Boosting hydrogen evolution performance of nanofiber membrane-based composite photocatalysts with multifunctional carbon dots.

Recent progress in the co-spinning of nanofibers and semiconductor particles offers a promising strategy for the development of photocatalytic devices, solving aggregation and catalyst recovery challenges. However, composite photocatalysts based on nanofiber membranes often suffer from poor conductivity, low hydrophilicity, and easy recombination of photogenerated electron-hole pairs in the semiconductor components. Here, to tackle the aforementioned issues of ZnIn2S4/polyacrylonitrile (ZIS/PAN) nanofiber-based catalysts, we prepared a composite carbon dots/ZnIn2S4/polyacrylonitrile (CZP) nanofiber membrane by blending carbon dots (CDs) with ZIS/PAN using the electrospinning process. The hydrogen evolution performance of the CZP photocatalyst was significantly improved by CDs, which enhanced the hydrophilicity, increased the light absorption, facilitated the transfer of photogenerated electrons, and reduced the recombination of photogenerated electron-hole pairs. Notably, the optimal CZP photocatalyst achieved a hydrogen evolution rate of 2250 µmol g-1h-1, which is about 23 % higher than that of the nanofiber membrane without CDs and 4.55 times higher than that of ZIS particles. The present work successfully improved the CZP nanofiber membrane of photocatalytic hydrogen evolution performance, and the membrane may benefit further device development by eliminating the need for stirring and simplifying the recovery process.

Magnetic modulation on chiroptical activities of nematically assembled carbon dots.

Effectively harnessing the assembly of achiral carbon dots into a chiral manner is a prominent step for applying carbon dots into the area of stereoselective optoelectronics and theranostics. Herein, magnetic-modulated and circularly polarized luminescence (CPL)-active photonic thin films were presented in this article via co-assembly and magnetic-mediation strategy of cellulose nanocrystals, carbon dots and magnetic nanoparticles. The photonic bandgap of the composite films is modulated via interfacial interactions between the building blocks, and more efficiently via external magnetic field which can further enhance the selective reflection of the films with a maximum CPL anisotropic factor as high as -0.92, indicating the optimized condition for achieving CPL signals is basically when the photonic bandgap (PBG) are close to the emission peaks of nanocomposite films, which may essentially facilitate the selective reflection effect and leads to the output of opposite CPL signals. Such strategy would inevitably boost the development of carbon dots based chiral devices and reagents into the realm of chirality-related biological issues and next generation chiral optoelectronics.

d-arginine-functionalized carbon dots with enhanced near-infrared emission and prolonged metabolism time for tumor fluorescent-guided photothermal therapy.

Carbon dots (CDs) have garnered significant interest owing to their distinctive optical properties. However, their bioimaging and biomedical applications are limited by pronounced fluorescence (FL) quenching in aqueous media and low tumor accumulation efficacy associated with their ultra-small size. This study proposes a simple surface modification approach using functioning d-arginine on CDs (d-Arg@CDs) to improve their near-infrared (NIR) FL in aqueous solution and maintain their high photothermal conversion properties. Because of the low utilization rate of dextral amino acids in animals, modifying CDs with low molecular weight d-arginine did not increase particle size but extended the metabolism time in blood circulation, thereby leading to enhanced accumulation efficacy at tumor sites in the mice model. The enhanced tumor accumulation of d-Arg@CDs resulted in significantly superior tumor NIR FL imaging and photothermal therapy performance compared with pure CDs and l-arginine functionalized CDs. This dextral amino acid modification approach is expected to be an effective tool for enhancing the biomedical applications of CDs.

Mild near-infrared laser-triggered photo-immunotherapy potentiates immune checkpoint blockade via an all-in-one theranostic nanoplatform.

One of the primary challenges for immune checkpoint blockade (ICB)-based therapy is the limited infiltration of T lymphocytes (T cells) into tumors, often referred to as immunologically "cold" tumors. A promising strategy to enhance the anti-tumor efficacy of ICB is to increase antigen exposure, thereby enhancing T cell activation and converting "cold" tumors into "hot" ones. Herein, we present an innovative all-in-one therapeutic nanoplatform to realize local mild photothermal- and photodynamic-triggered antigen exposure, thereby improving the anti-tumor efficacy of ICB. This nanoplatform involves conjugating programmed death-ligand 1 antibody (aPD-L1) with gadolinium-doped near-infrared (NIR)-emitting carbon dots (aPD-L1@GdCDs), which displays negligible cytotoxicity in the absence of light. But under controlled NIR laser irradiation, the GdCDs produce combined photothermal and photodynamic effects. This not only results in tumor ablation but also induces immunogenic cell death (ICD), facilitating enhanced infiltration of CD8+ T cells in the tumor area. Importantly, the combination of aPD-L1 with photothermal and photodynamic therapies via aPD-L1@GdCDs significantly boosts CD8+ T cell infiltration, reduces tumor size, and improves anti-metastasis effects compared to either GdCDs-based phototherapy or aPD-L1 alone. In addition, the whole treatment process can be monitored by multi-modal fluorescence/photoacoustic/magnetic resonance imaging (FLI/PAI/MRI). Our study highlights a promising nanoplatform for cancer diagnosis and therapy, as well as paves the way to promote the efficacy of ICB therapy through mild photothermal- and photodynamic-triggered immunotherapy.

Highly efficient and broad-spectrum antibacterial carbon dots combat antibiotic resistance.

Bacterial infections have become a major global public health issue, particularly with the emergence of multidrug-resistant strains. Therefore, developing non-antibiotic antimicrobial agents is crucial for treating drug-resistant bacterial infections. Building on previous research into natural products as novel antibacterial agents, this study synthesized curcumin-derived carbon dots using curcumin and ethylenediamine as raw materials through a hydrothermal method. The resulting carbon dots not only improved the water solubility and stability of curcumin but also exhibited highly efficient broad-spectrum antibacterial activity. Detailed investigations into the antibacterial performance and mechanisms of the carbon dots were conducted through experiments such as minimum inhibitory concentration (MIC) determination, live/dead bacterial staining, morphological studies, nucleic acid concentration detection, and reactive oxygen species (ROS) detection. The results indicated that the carbon dots significantly damaged the structural integrity of bacteria and generated large amounts of ROS. They exhibited remarkable antibacterial effects against Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus, and effectively inhibited drug-resistant MRSA. Their antibacterial efficacy was notably superior to that of broad-spectrum antibiotics such as chloramphenicol and Sulfadiazine. This study highlights the potential application of curcumin-derived carbon dots in combating bacterial infections and provides valuable insights for developing novel antibacterial agents derived from natural products.

Surface State-Based panchromatic luminescent carbon dots.

Carbon dots have shown a broad application prospect in the fields of sensing and detection, biological imaging, and optoelectronic devices. However, it is still challenging to adopt a simple and green synthesis route and to develop new precursor systems to prepare full-color luminescent carbon dots. This study proposes a mechanism for fine regulation of carbon dot fluorescence spectra based on surface states of CN, COC, and OH, among which CN play a major role in long wavelength emission while COC and OH are responsible for the blue shift of emission wavelength. Using 4,4-bipyridine and p-phenylenediamine as precursors in safe and environmentally friendly glycol and water as solvents for the first time, the fine spectral carbon dots with full spectrum luminescence from purple (441 nm) to red (627 nm) were successfully synthesized by simply changing the composition of the reaction solvent and using a short reaction time. Compared with other reports on regulating polychromatic carbon dots, our method is more refined and has a wider distribution of luminescent colors. In addition, the obtained carbon dots based on such surface state luminescence mechanism have shown good application prospects in specific detection of Fe3+and cell labeling.

Preventive conservation of paper-based relics with visible light high-transmittance ultraviolet blocking film based on carbon dots.

Paper-based relics is an important carrier for recording and preserving information, however, it faces irreversible UV-induced damage, including photocleavage, oxidation, acidification and discoloration, which seriously affects its value and lifespan. Carbon dots (CDs) possess excellent UV absorption and good chemical stability, making them suitable for UV protection. Herein, we propose a high-security and efficient method utilizing CDs films (CDFs) for preventive protection of paper against UV damage. The CDFs with high tunable UV absorbance and minimal absorbance in the visible light range, effectively shield paper from UV radiation while preserving its visual appeal. Moreover, the UV transmittance of the film can be fine-tuned to the content of CDs and can be easily removed from the paper without residue. Artificial accelerated UV aging experiments demonstrate the deceleration of acidification, oxidation, and photocleavage in the protected bamboo paper and Xuan paper. This research paces a new direction for the protection of paper and paper-based relics and artworks with emerging carbon materials, offering customizable protection effects tailored to specific preservation and exhibition requirements. This research pioneers a novel approach to preventive protection of paper and paper-based relics using emerging carbon dots materials, offering tailored protection for diverse preservation needs.

Construction of a one-stop N-doped negatively charged carbon dot nanoplatform with antibacterial and anti-inflammatory dual activities for wound infection based on biocompatibility.

The development of bacterial resistance significantly contributes to the persistence of infections. Although previous studies have highlighted the benefits of metal-doped positive carbon nanodots in managing bacterial wound infections, their mechanism of action is relatively simple and they may pose potential hazards to human cells. Therefore, it is essential to develop a one-stop carbon dot nanoplatform that offers high biocompatibility, antibacterial properties, and anti-inflammatory activities for wound infection management. This study explores the antibacterial efficacy, without detectable resistance, and wound-healing potential of nitrogen-doped (N-doped) negatively charged carbon dots (TPP-CDs). These carbon dots are synthesized using tannic acid (TA), polyethylene polyamine, and polyethylene glycol (PEG) as precursors, with a focus on their biocompatibility. Numerous systematic studies have shown that TPP-CDs can effectively destroy bacterial biofilms and deoxyribonucleic acid (DNA), while also inducing oxidative stress, leading to a potent antimicrobial effect. TPP-CDs also demonstrate the ability to scavenge excess free radicals, promote cellular proliferation, and inhibit inflammatory factors, all of which contribute to improved wound healing. TPP-CDs also demonstrate favorable cell imaging capabilities. These findings suggest that N-doped negatively charged TPP-CDs hold significant potential for treating bacterial infections and offer practical insights for their application in the medical field.

Carbon dots-based dual-mode sensor for highly selective detection of nitrite in food substrates through diazo coupling reaction.

As an antioxidant and preservative agent, nitrite (NO2-) plays an essential role in the food industry to maintain freshness or inhibit microbial growth. However, excessive addition of NO2- is detrimental to health, so accurate and portable detection of NO2- is critical for food quality control. Notably, the selectivity of most carbon dots (CDs)-based fluorescence sensors was not enough due to the nonspecific interaction mechanism of hydrogen bond, electrostatic interaction and inner filter effect etc. Herein, a novel fluorescence/UV-vis absorption (FL/UV-vis) dual-mode sensor was developed on basis of mC-CDs, which were prepared by simple solvothermal treatment of m-Phenylenediamine (m-PDA) and cyanidin cation (CC). The fluorescence of these mC-CDs could be selectively responded by NO2- through the specific diazo coupling reaction between NO2- and amino groups on the surface of mC-CDs, thus effectively improving the selectivity of NO2- detection. The CDs-based fluorescence sensor possessed a low detection limit of 0.091 µM and 0.143 µM for FL and UV-vis methods and the excellent linear range of 0.0-60.0 µM. Furthermore, the mC-CDs sensor was employed to detect NO2- in real samples with a recovery rate of 97.11 %-104.15 % for quantitative addition. Moreover, the smartphone-assisted fluorescence sensing platform developed could identify the subtle color changes that could not be distinguished by the naked eye, and had the advantages of fast detection speed and intelligence. More importantly, the portable solid phase sensor based on mC-CDs had been successfully applied to the specific fluorescence identification and concentration monitoring of NO2-. Accordingly, the designed sensor provided a new strategy for the highly selective and convenient sensing of NO2- in food substrates, and paved the way for the wide application of CDs-based nanomaterials in the detection of food safety.

Platinum-based fluorescent nanozyme-driven "loong frolic pearls" multifunctional nanoplatform for tri-mode ultrasensitive detection and synergistic sterilization of Burkholderia gladioli.

Rapid and accurate detection of Burkholderia gladioli (B. gladioli) and effective sterilization are crucial for ensuring food safety. Hence, a novel "loong frolic pearls" platform based on platinum-based fluorescent nanozymes (Pt-OCDs) and strand exchange amplification (SEA) was reported. Magnetic nanoparticles were modified on primer SEAF, while Pt-OCDs were covalently coupled with primer SEA-R. The highly efficient amplification capability of SEA permitted the accumulation of a large number of double-labeled amplicons. After magnetic adsorption, the supernatant was detected in reverse direction to collect colorimetric-fluorescence-photothermal signal values, enabling ultra-precise detection within 1 h. Furthermore, the Pt-based multifunctional nanoplatform generated abundant •OH and 1O2, which synergistically attacked B. gladioli and its biofilm, resulting in significant bactericidal efficacy within 30 min. This "triple-detection and double-sterilization" platform has been successfully applied in the field of food analysis with good recovery rates and immediate control over B. gladioli, thus demonstrating promising prospects for broad applications.

A smartphone-integrated ratiometric fluorescent sensor for ascorbic acid determination using microplasma-enabled carbon dots and rhodamine B.

A switchable ratiometric fluorescent smartphone-assisted sensing platform based on nitrogen-doped carbon dots (N-CDs) and Rhodamine B was fabricated for the determination of the ascorbic acid (AA) content in fruits by quenching the fluorescence of N-CDs with Hg2+ (turn-off) and recovering with AA (turn-on). The blue-emission N-CDs was synthesized by liquid dielectric barrier discharge microplasma with an average size of 3.65 nm and an absolute quantum yield of 18 % (excited at 345 nm). In addition, the fluorescence color was converted to RGB values, enabling visual and quantitative determination of AA. Under optimal parameters, the linear ranges for detecting AA were found to be 3-170 µM and 5-170 µM for fluorescence spectrometer and smartphone sensing platform. The detection limits were 0.98 µM and 2.90 µM, respectively. Furthermore, the satisfactory recoveries in fruits were obtained by RF probe and smartphone platform. This smartphone-assisted platform will facilitate sensitive and visual determination for AA.

Construction of eco-friendly dual carbon dots ratiometric fluorescence probe for highly selective and efficient sensing mercury ion.

In present work, blue carbon dots (b-CDs) were derived from ammonium citrate and guanidine hydrochloride, and red carbon dots (r-CDs) were stemmed from malonate, ethylenediamine and meso­tetra (4-carboxyphenyl) porphin based on facile hydrothermal method. Eco-friendly ratiometric fluorescence probe was innovatively constructed to effectively measure Hg2+ utilizing b-CDs and r-CDs. The developed probe displayed two typical emission peaks at 450 nm from b-CDs and 650 nm from r-CDs under the excitation at 360 nm. Mercury ion has strong quenching effect on the fluorescence intensity at 450 nm due to the electron transfer process and the fluorescence change at 450 nm was used as the response signal, whereas the fluorescence intensity at 650 nm kept unchangeable which resulted from the chemical inertness between Hg2+ and r-CDs, serving as the reference signal in the sensing system. Under optimal circumstances, this probe exhibited an excellent linearity between the fluorescence response values of ΔF450/F650 and Hg2+ concentrations over range of 0.01-10 µmol/L, and the limit of detection was down to 5.3 nmol/L. Furthermore, this probe was successfully employed for sensing Hg2+ in practical environmental water samples with satisfied recoveries of 98.5%-105.0%. The constructed ratiometric fluorescent probe provided a rapid, environmental-friendly, reliable, and efficient platform for measuring trace Hg2+ in environmental field.

An all-in-one smartphone-assisted ratiometric fluorescent device for visual and quantitative detection of glutathione.

The daily consumption of foods abundant in Glutathione (GSH) can be supplemented to maintain the homeostasis of GSH in human health and alleviate pathologies resulting from abnormal GSH levels. The fluorescence-based visual determination of GSH has gradually attracted the attention of researchers due to its robust performance and versatile implementation. However, the current GSH visual strategy primarily relies on variations in fluorescence intensity at a single emission wavelength, which poses challenges for naked-eye and portable readout, as well as distorted signals caused by complex matrix effects in real samples. Herein, a ratiometric fluorescence sensor based on carbon dots (CDs) combined with an all-in-one 3D-printed smartphone-based device was successfully developed for low-cost, visual and rapid detection of GSH without the need for an external excitation light source. The ratiometric fluorescent materials were synthesized by conjugating blue carbon dots (B-CDs) with yellow carbon dots (Y-CDs) through the utilization of selected Cu2+ ions. The resulting mechanism demonstrated that the coordination interaction between Cu2+ and residual aromatic amino groups in Y-CDs (Y-CDs-Cu2+) contributed to a newly emitted peak at 580 nm, thereby inducing fluorescence resonance energy transfer from B-CDs to Y-CDs-Cu2+. A linear correlation was found between GSH concentrations and R/B values in the range of 10-100 µM, with a limit of detection observed at 4.8 µM. By utilizing this portable device in combination with RGB analysis, the quantitative detection of GSH can be achieved even in complex food matrices such as tomatoes and grapes. The universality of this all-in-one device was further validated by pre-spraying CDs onto a paper strip for visual measurement of GSH. This work offers a portable, visual, and accessible approach to evaluating food safety and nutrition, thereby demonstrating significant economic value and holding profound implications for human health.

Synthesis and application of optically stable red fluorescent carbon dots for sensitive and selective detection of ceftazidime.

This study reports the successful synthesis of optically stable red-emitting carbon dots (R-CDs) through a solvothermal method, using glycine as the carbon source and o-phenylenediamine as the nitrogen-doping agent. The R-CDs exhibit long-wavelength emission characteristics with optimal excitation and emission wavelengths of 533 nm and 600 nm, respectively, and a quantum yield of 26.7 %. The results demonstrate that R-CDs possess excellent salt resistance and photostability. The R-CDs display bright fluorescence emission and show a sensitive response to ceftazidime (CF). Leveraging these properties, a fluorescent probe based on R-CDs was developed for the sensitive determination of CF. The fluorescence quenching intensity of this system exhibits a good linear relationship with CF concentration in the range of 0-0.7 mmol/L. The linear equation is (F0-F)/F0=0.9564CCF(mmol/L)+0.0089, with a linear correlation coefficient (R2) of 0.9945. The detection limit is 4.9 µmol/L, with recovery rates ranging from 94.2 % to 100.5 % and relative standard deviations between 2.2 % and 3.2 %. This work provides a theoretical basis for the detection of CF using red-emitting carbon dots and demonstrates promising potential for practical applications.

Poria cocos-derived carbon dots for parallel detection of Cr6+/Fe3+ in complex environments with superior sensitivity.

Multifunctional sensor capable of parallel sensing is of great importance thanks to their wide applications and great practicality. In this report, Poria cocos-derived carbon dots (CDs) were adopted for the development of multifunctional sensor for the parallel detection of Cr6+ and Fe3+ with superior sensitivity and applicability. Specifically, extremely low limit of detection (LOD) of 1.07 × 10-3 nM and 1.98 × 10-3 nM were achieved for Cr6+ and Fe3+, respectively. Systematic mechanism explorations revealed that the highly sensitive detection of Cr6+ was attributed to an efficient inner filter effect (IFE), while the sensing of Fe3+ was realized due to a strong static quenching process. Furthermore, the assay was found to be extremely versatile, achieving the reliable detection of Cr6+ and Fe3+ in multiple natural water environments and even biological environment. Utilizing the different reactions of Cr6+ and Fe3+ towards masking reagents, a logic gate that could effectively eliminate the mutual interference of Cr6+ and Fe3+ was successfully designed.

Carbon quantum dots in breast cancer modulate cellular migration via cytoskeletal and nuclear structure.

Carbon nanomaterials have been widely applied for cutting edge therapeutic applications as they offer tunable physio-chemical properties with economic scale-up options. Nuclear delivery of cancer drugs has been of prime focus since it controls important cellular signaling functions leading to greater anti-cancer drug efficacies. Better cellular drug uptake per unit drug injection drastically reduces severe side-effects of cancer therapies. Similarly, carbon dots (CDs) uptaken by the nucleus can also be used to set-up cutting edge nano delivery systems. In an earlier paper, we showed the cellular uptake and plasma membrane impact of combustion generated yellow luminescing CDs produced by our group from fuel rich combustion reactors in a one-step tunable production. In this paper, we aim to specifically study the nucleus by establishing the uptake kinetics of these combustion-generated yellow luminescing CDs. At sub-lethal doses, after crossing the plasma membrane, they impact the actin and microtubule mesh, affecting cell adhesion and migration; enter nucleus by diffusion processes; modify the overall appearance of the nucleus in terms of morphology; and alter chromatin condensation. We thus establish how this one-step produced, cost and bulk production friendly carbon dots from fuel rich combustion flames can be innovatively repurposed as potential nano delivery agents in cancer cells.

Novel sulphur-selective method for simultaneous determination of thiram and asomate based on carbon dots and its application in fruits.

Thiram (THI) and asomate (ASO) are frequently detected agrochemicals in food samples due to widespread use as fungicides. However, their detection suffers from matrix interference, or the necessity of derivatization before measurement. Integrating HPLC with a post-column carbon dots (CDs)-enhanced chemiluminescence (CL) system makes it possible to simultaneously separate and selectively detect ASO and THI in fruit samples free of derivatization and deep purification. The studies on mechanisms demonstrated that CD intermediates of anionic radical were responsible for the remarkable CL enhancement of ASO or THI. The CL intensity is directly proportional to the fungicide concentration, with the ranges of linearity for ASO and THI being 5-250 µg·L-1 (R 2  = 0.9993) and 4-200 µg·L-1 (R 2  = 0.9986), respectively, and the corresponding limits of detection (S/N = 3) being 1.61 and 1.33 µg·L-1, respectively. The developed method enables the exploration of the novelly sulphur-targeted CL application based on carbon nanomaterials.

Blazing Carbon Dots: Unfolding its Luminescence Mechanism to Photoinduced Biomedical Applications.

Carbon dots (CDs) are carbon-based nanomaterials that have garnered immense interest due to their exceptional photophysical and optoelectronic properties. They have been employed extensively for biomedical imaging and phototherapy due to their superb water dispersibility, low toxicity, outstanding biocompatibility, and exceptional tissue permeability. This review summarizes the luminescence mechanism of CDs. The modification in CDs via various doping routes is comprehensively reviewed, and the effect of such alterations on their photophysical properties, such as photoluminescence (PL), absorbance, and reactive oxygen species generation ability, is also highlighted. This review also aims to summarize the role of CDs in cellular imaging and fluorescence lifetime imaging for cellular metabolism. Subsequently, recent advancements and the future prospects of CDs as nanotheranostic agents have been discussed. Herein, we have discussed the role of CDs in photothermal, photodynamic, and synergistic therapy of anticancer, antiviral, and antibacterial applications. The overall summary of the review highlights the future prospects of CD-based research in bioimaging and biomedicine.

DES-driven sustainable dual valorization of lignocellulose into carbon dots and porous biochar for effective wastewater remediation.

Deep eutectic solvents (DES) are renowned for their effectiveness in deconstructing lignocellulose and extracting lignin, yet the challenges lie in lignin condensation and the disposal of the DES remnants after pretreatment. To overcome these issues, this work proposed a holistic strategy utilizing deep eutectic solvent (DES)-driven lignocellulose deconstruction to upgrade lignocellulose into nitrogen-doped carbon dots (CDs) and iron-decorated porous carbons, serving as photocatalysts and adsorbents, respectively. These nitrogen-doped CDs via the choline chloride/FeCl3 DES pretreatment exhibited abundant nitrogen/oxygen functional groups, enhancing photocatalytic activities and facilitating effective charge separation and transfer. The photocatalytic efficiency of the CDs on dyes reached 97 % under acidic conditions primarily, and free radical quenching experiments indicated that singlet oxygen was the dominant oxidant species. Moreover, the adsorption capabilities of Fe-decorated porous carbons for Congo red reached 2432.3 mg·g-1, surpassing most existing carbon materials. The adsorption mechanism was due to a synergistic effect including physical adsorption, coordination, hydrogen bonding, electrostatic, and π-π interactions. This study proposed a synergetic conversion of DES and lignocellulose into functional carbon materials for wastewater remediation, which inspired the development of a green and cost-effective biorefinery.

A pH visual sensing platform based on dual-emission chiral carbon dots for discrimination of normal/cancer cells and monitoring food freshness.

Accurate detection of pH is important in pathological processes and food freshness. Developing sensors of sensitive response and visualization for pH is highly demanded. In this work, Chiral carbon dots (CCDs) was synthesized via one-pot hydrothermal process using o-phenylenediamine and L-Tryptophan, which displayed circular dichroism (CD) signals at 200-255 nm and 255-300 nm. The CCDs exhibited dual-emission peaks with blue and red emission bands when excited at 360 nm. The ratiometric signals of UV-vis absorption and fluorescence intensity of L-CDs were responsive over the pH range of 2.0-11.0 with significant color changes in solution. Fluorescence imaging of live cells displayed different signals related to pH in both the blue and red channels, allowing accurate measurement of the pH of the cellular environment. Furthermore, the pH test paper based on L-CDs enabled monitoring the freshness of shrimp and pork under 365 nm UV light. Therefore, L-CDs provided a multifunctional visual pH sensing platform for environmental monitoring and biosensing.