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

Facile fluorescence detection of malachite green in fish using molecularly imprinted polymers doped CdTe quantum dots based system

Malachite green (MG) possesses high toxicity, therefore, the detection of MG in fish tissues is of vital importance. A novel core-shell MIPs doped CdTe quantum dots coated silica nanoparticles (CdTe-MIP/SiO2 NPs) were synthesized via a simple one-pot strategy. The materials were characterized carefully. The resulting CdTe-MIP/SiO2 NPs were coated on the thin layer chromatography plate, and coupled with miniaturized fluorimeter for fluorescence detection of MG in fish samples. The resulting CdTe-MIP/SiO2 NPs based system possessed good linearity (0.01 ∼ 20 μmol/L), high recoveries (98.36 %∼101.45 %) and low detection limit (3.7 nmol/L) for MG. Furthermore, CdTe-MIP/SiO2 NPs based system were employed to measure fish samples spiked with MG, meanwhile, HPLC was utilized to evaluate the accuracy and reliability. And the paired t-test was conducted to evaluate differences between fluorescence method and HPLC, P > 0.05 means no significant difference was observed, the results demonstrated that both fluorescence method and HPLC are suitable for MG analysis.

MIP-based immunoassays: A critical review

Molecularly imprinted polymers, MIPs, are man-made receptors mimicking the thermodynamic and kinetic binding behaviour of natural antibodies. Therefore, it is not surprising that many researchers have thought about MIPs as artificial receptors in immunoassay-like analytical applications, where the general machinery of the assay is maintained, but the molecular recognition is no longer assured by an antibody but by an artificial receptor. However, the number of papers devoted explicitly to applications of MIPs in the immunoassay field is quite limited if compared to the huge number of papers covering the multifaceted molecular imprinting technology. For this reason, this critical review wants to give a general view of MIP-based immunoassays, trying to highlight the critical points that have so far prevented a wider application of molecular imprinting technology in the immunoassay field and, possibly, try to suggest strategies to overcome them.

Recent Advances in Functional Nanomaterials for Diagnostic and Sensing Using Self-Assembled Monolayers

Functional nanomaterials have attracted attention by producing different structures in any field. These materials have several potential applications, including medicine, electronics, and energy, which provide many unique properties. These nanostructures can be synthesized using various methods, including self-assembly, which can be used for the same applications. This unique nanomaterial is increasingly being used for biological detection due to its unique optical, electrical, and mechanical properties, which provide sensitive and specific sensors for detecting biomolecules such as DNA, RNA, and proteins. This review highlights recent advances in the field and discusses the fabrication and characterization of the corresponding materials, which can be further applied in optical, magnetic, electronic, and sensor fields.

Ratiometric Fluorescence Immunoassay Based on Carbon Quantum Dots for Sensitive Detection of Malachite Green in Fish

Malachite green (MG) is a synthetic poisonous organic compound that has been banned in many countries as a veterinary drug for aquaculture. An efficient, fast and sensitive method is urgently needed for monitoring the illegal use of malachite green (MG) in aquaculture. In this study, a novel ratiometric fluorescence immunoassay was established. Nitrogen-doped carbon quantum dots were used as ratiometric fluorescent probes with a fluorescence peak at 450 nm. Horseradish peroxidase was employed to convert o-phenylenediamine to 2,3-diaminophenazine, with a new fluorescence peak at 580 nm and a strong absorption at 420 nm. The inner filter effect between N-CQD fluorescence and DAP absorption was identified. It allows for the ratiometric detection of MG using a fluorescent immunoassay. The results demonstrated a linear ratiometric fluorescence response for MG between 0.1 and 12.8 ng·mL^-1. The limit of detection of this method was verified to be 0.097 μg·kg^-1 with recoveries ranging from 81.88 to 108%, and the relative standard deviations were below 3%. Furthermore, this method exhibited acceptable consistency with the LC-MS/MS results when applied for MG screening in real samples. These results demonstrated a promising application of this novel ratiometric fluorescence immunoassay for MG screening with the merits of rapid detection, simple sample preparation, and stable signal readout. It can be an alternative to other traditional methods if there are difficulties in the availability of expensive instruments, and achieve comparable results or even more sensitivity than other reported methods.

Dual-reverse-signal ratiometric fluorescence method for malachite green detection based on multi-mechanism synergistic effect

The proposition of ratiometric detection mode has demonstrated great superiority in improving analysis accuracy by forming self-calibration. Herein, the novel dual-reverse-signal ratiometric fluorescence detection for malachite green (MG) was first achieved based on synergistic effect of fluorescence resonance energy transfer (FRET) and inner filter effect (IFE). The ratiometric fluorescence probe (B-RCDs) was self-assembled via electrostatic attraction between blue-emission carbon dots (BCDs) and red-emission carbon dots (RCDs), followed with FRET effect from BCDs to RCDs and exhibited dual-emission at 450 nm and 627 nm. In the presence of MG, the IFE effect between MG and RCDs quenched the fluorescence at 627 nm and restored the fluorescence at 450 nm, sending out two reverse signals along with an obvious color change from pink to purple (302 nm UV lamp). This ratiometric method not only simplified the preparation process, but also improved the detection sensitivity, showing a low limit of detection (LOD) of 41.8 nM, which exhibited superiority than that of single-signal RCDs (157.3 nM). This method held a rapid response of 10 min and represented satisfactory recoveries (99.14%-109.08%) in real water samples, revealing it was a promising candidate in the fast, sensitive and practical detection of MG. Moreover, the design of synergistic effect supplied a new perspective for the development of ratiometric sensing in the future.

A Rapid Tricolour Immunochromatographic Assay for Simultaneous Detection of Tricaine and Malachite Green

In this research, we designed a rapid tricolour immunochromatographic test strip with double test lines (TS-DTL) and two-colour AuNP probes, which realised the simultaneous detection of tricaine mesylate (TMS) and malachite green (MG). Through a distinct tricolour system (red T₁ line, blue T₂ line and purple C line), a visual identification of TMS (0.2 μg/mL) and MG (0.5 μg/mL) was quickly achieved on site, which improved the accuracy of naked eye observations. The LODs of TMS in aquaculture water, fish and shrimp were 11.0, 29.6 and 61.4 ng/mL, respectively. MG LODs were 47.0 ng/mL (aquaculture water), 82.8 ng/mL (fish) and 152.4 ng/mL (shrimp). The LOD of MG was close to the similar TS methods. However, visual detection of TMS could meet the requirements of the residue limit (1 μg/mL) of TMS in the USA, and the quantitative detection of TMS was over 16 times lower than the USA standard. The developed platform was rapid (~20 min, HPLC~3 h) and accurate, which was verified using a traditional HPLC method. The recovery rates ranged from 82.2% to 108.6% in three types of real samples, indicating a potential application in on-site fast screening or multiple detection for TMS and MG residues in aquatic products.

Branched poly(ethylenimine) carbon dots-MnO2 nanosheets based fluorescent sensory system for sensing of malachite green in fish samples

Malachite green (MG) is an organic dye compound that is frequently used as a fungicide and antiseptic in aquaculture. However, human or animal exposure to MG causes carcinogenic, teratogenic and mutagenic effects. Herein, a novel fluorescent assay was designed for the detection of MG using manganese dioxide nanosheets (MnO₂ NS) as an energy acceptor to quench the fluorescence of branched poly(ethylenimine) carbon dots (BPEI-CDs) via Förster resonance energy transfer. When butyrylcholinesterase is introduced to form thiocholine in the presence of S-butyrylthiocholine iodide, MnO₂ NS can be recovered by thiocholine to Mn²⁺, resulting in restoration of the fluorescence of BPEI-CDs. Exploiting these changes in fluorescence intensity in the above system, a fluorescence probe was successfully developed for the quantitative detection of MG. Besides, this assay was applied to fish samples, verifying the high potential for practical application of the proposed sensor for the monitoring of MG in aquatic products.

Quantitative analysis of polypropylene glycol polymers by liquid chromatography tandem mass spectrometry based on collision induced dissociation technique

Polypropylene glycol (PPG) is a commonly used synthetic polymer in many fields. Investigating the toxicity and pharmacokinetic behavior of PPG polymers is necessary and important for evaluating their safety in medicine and daily cosmetics. In this study, PPG425, PPG1K and PPG2K were selected as the target polymers for cytotoxicity and cellular pharmacokinetics study of PPG polymers. Structural diversity and polydisperse molecular weights (MWs) are significant challenges for quantification of PPG polymers by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Collision induced dissociation in source or collision cell generated a series of PPG-related product ions at m/z 59.0, 117.1, 175.1, 233.2, 291.2, 349.3, 407.2, 465.3 and 523.5 corresponding to fragments containing 1, 2, 3, 4, 5, 6, 7, 8, 9 repeating propylene oxide subunits. PPG425 was determined by the sum of the MRM acquisitions used the transitions [M+H]⁺¹ precursor ions → product ions. PPG1K and PPG2K were determined by the MRM acquisitions used the transitions [M+H]⁺¹ precursor ions → product ions at m/z 233.2(four subunits)→59.0(one subunit). Based on the collision induced disassociation technique and structural specific product ions, pharmacokinetic studies of PEG425, PPG1K and PPG2K were successfully conducted in McF-7 cells. The experimental results revealed that PPG polymers are not biologically inert and they can enter into McF-7 cells. The safety of PPG polymers should be considered when they are used as pharmaceutical or cosmetic excipients.

Research on Cold Chain Logistics Traceability System of Fresh Agricultural Products Based on Blockchain

Traditional cold chain logistics has problems such as centralized data storage, low data reliability, easy data tampering, and difficulty in locating responsible persons, which leads to the inability to guarantee consumer rights. To solve these problems, a cold chain logistics traceability system is proposed for fresh agricultural products based on blockchain. Both alliance chain and private chain are used in the paper in order to ensure that the product traceability system not only has certain openness but also must contain enough privacy and security. Alliance chain is mainly used to query and share product traceability information. The private chain will be used to collect and store the product traceability information of each enterprise and then connected to the alliance chain via hash pointers. The proposed system is beneficial for reducing the burden of network transmission of alliance chain and improving the efficiency of consumer product data query. At the same time, the private chain ensures the security and privacy of enterprise product data, which not only has high data storage efficiency but also can meet the requirements of all participants for the traceability system. In the experimental part, the feasibility of this system is verified through simulation experiments, which provides a reference for the combination of blockchain technology and cold chain logistics traceability system.

Competitive plasmonic biomimetic enzyme-linked immunosorbent assay for sensitive detection of bisphenol A

A plasmonic biomimetic enzyme-linked immunosorbent assay (PBELISA) method was developed for ultrasensitive and on-site visual detection of bisphenol A (BPA). The PBELISA was an enzyme-linked immunoassay using molecularly imprinted polymer (MIP) film as biomimetic antibody combined with catalase (CAT)-mediated growth of plasmonic gold nanoparticles (AuNPs). With the BPA concentration increased, a distinguished color change was observed from colorless to blue and then red. Therefore, the proposed method could be employed with naked-eye observation to detect BPA with visual limit of detection (LOD) of 40 pg/mL. For quantitative analysis, this method also exhibited a good dynamic linear response to the logarithmic BPA concentrations ranged from 10 pg/mL to 1.024 × 10⁴ pg/mL with a correlation coefficient of R² = 0.9922 and LOD of 6.20 pg/mL. The recovery rates in tap water, milk and orange juice ranged from 91.83% to 107.39%. In brief, the developed PBELISA method is sensitive, cost-effective and easy-to-use for BPA detection.

Direct extraction and detection of malachite green from marine sediments by magnetic nano-sized imprinted polymer coupled with spectrophotometric analysis

This research describes the application of magnetic molecularly imprinted nano-sized polymers (MMIPs) for the selective extraction and fast detection of malachite green (MG) from marine sediment samples followed by UV-Vis spectrophotometry. The novel material was prepared by surface imprinting using methacrylic acid as the functional monomer for fixing the template molecules. The polymers obtained at each step were thoroughly studied by transmission electron microscopy, FTIR spectroscopy and thermogravimetric analysis. Simultaneously, the adsorption performances of the resulting nanoparticles were analysed in detail and an excellent affinity with the MG was revealed. Further, the main parameters of magnetic molecular imprinted solid-phase extraction (MMIP-SPE) were screened via multivariate optimization methods. The magnetic nanoparticles were used as special adsorbents to directly extract MG from crude marine sediment extracts. The developed method exhibits satisfactory recoveries from the spiked samples, ranging from 80.40 to 92.96% with an RSD of less than 5.18% (n = 3).

Sensitive and Simple Competitive Biomimetic Nanozyme-Linked Immunosorbent Assay for Colorimetric and Surface-Enhanced Raman Scattering Sensing of Triazophos

The biomimetic enzyme-linked immunosorbent assay (BELISA) is widely used for detection of small-molecule compounds as a result of low cost and reagent stability of molecularly imprinted polymers (MIPs). However, enzyme labels used in BELISA still suffer some drawbacks, such as high production cost and limited stability. To overcome the drawbacks, a biomimetic nanozyme-linked immunosorbent assay (BNLISA) based on MIPs and nanozyme labels was first proposed. For nanozyme labels, platinum nanoparticles (PtNPs) acted as peroxidase by catalyzing the oxidation of colorless 3,3',5,5'-tetramethylbenzidine (TMB) into an ideal surface-enhanced Raman scattering (SERS) marker. Blue TMB²⁺ and bovine serum albumin (BSA)-hapten showed superior selectivity when competing with targets for binding sites on MIPs, named the Pt@BSA-hapten probe. The BNLISA method was employed to detect triazophos with a limit of detection of 1 ng mL^-1 via colorimetric and SERS methods. Replacing traditional enzymes with nanozymes for combination with MIPs may bring about a new prospect for other compound analyses.

Detection of Malachite Green using a colorimetric aptasensor based on the inhibition of the peroxidase-like activity of gold nanoparticles by cetyltrimethylammonium ions

A specific and sensitive colorimetric aptasensor is described for the determination of Malachite Green (MG). It is exploiting the inhibition of the peroxidase-like activity of gold nanoparticles (AuNPs). The AuNPs act as enzyme mimics that catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) by H₂O₂ to yield a dark blue solution. The catalytic activity is inhibited by hexadecyl trimethyl ammonium ion, specifically by cetyltrimethylammonium bromide (CTAB), which causes the aggregation of AuNPs. If a (negatively charged) RNA-aptamer against MG is added, it binds to the positively charged CTAB and prevents aggregation. This enhances the enzyme mimicking activity of the AuNPs and leads to the formation of a dark blue solution. However, in the presence of MG, the aptamer binds to MG, and leads to the aggregation of AuNPs again. The aggregated AuNPs possess a light blue color. A colorimetric method (best performed at 650 nm) was work out that can detect MG in a concentration range from 10 to 500 nmol L^-1. The detection limit based on 3σ/k criterion is 1.8 nmol L^-1. The assay is highly specific and accurate. Recoveries from spiked real samples (aquaculture water) ranged from 80% to 120%. Graphical abstract Based on the inhibition of cetyltrimethyal ammonium ion and the enhancement of RNA-aptamer, the differences of the peroxidase-like activities of AuNPs can be greatly enlarged with and without MG, by which a colorimetric aptasensor can be constructed for the detection of Malachite Green (MG).

A Novel CdSe/ZnS Quantum Dots Fluorescence Assay Based on Molecularly Imprinted Sensitive Membranes for Determination of Triazophos Residues in Cabbage and Apple

In the present study we have developed a direct competitive CdSe/ZnS quantum dot (QD) fluorescence assay based on micro-array-imprinted membranes for the determination of triazophos in cabbage and apple. The imprinted membranes were directly synthesized on the surface of a 96-well plate by thermal polymerization using triadimefon as the dummy template. Under optimal conditions, the assay showed an excellent linear response over the concentration ranges of 0.1-10,000 μg L-1 with a good coefficient of determination (R 2= 0.982). The sensitivity (IC50) and limit of detection (LOD, expressed as IC15) of the developed assay were 3.63 mg L-1 and 0.31 μg L-1, respectively. The applicability of the developed approach was tested for detecting triazophos in incurred samples. The method showed excellent recoveries (109.6-118.9%) and relative standard deviations (RSDs) between 9.9 and 19.5%. The obtained results correlated well with those obtained by LC-MS/MS (R 2= 0.9995). The competitive assay using CdSe/ZnS QDs as fluorescence-labeled probe showed good sensitivity, steady and fast response, and excellent anti-interference ability compared to conventional fluorescence-quenching methods. Finally, the feasibility of the proposed methodology was successfully applied for detection of triazophos in real samples.

Sensitive, simple and rapid colorimetric detection of malachite green in water, salmon and canned tuna samples based on gold nanoparticles

BACKGROUND

Malachite green is used in aquaculture and fisheries as a fungicide and antiseptic and it is also used in industry as a dye. However, malachite green is carcinogenic and highly toxic for humans and animals. In this study, a spectrophotometric method was developed to detect malachite green. The method was based on the surface plasmon resonance property of gold nanoparticles and interaction between malachite green and gold nanoparticles.

RESULTS

Malachite green-gold nanoparticles were rapidly aggregated in the acidic medium; as a result, a color change from red to blue was observed, which was easily detectable by the naked eye. The absorption ratio (A623/A520) of the gold nanoparticles in an optimized system exhibited a linear correlation with malachite green concentration. The method detection limit and linear range were 3 and 50-350 ng mL^-1 , respectively. The method was applied successfully to detect malachite green in different samples.

CONCLUSION

The method was simple and rapid to detect malachite green. The most important advantages of the method are the possibility of malachite green determination with very good accuracy and sensitivity using a simple UV-visible spectrometer without any expensive or sophisticated instrumentation and also the versatility of real samples. © 2018 Society of Chemical Industry.

Ratiometric fluorescence probe of MIPs@CdTe QDs for trace malachite green detection in fish

A facile and practical ratiometric fluorescence probe based on two CdTe quantum dots (QDs) coated with molecularly imprinted polymers (MIPs) was prepared for the detection of trace malachite green (MG) in fish. Two CdTe QDs coated with MIPs were fabricated by a one-pot method using MG, (3-aminopropyl) triethoxysilane (APTES) and tetraethyl orthosilicate (TEOS) as template, functional monomer, and cross-linker, respectively. CdTe QDs with λ_em 530 nm (gQDs) and 630 nm (rQDs) were used as the referential fluorophore and target sensitive fluorophore, respectively. The fluorescence intensity of gQDs remained unchanged in the presence of MG, while the fluorescence of rQDs could be quantitatively quenched by MG based on the strategy of fluorescence resonance energy transfer. The ratiometric fluorescence probe (MIPs@gQDs&rQDs) was characterized by transmission electron microscopy and Fourier transform infrared spectroscopy. The linear range of MG detection was 0.1-32 μmol L^-1 with a detection limit of 8.8 μg kg^-1. The constructed probe has been successfully applied to the detection of MG in fish with the recoveries of 92.3-109.1%, which were validated by the method of HPLC. The result indicated that the probe possessed rapid response, wide linear range, high sensitivity, and relatively high selectivity, and was low-cost and easy in operation in the detection of MG in fish samples.

Molecularly Imprinted Polymer as an Antibody Substitution in Pseudo-immunoassays for Chemical Contaminants in Food and Environmental Samples

The chemical contaminants in food and the environment are quite harmful to food safety and human health. Rapid, accurate, and cheap detection can effectively control the potential risks derived from these chemical contaminants. Among all detection methods, the immunoassay based on the specific interaction of antibody-analyte is one of the most widely used techniques in the field. However, biological antibodies employed in the immunoassay usually cannot tolerate extreme conditions, resulting in an unstable state in both physical and chemical profiles. Molecularly imprinted polymers (MIPs) are a class of polymers with specific molecular recognition abilities, which are highly robust, showing excellent operational stability under a wide variety of conditions. Recently, MIPs have been used in biomimetic immunoassays for chemical contaminants as an antibody substitute in food and the environment. Here, we reviewed these applications of MIPs incorporated in different analytical platforms, such as enzyme-linked immunosorbent assay, fluorescent immunoassay, chemiluminescent immunoassay, electrochemical immunoassay, microfluidic paper-based immunoassay, and homogeneous immunoassay, and discussed current challenges and future trends in the use of MIPs in biomimetic immunoassays.

Biomimetic enzyme-linked immunoassay based on a molecularly imprinted 96-well plate for the determination of triazophos residues in real samples

In this study, a direct competitive biomimetic enzyme-linked immune-sorbent assay (BELISA) based on a molecularly imprinted nanomembrane as an artificial antibody was developed for the determination of triazophos in real samples. The imprinted film was directly synthesized on the well surface of a 96-well plate using a dummy molecular template under the conditions of thermal polymerization. The developed BELISA using a hapten of triazophos as an enzyme-labeled probe is much more sensitive, simple, quick, steady and inexpensive than the other instrumental and immuno assay methods. Under optimal conditions, the linear range of the method was 0.001–10 000 μg L⁻¹ with a good regression coefficient of 0.977. The sensitivity (IC₅₀) and the limit of detection (LOD) of BELISA were 428 μg L⁻¹ and 0.001 μg L⁻¹, respectively. This method was performed to detect triazophos in cabbage and apple samples, and showed excellent recovery and relative standard deviations (RSDs) ranging from 70.5 to 119.8% and from 5.2 to 19.7%, respectively. The results correlated well with those obtained using high performance liquid chromatography-tandem mass spectrometry.

In this study, a direct competitive biomimetic enzyme-linked immune-sorbent assay (BELISA) based on a molecularly imprinted nanomembrane as an artificial antibody was developed for the determination of triazophos in real samples.

Molecularly imprinted polymer nanoparticle-based assay (MINA): application for fumonisin B1 determination

The enzyme-linked immunosorbent assay (ELISA) has been used as a standard tool for monitoring food and animal feed contamination from the carcinogenic fumonisin B1 (FB1).

Rapid and sensitive detection of trace malachite green and its metabolite in aquatic products using molecularly imprinted polymer-coated wooden-tip electrospray ionization mass spectrometry

In this study, a molecularly imprinted polymer-coated wooden-tip (MIPCWT) electrospray ionization mass spectrometry (ESI-MS) method was developed for rapid and sensitive detection of trace malachite green (MG) and its metabolite in aquatic products.