it will pollute the environment and cause serious harm to human beings. Therefore, it is necessary to use a simple and effective method to detect N 2 H 4 in environmental systems and organisms. Herein, a novel water-soluble fluorescent probe based on coumarin fluorophore, 2-(7-(diethylamino)-2-oxo-2H-chromen-3-yl)isoindoline-1,3-dione (C-Z1), is reported. The fluorescence intensity of the probe at 530 nm was enhanced gradually with the addition of N 2 H 4 , and the maximum enhancement was about 28 times. The probe has good selectivity and sensitivity, the detection limit of hydrazine hydrate is 1.48 × 10 -7  M, and the response mechanism of the probe is proved by theoretical calculation and experiment. C-Z1 has been shown to detect N 2 H 4 in a variety of environmental samples, including water, soil, air, cells, zebrafish and plants. In addition, C-Z1 can be made into test strips for easy portability and used for rapid quantitative detection of N 2 H 4 in the field by its distinct change in fluorescence color. Thus, C-Z1 has great potential for the analysis and detection of environmental contaminants., 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 © 2023 Elsevier B.V. All rights reserved.)

H 2 S is one of the signal molecules in live organisms and a poisonous gas, which is closely related to our life. The traditional synthetic small molecular organic probes often have the disadvantages of low biocompatibility. In this paper, a fluorescent nanoprobe for detecting H 2 S in live organisms was constructed based on chitosan. The structure of CH-CN was characterized by infrared spectroscopy, nuclear magnetic resonance, x-ray photoelectron spectroscopy (XPS), XRD and scanning electron microscope (SEM). In the presence of Na 2 S, the fluorescence intensity at 560 nm was significantly enhanced, and showed high selectivity and sensitivity toward H 2 S. Based on the good fluorescence response of CH-CN, the probe was also successfully applied to H 2 S imaging in HepG2 cells and zebrafish. These experimental results indicate that the probe has lower cytotoxicity and excellent stability. The present research shows a typical example of construction of chitosan-based macromolecular fluorescent materials and their bio-imaging application., Competing Interests: Declaration of competing interest The authors declare no conflicts of interest., (Copyright © 2023. Published by Elsevier B.V.)

The quality of wine can be affected by excess Cu 2+ due to the occurrence of oxidation reactions or precipitation. Therefore, it is essential to use simple and effective testing methods to ensure the Cu 2+ content in wine. In this work, we designed and synthesized a rhodamine polymer fluorescent probe (PEG-R). The water solubility of PEG-R was improved by the introduction of polyethylene glycol, which improved the performance and broadened its application in the food field. The PEG-R was characterized by high sensitivity, selectivity and fast response to Cu 2+ and was able to complete the response process within 30 s, with approximately 29-fold fluorescence enhancement of the probe after exposure to Cu 2+ , the limit of detection (LOD) was 1.295 × 10 -6 M. The probe can be used for the determination of Cu 2+ in living cells, zebrafish, white wine and food products, and it was made into practical gels and test strips., 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 © 2023 Elsevier Ltd. All rights reserved.)

A cellulose based polymer probe (HC-HS) was prepared for the detection of H 2 S. HC-HS can be applied to fluorescence imaging of H 2 S in living cells and zebrafish, and HC-HS was made into test strips to detect H 2 S produced in the process of food corruption.

The AIE bio-probes have attracted extensive attention because of their good brightness, long-term in situ retention ability, photostability and low cytotoxicity. Recently, the transformation of ACQ to AIE has become very popular, which is very important for the further development of AIE probes. Herein, a series of novel dyes (NR-Lyso-Ⅰ, NR-Lyso-Ⅱ, NR-Lyso-III, NR-Lyso-IV) were designed and synthesized. It was found that alkylation of 4-aminonaphthalimide could achieve the transformation of the dye from ACQ to AIE effect due to the growth of carbon chain. Moreover, the AIE probe NR-Lyso-IV exhibited dual-state emission (DSE) and large Stokes shift (＞100 nm), excellent selectivity, photostability, and low cytotoxicity, which was able to simultaneous visualize the lipid droplets (LDs) and lysosomes of HeLa cells and zebrafish., 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.)

Lipid droplets (LDs) are simple intracellular storage sites for neutral lipids and exhibit important impact on many physiological processes. For example, the changes in the polar microenvironment inside LDs could affect physiological processes, such as lipid metabolism and storage, protein degradation, signal transduction, and enzyme catalysis. Herein, a new fluorescent chemo-sensor (Couoxo-LD) was formulated by our molecular design strategy. The probe could be applied to effectively label intracellular lipid droplets. Intriguingly, Couoxo-LD demonstrated positive sensitivity to both polarity and viscosity, which might be attributed to its D-π-A structure and the twisted rotational behavior of the carbon-carbon double bond (TICT). Additionally, Couoxo-LD was successfully implemented in cellular imaging due to its excellent selectivity, pH stability, and low biotoxicity. In HeLa cells, the co-localization curve between Couoxo-LD and commercial lipid droplet dyes overlapped at 0.93. The results indicated that the probe could selectively sense LDs in HeLa cells. Meanwhile, Couoxo-LD can be applied for in vivo imaging of zebrafish.

Hypochlorous acid (HClO) plays a critical role in physiological activities of maintaining the stable oxidation balance of organisms, which was proved to relate to some serious diseases. In this work, 4-nitrobenzenesulfonylhydrazide based fast-responsive two-photon fluorescent probe CoPh-ClO was designed and synthesized reasonably, which possessed low cytotoxicity, good anti-interference characteristics, a large Stokes shift (85 nm), and good two-photon performance. In addition, probe CoPh-ClO was successfully applied to detect exogenous HClO in living HeLa cells and endogenous HClO in living RAW264.7 cells respectively. Moreover, we successfully achieved tissues imaging with a deep penetration depth of 65 µm and zebrafish imaging accompanied with a high contrast (about 45-fold). Interestingly, the introduce of benzene ring between fluorophore and reaction site made probe CoPh-ClO more sensitive (only 20 s) with a large turn-on signal. The probe CoPh-ClO was modified and possessed better stability (more than 10 mins) even in excessive HClO. All of mentioned above merits demonstrated that CoPh-ClO could be a promising imaging tool for monitoring HClO in various physiological processes, and the introduction of benzene ring would provide a new perspective for the development of multi-function probes., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Carbon monoxide (CO) is one of the most significant signal molecules and plays an important role in regulating human physiological and pathological processes. In this study, a novel Pd-based complex (Pd-BNP-OH) was developed for endogenous CO detection. The structure and morphology of Pd-BNP-OH was characterized by SEM, XPS, and NMR analyses. When Pd-BNP-OH was reacted with CO, a strong fluorescence enhancement at 510 nm was observed. In addition, Pd-BNP-OH exhibited high stability and selectivity toward CO in PBS buffer. In biological experiments, Pd-BNP-OH exhibited little cytotoxicity in cellular environment, and a bright fluorescence turn on was observed in the presence of exogenous CO and endogenous generated CO. The probe was then applied for CO detection in live zebrafish by both one-photon and two-photon excitation. Significantly, Pd-BNP-OH has excellent two-photon property, controllable structure and high biocompatibility. These features enable the probe to detect endogenously generated carbon monoxide in live organisms successfully., (Copyright © 2021 Elsevier B.V. All rights reserved.)