Fabrication of metal coordination-synergistic magnetic imprinted microspheres based on ligand-free Fe3O4-Cu for specific recognition of bovine hemoglobin

High performance enrichment and analysis of fluoroquinolones residues in environmental water using cobalt ion mediated paper-based molecularly imprinted polymer chips

BACKGROUND

Fluoroquinolones (FQs) are widely used for their excellent antimicrobial properties, yet their release into aquatic environments pose risks to ecosystems and public health. The accurate monitoring and analysis of FQs present challenges due to their low concentrations and the complex matrices found in actual environmental samples. To address the need for auto-pretreatment and on-line instrumental analysis, developing new microextraction materials and protocols is crucial. Such advancements will provide better analytical assurance for the effective extraction and determination of FQs at trace levels, which is of great significance to environmental protection and human health.

RESULTS

In this work, we presented a Co2+ mediated paper-based molecularly imprinted polymer chip (CMC@Co-MIP), combined with UPLC analysis, to develop an effective analytical method for identifying and quantifying trace amounts of ciprofloxacin (CIP) and enrofloxacin (ENR) in water samples. Notably, the addition of Co2+ in CMC@Co-MIP helped to capture the template molecule CIP through coordination before imprinting, which significantly improved the ordering of the imprinted cavities. CMC@Co-MIP exhibited a maximum adsorption capacity up to 500.20 mg g-1 with an imprinting factor of 4.12, surpassing previous reports by a significant margin. Furthermore, the enrichment mechanism was extensively analyzed by various characterization techniques. The developed method showed excellent repeatability and reproducibility (RSD < 13.0 %) with detection limits ranging from 0.15 to 0.21 μg L-1 and recoveries ranging from 64.9 % to 102.3 % in real spiked water samples.

SIGNIFICANCE

We developed a novel microextraction paper-based chip based on Co2+ mediation, which effectively improved the selectivity and convenience of extracting FQs. This breakthrough allowed the chip to have a high enrichment efficiency as well as provide a robust on-line instrumental program. It also confirms that the imprinting scheme based on metal ion coordination is a high-performance strategy.

Mechanistic investigation and dual-mode colorimetric-chemiluminescent detection of glyphosate based on the specific inhibition of Fe3O4@Cu nanozyme peroxidase-like activity

In this study, a dual-mode colorimetric/CL nanosensor was developed for glyphosate detection based on the specific inhibition of Fe3O4@Cu peroxidase-like activity. Synthesized Fe3O4@Cu exhibited high levels of peroxidase-like activity that triggered the oxidation of luminol/3,3',5,5'-tetramethyl benzidine dihydrochloride (TMB) to excited-state 3-aminophthalic acid/blue oxTMB, thereby delivering a CL signal/visible colorimetric signal, however, the presence of glyphosate inhibited this activity, resulting in a decrease in signal strength. In-depth investigation revealed that this inhibitory mechanism occurs via two pathways: one in which glyphosate chelates with Fe(III)/Cu(II) and occupy the catalytical active sites of Fe3O4@Cu, thereby decreasing the generation of OH, and another in which glyphosate competes with TMB to consume generated OH, thus reducing the oxidation of TMB. This mechanism formed the basis of our novel dual-mode colorimetric/CL glyphosate nanosensor, which achieved limits of detection (LODs) of 0.086 µg/mL and 0.019 µg/mL in tests, thus demonstrating its significant potential for on-site glyphosate monitoring.

Cu(II)-Loaded Polydopamine-Coated Urchin-like Titanate Microspheres as a High-Performance IMAC Adsorbent for Hemoglobin Separation

Immobilized metal ion affinity chromatography (IMAC) adsorbents generally have excellent affinity for histidine-rich proteins. However, the leaching of metal ions from the adsorbent usually affects its adsorption performance, which greatly affects the reusable performance of the adsorbent, resulting in many limitations in practical applications. Herein, a novel IMAC adsorbent, i.e., Cu(II)-loaded polydopamine-coated urchin-like titanate microspheres (Cu-PDA-UTMS), was prepared via metal coordination to make Cu ions uniformly decorate polydopamine-coated titanate microspheres. The as-synthesized microspheres exhibit an urchin-like structure, providing more binding sites for hemoglobin. Cu-PDA-UTMS exhibit favorable selectivity for hemoglobin adsorption and have a desirable adsorption capacity towards hemoglobin up to 2704.6 mg g-1. Using 0.1% CTAB as eluent, the adsorbed hemoglobin was easily eluted with a recovery rate of 86.8%. In addition, Cu-PDA-UTMS shows good reusability up to six cycles. In the end, the adsorption properties by Cu-PDA-UTMS towards hemoglobin from human blood samples were analyzed by SDS-PAGE. The results showed that Cu-PDA-UTMS are a high-performance IMAC adsorbent for hemoglobin separation, which provides a new method for the effective separation and purification of hemoglobin from complex biological samples.

Recent Advances in Molecular Imprinting for Proteins on Magnetic Microspheres

The separation of proteins in biological samples plays an essential role in the development of disease detection, drug discovery, and biological analysis. Protein imprinted polymers (PIPs) serve as a tool to capture target proteins specifically and selectively from complex media for separation purposes. Whereas conventional molecularly imprinted polymer is time-consuming in terms of incubation studies and solvent removal, magnetic particles are introduced using their magnetic properties for sedimentation and separation, resulting in saving extraction and centrifugation steps. Magnetic protein imprinted polymers (MPIPs), which combine molecularly imprinting materials with magnetic properties, have emerged as a new area of research hotspot. This review provides an overview of MPIPs for proteins, including synthesis, preparation strategies, and applications. Moreover, it also looks forward to the future directions for research in this emerging field.

Molecularly Imprinted Polymers with Shape-Memorable Imprint Cavities for Efficient Separation of Hemoglobin from Blood

Efficient separation and purification of hemoglobin from blood and other complicated biological fluids still remains a big challenge. Molecularly imprinted polymers (MIPs) of hemoglobin are potential choices; however, they suffer from severe problems including difficult template removal and low imprinting efficiency like other protein-imprinted polymers. Herein, a novel MIP of bovine hemoglobin (BHb) was designed in which a peptide crosslinker (PC), instead of the commonly used crosslinkers, was used. The PC, a random copolymer of lysine and alanine, adopts an α-helical conformation at pH 10 but transits to a random coil conformation at pH 5. The introduction of alanine residues lowers the pH range at which the PC undergoes helix-coil transition. The imprint cavities in the polymers are shape-memorable due to the reversible and precise helix-coil transition of the peptide segments in the polymers. They can be enlarged by lowering pH from 10 to 5, thus allowing complete removal of the template protein under mild conditions. When the pH is adjusted back to 10, their original size and shape will be recovered. Therefore, the MIP binds the template protein BHb with high affinity. Compared with the MIP crosslinked with the commonly used crosslinker, the imprinting efficiency of the PC-crosslinked MIP is significantly improved. In addition, both the maximum adsorption capacity (641.9 mg/g) and imprinting factor (7.2) are much higher than the BHb MIPs reported previously. The new BHb MIP also exhibits high selectivity toward BHb and good reusability. Thanks to the high adsorption capacity and high selectivity of the MIP, when it was applied to extract BHb from bovine blood, BHb in the blood sample was extracted almost completely, and high purity product was obtained.

Novel Dual-Signal SiO2-COOH@MIPs Electrochemical Sensor for Highly Sensitive Detection of Chloramphenicol in Milk

In view of the great threat of chloramphenicol (CAP) to human health and the fact that a few producers have illegally used CAP in the food production process to seek economic benefits in disregard of laws and regulations and consumer health, we urgently need a detection method with convenient operation, rapid response, and high sensitivity capabilities to detect CAP in food to ensure people's health. Herein, a molecularly imprinted polymer (MIP) electrochemical sensor based on a dual-signal strategy was designed for the highly sensitive analysis of CAP in milk. The NiFe Prussian blue analog (NiFe-PBA) and SnS₂ nanoflowers were modified successively on the electrode surface to obtain dual signals from [Fe(CN)₆]^3-/4- at 0.2 V and NiFe-PBA at 0.5 V. SiO₂-COOH@MIPs that could specifically recognize CAP were synthesized via thermal polymerization using carboxylated silica microspheres (SiO₂-COOH) as carriers. When the CAP was adsorbed by SiO₂-COOH@MIPs, the above two oxidation peak currents decreased at the same time, allowing the double-signal analysis. The SiO₂-COOH@MIPs/SnS₂/NiFe-PBA/GCE sensor used for determining CAP was successfully prepared. The sensor utilized the interactions of various nanomaterials to achieve high-sensitivity dual-signal detection, which had certain innovative significance. At the same time, the MIPs were synthesized using a surface molecular imprinting technology, which could omit the time of polymerization and elution and met the requirements for rapid detection. After optimizing the experimental conditions, the detection range of the sensor was 10^-8 g/L-10^-2 g/L and the limit of detection reached 3.3 × 10^-9 g/L (S/N = 3). The sensor had satisfactory specificity, reproducibility, and stability, and was successfully applied to the detection of real milk samples.

Amino acid-immobilized copper ion-modified carbon-based adsorbent for selective adsorption of bovine hemoglobin

We prepared an amino acid-immobilized copper ion-modified carbon-based adsorbent (C@TA@P@A-Cu) for selective bovine hemoglobin (BHb) adsorption in biological samples. Carbon nanoparticles were used as the matrix, and copper ions were attached to the amino acid-modified carbon nanoparticles as metal chelate complexes via immobilized metal affinity. BSA, Lyz, OVA, and HRP were chosen as reference proteins for further study. Furthermore, the synthesis conditions of adsorbents, SPE conditions, selectivity, competitivity, reproducibility, and reusability were extensively investigated. The results showed that the maximum adsorption capacity of C@TA@P@A-Cu microspheres for BHb under optimal conditions was 673.0 mg g^-1. The addition of a TiO₂ layer with an increased specific surface area of the adsorbent and the addition of poly-l-lysine (PLL) inhibited the adsorbent's binding ability to non-BHb proteins, but chelated Cu²⁺ increased the adsorbent's specific binding ability to BHb. Furthermore, after six adsorption-desorption cycles, the adsorbent has satisfactory reusability with no significant change in adsorption capacity. Furthermore, C@TA@P@A-Cu was successfully used to identify BHb from real blood samples, as confirmed by SDS-PAGE, and it is expected to have potential applications in protein purification and disease diagnosis.