Linear Range For Determination Research Articles

A three-dimensional composite film-modified electrode based on polyoxometalates and ionic liquid-decorated carbon nanotubes for the determination of L-tyrosine in food.

A stable and innovative composite film-modified electrode based on Dawson polyoxometalates H8P2Mo16V2O62 (P2Mo16V2) and ionic liquid (BMIMBr)-decorated carbon nanotubes, annotated as PEI/(P2Mo16V2/BMIMBr-CNTs)8, has been constructed by using the layer-by-layer self-assembly (LBL) method for the determination of L-tyrosine. The combination of three active components not only offers higher conductivity to facilitate rapid electron transfer, but also avoids the accumulation of P2Mo16V2 to expand the contact area and increase the reactive active sites. The modified electrode exhibits outstanding sensing performance for determination of Tyr with wide linear determination range of 5.8×10-7 M ~ 1.2×10-4 M, low determination limit of 1.7×10-7M (S/N=3), high selectivity for common interferences, and excellent stability at the potential of +0.78 V (vs. Ag/AgCl (3 M KCl)). The relative standard deviation (RSD) of 4.3% for five groups of parallel experiments shows the satisfactory repeatability of PEI/(P2Mo16V2/BMIMBr-CNTs)8. In addition, for determination of Tyr, the PEI/(P2Mo16V2/BMIMBr-CNTs)8 shows good recoveries of 98.8-99.8% in meat floss, which can be feasible in practical application.

2D nanoplate-shaped CaCo2O4 spinel as an oxidase nanozyme for the colorimetric sensing of sodium dodecyl benzene sulfonate under nearly neutral pH

Nanozymes are outstanding candidates of natural enzymes and have been aroused lasting interest. However, the development of oxidase mimics with highly and robust catalytic activity is still a challenge. Also, the activity of most nanozymes were restricted by pH condition, significantly limiting their extensive applications. Here, the spinel CaCo2O4 nanoplates with high oxidase-mimicking activity at nearly neutral pH were prepared by a simple hydrothermal-calcination method. Relative to the Co3O4 and CaO, the spinel CaCo2O4 exhibited lower electron transfer resistance and enhanced electron transfer rate. This endows the CaCo2O4 to maintain superior catalytic activity even in neutral pH condition (pH = 6.5). The oxidase-like activity of CaCo2O4 is 17.0-fold and 31.5-fold times that of Co3O4 and CaO, respectively. CaCo2O4 exhibited good affinity to TMB with a Km of 0.111 mM and Vmax value of 1.34 × 10−7 M·S−1. Based on the inhibition effect of sodium dodecyl benzene sulfonate (SDBS) on the TMB/CaCo2O4 color reaction, a colorimetric platform for the SDBS detection has been developed under nearly neutral pH. The linear range for SDBS determination was 0.2–70.0 μM, with a detection limit of 0.12 μM (3σ). The TMB/CaCo2O4 system was successfully applied to the determination of SDBS in real water samples. This work provided a new strategy to design spinel oxide-based high activity nanozyme at neutral pH media for colorimetric sensing of pollutant.

11-(triethoxysilyl) undecanal agent-based biosensor system using disposable ITO-PET electrode for tumour necrosis factor-alpha detection

In this study, a label-free electrochemical biosensor system based on a disposable indium tin oxide polyethylene terephthalate (ITO-PET) electrode modified with the 11-(triethoxysilyl) undecanal (11-TESU) agent was developed for the detection of tumour necrosis factor-alpha (TNF-α) in serum. The developed biosensor was observed with electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) techniques, square wave voltammetry (SWV) and single frequency impedance (SFI) technique which is utilized for the specific interaction between anti-TNF-α and TNF-α antigen. In addition, scanning electron microscopy was used to look at how the morphology of each ITO-PET surface changed (SEM). All parameters such as 11-TESU concentration, anti-TNF-α concentration and anti-TNF-α incubation time, were optimized. The biosensor system was characterized by measuring its linear determination range, repeatability, reproducibility, reusability, storage stability, and surface coverage. The TNF-αelectrochemical biosensor showed high levels of repeatability and reproducibility as well as a large dynamic range of detection (from 0.03 pg mL-1 to 3 pg mL-1). The LOD and LOQ for the biosensor were extremely low at 1x10-4 pg mL-1 and 5x10-4 pg mL-1, respectively. It was applied to real samples to determine whether the proposed biosensor would be useful in clinical settings.

Determination of adenosine by CRISPR-Cas12a system based on duplexed aptamer and molecular beacon reporter linked to gold nanoparticles.

Adenosine as a potential tumor marker is of great value for clinical disease diagnosis. Since the CRISPR-cas12a system is only capable of recognizing nucleic acid targets we expanded the CRISPR-cas12a system to determine small molecules by designing a duplexed aptamer (DA) converting g-RNA recognition of adenosine to recognition of aptamer complementary DNA strands (ACD). Tofurther improve the sensitivity of determination, we designed a molecule beacon (MB)/gold nanoparticle (AuNP)-based reporter, which has higher sensitivity than traditional ssDNA reporter. In addition, the AuNP-based reporter enables more efficient and fast determination. The determination of adenosine under 488-nm excitation can be realized within 7 min, which is more than 4 times faster than traditional ssDNA reporter. The linear determination range of the assay to adenosine was 0.5-100 μM with the determination limit of 15.67 nM. The assay was applied torecovery determination of adenosine in serum samples with satisfactory results. The recoveries were between 91 and 106% and the RSD values of different concertation were below 4.8%. This sensitive, highly selective, and stable sensing system is expected to play a role in the clinical determination of adenosine and other biomolecules.

Highly Selective and Sensitive Sensor Based IL and CMC-MWCNTs Nanocomposite for Rutin Determination

Rutin is a natural antioxidant flavonoid compound with anti-inflammatory, antioxidant, and antiviral effects that is used to prepare drugs with wide application in clinical treatment. Therefore, the quantitative detection of rutin has important practical significance. In this work, a novel electrochemical sensor based on glassy carbon electrodes (GCEs) modified with sodium carboxymethylcellulose (CMC), multi-walled carbon nanotubes (MWCNTs), and 1-butyl-3-methylimid (ionic liquid, IL) was developed for the super-sensitive detection of the flavonoid rutin. The properties of these modified materials were analyzed by transmission electron microscope (TEM), cyclic voltammograms (CVs), and electrochemical-impedance spectroscopy (EIS). CMC was used to disperse MWCNTs to further enhance their hydrophilicity and biocompatibility. The modified MWCNTs improved the sensitivity of rutin detection. The square-wave voltammetry (SWV) technique showed that the linear range of rutin concentration determination was 0.01 μM to 1 µM and 1 µM to 10 µM. The minimum concentration detection of rutin was 0.83 nM and 6.6 nM, respectively. The proposed sensor presented good selectivity for rutin and successfully analyzed rutin content in the pharmaceutical rutin tablets. These results are consistent with those measured by ultra-high-performance liquid chromatography (UHPLC). Therefore, this sensor has latent application value in the analysis of rutin in food and drug tablets and nutraceutical samples.

Fabrication of glucose bioelectrochemical sensor based on Au@Pd core-shell supported by carboxylated graphene oxide

The study presents a novel electrochemical glucose biosensor based on glucose oxidase (GOx) immobilized on Au@Pd core-shell nanoparticles supported on carboxylated graphene oxide (cGO). The immobilization of GOx was achieved by cross-linking the chitosan biopolymer (CS) including Au@Pd/cGO and glutaraldehyde (GA) on a glassy carbon electrode. The analytical performance of GCE/Au@Pd/cGO-CS/GA/GOx was investigated using amperometry. The biosensor had fast response time (5.2 ± 0.9 s), a satisfactory linear determination range between 2.0 × 10−5 and 4.2 × 10−3 M, and limit of detection of 10.4 μM. The apparent Michaelis-Menten constant (Kapp) was calculated as 3.04 mM. The fabricated biosensor also exhibited good repeatability, reproducibility, and storage stability. No interfering signals from dopamine, uric acid, ascorbic acid, paracetamol, folic acid, mannose, sucrose, and fructose were observed. The large electroactive surface area of carboxylated graphene oxide is a promising candidate for sensor preparation.

Highly catalytic nanoenzyme of covalent organic framework loaded starch- surface-enhanced Raman scattering/absorption bi-mode peptide as biosensor for ultratrace determination of cadmium.

High affinity peptides (PTs) have been used in nanoanalysis, but there are no reports which combine PTs with a liquid crystal (LC) covalent organic framework (COF) supported soluble starch (SS) catalytic amplification system as a biosensor recognition element. In this study, a new, highly sensitive and selective bi-mode molecular biosensor has been developed for the determination of cadmium ion (Cd2+). Specifically, a highly catalytic and stable COF supported SS nanosol catalyst was fabricated such that a nanocatalytic indicator reaction system for HAuCl4-sodium formate was established based on surface-enhanced Raman scattering (SERS). The Au nanoparticles produced exhibited a surface plasmon resonance (SPR) absorption peak at 535 nm and a SERS peak at 1,615 cm-1. Combining the nanocatalytic amplification indicator system with the specific PTs reaction permitted a sensitive and selective SERS/absorption bi-mode platform to be developed for the determination of cadmium in rice. The linear range for SERS determination was 0.025-0.95 nmol/L and the detection limit (DL) was 0.012 nmol/L.

Determination of Terbinafine at a Boron-Doped Diamond (BDD) Electrode Modified with Polypyrrole and γ-Cyclodextrin by Square Wave Voltammetry (SWV)

This work involved the determination of the antifungal agent, terbinafine (TR) using a boron-doped diamond electrode (BDD) that was modified with polypyrrole in the presence of cyclodextrin. The obtained modified layer was overoxidized and was used to develop a novel, sensitive method for terbinafine. Scan rate measurements confirmed the diffusion character of the recorded currents. Terbinafine was irreversibly oxidized, producing a well-defined peak at +1.05 V (versus the saturated calomel electrode) in Britton–Robinson (B–R) buffer at pH 6.09. Square wave voltammetry was employed to study the relationship between current and terbinafine concentration in the optimized conditions. A linear range for terbinafine determination was obtained between 7.04 × 10−8 and 9.09 × 10−7 mol/L with a limit of detection of 2.11 × 10−8 mol/L and good repeatability (2.56%, n = 6 measurements, at 3.7 × 10−7 mol/L). The procedure was employed to determine terbinafine in pharmaceutical preparations. The recovery values between 97.37 and 102.16% demonstrate the accuracy of the developed protocol.

Polymeric nanoparticle-based electrochemical sensor for the detection of CA 125.

In this paper, Cys-graft-p(HEMA) nanomaterials and a new electrochemical method were developed for determination of CA 125. Cys-graft-p(HEMA) nanomaterials were synthesized with emulsion polymerization method and modified with grafting procedure. It was determined that Cys-graft-p(HEMA) nanomaterials had 50 nm dimension and spherical morphology, and per gram polymeric material contained 0.011 mmol L-cysteine. Electrode surface was prepared step by step for electrochemical analysis with optimization process. Linear determination range was determined as 5-400 U/mL (R= 0.9935). Detection limit (LOD) was calculated as 1.87 U/mL, and quantification limit (LOQ) was determined as 5.62 U/mL. The fabricated sensor system showed good repeatability, accuracy, reality, and storage stability. According to the results obtained, Cys-graft p(HEMA) nanomaterials that is used for the first time in biosensor has the potential to find use in the sector with rapid determination time (10 min), extensive determination range, accuracy of methods. Novelties of this study are rapid analysis, determination range, appropriate of prototype device development, and developing new designed material. Developed material and method can be used in the preliminary diagnosis of the disease and combined with a prototype device that can allow the follow-up of the treatment process in diagnosed patients.

Digital image colorimetric detection of ceftazidime based on azo compound formation on a polyethyleneimine-modified cotton sponge.

A novel colorimetric platform using cotton sponges modified with polyethyleneimine (PEI) was fabricated for the detection of ceftazidime through the diazotization and coupling reaction. In this work, cotton sponges were initially prepared by freeze drying using 2 w/w% cotton fibers modified with 3-aminopropyl triethoxysilane (APTES), followed by grafting of PEI through a crosslinking reaction using epichlorohydrin (ECH). The optimal concentrations of modifying agents were 170 mM APTES for 1.0 g of cotton fibers and 210 μM PEI for 0.5 g of APTES sponges. With a sample volume of 150 mL, the extracted ceftazidime was detected through the reactions with 0.5 M HCl, 30 mM NaNO2, and 25 μM chromotropic acid on the sponge surface. The PEI-sponge platform provided good selectivity and sensitivity for ceftazidime determination within 30 min. The linear working range for ceftazidime determination was in the range of 0.5-3.0 mg L-1 with a limit of detection (LOD) of 0.06 mg L-1. The proposed method was successfully applied to detect ceftazidime in water samples with satisfactory recovery (83-103%) and reproducibility (<4.76% RSD).

A paper chromatographic-based electrochemical analytical device for the separation and simultaneous detection of carbofuran and carbaryl pesticides

We developed an electrochemical paper-based device (ePAD) for the online separation and simultaneous determination of structurally similar carbofuran (CBF) and carbaryl (CBR). Our device combined paper chromatography and an electrochemical sensor as a single system for increasing the selectivity to simultaneous detection of the two pesticides. During the simultaneous detection of CBF and CBR, the separation of the two carbamate compounds depends on the differences between the movements of the substances on the chromatographic paper in the moving phase flow. The isolated pesticides were electrochemically measured using an amperometric method. Under optimal conditions, which include the effect of the mobile phase, separation channel, and the applied potential, the proposed device provides a linear range for the simultaneous determination of CBF and CBR from 0.1 to 2.0 and 0.5–7.5 mg L−1, with the limits of detection at 0.06 and 0.40 mg L−1, respectively. Furthermore, we successfully used the developed device to determine CBF and CBR in water, cucumber, and cabbage samples. The obtained results correspond to results obtained from a standard method. This developed ePAD is low-cost and uses a low sample volume (2 µL). Moreover, it is disposable, portable, and a promising tool for the on-site quantification of pesticides in actual samples.

Fabricating a new immobilization matrix based on a conjugated polymer and application as a glucose biosensor

AbstractA new monomer named 4‐(dihexylamino)9,12‐di(thiophen‐2‐yl)‐7H‐benzo[de]benzo[4,5]imidazo[2,1‐a]isoquinolin‐7‐one (ThBN) is synthesized and used as a potential glucose biosensor after electropolymerization of the ThBN on the graphite pencil electrode. The amount of glucose is determined according to the decrease in the amount of oxygen by using cyclic voltammetry technique. Herein, conjugated polymer of ThBN is used as a immobilization matrix. The synthesized PThBN is found to be effective enzymatic biosensor having wide linear glucose determination range between 2.975 × 10−3 and 2.087 mM with a limit of detection of 0.0304 mM and a sensitivity of 0.1326 μA/mM cm2. This potential enzymatic biosensor has been also tested in commercial samples and found to be useful to detect the glucose concentration.

Graphite furnace atomic absorption spectrometry for the determination of trace gallium in whole blood

Objective: To establish a graphite furnace atomic absorption spectrometry method for the determination of trace gallium in whole blood. Methods: From January to May 2021, the five factors of ashing temperature, ashing time, atomization temperature, atomization time and matrix modifier concentration in the determination of gallium in whole blood by graphite furnace atomic absorption spectrometry were optimized by using L(16) (4(5)) orthogonal test design. At the same time, within-run, between-run, spiking recovery test and other methodological indicators were tested. Results: Under the optimized detection conditions, the linear range of determination of gallium in whole blood by graphite furnace atomic absorption spectrometry was 0.29-100.00 μg/L (r=0.9991) . The within-run and between-run relative standard deviations (RSD) of repetitive measurement at 10.0, 50.0, 80.0 μg/L concentration levels were 2.3%-4.4% and 1.5%-3.6%, the recovery rate of spiking was 98.1%-103.8%, and the detection limit of the method was 0.13 μg/L. Conclusion: Graphite furnace atomic absorption spectrometry for the determination of trace gallium in whole blood is easy to operate, has a wide linear range, low detection limit, accurate and reliable results, which is suitable for occupational health examinations and the determination of acute gallium poisoning.

Aptamer-functionalized 2D photonic crystal hydrogels for detection of adenosine.

Aptamer-functionalized two-dimensional photonic crystal (2DPC) hydrogels are reported for the detection of adenosine (AD). As a molecular recognition group, an AD-binding aptamer was covalently attached to 2DPC hydrogels. This aptamer selectively and sensitively binds AD, changing the conformation of the aptamer from a long single-stranded structure (AD-free conformation) to a short hairpin loop structure (AD-bound conformation). The AD-binding-induced changes of aptamer conformation reduced the volume of the 2DPC hydrogels and decreased the interparticle spacing of the 2DPC embedded in the hydrogel network. The particle spacing changes being dependent on AD concentration were determined by measuring 2DPC light diffraction using a simple laser pointer. The 2DPC hydrogel sensor showed a large particle spacing decrease of ~ 110nm in response to 1mM AD in phosphate-buffered saline (PBS). The linear range of determination of AD was 0.1nM to 1mM and the limit of detection was 0.09nM. The hydrogel sensor response for real samples was then validated in diluted fetal bovine serum (FBS) and human urine. The average % difference in particle spacing changes measured between diluted FBS and pure PBS was only 3.99%. In diluted human urine, the recoveries for the detection of AD were 95-101% and the relative standard deviations were 4.9-7.8%. The results demonstrate the potential applicability of the hydrogel sensor for real samples. This sensing concept, using the aptamer-functionalized 2DPC hydrogels, allows for a simple, sensitive, selective, and reversible detection of AD. It may enable sensor development for a wide variety of analytes by simply changing the aptamer recognition group.

Voltammetric chiral recognition of naproxen enantiomers by N-tosylproline functionalized chitosan and reduced graphene oxide based sensor

The chemical analysis of chiral compounds is of concern to researchers in the field of science and technology due to the various physiological and therapeutic properties of enantiomers. This experimental work provides novel sensor based on glassy carbon electrode (GCE) modified by N-tosylproline functionalized chitosan (TsPro-Cs) and reduced graphene oxide (rGO) for voltammetric recognition of naproxen (Nap) enantiomers. Each component of the modifying coating contributes to the improvement of the analytical and operational characteristics of sensor. The proposed sensor was characterized by fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Electrochemical recognition and quantification of Nap enantiomers were carried out using differential-pulse voltammetry (DPV). The oxidation peaks current ratio (IR/IS) of DPV measurements could be reached at 1.4 and peaks potential separation (ER–ES) of 40 mV. It was supposed that the chiral recognition occurred due to steric effect between N-tosylproline functionalized chitosan and Nap enantiomers. The binding energy of the chiral selector with the analyte molecule is higher for R-Nap than for S-Nap by 9.5 kcal/moll according to computational studies. The linear determination range was established as 20–500 μM for both enantiomers and detection limits of 0.4 μM and 0.9 μM were obtained for R- and S-Nap, respectively. The electrode showed good reproducibility with relative standard deviations of 1.8 % and 2.1 % for R- and S-Nap, respectively. The proposed sensor GCE/rGO-TsPro-Cs correctly determined Nap enantiomers in biological fluids with adequate precision and recovery ranged from 94 to 99 %. The developed sensor can determine the ratio of Nap isomers in enantiomeric mixture, which suggests that this sensor is an attractive candidate for practical use. This novel GCE/rGO-TsPro-Cs sensor can be a promising tool as an express device for monitoring the therapy of various diseases, as well as at the stage of drug production, and also for monitoring the impact of naproxen enantiomers on ecosystems and human health.

Enhanced ammonia sensitivity electrochemical sensors based on PtCu alloy nanoparticles in-situ synthesized on carbon cloth electrode

The alloying of Pt with transition metals is significant in boosting the performance of Pt-based electrochemical sensors. In this paper, Platinum and copper alloy nanoparticles (PtCu NPs) were in-situ loaded on carbon cloth (CC) by electrochemical deposition to obtain a self-supported electrode (PtCu-CC) for electrochemical detection of ammonia. The alloying of Pt and Cu reduced the crystal lattice spacing of Pt and improved the catalytic performance of ammonia. Therefore, the PtCu-CC electrode displayed visibly enhanced ammonia detection performance compared with the Pt-CC electrode and commercial Pt electrode. The linear range for ammonia determination was from 0.5 to 40 and 40–500 μM, and the sensitivity of the Pt7Cu1-CC sensor was 9.5 μA μM−1 cm−2 and 0.778 mA lg μM−1 cm−2, respectively. The detection limit was 8.6 ± 0.32 nM, and the quantification limit was 28.67 ± 0.73 nM. The developed sensor shows good anti-interference capability, reproducibility and stability; in addition, it exhibited good capacity in the actual water sample test. PtCu alloy nanoparticles were applied to ammonia detection in water, which may broaden the ways of ammonia detection in water.

An electrochemical immunosensor based on graphite paper electrodes for the sensitive detection of creatine kinase in actual samples

• The electrochemical immunosensor designed very stable, low-cost and sensitive method for determination of Creatine Kinase. • CK immunosensor exhibited high analytical performance with a linear range 0.150 pg/mL and low detection limit (0.045 pg/mL). • Disposable graphite paper electrodes were firstly used to detection CK antigen for a novel biosensor system. • The optimization was performed for all fabrication steps of the electrochemical biosensor system. The enzyme creatine kinase (CK) is one of the most well-established biomarkers in cardiovascular disease. For acute myocardial infarction (AMI) diagnosis, CK has a clinical comorbidity rate of 90%. This study has developed a novel electrochemical immunosensor using disposable graphite paper electrodes (GP). The GP electrodes were modified with gold nanoparticles (AuNP) to facilitate CK detection. Afterwards, GP electrodes were covalently immobilized with 6-mercapto-1-hexanol (6-MH), resulting in self-assembled monolayers (SAMs). Then, the electrodes were formed with a 3-Glycidyloxypropyltrimethoxysilane (3-GOPE) agent. Afterwards, the electrodes were immobilized with anti-CK (antibody creatine kinase) protein. In the final immobilization step, BSA (bovine serum albumin) protein was used to block non-covalent interactions. All parameters of the proposed immunosensor were optimized, including concentrations and incubation times. Analytical characteristics such as square wave voltammetry, linear determination range, repeatability, reproducibility, and regeneration of biosensors were determined. All characterization steps were monitored by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV). Moreover, the single frequency impedance (SFI) technique interacted with anti-CK and CK antigens. Furthermore, the proposed immunosensor was characterized using scanning electron microscopy (SEM). The proposed immunosensor exhibited a wide detection range (0.1–50 pg mL −1 ), and low limit of detection (LOD), and a low limit of quantification (LOQ); 0.045 pg mL −1 and 0.171 pg mL −1 , respectively. Finally, the developed biosensor was tried in an actual blood sample, which showed it could be utilized in clinical applications.

Development and Practical Application of Glucose Biosensor Based on Dendritic Gold Nanostructures Modified by Conducting Polymers.

In this study, graphite rod (GR) electrodes were electrochemically modified by dendritic gold nanostructures (DGNs) followed by immobilization of glucose oxidase (GOx) in the presence of mediator phenazine methosulfate (PMS). Modified with polyaniline (PANI) or polypyrrole (Ppy), GOx/DGNs/GR electrodes were used in glucose biosensor design. Different electrochemical methods were applied for the registration of glucose concentration, and constant potential amperometry (CPA) was chosen as the best one. PANI and Ppy layers synthesized enzymatically on the GOx/DGNs/GR electrodes extended the linear glucose determination range, the width of which depended on the duration of PANI- and Ppy-layers formation. Enzymatically formed polypyrrole was determined as the most suitable polymer for the modification and formation of the glucose biosensor instead of polyaniline, because it was 1.35 times more sensitive and had a 2.57 times lower limit of detection (LOD). The developed glucose biosensor based on the Ppy/GOx/DGNs/GR electrode was characterized by appropriate sensitivity (59.4 μA mM−1 cm−2), low LOD (0.070 mmol L−1), wide linear glucose determination range (up to 19.9 mmol L−1), good repeatability (8.01%), and appropriate storage stability (33 days). The performance of the developed glucose biosensor was tested in biological samples and beverages.

A Universal Biofilm Reactor Sensor for the Determination of Biochemical Oxygen Demand of Different Water Areas.

In this study, we developed a simple strategy to prepare a biofilm reactor (BFR) sensor for the universal biochemical oxygen demand (BOD) determination. The microorganisms in fresh water were domesticated by artificial seawater with different salinity gradients successively to prepare the BFR sensor. The prepared BFR sensor exhibits an efficient ability to degrade a variety of organic substances. The linear range of BOD determination by the BFR sensor is 1.0–10.0 mg/L−1 with a correlation coefficient of 0.9951. The detection limit is 0.30 mg/L according to three times of signal-to-noise ratio. What is more, the BFR sensor displayed excellent performances for the BOD determination of different water samples, including both fresh water and seawater. The 16S-rRNA gene sequencing technology was used to analyze the microbial species before and after the domestication. The results show that it is a general approach for the rapid BOD determination in different water samples.

Electrochemical sensing of indole in plasma using Pd nanoparticles modified metal-organic framework Cr-MIL-101/ionic liquid sensor

Herein, an electrochemical sensor for detection of indole was fabricated based on Pd nanoparticles modified Metal-Organic Framework Cr-MIL-101 (Pd@Cr-MOF) and ionic liquid (IL). The electrochemical behavior of indole was investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) at the surface of the modified electrode. The sensor was developed by incorporating of ultra-small nano-sized palladium particles stabilized on metal–organic framework Cr-MIL-101 and 1-hexyl-3-methylimidazolium chloride in the carbon paste electrode (CPE). The synthesized Pd nanoparticles modified Metal-Organic Framework Cr-MIL-101 (Pd@Cr-MOF) was characterized using Brunauer-Emmett-Teller (BET), EDS, XRD, SEM and TEM techniques. The Pd@Cr-MOF/IL/CPE exhibited the good sensitivity towards indole compared to the unmodified electrode. The linear range for determination of indole by this sensor was found to be 1 to 1100 nM with a detection limit of 0. 3 nM. Also, the proposed sensor was successfully applied for monitoring of indole in human serum sample and satisfactory results were obtained. Ultimately, high performance liquid chromatography (HPLC) method was applied for the validation of the electrochemical method for the determination of indole in human serum sample.