Optimized LC-MS/MS methods for quantifying antibody-drug conjugate payloads in cell culture media containing phenol red.

Aim: Phenol red is commonly used in cell culture media, but can be detrimental to bioanalysis of in vitro samples as it may impact instrument reliability. Many researchers do their final stage of culture in 'phenol red free' media, but in collaborative work this is not always feasible.Materials & methods: A comparison was made between typical extraction methods to reduce phenol red matrix interferences, including organic solvent precipitation and solid phase extraction.Results: The final method was demonstrated to be precise and accurate for the measurement of a target analyte by LC-MS/MS, and was applied to an in vitro ADC deconjugation study.Conclusion: This method allows for for continued bioanalytical support of in vitro models used in drug development.

[Box: see text].

Multifunctional Janus Membrane for Diabetic Wound Healing and Intelligent Monitoring.

The complex microenvironment of diabetic wounds often hinders the healing process, ultimately leading to the formation of diabetic foot ulcers and even death. Dual monitoring and treatment of wounds can significantly reduce the incidence of such cases. Herein, a multifunctional Janus membrane (3D chitosan sponge-ZE/polycaprolactone nanofibers-ZP) was developed by incorporating the zinc metal-organic framework, europium metal-organic framework, and phenol red into nanofibers for diabetic wound monitoring and treatment. The directional water transport capacity of the resulting Janus membrane allows for unidirectional and irreversible drainage of wound exudate, and the multifunctional Janus membrane creates up to a 99% antibacterial environment, both of which can treat wounds. Moreover, the pH (5-8) and H2O2 (0.00-0.80 µM) levels of the wound can be monitored using the color-changing property of phenol red and the fluorescence characteristic of Eu-MOF on the obtained membrane, respectively. The healing stages of the wound can also be monitored by analyzing the RGB values of the targeted membrane images. This design can more accurately reflect the wound state and treat the wound to reduce bacterial infection and accelerate wound healing, which has been demonstrated in in vivo experiments. The results provide an important basis for early intervention in diabetic patients.

Simultaneous Plate-Reader Characterization of Promoter Activity and Cell Growth in Engineered Mammalian Cells.

Automated high-throughput methods that support tracking of mammalian cell growth are currently needed to advance cell line characterization and identification of desired genetic components required for cell engineering. Here, we describe a high-throughput noninvasive assay based on plate reader measurements. The assay relies on the change in absorbance of the pH indicator phenol red. We show that its basic and acidic absorbance profiles can be converted into a cell growth index consistent with cell count profiles, and that, by adopting a computational pipeline and calibration measurements, it is possible to identify a conversion that enables prediction of cell numbers from plate measurements alone. The assay is suitable for growth characterization of both suspension and adherent cell lines when these are grown under different environmental conditions and treated with chemotherapeutic drugs. The method also supports characterization of stably engineered cell lines and identification of desired promoters based on fluorescence output.

The phenol red compound: A potential artifact in pharmacological induction of ferroptosis.

Phenol red (PR) is a commonly used compound in culture media as a pH indicator. However, it is unknown whether this compound can interfere with the pharmacological induction of ferroptosis. Here, using high-content live-cell imaging death analysis, we determined that the presence of PR in the culture medium preconditioned normal and tumor cells to ferroptosis induced by system xc- inhibition mediated by imidazole ketone erastin (IKE) or GPX4 blockade in response to RSL-3, but had no significant effects against treatment with the endoperoxide FINO2. Mechanistically, we revealed that PR decreases the levels of the antiferroptotic genes Slc7a11, Slc3a2, and Gpx4, while promoting the overexpression de Acls4, a key inducer of ferroptosis. Additionally, through superresolution analysis, we determined that the presence of PR mislocalizes the system xc- from the plasma membrane. Thus, our results show that the presence of PR in the culture medium can be a problematic artifact for the accurate interpretation of cell sensitivity to IKE or RSL-3-mediated ferroptosis induction.

Rapid detection of FadA in Fusobacterium nucleatum using the quantitative LAMP colorimetric phenol red method in stool samples from colorectal cancer patients.

The study aimed to develop a quantitative colorimetric loop-mediated isothermal amplification technique using the phenol red indicator (QLAMP-PhR) for detecting Fusobacterium nucleatum (Fn) levels in colorectal cancer (CRC) patients and healthy individuals. QLAMP-PhR assays were conducted on 251 stool samples specific for the Fn FadA gene. Six primers were synthesized and utilized with master mix reagents, and a phenol red indicator was employed to enhance the QLAMP-PhR technique. A standard quantitative analysis curve was generated using a logarithmic function (absorbance vs. concentration) by serially diluting the copy number of genomic DNA templates (Fn ATCC25586). The CRC group exhibited a significantly higher abundance of Fn compared to the healthy control group (P < 0.001). These findings suggest that the QLAMP-PhR technique effectively identifies Fn specifically by its gene for the key virulence factor FadA. Additionally, ideas for developing a real-time QLAMP-PhR test were presented. Compared to the traditional polymerase chain reaction (PCR) technique, QLAMP-PhR offers several advantages including rapidity, simplicity, specificity, sensitivity, and cost-effectiveness method that can quantitatively screen for Fn presence in normal populations. The QLAMP-PhR method represents a sensitive and specific amplification assay for the rapid detection of the Fn pathogen. To the best of our knowledge, this study is the first to report the application of QLAMP-PhR for detecting FadA in Fn.

Development of a RP-HPLC method for simultaneous determination of atenolol, metoprolol tartrate and phenol red for in-situ rat intestinal perfusion studies.

Single-pass intestinal perfusion (SPIP) method is a widely used experimental model to determine the intestinal permeability of drugs. These studies are performed in the presence of a reference standard (metoprolol, MT) and a zero permeability marker (phenol red, PR). Therefore, it is important to develop a validated method for simultaneous determination of the investigated compound along with MT and PR. The aim of this study was to develop a reversed phase high-performance liquid chromatography (RP-HPLC) method with UV-detection for the simultaneous determination of atenolol (ATN), MT, and PR in the perfusion medium used in SPIP experiments. Separation of compounds were performed using an InertSustain C18 (250 × 4.6 mm, 5 µm) HPLC column at 35 °C. The mobile phase was a mixture of acetonitrile and phosphate buffer (pH 7.0, 12.5 mM) in gradient elution, and was delivered at a flow rate of 1 mL/min. The acetonitrile ratio of the mobile phase increased linearly from 10 to 35 % over 15 min. The injection volume was 20 µL, and ATN, MT and PR were detected at 224 nm. The retention times under optimum HPLC conditions were 5.028 min, 12.401 min, and 13.507 min for ATN, MT and PR, respectively. The developed RP-HPLC method was validated for selectivity, specificity, calibration curve and range, accuracy and precision, carry-over effect, stability, reinjection reproducibility, recovery and robustness. The method was linear for ATN (0.76-50 µg/mL), MT (1.14-50 µg/mL), and PR (0.47-20 µg/mL) with determination coefficients of 0.9999, 0.9994 and 0.9998, respectively. The results obtained for all validation parameters of the developed RP-HPLC method met the required limits of the ICH M10 Guideline.

Plasma catalysis. A study of the influence of oxysulfur, SOx• species through the degradation of sulfonated dyes by non-thermal plasma.

This work studied the degradation reaction of sulfonated dyes, indigo carmine, phenol red, and their mixtures by non-thermal plasma (NTP). Interestingly, the degradation rate constant showed a faster process and lower activation energy (Ea) for the dye mixtures than for the degradation reaction of the individual dyes. This unexpected result opened up new opportunities for understanding plasma chemistry and the interaction between reactive species formed by the plasma and the target molecule. As no catalyst or chemical additive was added to the reactor, the decrease in Ea came from a self-synergistic effect (SSE), through the dye molecules fragmentation, which resulted in plasma catalysis. The hypothesis proposed in this work is that oxysulfur (SOx) species are formed by the desulfonation reaction of dyes. The sulfonic groups (SO3) present in the chemical structures of dyes can function as precursors for forming several SOx•- species. Studies based on oxygenated sulfonated species such as SO3•-, SO4•- and SO5•- have been widely applied in advanced oxidative and reductive processes due to their satisfactory efficiency and low cost. Among them, SO4•- is the key reactive species with the best performance in the degradation of pollutants due to its high oxidation potential (E° = 2.60 V). In addition, it is an alternative source of HO• in aqueous media, improving the oxidation reaction. In order to elucidate the SSE, the kinetic process was followed by UV-Vis analysis, and the reactive species, such as alkyl, hydroxyl, and oxy-sulfur radicals were identified by Electron Paramagnetic Resonance. The by-products of the NTP degradation reaction were analyzed by ultrafast liquid chromatography coupled with a mass spectrometer, and a fragmentation route was proposed.

A smartphone-assisted sensing hydrogels based on UCNPs@SiO2-phenol red nanoprobes for detecting the pH of aquatic products.

For some aquatic products, pH has been considered a useful index to reflect the changes in materials during the loss of freshness. Based on the inner filter effect (IFE) between deprotonated phenol red (PR) and upconversion nanoparticles (UCNPs), UCNPs coated with PR-doped SiO2 shell were embedded in agarose hydrogel to develop a smartphone-assisted method for pH sensing. With the enhancement of pH response using a phase transfer agent (i.e., tetra butyl ammonium hydroxide, TBAH), the proposed senor realized the colorimetric and fluorescence detection of pH in the range of pH 6.6-8 and pH 6-8, respectively. The sensor also showed satisfied reversibility when switched between pH 6 and 8 for at least 5 cycles. Moreover, this sensor displayed great sensitivity, stability, and portability in analyzing actual fish, shrimp, and shellfish samples, providing a new sight for evaluating the freshness of aquatic products.

Development of a pH-responsive intelligent label using low molecular weight chitosan grafted with phenol red for food packaging applications.

In this study, we successfully developed a screen-printed pH-responsive intelligent label using low molecular weight chitosan grafted with phenol red (LCPR) as a colorant for screen printing ink. The LCPR was synthesized via a Mannich reaction, and its successful grafting was confirmed through FT-IR, UV-vis, and NMR spectroscopy. The LCPR exhibited lower crystallinity and thermal stability compared to low molecular weight chitosan (LC) and demonstrated zwitterionic behavior. To create intelligent labels, the LCPR-based ink was efficiently printed on cotton substrates with high resolution. The label exhibited remarkable sensitivity to buffer pH solutions and ammonia gas, leading to distinctive color changes from orange to red to purple. Additionally, the label showed excellent reversibility, storage stability, and leaching resistance to different food simulant solutions. The label was utilized to monitor shrimp freshness, successfully detecting a noticeable color shift upon spoilage. These findings highlight the significant potential of the LCPR-based label as an intelligent food packaging solution, offering pH-responsiveness and color stability for qualitative freshness detection of protein-rich food.

Tannic acid and carboxymethyl chitosan-based multi-functional double-layered hydrogel with pH-stimulated response behavior for smart real-time infection monitoring and wound treatment.

The dramatic increase of drug-resistant pathogenic bacteria has seriously effect on human health, appealing the needs of developing theranostic platforms with stimuli-responsive materials to realize the accurate bacterial diagnostics and therapeutics. Herein, a tannic acid and carboxymethyl chitosan-based multifunctional ZIF-90@i-PPOPs-phenol red double-layered hydrogel with stimuli-responsiveness and antibacterial activity was fabricated. The inner layer hydrogel (ZIF-90@i-PPOPs-based TFC hydrogels) was fabricated based on ZIF-90@i-PPOPs, integrate tannic acid and carboxymethyl chitosan linked by formylphenylboronic acid (FPBA), which exhibited outstanding injectable, biodegradability and antibacterial activity. The outer layer hydrogel (PR@PAM hydrogels) were constructed from polyacrylamide (PAM) and pH indicator phenol red, owning porous structure and excellent tissue adhesion. Due to the weakly acidic microenvironment within wound, the inner-layer hydrogel was stimulus-responsively decomposed, resulting in the accurate delivery of the positively charged ZIF-90@i-PPOPs to the lesion site to capture and kill bacteria by enhanced Zn2+ and ROS release. Meantime, the outer-layer hydrogel could real-timely monitor the pH changes to evaluate the wound recovery status. These double-layered hydrogels possessed precisely pH monitoring capacity, excellent antibacterial ability and negligible side effect to normal tissue in vivo, implying the high potential of the suggested hydrogels as theranostic platform for antibacterial treatment.

Validation of the phenol red thread test in a Chinese population.

BACKGROUND: To investigate the validation of phenol red thread (PRT) test in a Chinese population by evaluating the intraobserver repeatability and interobserver reproducibility, determining correlations between the PRT test and other dry eye disease (DED) parameters including tear meniscus height (TMH) and Schirmer I test, and testing the accuracy of diagnosing DED when using the PRT test alone. METHODS: A total of 108 eyes were involved in this prospective and diagnostic study, and were divided into two groups (with and without DED). Each subject underwent a series of ocular surface examinations, including Ocular Surface Disease Index (OSDI) questionnaire, non-invasive tear breakup time (NIBUT), tear meniscus height (TMH) assessment, PRT test, fluorescein tear breakup time (FBUT), corneal fluorescein staining and Schirmer I test. RESULTS: In the experimental group and the control group, the intra-class correlation coefficients (ICCs) of the repeatability were 0.747 and 0.723, respectively (all P < 0.05). The ICCs of the reproducibility in both groups were 0.588 and 0.610, respectively (all P < 0.05). The PRT test correlated weakly with the Schirmer I test and the tear meniscus height, with Spearman coefficients of 0.385 and 0.306, respectively (all P < 0.05). The PRT test is available to diagnose DED, with an area under the curve of 0.806 and a Youden index of 0.556 at the cutoff point of 8.83 mm. CONCLUSIONS: The PRT test can provide patients a comfortable, timesaving and less irritating approach to screening and diagnosing DED compared to Schirmer I test.

Direct cord blood LAMP colorimetric phenol red assay for detecting α0-thalassemia (SEA deletion); the validation and post-natal screening in Thailand.

Post-natal or newborn screening for thalassemia and hemoglobinopathies is useful for genetic counseling and managing thalassemia in children. We characterized thalassemia genotypes in newborns from the eastern part of Thailand. The results demonstrated a high heterogeneity of thalassemia and hemoglobinopathies with seventeen genotypes. We focused on α0- thalassemia (Southeast Asian [SEA] deletion) in this study. We developed and validated the loop-mediated isothermal amplification (LAMP) colorimetric assay for detecting α0- thalassemia (SEA deletion) using simple direct cord blood sampling compared to genomic DNA. A total of 160 cord blood samples were evaluated with the LAMP assay. The sensitivity and specificity of the LAMP colorimetric assay for α0-thalassemia (SEA deletion) using direct cord blood showed 100% (6/6 x 100) and 98.05% (151/154 x 100) whereas, genomic DNA showed 100% (6/6 x 100) and 100% (154/154 x 100), respectively. Moreover, we demonstrated other simple screening tools for α0-thalassemia with %Hb Bart's, MCV, and MCH values and found that these parameters were not diagnostic in our samples. The direct cord blood with colorimetric LAMP assay is simple, rapid, and does not require a post-LAMP step compared to conventional PCR. These techniques could be applied in post-natal or large population screening for α0-thalassemia (SEA deletion). Finally, this could support early prevention of complications, early management, genetic counseling for α-thalassemia disease in children, or a long-term prevention and control program of severe thalassemia in Thailand.

The Breastfeeding Effect On The Tear Film Of Women: An Observational Study.

OBJECTIVE: To assess the tear film parameters in breastfeeding women. satisfaction. Methods: The observational study was conducted at the College of Applied Medical Sciences, Riyadh, Saudi Arabia, from December 15, 2021, to February 12, 2022, and comprised healthy women aged 18-40 years who had no ocular diseases. Breastfeeding women were in group A and non-breastfeeding women formed the control group B. Ocular surface disease index, phenol red thread, and tear ferning tests were used in that order to assess the tear film for all the subjects. A gap of 5 minutes was allowed between phenol red thread and tear ferning tests. Data was analysed using SPSS, version 22. RESULTS: Of the 50 subjects, 25(50%) were in group A with mean age 30.4±5.9 years having a mean breastfeeding period of 5.4±5.0 months. The remaining 25(50%) women were in group B with mean age 28.5±2.1 years. Significant differences were found between the groups for ocular surface disease index, phenol red thread, and tear ferning (p<0.05). Significant moderate correlation was found between tear ferning grades and breastfeeding duration (p<0.05). Conclusion: Breastfeeding was found to increase dry eye symptoms in women.

Immobilization of commercial horseradish peroxidase in calcium alginate-starch hybrid support and its application in the biodegradation of phenol red dye.

In this study, horseradish peroxidase (HRP) was immobilized for the first time on Ca alginate-starch hybrid beads and employed for the biodegradation of phenol red dye. The optimal protein loading was 50 mg/g of support. Immobilized HRP demonstrated improved thermal stability and maximum catalytic activity at 50 °C and pH 6.0, with an increase in half-life (t1/2) and enzymatic deactivation energy (Ed) compared to free HRP. After 30 days of storage at 4 °C, immobilized HRP retained 109% of its initial activity. Compared to free HRP, the immobilized enzyme exhibited higher potential for phenol red dye degradation, as evidenced by the removal of 55.87% of initial phenol red after 90 min, which was 11.5 times greater than free HRP. In sequential batch reactions, the immobilized HRP demonstrated good potential efficiency for the biodegradation of phenol red dye. The immobilized HRP was used for a total of 15 cycles, degrading 18.99% after 10 cycles and 11.69% after 15 cycles, with a residual enzymatic activity of 19.40% and 12.34%, respectively. Overall, the results suggest that HRP immobilized on Ca alginate-starch hybrid supports shows promise as a biocatalyst for industrial and biotechnological applications, particularly for the biodegradation of recalcitrant compounds such as phenol red dye.

A New Culture Model for Enhancing Estrogen Responsiveness in HR+ Breast Cancer Cells through Medium Replacement: Presumed Involvement of Autocrine Factors in Estrogen Resistance.

Hormone receptor-positive breast cancer (HR+ BC) cells depend on estrogen and its receptor, ER. Due to this dependence, endocrine therapy (ET) such as aromatase inhibitor (AI) treatment is now possible. However, ET resistance (ET-R) occurs frequently and is a priority in HR+ BC research. The effects of estrogen have typically been determined under a special culture condition, i.e., phenol red-free media supplemented with dextran-coated charcoal-stripped fetal bovine serum (CS-FBS). However, CS-FBS has some limitations, such as not being fully defined or ordinary. Therefore, we attempted to find new experimental conditions and related mechanisms to improve cellular estrogen responsiveness based on the standard culture medium supplemented with normal FBS and phenol red. The hypothesis of pleiotropic estrogen effects led to the discovery that T47D cells respond well to estrogen under low cell density and medium replacement. These conditions made ET less effective there. The fact that several BC cell culture supernatants reversed these findings implies that housekeeping autocrine factors regulate estrogen and ET responsiveness. Results reproduced in T47D subclone and MCF-7 cells highlight that these phenomena are general among HR+ BC cells. Our findings offer not only new insights into ET-R but also a new experimental model for future ET-R studies.

Enterotoxigenic profiles and submerged and interface biofilms in Bacillus cereus group isolates from foods.

Biofilm formation by Bacillus cereus strains is now recognized as a systematic contamination mechanism in foods; the aim of this study was to evaluate the production of submerged and interface biofilms in strains of B. cereus group in different materials, the effect of dextrose, motility, the presence of genes related to biofilms and the enterotoxigenic profile of the strains. We determine biofilm production by safranin assay, motility on semi-solid medium, toxin gene profiling and genes related to biofilm production by PCR in B. cereus group isolated from food. In this study, we observe strains used a higher production of biofilms in PVC; in the BHI broth, no submerged biofilms were found compared to phenol red broth and phenol red broth supplemented with dextrose; no strains with the ces gene were found, the enterotoxin profile was the most common the profile that includes genes for the three enterotoxins. We observed a different distribution of tasA and sipW with the origin of isolation of the strain, being more frequent in the strains isolated from eggshell. The production and type of biofilms are differential according to the type of material and culture medium used.

New insights on the adsorption of phenol red dyes from synthetic wastewater using activated carbon/Fe2(MoO4)3.

Water shortage is considered as one of the main challenges of human life. A practical solution to this problem is the wastewater treatment. The removal of dyes from wastewaters has received considerable critical attention by researchers due to their high volume and toxicity. In the current research, the adsorption of phenol red dyes from synthetic wastewater using the activated carbon produced from Mespilus germanica modified with Fe2(MoO4)3 was studied. The proposed adsorbent was characterized by Fourier transform infrared (FTIR), X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive X-ray analysis (EDX)/Map, Brunauer-Emmett-Teller (BET), and Raman techniques. The optimal adsorption operating parameters including pH, stirring rate, temperature, dosage of adsorbent, dye initial concentration, and contact time were 3, 500 rpm, 25 °C, 1 g/L, 10 mg/L, and 60 min, respectively. Furthermore, the successful regeneration of the adsorbent for 3 times, using methanol solution as a regeneration medium, denoted its capability in performing adsorption and desorption processes. Equilibrium studies showed that the adsorption of phenol red dyes by activated carbon (AC)/Fe2(MoO4)3 was desirable and physical and the experimental data were fitted well by the Freundlich model. In addition, the kinetic behavior of the current adsorption process was well described by the pseudo-second-order kinetic model, while thermodynamic calculations showed that the process was exothermic and spontaneous.

N-Doped Carbon/CeO2 Composite as a Biomimetic Catalyst for Antibacterial Application.

Exploring new and high efficiency mimic enzymes is a vital and novel strategy for antibacterial application. Haloperoxidase-like enzymes have attracted wide attention thanks to their amazing catalytic property for hypohalous acid generation from hydrogen peroxide and halides. However, few materials have displayed halogenating catalytic performance until now. Herein, we synthesized N-doped C/CeO2 (N-C/CeO2) composite materials by a combination of the liquid and solid-state method. N-C/CeO2 can possess haloperoxidase-like catalytic activity by catalyzing the bromination of organic signaling compounds (phenol red) with H2O2 at a wide range of temperatures (20 °C to 55 °C), with a solution color changing from yellow to blue. Meanwhile, it exhibits high catalytic stability/recyclability in the catalytic reaction. The synthesized N-C/CeO2 composite can effectively catalyze the oxidation of Br- with H2O2 to produce HBrO without the presence of phenol red. The produced HBrO can resist typical marine bacteria like Pseudomonas aeruginosa. This study provides an efficient biomimetic haloperoxidase and a novel sustainable method for antibacterial application.

Siraitia grosvenorii Extract Attenuates Airway Inflammation in a Murine Model of Chronic Obstructive Pulmonary Disease Induced by Cigarette Smoke and Lipopolysaccharide.

We studied the activities of Siraitia grosvenorii extracts (SGE) on airway inflammation in a mouse model of chronic obstructive pulmonary disease (COPD) stimulated by cigarette smoke extract (CSE) and lipopolysaccharide (LPS), as well as in LPS-treated human bronchial epithelial cell line (BEAS-2B). SGE improved the viability of LPS-incubated BEAS-2B cells and inhibited the expression and production of inflammatory cytokines. SGE also attenuated the mitogen-activated protein kinase (MAPK)-nuclear factor-kappa B (NF-κB) signaling activated by LPS stimulation in BEAS-2B cells. In mice stimulated by CSE and LPS, we observed the infiltration of immune cells into the airway after COPD induction. SGE reduced the number of activated T cells, B cells, and neutrophils in bronchoalveolar fluid (BALF), lung tissue, mesenteric lymph node, and peripheral blood mononuclear cells, as well as inhibited infiltration into organs and mucus production. The secretion of cytokines in BALF and the expression level of pro-inflammatory cytokines, mucin 5AC, Transient receptor potential vanilloid 1, and Transient receptor potential ankyrin 1 in lung tissue were alleviated by SGE. In addition, to investigate the activity of SGE on expectoration, we evaluated phenol red secretions in the trachea of mice. SGE administration showed the effect of improving expectoration through an increase in phenol red secretion. Consequently, SGE attenuates the airway inflammatory response in CSE/LPS-stimulated COPD. These findings indicate that SGE may be a potential herbal candidate for the therapy of COPD.

Coordination polymer nanoprobe integrated carbon dot and phenol red for turn-on fluorescence detection of urease activity.

The potential of coordination polymers (CPs) as a host of integrating multiple guest species to construct a fluorescence resonance energy transfer (FRET) nanoprobe was demonstrated. The ZnCPs built from zinc(II) and adenine was employed as a model of CPs to integrate carbon dot (CD) and phenol red (PR) for producing the FRET nanoprobe (CD/PR@ZnCPs). Benefiting from the confinement effect of ZnCPs, the integrated CD and PR can be brought in close proximity to favor the occurrence of FRET process from CD to PR, which leads to the quenching of CD fluorescence. However, the FRET process was disrupted upon the red-shift of PR absorption from 428 to 562 nm in alkaline medium, and consequently switches on the fluorescence of CD/PR@ZnCPs. Based on this finding, by utilizing urease to hydrolyze urea and mediate medium pH, a turn-on fluorescent method was established for the detection of urease activity. This fluorescent method has a linear response that covers 5 to 150 U/L urease with a detection limit of 0.74 U/L and exhibits an excellent selectivity over other enzymes. The successful determination of urease in saliva samples demonstrates the applicability of the fluorescent nanoprobe in complex biological matrix.