Sample Pretreatment Procedure Research Articles

Construction of CdTe@γ-CD@RBD nanoprobe for Fe3+-sensing based on FRET mechanism in human serum

A Fe3+ optical sensor (CdTe@γ-CD@RBD) has been developed by using gamma-cyclodextrin (γ-CD) as a bridge to link CdTe quantum dots (QDs) and a Rhodamine B derivative (RBD). The RBD molecule can enter the cavity of the γ-CD anchored onto the surfaces of the QDs. In the presence of Fe3+, the fluorescence resonance energy transfer (FRET) process from QDs to RBD will be initiated, rendering the nanoprobe to display a response to Fe3+. The degree of fluorescence quenching presented a satisfactory linearity between 10 and 60 μΜ with the incremental concentrations of Fe3+, and the calculated limit of detection was 2.51 μΜ. Through sample pretreatment procedures, the probe has been used in the determination of Fe3+ in human serum. The average recoveries in the spiking levels are ranged from 98.60 % to 107.20 % with a relative standard deviation of around 1.43 %-2.96 %. This finding leads to a method for fluorescent detection of Fe3+ with high sensitivity and exceptional selectivity. We believe that this study can give a new insight into the rational design and application of FRET-based nanoprobes.

Automated and fast online method for simultaneously determining a broad spectrum of per- and polyfluoroalkyl substances in a small volume of cerebrospinal fluid.

Per- and polyfluoroalkyl substances (PFASs) are potentially neurotoxic compounds. Levels of PFASs in cerebrospinal fluid (CSF) could directly reflect their potential harm to the central nervous system. Because of the variety of PFASs and the rarity of CSF, there is an urgent need to establish a rapid online method to detect a broad spectrum of PFASs accurately and simultaneously by consuming a small amount of CSF. In this study, we developed a fast and automated method to analyze 52 PFASs in human CSF samples using online TurboFlow ultra-high-performance liquid chromatography-tandem mass spectrometry. Our method offered excellent matrix-matched standard curve linearity (correlation coefficient > 0.99), good limits of quantitation (MLOQs) (0.01 to 0.08 ng mL-1), satisfactory accuracy (recoveries of 74.6%-119.1%) and precision (relative standard deviations of 1.4%-13.2%), small sample amount consumption (50 μL), and fast analysis time (18 min per sample) without complex sample pretreatment procedures. These are advantageous for the high throughput screening of PFASs in environmental epidemiology studies. Repeated freeze-thaw experiments showed that it was better to perform the analytical process soon as possible after sample collection. The established method was used to analyze PFASs in 60 people. Short-chain PFASs, perfluorobutanoic acid (PFBA), perfluoropentanoic acid (PFPeA), and novel PFASs [sodium 2-(N-ethylperfluorooctane-1-sulfonamido)ethyl phosphate (SAmPAP), perfluoroethylcyclohexanesulfonate (PFECHS), and perfluoro-3, 7-dimethyloctanoic acid (P37DMOA)] were reported in CSF for the first time. PFBA and PFPeA were detected in all samples with mean concentrations of 0.24 and 0.22 ng mL-1, respectively. We also calculated the blood-brain barrier transmission efficiency of PFASs (RPFAS), and the mean RPFBA value was above 1, which indicated that PFBA might transfer from serum to CSF.

Paper-based electrodes with nitrogen-doped graphene quantum dots for detection of copper ions via electrochemiluminescence

Nitrogen-doped graphene quantum dots (N-GQDs) were prepared using pyrolysis, with citric acid and urea as the carbon and nitrogen sources, respectively, to be used for Cu2+ ion detection in a paper-based ECL sensor. Existing methods for Cu2+ detection require expensive equipment, specialized experimental chambers, or complex sample pretreatment procedures, which limit their functionality. Using first principles, the electronic and optical properties of graphene quantum dots (GQDs) and N-GQDs were calculated and analyzed. The N-GQDs showed clearer green fluorescence under long-wave ultraviolet light and a better, more stable electrochemiluminescence (ECL) performance. Using first principles, the electronic and optical properties of the GQDs and N-GQDs were calculated and analyzed, and A theoretical mechanism for the observed ECL enhancement in the N-GQDs was proposed. A paper-based ECL sensor with N-GQDs was then developed, using a screen-printing technique, to detect Cu2+ ions. The results showed that the ECL intensity of the sensor increased as the Cu2+ ion concentration increased, and the sensor demonstrated a linear detection range of 0.01–1000 μM. Overall, the sensor exhibited excellent ECL stability, reproducibility, and selectivity. This simple, inexpensive, and effective monitoring technique can be used to detect Cu2+ to prevent negative effects on human health and the environment.

Extraction and determination of aflatoxin B1 in cereal samples using pH-switchable hydrophobic deep eutectic solvents followed by HPLC-FL analysis.

A quick, simple and environmentally friendly liquid phase microextraction (LPME) sample pretreatment procedure was proposed based on pH-switchable hydrophobic deep eutectic solvents (HDESs) and high performance liquid chromatography coupled with a fluorescence detector (HPLC-FL). This method was used for the quantitative study of aflatoxin B1 (AFB1) and applied to eight widely consumed cereal samples. In this method, six different DESs were synthesized and then their pH-switchability was investigated. DESs that could be switched with pH were employed for separation and preconcentration of AFB1 in cereal samples. In this method, dispersing the extractant phase in the aqueous solution and subsequent phase separation are performed only by changing the pH. Important parameters affecting extraction, such as the type of DES and its volume, concentration of KOH, volume of HCL, effect of salt and extraction time were investigated and optimum conditions were obtained. Under the optimum conditions, relative standard deviation (RSD) values for intra-day and inter-day of the method based on seven replicate measurements of 5.0 μg kg-1 of AFB1 in cereal samples were 3.3 and 5.2%, respectively. The calibration graphs were linear in the range of 0.007-20 μg kg-1 and limit of detection (LOD) was 0.002 μg kg-1. The relative recoveries of real cereal samples which have been spiked with different levels of AFB1 were 90.8-107.5%.

Analysis of 15 anti-obesity drugs in urine using thermal-assisted paper spray mass spectrometry.

Anti-obesity drugs, used to suppress appetite and reduce fat absorption, have been circulated and traded illegally worldwide. The traditional methods of liquid chromatography tandem mass spectrometry (LC-MS/MS) and gas chromatography-mass spectrometry (GC-MS) for analyzing these drugs in in vivo samples require complex sample pretreatment and time-consuming procedures. To address this issue, a thermal-assisted paper spray mass spectrometry (PS-MS) method was developed in this study to analyze anti-obesity drugs in raw urine. By incorporating a heat source and optimizing the spray solvent and paper substrate, this technique demonstrates reduced matrix effect and higher sensitivity compared to traditional PS-MS methodology for direct analysis of anti-obesity drugs in urine samples. A temperature range of 100-200 °C can be set for screening anti-obesity drugs in urine samples, with the flexibility to adjust the temperature according to the specific drug being analyzed. The limits of detection (LODs) for these 15 anti-obesity drugs in urine ranged between 1 and 500 ng mL-1. Furthermore, the thermal-assisted PS-MS method exhibited good linearities (R2, 0.9903-0.9997) within the range from 10-100 to 1000 ng mL-1 for the direct quantitation of anti-obesity drugs in urine samples with an internal standard. Therefore, the thermal-assisted PS-MS technique may provide a novel approach for the direct analysis of drugs in complex samples.

Rapid Detection of Accelerants in Fire Debris Using a Field Portable Mid-Infrared Quantum Cascade Laser Based Analyzer

Arson presents a challenging crime scene for fire investigators worldwide. Key to the investigation of suspected arson cases is the analysis of fire debris for the presence of accelerants or ignitable liquids. This study has investigated the application and method development of vapor phase mid-Infrared (mid-IR) spectroscopy using a field portable quantum cascade laser (QCL) based system for the detection and identification of accelerant residues such as gasoline, diesel, and ethanol in fire debris. A searchable spectral library of various ignitable fluids and fuel components measured in the vapor phase was constructed that allowed for real-time identification of accelerants present in samples using software developed in-house. Measurement of vapors collected from paper material that had been doused with an accelerant followed by controlled burning and then extinguished with water showed that positive identification could be achieved for gasoline, diesel, and ethanol. This vapor phase mid-IR QCL method is rapid, easy to use, and has the sensitivity and discrimination capability that make it well suited for non-destructive crime scene sample analysis. Sampling and measurement can be performed in minutes with this 7.5 kg instrument. This vibrational spectroscopic method required no time-consuming sample pretreatment or complicated solvent extraction procedure. The results of this initial feasibility study demonstrate that this portable fire debris analyzer would greatly benefit arson investigators performing analysis on-site.

Extraction of bioactive coumarins from lime peel as sample pretreatment before chromatographic analysis

Abstract Analysis of lime peel was applied to assess their suitability for various intended purposes, e.g., application in perfumery, cosmetics, and cleaning products, or as a source of bioactive or other value-added compounds. Targeted analysis allows wider usability of the waste part of these natural materials. In the present study, a novel, efficient, lab-simple, time-saving analytical method for coumarins determination in lime peel, including sample pretreatment by extraction and quantification by HPLC with fluorescence detection (FLD), is introduced. Optimal conditions of ultrasound assisted extraction included water as extraction solvent, temperature of 40 °C, and extraction time of 10 min. A magnetic molecularly imprinted polymer was employed as solid phase extraction adsorbent for primary extract cleaning, isolation, and enrichment of coumarins before chromatographic analysis. Recovery of herniarin and umbelliferone was more than 86 % ((RSD ≤ 4.8 %). Linear range of 50—1000 ng/mL with correlation coefficient above 0.998 was obtained for the proposed HPLC-FLD method. The limit of quantification was 8.2 and 44 ng/mL for herniarin and umbelliferone, respectively. These results show that the proposed sample pretreatment procedure is suitable for analytical purposes and is perspective also for the analysis of other citrus samples, as well as for future scale-up preparative isolation of bioactive coumarins from citrus peel.

Electrochemical Determination of Morphine in Urine Samples by Tailoring FeWO4/CPE Sensor.

Morphine (MORPH) is natural alkaloid and mainly used as a pain reliever. Its monitoring in human body fluids is crucial for modern medicine. In this paper, we have developed an electrochemical sensor for submicromolar detection of MORPH. The sensor is based on modified carbon paste electrode (CPE) by investigating the FexW1-xO4 ratio in iron tungstate (FeWO4), as well as the ratio of this material in CPE. For the first time, the effect of the iron-tungsten ratio in terms of achieving the best possible electrochemical characteristics for the detection of an important molecule for humans was examined. Morphological and electrochemical characteristics of materials were studied. The best results were obtained using Fe1W3 and 7.5% of modifier in CPE. For MORPH detection, square wave voltammetry (SWV) was optimized. Under the optimized conditions, Fe1W3@CPE resulted in limit of detection (LOD) of the method of 0.58 µM and limit of quantification (LOQ) of 1.94 µM. The linear operating range between 5 and 85 µM of MORPH in the Britton-Robinson buffer solution (BRBS) at pH 8 as supporting electrolyte was obtained. The Fe1W3@CPE sensor resulted in good selectivity and excellent repeatability with relative standard deviation (RSD) and was applied in real-world samples of human urine. Application for direct MORPH detection, without tedious sample pretreatment procedures, suggests that developed electrochemical sensor has appeared to be a suitable competitor for efficient, precise, and accurate monitoring of the MORPH in biological fluids.

Simple and efficient solid phase extraction based on molecularly imprinted resorcinol–formaldehyde resin nanofibers for determination of trace sulfonamides in animal-origin foods

Novel molecularly imprinted resorcinol–formaldehyde resin nanofibers (MIRF NFs) was prepared using polydopamine as an intermediate. With high specific surface area and favorable usability, MIRF NFs presented high efficiency for the solid phase extraction (SPE) of sulfonamides (SAs) in complex animal foods. After optimizing the operating conditions, a new method for SAs quantification coupled with HPLC–MS/MS was developed. By simple water dilution of the solvent extracts, SPE could be carried out. In addition, the eluent could be analyzed directly without any further treatment. The newly developed method was simplified greatly with much fewer sample pretreatment procedures (4 steps). Moreover, much fewer amounts of sample (1.0 g), adsorbent (3.0 mg), organic solvent (1.5 mL) and preparation time (20 min for 24 samples) were needed. The obtained good linearity (R2 > 0.9957), low detection limits (0.01–0.14 μg kg−1), satisfactory recoveries (83.0 %–112.9 %) and precisions (RSDs < 12.6 %) further proved the feasibility of the method in practical application.

Development of a photothermal bead-based nucleic acid amplification test (pbbNAAT) technique for a high-performance loop-mediated isothermal amplification (LAMP)–based point-of-care test (POCT)

We have developed a novel molecular diagnostic platform (photothermal bead-based nucleic acid amplification test; pbbNAAT) that greatly improves the low sensitivity of direct loop-mediated isothermal amplification (LAMP) and allows for specific detection of LAMP amplicons in complex samples. The pbbNAAT integrates specific ligand-functionalized polypyrrole-coated iron oxide particles (PPy@IOs) capable of photothermal conversion and single-molecule magnetic capture of target analytes, the released nucleic acid, and LAMP-amplified products under external light energy control and magnetic manipulations. This allows for sample pretreatment, pbbLAMP amplification, and subsequent amplicon detection with bead-based ELISA in a one-stop microreactor without loss. In addition, photonic heating with PPy@IOs and external light control provide instant and uniform heating for thermolysis and pbbLAMP implementations. Moreover, it generates higher primer annealing stringency for LAMP primers in pbbLAMP; thus, it can detect pathogen-specific DNA accurately and promptly in pathogen-spiked complex materials. The sample pretreatment procedure of pbbNAAT can greatly reduce inhibitors originating from complex samples, which enables the maintenance of maximal enzyme activities for highly sensitive detection. More importantly, the pbbLAMP assay coupled with magnetic capture permits subsequent bead-based ELISA detection to determine true positive LAMP amplicons on PPy@IOs. The pbbNAAT platform has a high tolerance to inhibitors originating from complex samples, high analytical specificity, and limitation of detection (LoD) as low as 8 CFU/reaction to detect E. coli spiked in human whole blood, bovine milk, and can be completed in less than 1 h. Therefore, we believe that pbbNAAT can serve as a suitable direct LAMP platform for on-site POCTs.

Sample pretreatment and analytical methodology for the determination of antibiotics in swine wastewater and activated sludge.

An analytical method for the simultaneous extraction and determination of eight veterinary antibiotics in swine wastewater and activated sludge was developed and validated based on the instrumental determination by liquid chromatography tandem quadrupole mass spectrometry. Ultrasound-assisted extraction and solid-phase extraction were introduced into the pretreatment procedure of the two complex environmental matrices. The critical steps involved in the sample pretreatment procedure and the instrumental analysis conditions were optimized progressively. Recoveries of the optimized method were good with 75.3-118.2% in wastewater and 82.8-130.1% in sludge. The absolute deviations of methods were lower than 11.7%, presenting a high reproducibility and precision. The limits of quantification for the eight pharmaceuticals in wastewater and sludge were 5-15 ng·L-1 and 2-6 ng·g-1, showing high sensitivity of the methods. The developed method has been successfully applied to evaluate the actual concentration levels of tetracyclines, quinolones, and sulfonamides in actual swine wastewater (maximum detected concentration of 87.377 μg·L-1) and activated sludge (maximum detected concentration of 51242.3 ng·g-1).

Magnetic polymer particles as a highly efficient and facile cleanup adsorbent for multi-pesticide residues analysis in aquatic products

A novel and efficient sample pretreatment procedure using magnetic particles was exploited for the determination of multi-pesticide residues in aquatic products. The magnetic adsorbent was prepared using divinyl benzene and N-vinyl pyrrolidone as functional monomers modified on the Fe3O4 @SiO2. The obtained magnetic adsorbent, octadecylsilane sorbents, and graphitized carbon black were employed as effective adsorbents to remove matrix interferences in aquatic products, and their dosages were optimized. Satisfactory levels of accuracy and precision were procured under optimum conditions. The method limits of quantification ranged from 0.1 to 2.0 μg/kg. The analytical accuracy of the developed method for the analysis of multi-pesticide residues in freshwater and seafood products was validated. It was found to be suitable for the analysis of multi-pesticide residues in different types of aquatic products. Additionally, the method was successfully applied for the analysis of pesticide residues in fish samples obtained from aquaculture plants located in Zhejiang Province, China. The detected concentrations of pesticides ranged from 0.14 to 0.95 μg/kg. In general, this method shows promising application prospects for the rapid determination of multi-pesticide residues in aquatic products.

Graphene thin film microextraction and nanoparticle enhancement for fast LIBS metal trace analysis in liquids

Several strategies have been effectively tested in the past to improve the Laser Induced Breakdown Spectroscopy (LIBS) signal for the analysis of liquid samples, involving peculiar experimental configurations, such as Double Pulse LIBS (DP-LIBS). Recently, sample treatment has proven to be a viable and simple way to enhance the performances of LIBS towards the analysis of solutions. Among the various strategies, the most promising and versatile appears to be Thin Film Microextraction (TFME) using carbon-based adsorbents.Another sample pre-treatment procedure, Nanoparticle-Enhanced LIBS (NELIBS), has gained significant interest due to its relative simplicity and effectiveness. This methodology uses a deposition of silver nanoparticles (AgNPs) on the sample to greatly increase the emission of the LIBS plasma.In this work, we investigate for the first time the possibility of combining TFME and NELIBS. We developed TFME supports by depositing an aqueous graphene nano-sheets (aq-GRA) prepared by Pulsed Laser Ablation in Liquid (PLAL) on a glass substrate. The preparation of the supports was optimized with regards to the substrate nature, deposition method, sorbent volume and drying method. Then, the TFME supports were tested for the extraction of Chromium from aqueous solution at different extraction times and analyte concentration. Subsequently, the TFME supports were treated with a deposition of silver nanoparticles (AgNP) to test the feasibility of the NELIBS approach.We observed an enhancement in the emission lines of Cr when the AgNPs were applied, as well as a lower estimated LOD value when compared to plain graphene TFME supports.

On-Site Determination of Methylmercury by Coupling Solid-Phase Extraction and Voltammetry.

A measurement and speciation procedure for the determination of total mercury (HgTOT), inorganic mercury (HgIN), and methylmercury (CH3Hg) was developed and the applicability for on-site determination was demonstrated. A simple, portable sample pretreatment procedure was optimized to extract the analytes. Home-made columns, packed with a new sorbent material called CYXAD (CYPHOS 101 modified Amberlite XAD), were used to separate the two forms of the analyte. HgTOT and CH3Hg were determined by anodic stripping voltammetry (ASV), using a solid gold electrode (SGE). Two certified reference materials (BCR-463 Tuna Fish and Tuna Fish ERM-CE 464) and eight fresh fishes were analyzed. Then, the results that were obtained following the optimized portable procedure were compared with the concentrations obtained, using a direct mercury analyzer (DMA). This quantification, using the two techniques, demonstrated the good performance of the proposed method.

Simultaneous preconcentration and pre-column derivatization for rapid analysis of nitrilotriacetic acid in environmental waters by high performance liquid chromatography

A simplified sample pretreatment procedure was developed for quantitative measurement of nitrilotriacetic acid (NTA) in environmental water. On the basis of coordination capacity between NTA and metal ions, aluminum-based metal organic framework (MOF, MIL-53(Al)) was adopted for the adsorption of NTA, followed by stripping with copper sulfate as the eluent. The adsorbed NTA was converted into Cu-NTA during the desorption process, which facilitated the ensuing measurement by high performance liquid chromatography (HPLC). A linear range within 0.10 - 10 mg L−1 was achieved, along with a limit of detection (LOD, S/N=3, n=7) of 0.03 mg L−1 and an enrichment factor of 10.4. The developed method was validated by the analysis of sea water, influent of wastewater treatment plant and industrial wastewater, with satisfactory recoveries (90.2 - 91.1%) obtained.

Development and application of a flow cytometry-based method for rapid and multiplexed quantification of three foodborne pathogens in chicken breast

Chicken breast is prone to Listeria monocytogenes, Salmonella spp., and E. coli O157:H7 contaminations. Therefore, a quantitative method for the rapid detection of these pathogens simultaneously in chicken breast is highly desirable for food safety control. This study reports a flow cytometry (FCM)-based method for rapid and multiplexed quantification of the above-stated three pathogens without enrichment. Using the developed method, the complete detection process, including a sample pretreatment procedure, the multiplex staining, and the FCM analysis, could be realized within 1 h, rendering this method more efficient than the plate counting method. The bacterial recovery rates were 96.24% for Listeria monocytogenes, 96.74% for Salmonella, and 96.42% for E. coli O157:H7. A good linear correlation was realized between the FCM-based method and the plate counting method for all three pathogens. The relative standard deviations were 3.0%, 2.7%, and 2.9% for Listeria monocytogenes, Salmonella, and E. coli O157:H7, which indicated excellent reproducibility of the method. This study is the first one to report the rapid and simultaneous quantification of foodborne pathogens in chicken breast using FCM. Moreover, the developed method was also applied successfully to the multiplexed detection of bacteria, which indicated that the method has great potential in food contamination monitoring.

Solid phase extraction materials as a key for improving the accuracy of silver nanoparticle characterization with single-particle inductively coupled plasma mass spectrometry in natural waters through dissolved silver removal

The accurate characterization of silver nanoparticles (Ag NPs) in environmental samples is crucial for understanding the potential impact of these materials on the environment and human health. Single-particle inductively coupled plasma mass spectrometry (spICP-MS) is one of the few techniques available for quantifying NPs at environmentally relevant concentrations. However, the spICP-MS detection of Ag NPs can be interfered with coexisting dissolved analyte causing high background signals, which mask NP signals leading to a significant bias in NP characterization. In this paper, a simple sample pre-treatment procedure for efficient removal of dissolved silver in natural waters is proposed using solid phase extraction (SPE) materials, allowing more accurate characterization of NPs in environmental water matrices. The applicability of eight commercially available SPE materials was evaluated based on their effects on sample Ag NP properties and dissolved silver extraction efficiency in environmental waters, which were shown to depend on sample matrix. The SPE materials found most efficient in dissolved silver extraction were further studied for improving the characterization of 30 nm Ag NPs in colorless and dark-colored waters. Whereas dissolved silver concentrations of ≤1 μg kg−1 were shown to lead to a significant bias in NP characterization (up to +58% increase in NP size and − 90% decrease in particle concentration), pre-treatment of the samples with SPE materials ‘SiliaMetS Thiol’ and ‘Purolite C115HMR’ minimized the effect of dissolved silver interference. As a result, highly more accurate NP sizing (28 ± 2 nm) and relatively stable particle concentration was obtained for 30 nm Ag NPs in environmental waters.

Facile synthesis disposable MOF membrane filter: Growth of NH2-MIL-125 (Ti) on filter paper for fast removal of organophosphorus pesticides in aqueous solution and vegetables

Metal-organic frameworks (MOFs) have great potential to remove pesticide residues. However, the lack of affinity between the materials and target and the process of trivial sample preparation resulted in limited removal efficiency. Here, we report a one-pot method for the fast preparation of NH2-MIL-125 (Ti)-based filter paper to synthesise NH2-MIL-125 (Ti)-based filter paper membranes. The NH2-MIL-125 (Ti)-based filter paper membrane takes advantage of π-π interactions between the organophosphorus pesticides (OPPs) and the benzene ring of MOFs. The affinity of amino groups and metal Ti for phosphorus atoms in the OPPs exhibits rapid removal efficiency for three OPPs, imidan, fenthion, and fenitrothion. The isothermal adsorption results for imidan, fenthion, and fenitrothion were consistent with the Langmuir, Freundlich, and Langmuir models, respectively. The kinetic results for imidan, fenthion, and fenitrothion agreed with the pseudo-second-order kinetic model, and the removal efficiency reached equilibrium within 1 min. There was no significant change in the adsorption capacity of OPPs in different pH solutions (pH = 2–10). Compared with that of MOFs, the NH2-MIL-125 (Ti)-based filter paper membrane removal efficiency of OPPs is the same, and it also has better removal efficiency in actual spinach samples. As a result, the sample pretreatment procedure was simplified using a low-cost and simple-to-synthesize disposable NH2-MIL-125 (Ti)-based filter paper membrane, samples’ quick separation and the simultaneous fast removal of OPPs.

Liquid Contact Ion Selective Electrode Green Method for the Determination of Flavoxate HCl Main Active Metabolite in Pure Powder and Human Urine with Establishment of Urinary Excretion Pattern

The main aim of this work is to develop the first liquid contact ion selective electrode potentiometric method for determination of flavoxate HCl main metabolite; 3-methylflavone-8-carboxylic acid (MFC). The method can be used for studying flavoxate HCl bioavailability through tracing its active metabolite; MFC, excreted in human urine. The metabolite was determined in pure powder and in human urine with establishment of urinary excretion pattern without any sample extraction or pretreatment procedures. The suggested sensor's performance was assessed in accordance with IUPAC guidelines. According to the Bioanalytical Method Validation Guidance for Industry, the suggested method was validated where good results were obtained. The proposed method is an excellent green eco-friendly analytical method.

Quantifying H2O2 by ratiometric fluorescence sensor platform of N-GQDs/rhodamine B in the presence of thioglycolic acid under the catalysis of Fe3+

In the presence of thioglycolic acid (TGA) and under the catalysis of Fe3+, a simple, rapid, sensitive, selective and effective ratiometric fluorescence sensor platform based on the mixed physically blue nitrogen-doped graphene quantum dots (N-GQDs) as probe signals and orange rhodamine B as internal standard signals has been constructed for analysis of H2O2 in human serum. TGA is the key factor for fluorescence response toward H2O2 by N-GQDs and the mechanism is H2O2 reacts speedily with TGA under the catalysis of Fe3+, and produces intermediate of superoxide anions (O2−), which accepts electrons from N-GQDs, and generates graphene oxide, causing the fluorescence quench of N-GQDs. Compared with N-GQDs probe, the sensitivity of the ratiometric fluorescence sensor platform of N-GQDs/rhodamine B for analysis of H2O2 has been improved by nearly 5-folds. Under the optimum conditions, Fλ=580nm/Fλ=440nm has a good linear relationship with the concentration of H2O2 and the detection limit of H2O2 is 0.46 μmol/L with 3.5% RSD. The established sensor platform has been successfully used for probing H2O2 in human serum with satisfactory results. The superior performance of the probe lies in its high selectivity and can be directly employed in detecting H2O2 in serum samples without any sample pretreatment procedures.