Zheng-zhong Lin

Determination of malachite green in aquatic products based on magnetic molecularly imprinted polymers

Magnetic molecularly imprinted polymers (MMIPs) were synthesized through precipitation polymerization using malachite green (MG) as template, methacrylic acid as monomer, ethylene dimethacrylate as crosslinker, and Fe3O4 magnetite as magnetic component. MMIPs were characterized by scanning electron microscopy, Fourier transform infrared spectrometry, and vibrating sample magnetometry. Under the optimum condition, the MMIPs obtained exhibited quick binding kinetics and high affinity to MG in the solution. Scatchard plot analysis revealed that the MMIPs contained only one type of binding site with dissociation constant of 24.0 μg mL(-1). The selectivity experiment confirmed that the MMIPs exhibited higher selective binding capacity for MG than its structurally related compound (e.g., crystal violet). As a sorbent for the extraction of MG in sample preparation, MMIPs together with the absorbed analytes could easily be separated from the sample matrix with an external magnet. After elution with methanol/acetic acid (9:1, v/v), MG in the eluent was determined by high-performance liquid chromatography coupled with UV detector with recoveries of 94.0-115%. Results indicated that the as-prepared MMIPs are promising materials for MG analysis in aquatic products.

Rapid detection of malachite green in fish based on CdTe quantum dots coated with molecularly imprinted silica

A sensitive fluorescence sensor for the detection of malachite green (MG) was fabricated by grafting molecularly imprinted polymers (MIPs) onto the surface of CdTe quantum dots (QDs). The MIP-coated QDs were synthesized via a reverse microemulsion method using (3-aminopropyl)triethoxysilane (APTES) and tetraethyl orthosilicate (TEOS) as functional monomer and cross-linker, respectively. The optimum molar ratio of MG, functional monomer and cross-linker was 1:3:10. The MIP-coated QDs exhibited uniform spheres with diameter around 49nm and excellent fluorescence emission at λex 370nm. A linear relationship with two segments between the relative fluorescence intensities and the MG concentrations ranging from 0.08 to 20μmol·L-1 could be obtained with a detection limit of 12μg·kg-1. The fluorescent probe was successfully applied to the determination of MG in fish samples with the spiked recoveries ranging from 94.3% to 109.5% which were in accordance with those of the measurement by HPLC-UV.

A fluorescent probe based on N-doped carbon dots for highly sensitive detection of Hg2+ in aqueous solutions

A facile and green hydrothermal method was developed for the preparation of highly luminescent nitrogen-doped carbon dots (NCDs) by using anhydrous citric acid and urea as the carbon source and nitrogen source, respectively. The NCDs show good water-solubility and exhibit excitation-independent fluorescence behaviors at excitations of 300–390 nm with a quantum yield of 42.5% at a λem of 440 nm. Based on the fluorescence quenching strategy, the NCDs were successfully applied to the measurement of Hg2+ in tap and lake water samples with high sensitivity and excellent selectivity. The detection limit was 7.3 nmol L−1 (3σ, n = 9), indicating its potential applications for the detection of trace Hg2+ in water samples.

Biomimetic ELISA detection of malachite green based on magnetic molecularly imprinted polymers

A direct competitive enzyme-linked immunosorbent assay (ELISA) method was used for the detection of malachite green (MG) with a high sensitivity and selectivity using magnetic molecularly imprinted polymers (MMIPs) as a bionic antibody. MMIPs were prepared through emulsion polymerization using Fe3O4 nanoparticles as magnetic nuclei, MG as a template, methacrylic acid (MAA) as a functional monomer, ethylene glycol dimethacrylate (EGDMA) as a crosslinking agent and span-80/tween-80 as mixed emulsifiers. The MMIPs were characterized by scanning electron micrographs (SEM), thermal-gravimetric analyzer (TGA), Fourier transform infrared spectrometer (FT-IR) and vibrating sample magnetometer (VSM), respectively. A high magnetic saturation value of 54.1emug-1 was obtained, resulting in rapid magnetic separation of MMIPs with an external magnet. The IC50 of the established ELISA method was 20.1μgL-1 and the detection limit (based on IC85) was 0.1μgL-1. The MMIPs exhibited high selective binding capacity for MG with cross-reactivities less than 3.9% for MG structural analogues. The MG spiking recoveries were 85.0%-106% with the relative standard deviations less than 4.7%. The results showed that the biomimetic ELISA method by using MMIPs as bionic antibody could be used to detect MG rapidly in fish samples with a high sensitivity and accuracy.

Biomimetic ELISA detection of malachite green based on molecularly imprinted polymer film

A highly selective and sensitive enzyme-linked immunosorbent assay (ELISA) was developed for the detection of malachite green (MG) using a molecularly imprinted polymer (MIP) film as bionic antibody. The MIP film, based on the self-polymerization of dopamine, was fabricated on the surfaces of a 96-well microplate. It showed specific recognition for MG in aqueous solution. A direct competitive ELISA method was established with the sensitivity reaching 10.31μgL-1 and the detection limit being 0.3μgL-1. The cross-reactivity of two structural analogues to MG was less than 10%. The average recovery tested by MG standard spiking was 88.8% for bass and 90.4% for water, and the relative standard deviations were less than 3.6%. All the above results indicated that the developed method could be used to detect MG in fish and water samples rapidly, specifically and accurately.

Preparation and Adsorption Ability of Molecularly Imprinted Polymer Microspheres for Malachite Green

Molecularly imprinted polymer (MIP) microspheres were synthesized through precipitation polymerization using malachite green (MG) as template, methacrylic acid (MAA) as monomer, and trimethylolpropane trimethacrylate (TRIM) as cross-linker. The microsphere structure of MIP was characterized by IR spectroscopy and SEM. The influence of preparation conditions such as monomer and cross-linker dosages on the polymer absorption of MG in acetonitrile solution was also explored. Under the optimum synthesis conditions (0.25 mmol MG, 1.5 mmol MAA, 2.5 mmol TRIM, 40 mL acetonitrile), the prepared MIP microspheres have a binding capacity as high as 2000 µg g−1 of MG with an imprinting factor of above 4.0. The result suggests that the prepared MIP microspheres are promising material for the selective extraction of MG in complicated matrix solutions.

Detection of trace tetracycline in fish via synchronous fluorescence quenching with carbon quantum dots coated with molecularly imprinted silica

A novel fluorescence-based sensor combining synchronous fluorescence spectroscopy (SFS) with molecularly imprinted polymers (MIPs) was fabricated with reverse microemulsion method. Tetracycline (TC), (3-aminopropyl) triethoxysilane (APTES), tetraethyl orthosilicate (TEOS) and carbon quantum dots (CDs) were used as template, functional monomer, cross-linker and signal sources respectively in the probe preparation. A synchronous fluorescence emission (λem) at 355nm was observed for the prepared MIP-coated CDs (MIP@CDs) particles when the wavelength interval (Δλ) was set as 70nm, and the synchronous fluorescence intensity could be rapidly and efficiently quenched by TC based on inner filter effect (IFE). The quenching efficiencies of synchronous fluorescence intensity was linearly fitted with tetracycline (TC) concentrations ranging from 0.1 to 50μmolL-1 with a detection limit (DL) of 9nmolL-1 (3σ, n=9). The MIP@CDs was used as a probe to detect TC in fish samples with the recoveries ranging from 98.4% to 103.1% and the relative standard deviation less than 6.0%. The results illustrated that the as-prepared MIP@CDs could be applied to the detection of trace TC in fish samples with rapidity, high sensitivity and accuracy.

Extraction and determination of malachite green from aquatic products based on molecularly imprinted polymers

ABSTRACT Molecularly imprinted polymers (MIPs) were synthesized using malachite green (MG) as template, and methacrylic acid/sodium methacrylate as composite monomers. The equilibrium dissociation constant and apparent maximum adsorption capacity of the MIPs reach 12.2 mg·L−1 and 3.2 mg·g−1, respectively. The MIPs demonstrate excellent recognition ability due to high-affinity sites constructed by the electrostatic interaction and hydrogen bonds between template and composite monomers. The MIPs were successfully employed for the detection of MG residue in aquatic products coupled with high-performance liquid chromatography (HPLC) with a detection limit of 0.57 μg·kg−1.

Detection of trace leucomalachite green with a nanoprobe of CdTe quantum dots coated with molecularly imprinted silica via synchronous fluorescence quenching

A novel fluorescence nanoprobe using CdTe quantum dots as signal sources coated with a molecularly imprinted polymer was synthesized by a reverse microemulsion method. The nanoprobe was designed for the detection of leucomalachite green (LMG) in fish samples via synchronous fluorescence quenching based on the inner filter effect. LMG, (3-aminopropyl) triethoxysilane and tetraethyl orthosilicate were used as the template, functional monomer and cross-linker respectively in the probe. A synchronous fluorescence emission of the probe at 260 nm was observed when the wavelength interval was set as 340 nm, and the synchronous fluorescence could be linearly quenched with LMG at concentrations ranging from 0.1 to 20 μmol L−1. The as-prepared nanoprobes were nearly spherical with a diameter of about 50 nm. The detection limit was 23 nmol L−1 (3σ, n = 9) and the recoveries ranged from 96.2% to 104.9% for the fish samples. The results illustrated that the nanoprobe could be used for trace LMG measurement in fish samples.

HPLC determination of domoic acid in shellfish based on magnetic molecularly imprinting polymers

ABSTRACT A magnetic molecularly imprinting polymer for domoic acid was fabricated. Synthesis conditions were optimized. The polymer particles have high magnetization for rapid magnetic separation. The apparent maximum absorption amount and dissociation constant of the polymer were 1,600 µg g−1 and 20.6 µg mL−1, respectively. The polymer retained 90% of adsorption amount after 5 times of repeated use. It was used as an adsorbent for purification and HPLC detection of domoic acid in shellfish with a detection limit of 0.050 µg g−1. Thus, the polymer could be applied to the sample pretreatment of aquatic products.