Combination of core-shell structured NH2-UiO-66@ZIF-8 loaded Ru (bpy)3 2+ and molecularly imprinted copolymer for the sensitive ECL detection of tetracycline.

A molecularly imprinted electrochemiluminescent sensor is developed for the sensitive detection of tetracycline in environmental and food samples. The sensor uses an ionic liquid (i.e. [APMIM]Br) modified graphene-carbon nanotube composite (GMI) material as substrate, a double-layered core-shell metal-organic framework NH2-UiO-66@ZIF-8 (NUZ) loaded bipyridyl ruthenium (NUZ@Ru) as luminescent material, and a molecularly imprinted copolymer of o-phenylenediamine and hydroquinone as recognition element. The ionic liquid-modified graphene-carbon nanotube composite has a favorable three-dimensional structure, high specific surface area, and good hydrophilicity; the core-shell structured metal-organic framework has high stability and plentiful reaction sites for loading; the molecularly imprinted copolymer film has enhanced stability and recognition effect. Hence, the resulting sensor combines the merits of several materials and presents improved performance. Under the optimum detection conditions, it shows a wide linear range of 0.05 µM - 1 mM, a low detection limit of 20 nM, high selectivity, and excellent stability. It has been successfully applied to the detection of tetracycline in different samples.

Autonomously Assembled Living Capsules by Microbial Coculture for Enhanced Bacteriotherapy of Inflammatory Bowel Disease.

Microorganism-mediated self-assembling of living formulations holds great promise for disease therapy. Here, we constructed a prebiotic-probiotic living capsule (PPLC) by coculturing probiotics (EcN) with Gluconacetobacter xylinus (G. xylinus) in a prebiotic-containing fermentation broth. Through shaking the culture, G. xylinus secretes cellulose fibrils that can spontaneously encapsulate EcN to form microcapsules under shear forces. Additionally, the prebiotic present in the fermentation broth is incorporated into the bacterial cellulose network through van der Waals forces and hydrogen bonding. Afterward, the microcapsules were transferred to a selective LB medium, which facilitated the colonization of dense probiotic colonies within them. The in vivo study demonstrated that PPLC-containing dense colonies of EcN can antagonize intestinal pathogens and restore microbiota homeostasis by showing excellent therapeutic performance in treating enteritis mice. The in situ self-assembly of probiotics and prebiotics-based living materials provides a promising platform for the treatment of inflammatory bowel disease.

Simultaneous Detection of Ovarian Cancer-Concerned HE4 and CA125 Markers Based on Cu Single-Atom-Triggered CdS QDs and Eu MOF@Isoluminol ECL.

Simultaneous detection of different disease markers is significant for clinical diagnosis. In this work, a dual-signal electrochemiluminescence (ECL) immunosensor was constructed for the simultaneous detection of carbohydrate antigen 125 (CA125) and human epithelial protein 4 (HE4) markers of ovarian cancer. The results showed that the Eu metal-organic framework-loaded isoluminol-Au nanoparticles (Eu MOF@Isolu-Au NPs) could generate a strong anodic ECL signal through synergistic interaction; as cathodic luminophore, the composite of carboxyl-functionalized CdS quantum dots and N-doped porous carbon-anchored Cu single-atom catalyst could catalyze H2O2 co-reactant to produce a large amount of •OH and O2•-, making the anodic and cathodic ECL signals significantly increase and become stable. Based on the enhancement strategy, a sandwich immunosensor was constructed for the simultaneous detection of ovarian cancer-associated CA125 and HE4 markers by combining antigen-antibody specific recognition and magnetic separation technique. The resulting ECL immunosensor displayed high sensitivity, a wide linear response range of 0.005∼500 ng mL-1, and low detection limits of 0.37 and 1.58 pg mL-1 for CA125 and HE4, respectively. Furthermore, it had excellent selectivity, stability, and practicability in the detection of real serum samples. This work establishes a framework for in-depth design and application of single-atom catalysis in ECL sensing.

A magnetic porous carbon material derived from an MIL-101(Fe) complex for efficient magnetic solid phase extraction of fluoroquinolone antibiotics.

Extraction and determination of trace hazardous components from complex matrices continue to attract public attention. In this work, magnetic porous carbon (MPC) was prepared for efficient magnetic solid phase extraction (MSPE) of fluoroquinolone (FQ) antibiotics in food and water samples. To prepare the MPC, an Fe-based metal-organic framework (MIL-101(Fe)) was grown on a network of graphene oxide and multi-walled carbon nanotubes through a hydrothermal method, and then a carbonization process under a nitrogen atmosphere was carried out to obtain the MPC with high specific surface area and good magnetism. Four target FQs including ciprofloxacin (CIP), enrofloxacin (ENO), lomefloxacin (LOM) and ofloxacin (OFX) were enriched using the as-prepared MPC and determined by coupled high-performance liquid chromatography. Under the optimal conditions, the established MSPE-HPLC-UV detection method exhibited a linear range of 0.5-800 µg L-1 and detection limits of 0.11-0.18 µg L-1 with relative standard deviations (RSDs) of 0.5-4.8%. When applied in the determination of the above four FQs in real samples such as lake water, milk and pork, good recoveries between 85.2 and 103.7% were obtained, and the RSDs were less than 4.8%. This work indicates that the MPC material can be a good adsorption material and has good application prospects in antibiotics enrichment and/or removal from complex samples.

Sensitive dual-mode detection of carbendazim by molecularly imprinted electrochemical sensor based on biomass-derived carbon-loaded gold nanoparticles.

A dual-mode electrochemical sensor was fabricated for carbendazim (CBD) detection. Biomass-derived carbon loaded gold nanoparticles (AuNPs/BC) were firstly coated on a glassy carbon electrode (GCE), and then molecularly imprinted polymer (MIP) of o-aminophenol was prepared on the resulting AuNPs/BC/GCE through electrochemical method in the presence of CBD. The AuNPs/BC had excellent conductivity, large surface and good electrocatalysis, while the imprinted film presented good recognition. Thus, the obtained MIP/AuNPs/BC/GCE exhibited sensitive current response to CBD. Furthermore, the sensor displayed good impedance response to CBD. Hence, a dual-mode detection platform for CBD was established. Under optimum conditions, the linear response ranges were as wide as 1.0 nM - 15 µM (by differential pulse voltammetry, DPV) and 1.0 nM - 10 µM (by electrochemical impedance spectroscopy, EIS), and the detection limits for these two methods were as low as 0.30 nM (S/N = 3) and 0.24 nM (S/N = 3), respectively. The sensor also had high selectivity, stability and reproducibility. The sensor was applied to detect CBD in spiked real samples, including cabbage, peach, apple and lake water, and the recoveries were 85.8-108% (by DPV) and 91.4-110% (by EIS); the relative standard deviations (RSD) were 3.4-5.3% (by DPV) and 3.7-5.1% (by EIS), respectively. The results were consistent with that obtained by high-performance liquid chromatography. Therefore, this sensor is a simple and effective tool for CBD detection, and it has good application potential.

Molecular imprinting electrochemiluminescence sensor based on nitrogen-doped carbon quantum dots /Ru(bpy)3@SiO2 for the determination of citrinin.

An electrochemiluminescence (ECL) sensor based on molecular imprinting polymer and SiO2 nanoparticles loaded Ru(bpy)3 and nitrogen-doped carbon quantum dots (NCQDs) is constructed for citrinin detection. The Ru(bpy)3 acts as ECL emitter, and the NCQDs cooperate with tri-n-propylamine (TPA) in solution as a coreactant to facilitate the luminescence. The citrinin imprinted poly(p-aminothiophenol) film is deposited on the surface of the luminophore by electrochemical method, which can immobilize the luminophore besides recognizing the target. The obtained ECL sensor exhibits high sensitivity, stability, and reproducibility. The change of ECL intensity and the logarithm of citrinin concentration display a good linear relationship in the range 1.0 to 100 pg mL-1, and the detection limit is 5 fg mL-1. When it is applied to the detection of citrinin contents in food sample (i.e., rice and millet) solutions, the RSD is less than 6.1%, and the recoveries for spiked standards range from 95.5 to 102.0%. Hence, this work provides a promising alternative for citrinin detection.

Detection of Gastric Cancer-Associated d-Amino Acids and Carcinoembryonic Antigen by Colorimetric and Immuno ECL Sensing Platform Based on the Catalysis of N/S-Doped Carbon Dots @ N-Rich Porous Carbon Nanoenzyme.

Gastric cancer is a malignant tumor, and its early diagnosis remains challenging due to the lack of simple and sensitive detection methods and specific biomarkers. In this work, to improve the detection reliability, we developed a dual-mode detection strategy for the detection of two biomarkers associated with it. First, an N- and S-doped carbon dots-N-rich porous carbon nanoenzyme (N/S-CDs@NC) was prepared by a two-step pyrolysis of thiourea-penetrated zinc-based zeolite imidazole framework. It was then combined with the 3,3',5,5'-tetramethylbenzidine-H2O2 system for the colorimetric detection of d-amino acids (i.e., d-proline (d-Pro) and d-alanine (d-Ala)) in saliva, based on d-amino acid oxidase catalyzing d-amino acid oxidation to produce H2O2. In this way, the low detection limits (S/N = 3) of d-Pro and d-Ala were 0.14 and 0.35 µM, respectively. Furthermore, N/S-CDs@NC was combined with the luminol-H2O2 electrochemiluminescence (ECL) system and magnetic immune accumulation/separation strategy to detect the carcinoembryonic antigen (CEA) in serum. The porous N/S-CDs@NC could facilitate participant contact, promote the generation of hydroxyl radical (•OH), and electrostatically attract •OH, thereby significantly amplifying the ECL signal of luminol and improving the signal stability. Thus, the detection mode showed considerable sensitivity and selectivity, with a low detection limit of 0.26 pg mL-1. The strategy proposed in this work can also be used for the detection of other disease markers by substituting the recognition elements, thus having good application potential.

Molecularly imprinted ratiometric electrochemical sensor based on carbon nanotubes/cuprous oxide nanoparticles/titanium carbide MXene composite for diethylstilbestrol detection.

Conventional molecularly imprinted polymers (MIP)-based electrochemical sensors are generally susceptible to the changes of personal operation, electrode surface, and solution conditions. Herein, a ratiometric strategy was employed through introducing Cu2O nanoparticles (NPs) as inner reference probe to realize the reliable detection of diethylstilbestrol (DES). MIP film was prepared by electropolymerization of 1H-pyrrole-3-carboxylicacid in the presence of DES on carbon nanotubes/cuprous oxide/titanium carbide (CNT/Cu2O NPs/Ti3C2Tx) modified electrodes. The Ti3C2Tx with accordion-like structure not only possessed good electrical conductivity, but also facilitated the immobilization of Cu2O NPs, which contributed to stabilizing the signal. CNT was introduced to further improve the sensitivity of the sensor. Under optimum conditions, the MIP/CNT/Cu2O NPs/Ti3C2Tx electrochemical sensors showed a broad linear response range of 0.01 to 70 µM, and a low detection limit of 6 nM (S/N = 3). Moreover, the sensor was applied to detect DES in real samples including lake water, milk, and pork, and the recoveries for spiked standard were 88-112%. Thus, this work provides a new way for reliable DES detection.

Determination of patulin using dual-dummy templates imprinted electrochemical sensor with PtPd decorated N-doped porous carbon for amplification.

A novel dual-dummy templates imprinted electrochemical sensor has been fabricated for the detection of patulin. Herein, 2-oxindole (2-oxin) and 6-hydroxynicotinic acid (6-HNA) as the dummy templates, 4-aminothiophenol as functional monomer, and ionic liquid (IL) as electropolymerization electrolyte are employed to prepare molecularly imprinted polymer (MIP) film. 2-Oxin and 6-HNA have multiple groups and the obtained MIP possesses different types of imprinted sites, thereby achieving a better recognition capacity than that of single-dummy imprinted film. ILs can regulate the density of molecularly imprinted film and facilitate effective molecular recognition. The composite of PtPd decorated N-doped porous carbon has good conductivity and large surface area, and can amplify the signal. With the aid of electrochemical probe [Fe(CN)6]3-/4- (0.16 V vs. SCE) patulin can be detected. Under the optimal conditions, this sensor shows a detection range from 0.01 to 10 µg L-1, with a detection limit of 7.5 × 10-3 µg L-1 (S/N = 3). Two spiked juice samples were analyzed by this method, and the recovery ranges from 94 to 99.8% with RSD values of 2.4-4.6% (n = 3), indicating that this method can be applied for the detection of patulin in real samples. A novel dual-dummy templates imprinted electrochemical sensor is firstly fabricated for the detection of patulin. This sensor exhibits high recognition capacity and sensitivity.

Fe3 O4 /reduced graphene oxide-carbon nanotubes composite for the magnetic solid-phase extraction and HPLC determination of sulfonamides in milk.

A novel magnetic adsorbent Fe3 O4 /reduced graphene oxide-carbon nanotubes, was prepared by one-pot solvothermal synthesis method. It was characterized by scanning electron microscopy, X-ray powder diffraction and vibrating sample magnetometry. The diameter of Fe3 O4 microparticles was about 350 nm, which were covered by carbon nanotubes and reduced graphene oxide sheets, while carbon nanotubes inserted between the reduced graphene oxide sheets effectively prevented their aggregation. The composite had large surface area and good magnetic property, suiting for magnetic solid-phase extraction and the determination of sulfonamides, by coupling with high-performance liquid chromatography. Under the optimized conditions (including extraction time, amount of adsorbent, solution pH, ionic strength and desorption conditions), a good linear was achieved in the concentration range of 5-500 µg/L and the low limits of detection and low limits of quantification were 0.35-1.32 and 1.16-4.40 µg/L, respectively. The enrichment factors were estimated to be 24.72 to 30.15 fold. The proposed method was applied for the detection of sulfonamides in milk sample and the recoveries were 88.4-105.9%, with relative standard deviations of 0.74-5.38%.

Space-confined synthesis of ordered mesoporous carbon doped with single-layer MoS2-boron for the voltammetric determination of theophylline.

A space-confined synthesis method is employed for the preparation of a single-layer MoS2-boron doped ordered mesoporous carbon nanocomposite. A phenol-formaldehyde resin is used as carbon source to create a confined space for the formation of single-layer MoS2. The addition of pluronic F127, as a soft template, suppresses the stacking of MoS2 layers and makes the composite porous. The nanocomposite is characterized by scanning electron and transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and energy dispersive X-ray spectroscopy. The single-layer MoS2 sheets have a lateral size of about 5 nm and are uniformly embedded in the composite. They possess numerous active edge sites and display a strong synergistic effect with other components. The composite is modified on a glassy carbon electrode, followed by the electrochemical imprinting of theophylline, and the resulting electrode exhibits good electrochemical response to theophylline. The linear response range is 0.01-250 µM by differential pulse voltammetry, and the lower detection limit is 5 nM. It has been successfully applied to the determination of theophylline in spiked tea drink samples. Graphical abstract Single-layer MoS2-boron doped ordered mesoporous carbon nanocomposite has large surface area and high catalysis, when coupling with molecularly imprinted polymer the resulting electrode shows highly sensitive and selective response to theophylline.

Graphene-doped electrochemical copolymer coating of 2,2-bithiophene and 3-methylthiophene for the highly effective solid-phase microextraction of volatile benzene homologues.

We report the electrochemical fabrication of a poly(2,2-bithiophene-co-3-methylthiophene)-graphene composite coating and its application in the headspace solid-phase microextraction and gas chromatography determination of benzenes (i.e., bromobenzene, 4-bromotoluene, 2-nitrotoluene, 3-nitrotoluene and 1,2,4-trichlorobenzene). The coating was uniform and showed cauliflower-like microstructure. It had high thermal stability (up to 375°C) and could be used for at least 180 times of solid-phase microextraction without a decrease in extraction performance. Furthermore, it presented high extraction capacity for the benzenes due to the hydrophobic effect and π-π interaction between the analytes and the coating. Under optimized extraction conditions, good linearity (correlation coefficients higher than 0.9946), wide linear range (0.01-50 µg/L), and low limits of detection (5.25-12.5 ng/L) were achieved for these analytes. The relative standard deviation was lower than 5.7% for five successive measurements with one fiber, and the relative standard deviation for fiber-to-fiber was 4.9-6.8% (n = 5). The solid-phase microextraction and gas chromatography method was successfully applied for the determination of three real samples, and the recoveries for standards added were 89.6-106% for nail polish, 85.8-110% for hair dye, and 90-106.2% for correction fluid, respectively.

Graphene Paper Decorated with a 2D Array of Dendritic Platinum Nanoparticles for Ultrasensitive Electrochemical Detection of Dopamine Secreted by Live Cells.

To circumvent the bottlenecks of non-flexibility, low sensitivity, and narrow workable detection range of conventional biosensors for biological molecule detection (e.g., dopamine (DA) secreted by living cells), a new hybrid flexible electrochemical biosensor has been created by decorating closely packed dendritic Pt nanoparticles (NPs) on freestanding graphene paper. This innovative structural integration of ultrathin graphene paper and uniform 2D arrays of dendritic NPs by tailored wet chemical synthesis has been achieved by a modular strategy through a facile and delicately controlled oil-water interfacial assembly method, whereby the uniform distribution of catalytic dendritic NPs on the graphene paper is maximized. In this way, the performance is improved by several orders of magnitude. The developed hybrid electrode shows a high sensitivity of 2 µA cm(-2) µM(-1), up to about 33 times higher than those of conventional sensors, a low detection limit of 5 nM, and a wide linear range of 87 nM to 100 µM. These combined features enable the ultrasensitive detection of DA released from pheochromocytoma (PC 12) cells. The unique features of this flexible sensor can be attributed to the well-tailored uniform 2D array of dendritic Pt NPs and the modular electrode assembly at the oil-water interface. Its excellent performance holds much promise for the future development of optimized flexible electrochemical sensors for a diverse range of electroactive molecules to better serve society.

Ionic liquid supported on an electrodeposited polycarbazole film for the headspace solid-phase microextraction and gas chromatography determination of aromatic esters.

A polycarbazole film was electrodeposited on a stainless-steel wire from a solution of N,N-dimethylformamide/propylene carbonate (1:9 v/v) containing 0.10 M carbazole and 0.10 M tetrabutylammonium perchlorate. The obtained polycarbazole fiber was immersed into an ionic liquid (1-hydroxyethyl-3-methyl imidazolium bis[(trifluoromethyl)sulfonyl]imide) solution (in dimethylsulfoxide) for 30 min, followed by drying under an infrared lamp. The resulting polycarbazole/ionic liquid fiber was applied to the headspace solid-phase microextraction and determination of aromatic esters by coupling with gas chromatography and flame ionization detection. Under the optimized conditions, the limits of detection were below 61 ng/L (S/N = 3) and the linear ranges were 0.061-500 µg/L with correlation coefficients above 0.9876. The relative standard deviations were below 4.8% (n = 5) for a single fiber, and below 9.9% for multi-fiber (n = 4). This fiber also exhibited good stability. It could be used for more than 160 times of headspace solid-phase microextraction and could withstand a high temperature up to 350°C.

Electrochemical fabrication of a novel polycarbazole coating for the headspace solid-phase microextraction and GC determination of some chlorobenzenes.

A novel polycarbazole coating was prepared by cyclic voltammetry on a platinum wire. The solution for electropolymerization contained N,N-dimethylformamide, propylene carbonate (v/v = 1:9), 0.10 M carbazole and 0.10 M tetrabutylammonium perchlorate; the cyclic scan potential range was 0.8-2.0 V (versus Ag/AgCl). The resulting polycarbazole coating showed a porous structure and had a large specific surface area. When it was used for the headspace solid-phase microextraction of chlorobenzenes (i.e. chlorobenzene, 2-chlorotoluene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,2,4-trichlorobenzene) followed by GC analysis, it presented excellent analytical performance. Under the optimized conditions the linear ranges were 0.25-250 µg/L with correlation coefficients >0.985, and the low detection limits were 15-61 ng/L (S/N = 3) for different chlorobenzenes. The RSDs were 2.4-4.9% for five successive measurements with a single fiber, and for fiber-to-fiber they were 6.3-13.1% (n = 5). Furthermore, the polycarbazole coating displayed good thermal stability (>350°C) and durability (more than 250 times). The proposed method was successfully applied to the extraction and determination of chlorobenzenes in waste water and lake water, and the recoveries for standards added were 86-114% for different analytes.

Novel ferrofluid based on water-based deep eutectic solvents: application in dispersive liquid-liquid microextraction of naphthalene-derived plant growth regulators in edible oil.

A new ferrofluid extractant (Fe3O4 @SiO2-WDES) was ingeniously prepared by coating magnetic Fe3O4 @SiO2 microspheres with water-based deep eutectic solvent (WDES) and used for dispersive liquid-liquid microextraction (DLLME) and HPLC determination of naphthalene-derived plant growth regulators (PGRs, i.e., 1-naphthylacetic acid, 2-naphthylacetic acid, 1-naphthoxy acetic acid, 2-naphthyloxyacetic acid and 1-naphthylacetamide) in edible oil. Herein, mass transfer of the analytes in DLLME was significantly enhanced via increasing the contact surface by employing the microspheres as the supporter and dispersant of WDES, and phase separation can be efficiently achieved using an external magnet rather than centrifugation in traditional DLLME. Response surface methodology (RSM) based on Box-Behnken design (BBD) was employed for the optimization of core experimental conditions, and Analytical Eco-Scale and Analytical GREEnness Metric Approaches were adopted to evaluate the degree of greenness of the procedure. Under the optimal conditions, satisfactory performances of linearity ranged from 5 to 100 µg/L (R2 ≥ 0.9982), limit of detection (0.58-0.91 µg/L), limit of quantitation (1.9-3.0 µg/L), precision (RSDs ≤ 5.5%), recovery (81.3%-108.1%) and negligible matrix effect were achieved, which introduced a promising alternative route for the determination of naphthalene-derived plant growth regulators in edible oil.

CdS/Bi2S3/NiS ternary heterostructure-based photoelectrochemical immunosensor for the sensitive detection of carbohydrate antigen 125.

The sensitive, accurate and rapid detection of carbohydrate antigen 125 (CA125) is essential for the early diagnosis and clinical management of ovarian cancer, but there is still challenge. Herein, a photoelectrochemical (PEC) immunosensor based on CdS/Bi2S3/NiS ternary sulfide heterostructured photocatalyst was presented for the detection of CA125. The CdS/Bi2S3/NiS was synthesized by a one-step hydrothermal approach. The heterojunction comprising of CdS and Bi2S3 could separate photogenerated carriers, the introduced narrow bandgap NiS could act as electron-conducting bridge to facilitate the transfer of interfacial photogenerated electrons, thereby improving the photoelectric conversion efficiency. Due to their synergistic effect, the photocurrent response produced by the composite was up to 14.6 times of pure CdS. On the basis, a PEC immunosensor was constructed by introducing the CA125 antibody through thioglycolic acid linkage. It was found that the resulting immunosensor showed good performance. Under the optimized conditions, its linear detection range was as wide as 1 pg mL-1-50 ng mL-1, and the detection limit was low to 0.85 pg mL-1. Furthermore, we experimentally tested its anti-interference, stability and reproducibility, and satisfactory results were achieved. The practicable feasibility of the sensor was confirmed by testing serum sample. Thus this work provided a simple, fast and enough sensitive approach for CA125 monitoring.

A novel electrochemical sensor based on a Cu-coordinated molecularly imprinted polymer and MoS2 modified chitin-derived carbon for selective detection of dextromethorphan.

Dextromethorphan (DXM) is a widely utilized central antitussive agent, which is frequently abused by individuals seeking its recreational effect. But DXM overdose can cause some adverse effects, including brain damage, loss of consciousness, and cardiac arrhythmias, and hence its detection is significant. Herein, an electrochemical sensor based on a Cu-coordinated molecularly imprinted polymer (Cu-MIP) was fabricated for its detection. For constructing the sensor, nitrogen-doped carbon nanosheets (CCNs) were prepared through calcining chitin under an argon atmosphere, and molybdenum disulfide (MoS2) was allowed to grow on their surface. Subsequently, the obtained MoS2/CCNs composite was employed to modify a glassy carbon electrode (GCE), and the Cu-MIP was electrodeposited on the electrode in a Cu-1,10-phenanthroline (Cu-Phen) solution containing DXM, where Cu2+ played a role in facilitating electron transfer and binding DXM. Due to the large specific surface area, good electrocatalytic properties and recognition of the resulting composite, the resulting Cu-MIP/MoS2/CCNs/GCE showed high selectivity and sensitivity. Under optimized experimental conditions, the peak current of DXM and its concentration exhibited a good linear relationship over the concentration range of 0.1-100 µM, and the limit of detection (S/N = 3) was 0.02 µM. Furthermore, the electrochemical sensor presented good stability, and it was successfully used for the determination of DXM in pharmaceutical, human serum and urine samples.

A liposome encapsulated methylene blue-mediated electrochemical and UV-visible dual mode split-type immunoassay for the detection of 17ß-estradiol.

Herein, we fabricated an electrochemical (EC) and UV-visible absorption (UV-vis) dual mode split-type immunoassay for the detection of 17ß-estradiol (E2), which was mediated by liposome encapsulated methylene blue (MB@lip). MB molecule acted as the probe in the EC and UV-vis absorption dual mode detections, and its release was controlled by liposome. The competitive immune recognition was conducted between the E2 in the sample and E2 conjugated bovine serum protein (E2-BSA) adsorbed on the 96-wells plate in combining with E2 antibody labeled with MB@lip (E2-Ab/MB@lip). MB molecule could be released from the resulting immune composite of E2-BSA/E2-Ab/MB@lip in the presence of Triton X-100, and quantified by UV-vis and EC methods. The three-dimensional cross-linked reduced graphene oxide/Ti3C2 (3D-rGO/Ti3C2) aerogel was prepared through hydrothermal method, then complexed with the electroactive anthraquinone (AQ) and used as the electrode modified material. The AQ/3D-rGO/Ti3C2 composite had high surface area and provided abundant adsorption sites for MB, and the displacement/competitive behavior between AQ and MB could dexterously achieve the ratiometric EC detection of E2. In addition, the inherent blue color of MB allowed it to be analyzed by UV-vis absorption method. The proposed dual mode detection method exhibited broad linear ranges of 0.1 pg mL-1 to 50 ng mL-1 (by UV-vis) and 0.03 pg mL-1 to 50 ng mL-1 (by EC) for E2 detection, and the detection limits were 0.023 pg mL-1 (S/N = 3) and 8.0 fg mL-1 (S/N = 3), respectively. Moreover, the proposed immunoassay exhibited good practicability and was applied to monitor E2 in milk and serum successfully.

A ratiometric electrochemical sensing platform based on multifunctional molecularly imprinted polymer with catalytic activity for the detection of psychoactive substances.

Molecularly imprinted polymers (MIPs) are widely used as artificial recognition element in sensing field, but their electrochemical sensing performances are generally affected by their poor catalytic activity and unruly condition change. In this work, an MIP film with catalysis (Fe-DMMIP) is constructed by electrodeposition of Fe-coordinated aminophenanthroline and 3,4-ethylenedioxythiophene on N, S doped C material, using cannabinoid (CBD) as template molecule. Due to the presence of Fe-N active sites, the obtained Fe-DMMIP possesses enzyme-like catalytic activity besides conventional recognition capability. Accordingly, the sensor exhibits high electrocatalytic activity and selectivity. Moreover, the Fe-DMMIP can produce a stable and well-defined signal as an internal reference around 0 V (vs. Ag/AgCl) for ratiometric sensing. Under the optimal conditions, the ratiometric signal is linear to CBD concentration in the range of 0.004-0.8 µmol L-1 (R2 = 0.9946) with a detection limit of 2.9 nmol L-1. The ratiometric sensor shows high reproducibility, stability and applicability. In addition, through replacing the template molecule, the resulting biomimetic sensor also exhibits good performance in sensing other psychoactive substances such as melatonin and 5-hydroxytryptophan, with LODs of 19 nmol L-1 and 8 nmol L-1for them, respectively. Therefore, the developed sensing platform has good prospects, and this work provides a new way for developing ratiometric electrochemical sensors with high sensitivity, reproducibility and anti-interference ability.