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.

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.

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.

Dual-Mode Electrochemical Competitive Immunosensor Based on Cd2+/Au/Polydopamine/Ti3C2 Composite and Copper-Based Metal-Organic Framework for 17ß-Estradiol Detection.

Herein, a dual-mode electrochemical competitive immunosensor was constructed for the detection of 17ß-estradiol (E2) based on differential pulse voltammetry (DPV) and chronoamperometry (i-t). During the immune recognition process, the E2 antibody (E2-Ab) was immobilized on the Cd2+/Au/polydopamine/Ti3C2 (Cd2+/Au/pDA/Ti3C2) composite-modified electrode; then, the E2-conjugated bovine serum albumin (E2-BSA) was labeled with a copper-based metal-organic framework (Cu-MOF) and competed with E2 in combining the E2-Ab. The Cu-MOF was not only an electroactive species but also possessed good electrocatalytic activity toward H2O2. Thus, E2 could be quantified according to the peak current change of the Cu-MOF in DPV curve or the variation of H2O2 reduction current. For DPV quantification, Cd2+ was introduced as an internal reference in this case, and a highly reproducible ratio readout was obtained. The as-prepared dual-mode E2 electrochemical immunosensor showed good linear relationship in the ranges of 1 pg mL-1-10 ng mL-1 (DPV) and 10 pg mL-1-10 ng mL-1 (i-t), and the detection limits were 0.47 and 5.4 pg mL-1 (S/N = 3), respectively. Furthermore, the dual-mode electrochemical immunosensor exhibited good practicability in real sample analysis.

A ratiometric electrochemical sensor based on Cu-coordinated molecularly imprinted polymer and porous carbon supported Ag nanoparticles for highly sensitive and selective detection of perphenazine.

In this work, a ratiometric electrochemical sensor was developed for the detection of perphenazine (PPZ). The sensor was constructed by electrodepositing Cu-coordinated molecularly imprinted polymer (Cu-MIP) on Ag nanoparticles (NPs) modified flexible porous carbon cloth. The Cu-MIP showed highly electrochemical response because of the enhanced adsorptive ability and electronic properties of Cu2+ chelation; Ag NPs could provide a stable and effective reference signal for ratiometric quantification. Thus the resulted sensor not only displayed high selectivity and sensitivity, but also exhibited satisfactory reproducibility and anti-interference ability. Under the optimum conditions, the quantitative detection of PPZ was performed with differential pulse voltammetry. It was found that the peak current ratio of PPZ and Ag NP was linear to the concentration of PPZ in the range of 1-700 nmol L-1 (R2 = 0.9968), and the limit of detection was 0.43 nmol L-1 (S/N = 3). The practicability of the sensor was examined by determining human serum and pharmaceutical samples, and satisfactory results and recoveries (ranging from 92.46% to 104.90%) were achieved.

Colorimetric and electrochemical detection platforms for tetracycline based on surface molecularly imprinted polyionic liquid on Mn3O4 nanozyme.

In this work, a smart tetracycline (TC) imprinted material (DSMIP@Mn3O4) is prepared via atom transfer radical polymerization of dual ionic liquid (IL) monomers on the surface of Mn3O4 nanoparticles. The obtained DSMIP@Mn3O4 shows a core-shell structure with a sphere shape and has high oxidase-like activity and recognition ability. It has been used to construct colorimetric and electrochemical detection platforms for TC. The colorimetric detection is based on the recombined TC blocking the molecular channels on the surface of DSMIP@Mn3O4, which hinders the catalytic oxidation of 3,3',5,5'-tetramethylbenzidine to the blue product. The linear detection range is 0.5 µM-150 µM and the low detection limit is 0.1 µM. This system is further developed for the visual semi-quantitative detection of TC by using a smartphone. Furthermore, the DSMIP@Mn3O4 is combined with IL-modified carbon nanotube-graphene composite for the sensitively electrochemical detection of TC, which shows a wide linear range of 0.01 µM-20 µM and a low detection limit of 5 nM. The proposed methods have high selectivity and reproducibility and suit different detection situations. Their pracibility is evaluated by determining TC in different samples, and the measurement results are consistent with that obtained by high-performance liquid chromatography. Hence, the colorimetric and electrochemical detection platforms have good application potential.

Antifouling ionic liquid doped molecularly imprinted polymer-based ratiometric electrochemical sensor for highly stable and selective detection of zearalenone.

Zearalenone (ZEN) is a nonsteroidal estrogenic mycotoxin, and its accurate detection in complex biological samples is still a challenge. Herein, an antifouling ratiometric electrochemical sensor has been developed for its detection. In this system, black phosphorus-graphene oxide is used as substrate to amplify the signal; ionic liquid doped molecularly imprinted polymer (MIP) endows the sensing surface not only high recognition ability but also high capability to resist nonspecific adsorption. During MIP preparation a magnetic field is introduced to regulate polymer structure for improving the recognition efficiency of the sensor. The signals of ZEN and poly methylene blue (MB) serve as response signal and internal reference signal, respectively. The peak current of ZEN increases with the increase of ZEN concentration, while the peak current of poly(MB) decreases simultaneously; their ratio changes with ZEN concentration variation. The obtained ratiometric sensor shows a wide linear response range of 0.05-13 µM and a low limit of detection of 12.7 nM (S/N = 3). Furthermore, it has high selectivity, stability and reproducibility, thanks to the advanced antifouling MIP and the built-in correction of poly(MB). The sensor has been successfully applied to determine ZEN in human serum.

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.

A novel ratiometric electrochemical sensor based on dual-monomer molecularly imprinted polymer and Pt/Co3O4 for sensitive detection of chlorpromazine hydrochloride.

In this work, a novel signal on/off ratiometric electrochemical sensor for the selective detection of chlorpromazine (CPZ) was developed. The sensor was constructed by electrodepositing dual-monomer molecularly imprinted polymer (DMMIP) film on the surface of Pt/Co3O4 nanoparticles modified glassy carbon electrode, using CPZ as template molecule, methylene blue and catechol as functional monomers. The copolymerization of two monomers increased the diversity of functional groups for binding template molecules, and enhanced stability. The quantitative detection of CPZ was performed by differential pulse voltammetry, using the peak current of poly (methylene blue) as reference signal and the peak current of CPZ as indicating signal. The results showed that the developed DMMIP sensor not only possessed high selectivity and sensitivity, but also exhibited satisfactory anti-interference ability. Under the optimum conditions, a linear detection range of 0.005-9 µmol L-1 (R2 = 0.9962) was obtained, and the limit of detection was 2.6 nmol L-1. Moreover, the sensor showed good reproducibility and stability toward CPZ detection. It was applied to detect CPZ in serum and pharmaceutical samples, and satisfactory recoveries (ranging from 95.3% to 108.0%) were achieved.

A novel ratiometric electrochemical sensor for the selective detection of citrinin based on molecularly imprinted poly(thionine) on ionic liquid decorated boron and nitrogen co-doped hierarchical porous carbon.

Citrinin can cause serious human diseases, thus its detection in foods is necessary. Herein, a molecularly imprinted polymer-based ratiometric electrochemical sensor (MIP-RECS) was presented for citrinin detection. The sensor was fabricated by electropolymerization, using thionine as monomer and citrinin as template. The ionic liquid decorated boron and nitrogen co-doped hierarchical porous carbon (BN-HPC) as supporter, provided large surface for anchoring thionine and citrinin. Poly(thionine) not only acted as MIP, but also acted as reference probe. When [Fe(CN)6] 3-/4- was adopted as indicating probe, the resulting sensor demonstrated a wide linear detection range (i.e. 1 × 10-3-10 ng mL-1) and a low detection limit (i.e. 1 × 10-4 ng mL-1).The sensor was applied to the detection of spiked citrinin in real samples, and satisfactory recovery (i.e. 97% - 110%) was obtained. Hence, it was promising for citrinin 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.

Highly efficient reduction of 4-nitrophenolate to 4-aminophenolate by Au/γ-Fe2O3@HAP magnetic composites.

In this article, the catalyst Au/γ-Fe2O3@hydroxyapatite (Au/γ-Fe2O3@HAP) consisting of Au nanoparticles supported on the core-shell structure γ-Fe2O3@HAP was prepared through a deposition-precipitation method. The catalyst was characterized by transmission electron microscopy, X-ray powder diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, N2 adsorption-desorption and atomic absorption spectrometry. The as-prepared Au/γ-Fe2O3@HAP exhibited excellent performance for the reduction of 4-nitrophenolate (4-NP) to 4-aminophenolate (4-AP) in the presence of NaBH4 at room temperature. Thermodynamic and kinetic data on the reduction of 4-NP to 4-AP catalyzed by the as-prepared catalyst were studied. The as-prepared catalyst could be easily separated by a magnet and recycled 6 times with over 92% conversion of 4-NP to 4-AP. In addition, the as-prepared catalyst showed excellent catalytic performance on other nitrophenolates. The TOF value of this work on the reduction of 4-NP to 4-AP was 241.3 h-1. Au/γ-Fe2O3@HAP might have a promising potential application on the production of 4-AP and its derivatives.