Lower Limit Of Determination Research Articles

Antifouling coatings for electrochemical sensors

Electrochemical sensors are extremely promising for the analysis of a number of organic and inorganic compounds both in biological fluids and natural waters during environmental monitoring due to easing operation, ease of miniaturization, low cost, low limits of analyte determination and the possibility of modifying electrodes with a wide range of organic and inorganic compounds and nanomaterials. One of the main problems limiting the use of electrochemical sensors is electrode fouling. The main way to solve this problem is antifouling coatings. Depending on the application, various additional requirements are imposed on the antifouling coatings, such as, for example, biocompatibility or mechanical strength. In this review, various types of antifouling coatings for sensors are considered, the main areas of application of certain coatings are indicated. The main emphasis is placed on non-biocidal coatings, as the most promising ones.

Field Determination and Spatial Distribution of Se (IV) in Coastal Seawater of China

A portable electrochemical system based on rGO/AuNPs/Nafion was constructed for selenium (IV) field determination in coastal seawater of the North Yellow Sea, East China Sea and South China Sea. This system demonstrated a low determination limit (0.03 μg/L), a wide linear range of concentration (0.1–30 μg/L), exceptional reproducibility and repeatability, and excellent selectivity. Each individual, entire test could be accomplished within 8 min. In Yantai Sishili Bay, the Se (IV) concentrations ranged from 0.16–3.59 μg/L (average 1.43 μg/L). In Shengshan Island, the Se (IV) concentrations ranged from 0.20–5.18 μg/L (average 2.06 μg/L). In Zhelin Bay, the Se (IV) concentrations ranged from 0.87–4.87 μg/L (average 3.13 μg/L). The average concentrations of Se (IV) in surface seawater showcased an increasing trend from the north to the south of China, suggesting Zhelin Bay > Shengshan Island > Sishili Bay. The system develops a new, competitive method for water quality assessment, and contributes to the accurate study of the biogeochemical cycles of selenium.

Quantitative detection of luteolin and quercetin in natural samples with the composite of reduced graphene oxide and cyclotriveratrylene-based metal-organic framework

Design and construction of high-efficiency electrochemical sensors for luteolin (LU) and quercetin (QCT) are greatly necessary for the detection of their excessive intake. In this work, a new metal-organic framework (MOF), [Zn2L(OH-bdc)2]·2.5 H2O (1), was assembled with cyclotriveratrylene ligand (L), Zn(II) cation and 5-hydroxyisophthalic acid (OH-H2bdc). 1 featured a two-dimensional (2D) network structure. To improve the conductibility of 1, typical carbon materials, such as multi-walled carbon nanotube (MWCNT), mesoporous carbon (MC) and reduced graphene oxide (RGO) were respectively combined with the sample of 1. Markedly, synergistic effects between 1 and RGO enabled the 1@RGO(1:2) composite to exhibit efficient electrocatalytic performances for LU and QCT detection. Under the optimal condition, 1@RGO(1:2)/GCE featured the relatively wide linear range (0.02–14 μM for LU and 0.02–14 μM for QCT) and low limits of determination (LODs) (0.0022 μM for LU and 0.0049 μM for QCT). Remarkably, 1@RGO(1:2)/GCE showed good reproducibility, acceptable stability and satisfactory anti-interference. Importantly, the sensor was applied to detect LU and QCT in the natural samples with acceptable recoveries.

A point-of-care aptasensor based on the upconversion nanoparticles/MoS2 FRET system for the detection of Pseudomonas aeruginosa infection.

The rapid detection of Pseudomonas aeruginosa (P. aeruginosa) is of great significance for the diagnosis of medical infection. In view of the above, a novel aptasensor based on fluorescence resonance energy transfer (FRET) was developed. It contained aptamer-coupled upconversion nanoparticles (UCNPs-apt) as a donor (excitation 980nm) and molybdenum disulfide (MoS2) nanosheets as an acceptor. The upconversion fluorescence aptamer system was investigated to obtain the optimal parameters of MoS2 concentration, the incubation time of UCNPs-apt/MoS2 and P. aeruginosa, and pH. Based on the optimal parameters, a linear calibrationequation (emission 654nm) with a wide detection range 8.7 × 10 ~ 8.7 × 107cfu/mL, a high coefficient of determination R2 0.9941, and a low limit of determination (LOD) 15.5cfu/mL were established. The method was validated with P. aeruginosa infected foci of mouse wound. The advantage of this aptasensor isthat analysisresults can be obtained within 1.5h, which was much faster than that ofthe standard method (18-24h). Furthermore, combined with a portable instrument, it can be used as a point-of-care testing for the early detection of P. aeruginosa infection, which is useful for selecting the correct antibiotics to achieve good therapeutic effects. Additionally, it also has a broad application prospect in food and environmental areas.

In situ synthesis of self-supporting conductive CuCo-based bimetal organic framework for sensitive nonenzymatic glucose sensing in serum and beverage

Most MOFs are associated with the inherent defect of low conductivity, limiting their further application in electrochemical sensing. Herein, a self-supporting conductive CuCo-based bimetal organic framework with HHTP as the organic ligand was in situ synthesized on carbon cloth via a one-step hydrothermal method, namely CuCo-MOF/CC. Benefiting from the advantages of electrical conductivity and bimetallic synergies, CuCo-MOF/CC exhibited remarkable electrocatalytic performance toward glucose. Consequently, the prepared sensor demonstrated an outstanding sensitivity of 9317 μA mM−1 cm−2, a wide range of 0.25–2374.5 μM, a low determination limit (0.27 μM), and a rapid response time (1.6 s). The reproducibility, stability, and selectivity were also proved to be satisfactory. Furthermore, the remarkable feasibility of proposed sensor was confirmed in serum and beverages. With the convenience of the one-step hydrothermal method and portability of self-supporting electrode, CuCo-MOF/CC has emerged as a promising candidate for commercial glucose sensors.

A Novel Fluorescence Sensor for Iodide Detection Based on the 1,3-Diaryl Pyrazole Unit with AIE and Mechanochromic Fluorescence Behavior.

A D-A type of luminophore, TPA-CDP, was designed and synthesized by using triphenylamine (TPA) as D (electron donor), 1,3-diaryl pyrazole with cyano groups (CDP) as A (electron acceptor) and employing a cyanovinyl segment as a recognition group. Firstly, TPA-CDP demonstrates effective fluorescence quenching as a sensor for I- by the nucleophilic addition reaction of the cyanovinyl segment with a high level of sensitivity, selectivity and a low determination limit of 4.43 μM. Interestingly, TPA-CDP exhibited an AIE phenomenon with the fw value reaching 50%. In addition, TPA-CDP displayed distinct mechanochromic fluorescence behavior with 70 nm red shift, which was observed over four repeated cycles. Furthermore, the mechanochromic fluorescence behavior of TPA-CDP, as observed in powder XRD experiments, was found to be associated with the morphological transition from a crystalline state to an amorphous state. These results confirm the significant potential of CDP as a powerful electron-deficient component in the creation of D-A-type mechanochromic fluorescence materials and biosensors for detecting I-.

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.

New stochastic devices for simultaneous analysis of mismatch repair proteins and KRAS in biological samples

Two stochastic microsensors based on the immobilization of inulins: inutec and frutafit in a paste obtained from a graphene decorated with nitrogen (10.8 %), and boron (2.6 %), and paraffin oil (IR purity) were designed, characterized and validated for the molecular recognition and analysis of mismatch repair proteins like MLH1, MSH2, MSH6, PMS2, and of KRAS in biological samples such as: whole blood, urine, saliva, and tumoral tissues. The sensor based on inutec exhibited the largest working concentration range (10 decades of concentration) and the lowest limit of determination (0.32fg mL−1) when used for the assay of MLH1, and the wider working concentration range (8 decades of concentration), and the lowest limit of determination (2.30fg mL−1) when used for the assay of MSH6. The sensor based on frutafit exhibited the largest working concentration range (10 decades of concentration) when used for the determination of KRAS, and the wider working concentration range (5 decades of concentration), and the lowest limit of determination (1.00fg mL−1) when used for the assay of PMS2. No influence of the modifier (inutec and frutafit) was recorded on the linear concentration range (10 decades of concentration), and on the limit of determination (1.00 fg mL−1) for the assay of MSH2. The recoveries of MLH1, MSH2, MSH6, PMS2, and of KRAS in whole blood, urine, saliva, and tumoral tissues were higher than 98.00 with RSD (%) values lower than 0.10 %.

Preparation of COF-coated nickel foam adsorbents for dispersive solid-phase extraction of 16 polycyclic aromatic hydrocarbons from Chinese herbal medicines

Covalent organic framework coated nickel foam (NF@COF) was prepared as a sorbent for the dispersive solid phase extraction (DSPE) of polycyclic aromatic hydrocarbons (PAHs) from Chinese herbal medicines (CHMs) prior to their determination by gas chromatography-mass spectrometry (GC-MS). The structure and morphology of the as-synthesized NF@COF were characterized by different techniques. Various key parameters affecting the performance of the DSPE method, including the amount of sorbent, desorption solvent, desorption volume and time, extraction time, and sample volume, were investigated. Under the optimized conditions, NF@COF combined with GC-MS was successfully applied to the determination of 16 PAHs in CHMs. The method showed wide linearity (20–2000 ng mL−1), low limits of determination (0.3–2.7 ng mL−1), and high recoveries (78.0–124%). These results revealed that NF@COF has the potential for efficient extraction of PAHs from complex samples.

Nanoplatform-based analysis for the detection of HER3 and HER4 for gastric cancer diagnosis

Nanographene and α-cyclodextrin based sensors modified with gold nanoparticles and spheroidal copper were used to develop two stochastic sensors, which were then characterized and validated for the purpose of molecularly identifying and quantifying HER3 and HER4 in biological samples. In order to accomplish this goal, each of the stochastic sensors was incorporated in a nanoplatform. The two nanoplatforms were connected to a smartphone and recorded very low limits of determination (1 × 10−15 g ml−1) and wide linear concentration ranges (1 × 10−15–1 × 10−8 g ml−1) when a potential of 170 mV versus Ag/AgCl was applied. This allowed for the molecular identification and quantification of HER3 and HER4 in patients with gastric cancer, as well as in healthy individuals.

Rapid and Sensitive Detection of Sulfamethizole Using a Reusable Molecularly Imprinted Electrochemical Sensor.

Efficient methods for monitoring sulfonamides (SAs) in water and animal-source foods are of great importance to achieve environmental safety and protect human health. Here, we demonstrate a reusable and label-free electrochemical sensor for the rapid and sensitive detection of sulfamethizole based on an electropolymerized molecularly imprinted polymer (MIP) film as the recognition layer. To achieve effective recognition, monomer screening among four kinds of 3-substituted thiophenes was performed by computational simulation and subsequent experimental evaluation, and 3-thiopheneethanol was finally selected. MIP synthesis is very fast and green, and can be in situ fabricated on the transducer surface within 30 min in an aqueous solution. The preparation process of the MIP was characterized by electrochemical techniques. Various parameters affecting MIP fabrication and its recognition response were investigated in detail. Under optimized experimental conditions, good linearity in the range of 0.001-10 μM and a low determination limit of 0.18 nM were achieved for sulfamethizole. The sensor showed excellent selectivity, which can distinguish between structurally similar SAs. In addition, the sensor displayed good reusability and stability. Even after 7 days of storage, or being reused 7 times, higher than 90% of the initial determination signals were retained. The practical applicability of the sensor was also demonstrated in spiked water and milk samples at the nM determination level with satisfactory recoveries. Compared to relevant methods for SAs, this sensor is more convenient, rapid, economical, and eco-friendly, and had comparable or even higher sensitivity, which offered a simple and efficient method for SA detection.

Fast cathodic electrodeposition of ZnTCPP-functionalized metal-organic framework films forpreparation of a fluorescent aptamer sensor for microcystindetermination.

Aone-step electrodeposition-assisted self-assembly technique has been developedfor preparation of ZnTCPP@MOF films with three-dimensional mesoporous structure in a three-electrode system. The internal structure of the ZnTCPP@MOF films was tuned by adjusting the electrochemical deposition voltage, deposition time, and the concentration of ZnTCPP at room temperature. The ZnTCPP@MOF films under different deposition conditions were characterized by scanning electron microscopy, Fourier transformation infraredspectroscopy, and X-ray photoelectron spectroscopy. The prepared ZnTCPP@MOF films exhibited excellent fluorescence properties, in which ZnTCPP molecules were encapsulated inside the MOF as fluorescent signal probes and structure-directing agents, which affected the electrochemical response of the ZnTCPP@MOF films. The sensing platform based on ZnTCPP@MOF film wasused to detect microcystin with a wide determination range (1.0 × 10-12mol/L ~ 1.0 × 10-5mol/L), low determination limit (3.8 × 10-13mol/L), and high sensitivity. More importantly, the strategy is simple, low-cost, green, and environmentally friendly, and it provides a new strategy for the direct use of MOFs films as signaling components.

Preparation and application of 3D solid structure high performance liquid chromatography fillers in the detection of phthalates

Materials of 3D structure for HPLC columns have been prepared. Silica spheres with high purity were first funetionalized with Substance A and a range of other substances, and finally followed by quaternization with iodomethane to form the final product. A standard solution of four certain phthalates was used to verify the chromatographic performance of the resulting packing materia1. Quantification analysis was performed by the external standard method. Linear relationships were found between the peak areas and the mass concentrations of the four certain phthalates in definite ranges, with detection limits (3S/N) of 5 mg·kg-1 and the low limits of determination (10S/N) of 10 mg·kg-1. Recovery rates obtained by standard addition method were in the range of 100.8~106.8% and RSDs (n=6) were less than 4%, which meeting the requirement of routine experiment.

Determination of Four Certain Phthalates in the Electronic and Electrical Product by High Performance Liquid Chromatography

Precise detection of phthalates in the electronic and electrical product is essential. The method of the determination of four certain phthalates in the electronic and electrical product by high performance liquid chromatography (HPLC) was investigated in this study. The sample was extracted with n-hexane by Soxhlet extraction, then the extract was concentrated to dryness by rotary evaporation and diluted with methanol. The analytes were separated on a ADME (4.6×150 mm, 5 µm) chromatographic column with the column temperature 35 ℃. Methanol and water was used as mobile phase for gradient elution with the flow rate of 1.0 mL•min-1. The four certain phthalates were detected with DAD at the wavelength of 228 nm. Quantification analysis was performed by the external standard method. Linear relationships were found between the peak areas and the mass concentrations of the four certain phthalates in definite ranges, with detection limits (3S/N) of 5 mg·kg-1 and the low limits of determination (10S/N) of 10 mg·kg-1. Recovery rates obtained by standard addition method were in the range of 100.8~106.8% and RSDs (n=6) were less than 4%. The positive samples were further verified by LC-MS/MS.

Self-Supplied Electron Photoelectrochemical Biosensor with PTB7-Th as a Photoelectric Material and Biotin as an Efficient Quencher.

In this work, a self-supplied electron photoelectrochemical (PEC) biosensor for sensitive determination of Pb2+ was established by utilizing donor-acceptor (D-A)-type PTB7-Th (poly{4,8-bis[5-(2-ethylhexyl) thiophen-2-yl]benzo[1,2-b,4,5-b']dithiophene-2,6-diyl-alt-3-fluoro-2-[(2-ethylhexyl)carbonyl] thieno[3,4-b]-thiophene-4,6-diyl}) as a photoelectric material coupled with biotin as an efficient signal quencher. Impressively, compared with the traditional PEC signal quenchers, biotin was first applied as a PEC signal quencher in this work and it effectively avoided a cumbersome preparation process, complex DNA sequence design, and extra reagent assistance and greatly simplified experimental steps, which could achieve an efficient PEC signal quenching toward PTB7-Th. In addition, the execution of a DNAzyme-assisted Pb2+ recycling amplification reaction could release the quencher biotin, leading to the recovery of the PEC signal, thereby realizing the quantitative detection of Pb2+. Resultantly, the submitted self-supplied electron PEC biosensor presented an extensive coverage of assay Pb2+ (50 fM to 500 nM) along with a low determination limit (16.7 fM), which exhibited the advantages of high selectivity and excellent stability. Importantly, this work provided a powerful alternative to traditional heavy metal-ion assessment methods and possessed the potential for application in environment, biomedicine, and food-safety fields.

An Approach to the Simultaneous Determination of a Panel of Five Biomarkers for the Early Detection of Brain Cancer Using the Stochastic Method

The simultaneous determination of heregulin-α and HER 1–4 plays an important role in brain cancer diagnosis and treatment. To date, only enzyme-linked immunosorbent assay (ELISA) or a semiquantitative colorimetric method have been used for the assay of these biomarkers; these methods are quite expensive and can only determine one biomarker in a run. Four 3D stochastic microsensors based on multi-walled carbon nanotubes enriched with gold nanoparticles and modified with inulin were designed for the simultaneous determination of heregulin-α and HER 1–4 in tumor brain tissue and whole blood samples. For the simultaneous measurement of HRG-α and HER 1–4, all sensors demonstrated low limits of determination (as fg mL−1 magnitude order), high sensitivities, and wide concentration ranges. From biological samples, high recovery values of more than 96% of analytes were obtained. The proposed sensor can detect HER 1–4 and heregulin-α in whole blood and tumor tissue samples at the same time.

Simultaneous Analysis of MLH1, MSH2, MSH6, PMS2 and KRAS in Patients with Gastric and Colon Cancer Using Stochastic Sensors

Two stochastic sensors were characterized and validated for the molecular identification and quantification of MLH1, MSH2, MSH6, PMS2 and KRAS in biological samples using two types of doped-graphene modified with maltodextrin. When a potential of 125 mV vs. Ag/AgCl was applied, the two stochastic sensors recorded extremely low limits of determination (fg mL−1 magnitude order) and wide linear concentration ranges, which enabled the molecular identification and quantification of MLH1, MSH2, MSH6, PMS2 and KRAS in healthy individuals and patients with gastric or colon cancer. The recoveries of MLH1, MSH2, MSH6, PMS2 and KRAS in whole blood, saliva, urine and tumoral tissue samples exceeded 98.00% with a relative standard deviation of less than 1.00%.

Proton conduction and electrochemical enzyme-free glucose sensitive sensing based on a newly constructed Co-MOF and its composite with hydroxyl carbon nanotubes

It is a great challenge to construct MOFs-based materials with low activation energy for potential applications in proton exchange membrane fuel cells (PEMFCs) as well as fine electrocatalytic glucose sensing performance. Herein, we report a novel 2D Co-MOF {[Co(iip)(bbbm)(H2O)2]·2DMF·2H2O}n obtained through the assembly between Co(II) and 5-iodoisophthalic acid (H2iip) in the presence of the hydrophobic ligand 1,1-(1,4-butanediyl)bis-1H-benzimidazole (bbbm). Its composite with hydroxyl-functionalized carbon nanotubes (Co-MOF@CNTs) was fabricated under ambient conditions. The (8) hydrogen-bonded ring exists in Co-MOF. Both the composite membranes of Co-MOF and Co-MOF@CNTs with nafion exhibit interesting proton-conductive behavior, which are even superior to that of nafion in aqueous medium with the same pH values. Among them, the proton conductivity of the composite Co-MOF@CNTs/nafion membrane is expectedly superior to that of the composite Co-MOF/nafion membrane. Remarkably, the composite Co-MOF@CNTs/nafion membrane exhibited an exceptionally low activation energy (Ea = 0.082 eV, pH = 3), which is among one of the lowest Ea values for the reported novel proton-conducting polymeric materials/composites, resulting in almost unchanged conductivity over the measured temperature range, revealing its potential application in PEMFCs. Moreover, both the pristine Co-MOF and its composite Co-MOF@CNTs could serve as electrocatalytic materials toward glucose oxidation. The Co-MOF@CNTs electrode exhibits expectedly more rapid and sensitive electrochemical glucose sensing with relatively lower determination limit (LOD = 3 μM) and larger detection range (0.01–5 mM) in comparison with that of the pristine Co-MOF (LOD = 0.021 mM, 0.01–2.40 mM).

(Invited) New Challenges in Early Diagnosis of Gastric Cancer

Graphene proved to be an excellent material for sensors’ design. Therefore, we decorated it with different heteroatoms (e.g., N, B, S) and use it as electrode material for the design of new stochastic sensors. The graphene paste was modified with oleamides, inulins, dextrins in order to get the stochastic response of the sensor. Biomarkers like MSH6, MLH1, KRAS, p53 were analysed by screening the whole blood, urine, saliva, and tissue samples with the proposed sensors. High sensitivities and low limits of determination were obtained. Excellent correlations between the results obtained using the proposed screening method and the standard method were obtained.

An integrated nanoflower-like MoS2@CuCo2O4 heterostructure for boosting electrochemical glucose sensing in beverage

Excessive glucose in food poses a non-negligible threat to its inherent quality and human health, which makes it imperative to develop a highly sensitive sensor for real-time glucose detection. In this work, an integrated electrochemical glucose sensor based on a nanoflower-like MoS2@CuCo2O4 heterostructure was carefully constructed. Under optimal conditions, the as-fabricated sensor exhibited a high sensitivity of 1,303 μA mM−1 cm−2 over a wide range of 0.5–393.0 μmol/L, accompanied by a low determination limit (0.5 μmol/L) and short response time (2.1 s). The favorable sensing performance of the MoS2@CuCo2O4 nanocomposite-modified electrode in electrochemical analyses was attributed to the introduction of unique nanoflower-like heterostructure and the synergistic effects between MoS2 and CuCo2O4. Furthermore, the satisfactory applicability of this sensor in beverages was confirmed. These results demonstrate that the MoS2@CuCo2O4/GCE may be a promising platform for sensitive monitoring of glucose content in food samples.