Ratiometric Method Research Articles

An optical probe based on lanthanide light-emitting nanomaterials for detecting phosphate by ratiometric fluorescence method

Inorganic phosphate (Pi) not only sustains the physiological functions within organisms but also acts as an indicator of environmental water pollution. Thus, it is extremely significant to seek out a rapid and straightforward method for detecting Pi. In this paper, the lanthanide metal luminescent nanomaterial europium-pyromellitic acid (Eu-PMA, exhibiting characteristic fluorescence emission at 435 nm for PMA and 617 nm for Eu3+) is synthesized via a simple solvothermal approach and utilized as a probe for ratiometric fluorescence detection of Pi. As the amount of Pi increases, Pi has a strong complexation ability with ligand PMA, resulting in the structural damage of Eu-PMA. PMA cannot sensitize Eu3+ luminescence, thus the fluorescence intensity at 617 nm of the system is markedly decreased. Meanwhile, through energy transfer interaction, the fluorescence intensity at 435 nm of ligand PMA is weakly increased. Based on the ratio of the changes in fluorescence intensities of the two, a ratiometric fluorescence method is established for the detection of Pi. The method is not only rapid and simple, but also improves the sensitivity of Pi detection (Linear range is 0.1–90 mM). Moreover, the content of Pi in actual water samples has been analyzed and determined successfully by this method, which further broads the significance and application prospect of the ratiometric fluorescence method in detecting Pi.

Adsorption and detection of praseodymium ion by ion-imprinted polymer with ultra-low sensitivity.

A novel kind of carbon dot (CD) was prepared by one-step hydrothermal microwave assisted method using L-tryptophan and L-tartaric acid as raw materials. Monodisperse poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate) microspheres were utilized as the matrix, with praseodymium (Pr) ion (Pr3+) as the template, methacrylic acid as the functional monomer, and 5-amino-8-hydroxyquinoline (5-AHQ) acts as the ligand. A composite microsphere of ion-imprinted polymer (IIP) and CD (noted CD@IIP) was prepared by surface-initiated atom transfer radical polymerization (SI-ATRP). For comparison, IIP without CD (Pr-IIP) and non-imprinted polymer (NIP) were also prepared. Through static adsorption experiments, it was determined that the saturated adsorption amount of CD@IIP is 47.19mgg-1, that of Pr-IIP is 54.49mgg-1, while that of NIP is only 24.32mgg-1. Dynamic adsorption experiments showed that the equilibrium of three kinds of materials wasreached within 30min. Particularly, CD@IIP could emit two fluorescence peaks at 325nm and 421nm under ultraviolet irradiation, and exhibited excellent selectivity and fluorescence quenching effect on Pr3+. The fluorescence response of Pr3+ in the range 0-400μmol L-1 was determined by ratiometric fluorescence method, offering a two-stage model and robust linear regression coefficient. These results demonstrated that CD@IIP exhibited selective adsorption ability for Pr3+, and a sensitive, rapid and simple method for detection of Pr3+ was successfully developed.

In vivo targeted-imaging of mitochondrial acidification in an aristolochic acid I-induced nephrotoxicity mouse model by a fluorescent/photoacoustic bimodal probe

Aristolochic acid I (AAI), a natural compound in aristolochia type Chinese medicinal herb, is generally acknowledged to have nephrotoxicity, which may be associated with mitophagy. Mitophagy is a cellular process with important functions that drive AAI-induced renal injury. Mitochondrial pH is currently measured by fluorescent probes in cell culture, but existing probes do not allow for in situ imaging of AAI-induced mitophagy in vivo. We developed a ratiometric fluorescent/PA dual-modal probe with a silicon rhodamine fluorophore and a pH-sensitive hemicyanine dye covalently linked via a short chain to obtain a FRET type probe. The probe was used to measure AAI-mediated mitochondrial acidification in live cells and in vivo. The Förster resonance energy transfer (FRET)-mediated ratiometric and bimodal method can efficiently eliminate signal variability associated with the commonly used one-emission and single detection mode by ratiometric two channels of the donor and acceptor. The probe has good water-solubility and low molecular weight with two positively charged, facilitating its precise targeting into renal mitochondria, where the fluorescent/PA changes in response to mitochondrial acidification, enabling dynamic and semi-quantitative mapping of subtle changes in mitochondrial pH in AAI-induced nephrotoxicity mouse model for the first time. Also, the joint use of L-carnitine could mitigate the mitophagy in AAI-induced nephrotoxicity.

Dual emission BSA-capped bimetallic nanoclusters for detection of acrylamide in certain food matrices based on thiol-ene Michael addition click reaction

Dual-emissive gold and silver nanoclusters stabilized by bovine serum albumin (BSA@Au-Ag NCs) were engineered for the precise and sensitive estimation of acrylamide (ACM). The probe demonstrated emissions at 630 nm and 405 nm upon excitation at 320 nm. Decreasing the fluorescence of the probe at 630 nm was observed upon cysteine (Cys) addition while the emission band at 405 nm experienced a slight increase. The introduction of ACM into the probe led to the recovery of fluorescence at 630 nm, while the fluorescence at 405 nm remained largely unaffected. This selective response provides a ratiometric method for determining ACM. A linear relationship between the response ratio (F630/F405) and ACM concentration was established in the range of 0.12–450 µM, with LOD of 0.03 µM. The fluorescent probe boasts several advantages, including a low LOD, robustness against interference, and reliability. Furthermore, the synthesized probe was deployed for detecting ACM in certain food matrices. The recovery percentages ranged from 96.5 to 102.6 %, with RSD between 2.98 and 4.87 %, thus affirming the potential practical applications of the fluorescent probe.

L-asparaginase-mediated pH shift and carbon dot fluorescence modulation: A sensitive ratiometric method for quantifying L-asparagine in diverse potato varieties under variable storage conditions

This study presents a novel and selective method for the determination of l-asparagine in diverse potato varieties under various storage conditions. L-asparagine levels serve as a crucial indicator for acrylamide formation, a hazardous substance in processed potato products. The fluorometric method utilized blue-emitting CDs (B-CDs), orange-emitting CDs (O-CDs), and the enzyme L-asparaginase for ratiometric detection of L-asparagine. Upon enzymatic hydrolysis of L-asparagine by L-asparaginase, liberated ammonia induced a pH increase in the reaction medium. This pH shift enhanced the fluorescence of B-CDs while simultaneously decreasing that of O-CDs, enabling sensitive and selective L-asparagine quantification. Comprehensive characterization of the CDs was performed using various spectroscopic techniques and transmission electron microscopy. The method demonstrated excellent sensitivity (LOD = 0.31 μM) and a wide linear range (1.0–50.0 μM). When the method was applied to potato samples, high recovery values (98.00–100.33 %) with low relative standard deviations (RSDs) were achieved, confirming the accuracy and precision of the method. The approach was employed to determine L-asparagine levels in three potato varieties (Lady Rosetta, Spunta, and Nicola) under different storage temperatures and durations. This method provides a valuable tool for monitoring L-asparagine content in potatoes, potentially aiding in the mitigation of acrylamide formation during processing. The robust performance and simplicity of the proposed technique make it suitable for routine analysis in both research and industrial applications within the potato industry.

Regulating thermometric properties of single-band ratiometric luminescent thermometers based on Eu3+-activated Y2W3O12·3H2O nanoparticles via controlling doping content and excitation model

Series of Eu3+-activated Y2W3O12·3H2O nanoparticles were designed to realize high-sensitive optical thermometry. The resultant nanoparticles can emit bright visible emission from Eu3+ upon the excitation of 296 nm (charge-transfer state (CTS) of O2- → W6+), 394 nm (ground state absorption (GSA)) and 536 nm (excitation state absorption (ESA)), of which the fluorescence intensities were influenced by dopant content. The negative thermal expansion properties of studied nanoparticles were clarified via temperature-dependent X-ray diffraction patterns. Moreover, the thermal quenching behaviors of final products were also investigated through temperature-related emission spectra. Specifically, upon the CTS and GSA processes, the developed nanoparticles underwent significant thermal quenching effect, whereas the thermally enhanced luminescence was observed under ESA process. Herein, through using the single-band ratiometric (SBR) method to investigate the fluorescence intensity ratio of the red emission from 5D0 → 7F2 transition of Eu3+ at high temperature, the thermometric properties of prepared nanoparticles were studied. It was found that maximum absolute and relative sensitivities of Eu3+-activated Y2W3O12·3H2O nanoparticles reached up to 0.061 and 4.944 % K−1, respectively, and they can be regulated by changing Eu3+ dopant and SBR models (i.e., ESA+CTS and ESA+GSA combinations), realizing high-sensitive optical thermometry. Our findings may provide some guidelines for manipulating the thermometric properties of rare-earth ions activated materials and developing new SBR luminescence thermometers.

A Dual Emission Fluorescence Probe Based on Silicon Nanoparticles and Rhodamine B for Ratiometric Detection of Kaempferol.

In this paper, blue fluorescent silicon nanoparticles (SiNPs) with outstanding optical properties and robust stability were synthesized by a simple one-step hydrothermal method. By introducing red emissive rhodamine B (RhB) into SiNPs solution, a dual emission nanoprobe (SiNPs@RhB) was constructed, which showed excellent pH stability, salt resistance and photobleaching resistance. The SiNPs@RhB probe could emit two peaks at 444nm and 583nm under 365nm excitation. It was found that the fluorescence intensity of the two emission peaks decreased in different degrees with the addition of different concentrations of kaempferol (Kae). According to this phenomenon, a novel ratiometric fluorescence method was established for the detection of Kae via utilizing SiNPs@RhB as nanoprobe. The detection range and limit of detection (LOD) were 0.5 ~ 150 µM and 0.24 µM, respectively. The ratiometric fluorescence method exhibited the superiority of rapid detection, excellent stability, wide linear range and high sensitivity. The detection mechanism was studied by ultraviolet visible absorption spectra, fluorescence spectra and fluorescence lifetime. Furthermore, the method was applied to the detection of Kae in real samples (kaempferia powder, sea buckthorn granules and sea buckthorn dry emulsion).

Quantifying the viability of lactic acid bacteria using ratiometric fluorescence assays

Quantifying the viability of lactic acid bacteria (LAB) has become an important task in evaluating the quality, function and storage condition of LAB products. Propidium iodide (PI), as a DNA-binding dye that penetrates only dead bacteria, has been widely used for LAB viability assessments. However, high fluorescence background from live LAB was frequently occurred during PI-based staining, which led to the low sensitivity in probing minor amounts of dead LAB in a dead/live mixture. Here, we found that PI could be adsorbed nonspecifically in LAB periplasm, which contributed to the high fluorescence background of live LAB. CaCl2 was used to reduce this nonspecific adsorption and increase the fluorescence ratio of dead to live LAB. Combined with SYTO 9 (a membrane permeable dye) for double-staining, a ratiometric fluorescent method that could probe dead LAB at a ratio as low as 0.2 % was established. Using Lacticaseibacillus casei as a LAB model, an allometric correlation between the ratiometric fluorescence and theoretical ratio of live to dead LAB was acquired, with a correlation coefficient R2 of 0.993. The as-developed method was successfully applied to the viability assessment of LAB stored in different environments. We believe it would have practical applications in LAB food industry for quality management and control.

Construction of an upconversion luminescence composite nanoprobe for ratiometric single particle imaging detection of hydrogen peroxide in food

Hydrogen peroxide (H2O2) is associated with diseases and food safety. Thus, it is essential to achieve sensitive and efficient detection of H2O2. Herein, a ratiometric luminescence composite nanoprobe was designed for single particle imaging sensing of H2O2 by combining NaYbF4:Er@NaYbF4:Tm@NaGdF4:Yb upconversion nanoparticles (UCNPs) with cyanine dye IR-628. High brightness NaYbF4:Er@NaYbF4:Tm@NaGdF4:Yb UCNPs with double-peak emission (665 and 812 nm) were synthesised. Cyanine dye IR-628 with an absorption peak at 628 nm was synthesised and served as a recognition unit. More importantly, on the basis of the upconversion luminescence total internal reflection imaging technique, we developed a ratiometric single particle imaging quantitative analysis for sensing H2O2 with a limit of quantitation of 5 nM. This ratiometric single particle imaging method not only greatly eliminates the influence of the probe concentration and instrumental and environmental factors, but also reduces the dosage of the reagent used and improves the sensitivity of detection.

A ratiometric fluorescence immunoassay based on Ce4+ oxidized o-phthalylenediamine and polyvinylpyrrolidone protected copper nanoclusters for the detection of aflatoxin B1

As the most toxic mycotoxin, aflatoxin B1 (AFB1) can cause a variety of health problems in humans and animals. Therefore, it is very important and urgent to establish a sensitive and convenient method for the detection of AFB1. In this study, a ratiometric fluorescence method is established to detect AFB1 based on Ce4+ oxidized o-phthalylenediamine (OPD) and polyvinylpyrrolidone protected copper nanoclusters (PVP-CuNCs). The free Ce4+ with strong oxidative activity can oxidize OPD to 2,3-diaminophenazine (DAP) and emit intense fluorescence. Meanwhile, the fluorescence of PVP-CuNCs can be quenched by DAP. In the catalysis of alkaline phosphatase (ALP), adenosine triphosphate (ATP) is hydrolyzed and releases phosphate ions (PO43-). PO43- has a strong affinity for Ce4+ which reduces the free Ce4+ in solution. Thus, the OPD cannot be oxidized to DAP, and the fluorescence of PVP-CuNCs at 430 nm cannot be quenched. The limit of detection (LOD) of the new immunoassay is 26.79 pg/mL, and the linear detection range is 50–250 pg/mL. Besides, the recovery of AFB1 ranges from 84.66 % to 105.21 % and coefficient of variation (CV) is in the range of 1.18 %–4.88 %. Meanwhile, the new immunoassay exhibits satisfactory selectivity. These results indicate the ratiometric fluorescence immunoassay is sensitive and reliable for detection of AFB1 in actual samples.

In situ synthesis of luminescent dsDNA-Cu NCs stained with a dsDNA-lighted fluorophore for rapid and stable detection of histamine in food

Poisonous histamine is accumulated in stale meat and fermented foods. The rapid and stable detection of histamine is essential for food safety. Herein, a ratiometric fluorometric method for histamine detection was designed through in situ preparing double-stranded DNA‑copper nanoclusters (dsDNA-Cu NCs) stained with 4′,6-diamidino-2-phenylindole (DAPI). dsDNA-Cu NCs with red emission were rapidly synthesized via mixing Cu2+, ascorbate and dsDNA at room temperature for 5 min. When DAPI was added during preparation, DAPI coordinated with the Cu element accompanied by the quenched red emission of dsDNA-Cu NCs, and DAPI bound to dsDNA together with the enhanced blue emission of DAPI. Upon adding DAPI and histamine simultaneously, the coordination of histamine with the Cu element further decreased the red emission of dsDNA-Cu NCs, and drove the movement of DAPI from the Cu element to dsDNA along with the enhanced blue emission of DAPI. Significantly, ratiometric fluorescence was insensitive to variations in instrument and environment, causing stable measurement. Meanwhile, in situ synthesis integrated probe preparation with analyte detection, reducing time consumption. Additionally, this method quantified histamine in the concentration range of 7–50 μM with a detection limit of 3.6 μM. It was applied to determining histamine in food with satisfactory accuracy and precision.

A novel urease-assisted ratiometric fluorescence sensing platform based on pH-modulated copper-quenched near-infrared carbon dots and methyl red-quenched red carbon dots for selective urea monitoring.

A novel and sensitive fluorescence ratiometric method is developed for urea detection based on the pH-sensitive response of two fluorescent carbon dot (CD) systems: R-CDs/methyl red (MR) and NIR-CDs/Cu2+. The sensing mechanism involves breaking down urea using the enzyme urease, releasing ammonia and increasing pH. At higher pH, the fluorescence of NIR-CDs is quenched due to the enhanced interaction with Cu2+, while the fluorescence of R-CDs is restored as the acidic MR converts to its basic form, removing the inner filter effect. The ratiometric signal (F608/F750) of the R-CDs/MR and NIR-CDs/Cu2+ intensities changed in response to the pH induced by urea hydrolysis, enabling selective and sensitive urea detection. Detailed spectroscopic and morphological investigations confirmed the fluorescence probe design and elucidated the sensing mechanism. The method exhibited excellent sensitivity (0.00028 mMLOD) and linearity range (0.001 - 8.0 mM) for urea detection, with successful application in milk samples for monitoring adulteration, demonstrating negligible interference and high recovery levels (96.5% to 101.0%). This ratiometric fluorescence approach offers a robust strategy for selective urea sensing in complicated matrices.

Determination of acetaldehyde in Chinese Baijiu based on the light-activated oxidase-mimic activity of fluorine-containing carbon dots (dF-CDs)

Acetaldehyde (AH) is defined as a carcinogen, the widely existence in alcoholic beverages has led its determination an essential aspect related to human health. Fluorine doped carbon dots (dF-CDs) is developed, which process light-activated oxidase-mimic property and high stability at acidic condition. Under the UV irradiation, dF-CDs generate reactive oxygen species (ROS) to oxidize o-phenylenediamine (OPD) into 2,3-diaminophenazine (DAP), showing absorption peak at 450 nm and strong emission at 577 nm, meanwhile, the produced DAP quenches the original emission of dF-CDs at 455 nm via an inner filter effect (IFE). However, the introduction of AH inhibits such processes efficiently, thereby establishing a colorimetry and ratiometric fluorescence method for AH determination. Of note, this dual-responsive method has been used for the accurate AH determination in Chinese Baijiu. Therefore, the developed method not only provide a dual-sensing platform to determine AH, but also extends the applications of CDs in food analysis.

Rapid and Sensitive Quantification of Bacterial Viability Using Ratiometric Fluorescence Sensing.

Bacterial viability assessment plays an important role in food-borne pathogen detection and antimicrobial drug development. Here, we first used GelRed as a DNA-binding stain for a bacterial viability assessment. It was found that live bacteria were able to exclude GelRed, which however could easily penetrate dead ones and be absorbed nonspecifically on the bacterial periplasm. Cations were used to reduce the nonspecific adsorption and greatly increase the red fluorescence ratio of dead to live bacteria. Combined with SYTO 9 (a membrane-permeable dye) for double-staining, a ratiometric fluorescent method was established. Using Escherichia coli O157:H7 as a bacteria model, the ratiometric fluorescent method can probe dead bacteria as low as 0.1%. A linear correlation between the ratiometric fluorescence and the theoretical ratio of dead bacteria was acquired, with a correlation coefficient R2 of 0.97. Advantages in sensitivity, accuracy, and safety of the GelRed/SYTO9-based ratiometric fluorescent method against traditional methods were demonstrated. The established method was successfully applied to the assessment of germicidal efficacy of different heat treatments. It was found that even 50 °C treatment could lead to the death of minor bacteria. The as-developed method has many potential applications in microbial researches, and we believe it could be expanded to the viability assessment of mammalian cells.

Characterization Of The Electrothermal Conversion Mechanisms Of A Plasma Actuator For Icing Control

The characterization of a new icing protection system, specifically a dielectric barrier discharge (DBD) plasma actuator, is conducted in this study. The system operates by establishing an AC high voltage between two electrodes arranged on opposite sides of a dielectric material. This setup generates a plasma on the dielectric surface, which in turn induces a significant temperature rise (about 30°C) in both the dielectric surface and the surrounding air. To gain a comprehensive understanding of the electrothermal conversion mechanisms involved in the discharge, a Planar Laser Induced Fluorescence technique is employed. Using a two-colour one-dye ratiometric method (PLIF2c1d), the technique provides measurements of the temperature evolution of an ice droplet deposited on the actuator during its melting process by the discharge. An annular actuator configuration is chosen to minimise the effect of the generated ionic wind and maintain the droplet in the discharge. A pyranine and sucrose solution is identified and temperature calibrated. The calibration process involves depositing a droplet of the solution in a temperature-controlled enclosure capable of reaching temperatures as low as -22°C. Through detailed spectral analysis, two specific detection spectral bands are selected for the imaging applications. These bands enable measurements of the ice temperature with a sensitivity of 7.61%/°C. The effects of laser light scattering by ice and fluorescence reabsorption are also investigated by varying the ice thickness. They are found to have limited influence on the fluorescence emission when the solution in ice form. Finally, the capacity of the technique is evaluated by measuring the ice temperature evolution during the melting induced by a plasma discharge. Droplets are deposited on two dielectric materials, namely PTFE and Sapphire, which possess distinct thermal and dielectric properties. Comparisons under varying plasma discharge power levels provide valuable insights into the optimization of DBD plasma actuators for effective icing protection.

Highly efficient and sensitive detection of tetracycline in environmental water: Insights into the synergistic mechanism of biomass-derived carbon dots and N-methyl pyrrolidone solvent

The tetracycline (TC) residue in water environment has caused serious public safety issue. Thus, efficient sensing of TC is highly desirable for environmental protection. Herein, biomass-derived nitrogen-doped carbon dots (N-CDs) synthesized from natural Ophiopogon japonicus f. nanus (O. japonicus) were used for TC detection. The unique solvent synergism efficiently enhanced detection sensitivity, and the detailed sensing mechanism was deeply investigated. The blue fluorescence of N-CDs was quenched by TC via static quenching and inner filter effect. Moreover, the enhancement of green fluorescence from deprotonated TC was firstly proposed and sufficiently verified. The solvent effect of N-methyl pyrrolidone (NMP) and the fluorescence resonance energy transfer (FRET) with N-CDs achieved an instantaneous enhancement of the green emission by 64-fold. Accordingly, a ratiometric fluorescence method was constructed for rapid and sensitive sensing of TC with a low detection limit of 6.3 nM within 60 s. The synergistic effect of N-CDs and solvent assistance significantly improved the sensitivity by 7-fold compared to that in water. Remarkably, the biomass-derived N-CDs displayed low cost, good solubility, and desired stability. The deep insights into the synergism with solvent can provide prospects for the utilization of biomass-based materials and broaden the development of advanced sensors with promising applications.

Strand displacement-triggered FRET nanoprobe tracking TK1 mRNA in living cells for ratiometric fluorimetry of nucleic acid biomarker.

Aprecisely designed dual-color biosensor has realized a visual assessment of thymidine kinase 1 (TK1) mRNA in both living cells and cell lysates. The oligonucleotide probe is constructed by hybridizing the antisense strand of the target and two recognition sequences, in which FAM serves as the donor and TAMRA as the acceptor. Once interacting with the target, two recognition strands are replaced, and then the antisense complementary sequence forms a more stable double-stranded structure. Due to the increasing spatial distance between two dyes, the FRET is attenuated, leading to a rapid recovery of FAM fluorescence and a reduction of TAMRA fluorescence. A discernible color response from orange to green could be observed by the naked eye, with a limit of detection (LOD) of 0.38 nM and 5.22 nM for spectrometer- and smartphone-based assays, respectively. The proposed ratiometric method transcends previous reports in its capacities in visualizing TK1 expression toward reliable nucleic acid biomarker analysis, which might establish a general strategy for ratiometric biosensing via strand displacement.

A dual-signaling surface-enhanced Raman spectroscopy ratiometric strategy for ultrasensitive Hg2+ detection based on Au@Ag/COF composites

Heavy metal ion pollution poses significant risks to human health and ecological systems, and its monitoring is important. A sensitive and accurate surface-enhanced Raman spectroscopy (SERS) detection assay for Hg2+ was developed using Au@Ag/COF substrates and Y-shaped DNA labeled with two Raman reporters. The Au@Ag NPs in the COF produced robust and uniform E-fields, improving their detection reproducibility. The Y-shaped DNA design increased sensitivity with a low detection limit of 5.0 × 10−16 M by bringing the Raman reporter closer to the substrate surface. Additionally, the use of two Raman reporters allowed for a ratiometric method, improving detection accuracy by detecting both “signal-off” and “signal-on” signals. This selective sensor exhibited excellent recovery in river water, tap water, and milk samples, showcasing its robust biosensing capability for the detection of Hg2+ and its potential for sensing other heavy-metal ions in food and environmental applications.

A Novel Ratiometric Photoelectrochemical Biosensor Based on Front and Back Illumination for Sensitive and Accurate Glutathione Sensing.

The ratiometric detection method has a strong attraction for photoelectrochemical bioanalysis due to its high reliability and real-time calibration. However, its implementation typically depends on the spatial resolution of equipment and the pairing of wavelength/potential with photoactive materials. In this paper, a novel ratiometric photoelectrochemical biosensor based on front and back illumination was prepared for the detection of glutathione (GSH). Unlike traditional ratio methods, this ratiometric biosensor does not require voltage and wavelength modulation, thereby avoiding potential crosstalk caused by voltage and wavelength modulation. Additionally, the formation of a heterojunction between mTiO2 and Ag2S is conducive to enhancing light absorption and promoting charge separation, thereby boosting the photocurrent signal. Apart from forming a heterojunction with TiO2, Ag2S also shows a specific affinity towards GSH, thus enhancing the selectivity of the mTiO2/Ag2S ratiometric photoelectrochemical biosensor. The results demonstrate that the ratiometric photoelectrochemical biosensor exhibits a good detection range and a low detection limit for GSH, while also possessing significant interference elimination capability. The GSH detection range is 0.01-10 mmol L-1 with a detection limit of 6.39 × 10-3 mmol·L-1. The relative standard deviation of 20 repeated detections is 0.664%. Impressively, the proposed novel ratiometric PEC biosensor demonstrates enviable universality, providing new insights for the design and construction of PEC ratiometric sensing platforms.

Ratiometric fluorescence method comprising carbon dots and rhodamine 6G encapsulated in metal-organic framework microcubes for curcumin detection.

A ratiometric fluorescence method comprising carbon dots (CDs) and rhodamine 6G (Rh-6G) encapsulated in the microcubes of metal-organic framework (MOF-5) is introduced for the sensitive detection of curcumin (Cur) in condiments. CDs@MOF-5@Rh-6G, synthesized by the adsorption of Rh-6G on MOF-5 embedded with CDs, showed two distinct emission peaks at 435 and 560nm under excitation at 335nm, and could be used for Cur detection by ratiometric fluorescence. In the presence of Cur, the fluorescence of the CDs at 435nm (F435) was quenched by Cur owing to internal filtering and dynamic quenching effects, whereas the emission of Rh-6G at 560nm (F560) remained unchanged (335nm is the excitation wavelength, 435 and 560nm are the emission wavelengths, in which F435/F560 values are used as the output results). Under optimal conditions, a linear relationship was observed between the Cur concentration (in the range 0.1-5μmol/L) and F435/F560 value for CDs@MOF-5@Rh-6G, with a detection limit of 15nmol/L. Notably, the proposed method could accurately detect Cur in mustard, curry, and red pepper powders. Therefore, this study could improvethe quality control of food and facilitate the development of sensitive ratiometric fluorescence probes.