Aptamer-Functionalized Magnetic Conjugated Organic Framework for Selective Extraction of Traces of Hydroxylated Polychlorinated Biphenyls in Human Serum

Recent advance on microextraction sampling technologies for bioanalysis

The contents of target substances in biological samples are usually at low concentration levels, and the matrix of biological samples is usually complex. Sample preparation is considered a very critical step in bioanalysis. At present, the utilization of microextraction sampling technology has gained considerable prevalence in the realm of biological analysis. The key developments in this field focus on the efficient microextraction media and the miniaturization and automation of adaptable sample preparation methods currently. In this review, the recent progress on the microextraction sampling technologies for bioanalysis has been introduced from point of view of the preparation of microextraction media and the microextraction sampling strategies. The advance on the microextraction media was reviewed in detail, mainly including the aptamer-functionalized materials, molecularly imprinted polymers, carbon-based materials, metal-organic frameworks, covalent organic frameworks, etc. The advance on the microextraction sampling technologies was summarized mainly based on in-vivo sampling, in-vitro sampling and microdialysis technologies. Moreover, the current challenges and perspective on the future trends of microextraction sampling technologies for bioanalysis were briefly discussed.

Aptamer functionalized magnetic hydrophobic polymer with synergetic effect for enhanced adsorption of alternariol from wheat

A new adsorbent based on aptamer functionalized magnetic hydrophobic polymer (MHbPA) was developed for specific and efficient adsorption of alternariol (AOH). Through the synergistic effect of aptamer-AOH affinity and hydrophobic interaction of polymer, enhanced adsorption properties had been realized, in which AOH aptamer was the first selected through capture-SELEX with good specificity and affinity, and the targeting polymer was designed based on the hydrophobicity of AOH to increase the interaction. The proposed MHbPA demonstrated a high adsorption capacity of 187.6 ng/mg for AOH. The adsorption behavior was considered as Langmuir adsorption model and pseudo-secondary kinetic adsorption model. Notably, the adsorption of AOH in wheat powder samples could be accomplished within 10 mins with acceptable recoveries. The as designed adsorbent with synergistic effect provides new insights into the development of enhanced pretreatment materials for mycotoxin monitoring in complex food matrices with specific aptamer and targeting polymer.

Organic solvent-free solid-phase extraction of acetamiprid in food samples using Strep-Tag system integrated apta-magnetic sorbents

A novel magnetic sorbent, named ABA-(Strep-tag II)-STMB, was prepared by modifying the acetamiprid-binding aptamer (ABA) onto Strep-Tactin-coated magnetic beads (STMBs) via Strep-tag II. The integration of the Strep-tag system allows the elution of the target by the addition of D-biotin, which can compete with Strep-tag II for the Strep-Tactin sites on the magnetic beads, instead of organic solvents. The sorbent showed good selectivity and reusability, and the extraction efficiency could still reach 90.5 % after 8 reuses. Under the optimized conditions, the developed magnetic solid-phase extraction (MSPE) method exhibited good linearity in the range of 0.1-100 μM, with the limits of detection (LOD) of 0.017-0.019 μM, and the limits of quantification (LOQ) of 0.057-0.066 μM. The relative standard deviations (RSDs) were below 5.51 %. The spiked recoveries were 84.4 %-96.0 %. The analysis results were in good agreement with those of the QuEChERS method.

Ant nest-like hierarchical porous imprinted resin-dispersive solid-phase extraction for selective extraction and determination of polychlorinated biphenyls in milk

Polychlorinated biphenyls (PCBs) are persistent toxic, organic chemicals that tend to accumulate in the food chain. This study reports the rapid and selective extraction and determination of PCBs (PCB81, 153, 105, 126, and 157) in milk samples by a dispersive solid-phase extraction (DSPE) coupled with gas chromatography-tandem mass spectrometry (GC-MS/MS). An ionic liquid-molecularly imprinted porous resin (IL-MIPPR) as a DSPE adsorbent was synthesized from m-aminophenol, formaldehyde, and 2,2'-benzidinedisulfonic acid as the monomer, crosslinker, and virtual template, respectively. The IL-MIPPR had a fast mass transfer (1.0 min) and good selectivity (imprinting factors of 1.8-3.0). The IL-MIPPR - DSPE - GC-MS/MS method exhibited good linearity (R² ≥ 0.9995), the limit of detections (LODs) < 0.6 pg/g, and the recoveries ranged from 82.8 % to 106 % with relative standard deviations ≤ 6.6 %. This method is thus better than previously reported methods in terms of the LOD, the adsorbent dosage, and the extraction time.

Effective extraction of the metabolites of toluene and xylene based on a postsynthetic-modified magnetic covalent organic polymer

Toluene and xylene are volatile organic compounds, and long-term exposure to toluene and xylene may cause brain structure and nervous system damage. To evaluate exposure to toluene and xylene in the environment, it is usually possible to monitor their metabolites in organisms, hippuric acid (HA) and methylhippuric acid (MHA). In this work, we designed a new magnetic solid phase extraction (MSPE) sorbent, zirconium postsynthetic-modified magnetic covalent organic polymer (Fe₃O₄@COP-COOZr), for purifying and enriching HA and 4-MHA. Zirconium ions were immobilized on the magnetic COP surface by postsynthetic modification without the use of additional coating layers or chelating ligands. The developed Fe₃O₄@COP-COOZr interacted with HA and 4-MHA through the π-π stacking effect and electrostatic interactions, as well as strong chelation with coordinatively unsaturated zirconium sites. The promising affinity material of Fe₃O₄@COP-COOZr in MSPE had high stability and recyclability. The established MSPE-HPLC-UV method showed low sorbent consumption (10 mg) and high sensitivity (LODs less than 0.1 μg L^-1), and can be used for the analysis of HA and 4-MHA in real samples. The recoveries of the proposed method in real urine samples for the simultaneous determination of HA and 4-MHA were in the range of 83.5-103.2 %, and the RSDs were 0.9-7.1 %.

Aptamer-functionalized pH-responsive polymer-modified magnetic nanoparticles for specific enrichment and sensitive determination of lactoferrin

A new type of aptamer-functionalized pH-responsive polymer-modified magnetic nanoparticles (ApMNPs) is introduced for specific enrichment and sensitive determination of lactoferrin (Lf) in complex matrixes. In the construction, Fe₃O₄@3-(Triethoxysilyl)propylmethacrylate@poly(4-Vinyl-1, 3-dioxolan-2-one-acrylic acid) (Fe₃O₄@MPS@p(VEC-AA)) were synthesized as pH-responsive polymer-modified magnetic nanoparticles (pMNPs) through free radical polymerization to increase the tunable interaction. Lf-binding aptamers were conjugated onto pMNPs through the reaction of amino-group in aptamer and epoxide-group in VEC, innovatively applied to prepare Lf-ApMNPs. On the basis of the synergistic effect of specific affinity of aptamer on Lf and tunable hydrophobic/hydrophilic property of pH-responsive polymer, Lf-ApMNPs presented good selectivity toward Lf, excellent adsorption capacity (as high as 233.9 mg g^-1), as well as good recoveries in the range 93.6-99.6% in Lf-related nutrition samples. Significantly, the introduction of pH-responsive monomer (AA) effectively regulated the adsorption-desorption process of Lf, with the function similar to a switch. Moreover, the good performances of Ct-ApMNPs toward α-Chymotrypsin showed that ApMNPs exhibited universality to other proteins through easily changing the binding aptamer, thereby offering a facile and efficient approach for specific enrichment and sensitive determination of targets in real biological samples.

[Application progress of covalent organic framework materials in extraction of toxic and harmful substances]

Toxic and hazardous substances constitute a category of compounds that are potentially hazardous to humans, other organisms, and the environment. These substances include pesticides (benzoylureas, pyrethroids, neonicotinoids), persistent organic pollutants (polycyclic aromatic hydrocarbons, polychlorinated biphenyls, perfluorinated compounds), plasticizers (phthalate esters, phenolic endocrine disruptors), medicines (sulfonamides, non-steroid anti-inflammatory drugs, tetracyclines, fluoroquinone antibiotics), heterocyclic aromatic amines, algal toxins, and radioactive substances. Discharge of these toxic and harmful substances, as well as their possible persistence and bioaccumulation, pose a major risk to human health, often to the extent of being life-threatening. Therefore, it is important to analyze and detect toxic and hazardous substances in the environment, drinking water, food, and daily commodities. Sample pretreatment is an imperative step in most of the currently used analytical methods, especially in the analysis of trace toxic and harmful substances in complex samples. An efficient and fast sample pretreatment technology not only helps improve the sensitivity, selectivity, reproducibility, and accuracy of analytical methods, but also avoids contamination of the analytical instruments and even damages the performance and working life of instruments. Sample pretreatment techniques widely used in the extraction of toxic and hazardous substances include solid-phase extraction (SPE), solid-phase microextraction (SPME), and dispersed solid-phase extraction (DSPE). The adsorbent material plays a key role in these pretreatment techniques, thereby determining their selectivity and efficiency. In recent years, covalent organic frameworks (COFs) have attracted increasing attention in sample pretreatment. COFs represent an exciting new class of porous crystalline materials constructed via the strong covalent bonding of organic building units through a reversible condensation reaction. COFs present four advantages: (1) precise control over structure type and pore size by consideration of the target molecular structure based on the connectivity and shape of the building units; (2) post-synthetic modification for chemical optimization of the pore interior toward optimized interaction with the target; (3) straightforward scalable synthesis; (4) feasible formation of composites with magnetic nanoparticles, carbon nanotubes, graphene, silica, etc., which is beneficial to enhance the performance of COFs and meet the requirement of diverse pretreatment technologies. Because of the well-defined crystalline porous structures and tailored functionalities, COFs have excellent potential for use in target extraction. However, some issues need to be addressed for the application of COFs in the extraction of toxic and hazardous substances. (1) For the sample matrix, most of the reported COFs are highly hydrophobic, which limits their dispersibility in water-based samples, leading to poor extraction performance. COFs with good dispersibility in water-based samples are urgently required. (2) Besides, COFs rely on hydrophobic interaction, size repulsion, π-π stacking, and Van der Waals forces to extract target substances, but they are not effective for some polar targets. Thus, it is necessary to develop COFs with high affinity for polar toxic and hazardous substances. (3) Methods for the synthesis of COFs have evolved from solvothermal methods to room-temperature methods, mechanical grinding, microwave-assisted synthesis, ion thermal methods, etc. Most of the existing methods are time-consuming, laborious, and environmentally unfriendly. The starting materials are too expensive to prepare COFs in large quantities. More effort is required to improve the synthesis efficiency and overcome the obstacles in the application of COFs for extraction. This article summarizes and reviews the research progress in COFs toward the extraction of toxic and hazardous substances in recent years. Finally, the application prospects of COFs in this field are summarized, which serves as a reference for further research into pretreatment technologies based on COFs.

Covalent organic frameworks as multifunctional materials for chemical detection

Sensitive and selective detection of chemical and biological analytes is critical in various scientific and technological fields. As an emerging class of multifunctional materials, covalent organic frameworks (COFs) with their unique properties of chemical modularity, large surface area, high stability, low density, and tunable pore sizes and functionalities, which together define their programmable properties, show promise in advancing chemical detection. This review demonstrates the recent progress in chemical detection where COFs constitute an integral component of the achieved function. This review highlights how the unique properties of COFs can be harnessed to develop different types of chemical detection systems based on the principles of chromism, luminescence, electrical transduction, chromatography, spectrometry, and others to achieve highly sensitive and selective detection of various analytes, ranging from gases, volatiles, ions, to biomolecules. The key parameters of detection performance for target analytes are summarized, compared, and analyzed from the perspective of the detection mechanism and structure-property-performance correlations of COFs. Conclusions summarize the current accomplishments and analyze the challenges and limitations that exist for chemical detection under different mechanisms. Perspectives on how future directions of research can advance the COF-based chemical detection through innovation in novel COF design and synthesis, progress in device fabrication, and exploration of novel modes of detection are also discussed.

Aptamer functionalized and reduced graphene oxide hybridized porous polymers SPE coupled with LC-MS for adsorption and detection of human α-thrombin

In this study, reduced graphene oxide (rGO) hybridized high internal phase emulsions were developed and polymerized as porous carriers for aptamer (5'/5AmMC6/-AGT CCG TGG TAG GGC AGG TTG GGG TGA CT-3') modification to enrich human α-thrombin from serum. The structure and properties of the materials were confirmed by scanning electron microscope (SEM), Fourier transform infrared spectroscope (FT-IR), and X-ray photoelectron spectra (XPS). The adsorption ability and selectivity were studied and the thrombin was detected with liquid chromatography-mass spectrometry (LC-MS). The adsorption of thrombin onto the sorbent was achieved within 30 min and the desorption was realized using 5.0 mL of acetonitrile/water (80/20, v/v). The thrombin was quantified by LC-MS according to its characteristic peptide sequence of ELLESYIDGR.

Recent advances in metal/covalent organic framework-based electrochemical aptasensors for biosensing applications

The booming development of novel porous materials, metal-organic frameworks (MOFs) and covalent-organic frameworks (COFs) has been attracting a lot of attention due to their designabilities, diversities, and extensive applications. MOFs and COFs provide a new potential opportunity and platform to fabricate electrochemical aptasensors for biosensing applications. Compared to other traditional materials, MOF/COF-based electrochemical biosensors can appreciably amplify the electrochemical response signals to improve the sensing performance. Herein, we provide a comprehensive overview of MOF/COF-based electrochemical aptasensors for monitoring different ultra-trace analytes (e.g. antibiotics, pesticides, and cancer markers). This review systematically discusses the classification of electrochemical aptasensors based on various functional materials, including pure MOFs, MOF/conductive composites, metal nanoparticle/MOF composites, pure COFs, COFs/conductive composites, and other hybrid materials. Furthermore, some typical MOF/COF-based electrochemical aptasensors in the recognition of specific targets are described in detail to improve and guide further research for biosensing applications.

Preparation of chitosan-modified magnetic Schiff base network composite nanospheres for effective enrichment and detection of hippuric acid and 4-methyl hippuric acid

Chitosan-modified magnetic Schiff base network composite nanospheres (Fe₃O₄@SNW@Chitosan) were prepared for the enrichment and detection of hippuric acid (HA) and 4-methyl hippuric acid (4-MHA) via magnetic solid phase extraction (MSPE) connected with HPLC. The SNW was one of the covalent organic framework, which constructed through covalent bonds, shown comprising solvent stability, low density and accessible pores. The obtained Fe₃O₄@SNW@Chitosan has many merits as a magnetic sorbent, including a hydrophilic surface, uniform pore size, unique ordered channel structure, and superparamagnetism. The favourable linearity of this MSPE-HPLC method was in the range of 1-1000 μg L^-1, and LODs of HA and 4-MHA were 0.3 μg L^-1 and 0.2 μg L^-1, respectively. The recoveries in urine samples were range from 95.3 to 109.0 % with the RSD less than 9.6 %. When employed for the enrichment of HA and 4-MHA, Fe₃O₄@SNW@Chitosan exhibited great potential as a candidate for preconcentration.

Porphyrin-based covalent organic framework as bioplatfrom for detection of vascular endothelial growth factor 165 through fluorescence resonance energy transfer

A fluorescent aptasensor based on porphyrin-based covalent organic framework (p-COF) and carbon dots (CDs) was constructed for detecting vascular endothelial growth factor 165 (VEGF₁₆₅) and for imaging of the breast cancer cell line Michigan cancer foundation-7 (MCF-7). CDs synthesized with strong photoluminescence at λ∼380 nm were used as donors to label the VEGF₁₆₅-targeted aptamers (Apt_VEGF/CDs). Additionally, the p-COF nanostructure comprised rich functional groups of CN on the surface and π-stacking planar nanostructure, resulting in the CDs adsorption via weakly π-π stacking, hydrogen bond and the Van der Waals force. Thereby, the fluorescence resonance energy transfer (FRET) occurred due to the close distance between the p-COF network and CDs, leading to the quenching of the fluorescence feature of CDs and p-COF. In the presence of VEGF₁₆₅, the G-quadruplex was formed via the specific binding between VEGF₁₆₅ and aptamer. It impelled that the release of partial VEGF₁₆₅-Apt_VEGF/CDs complex, affording the fluorescence recovery of the sensing system to some extent. Consequently, the proposed Apt_VEGF/CDs/p-COF fluorescence biosensor offered excellent analytical performances for the VEGF₁₆₅ detection, displaying a detection limit of 20.9 fg mL^-1 within a wide linear range of the VEGF₁₆₅ concentration of 1.0 pg mL^-1-100 ng mL^-1. The developed fluorescence biosensor was also used to determine VEGF₁₆₅-overexpressed in MCF-7 cancer cells. Thereby, the present work can greatly widen the application of COFs in the development of aptasensors and cancer diagnosis.

Insights into the structure-performance relationships of extraction materials in sample preparation for chromatography

Sample preparation is one of the most crucial steps in analytical processes. Commonly used methods, including solid-phase extraction, dispersive solid-phase extraction, dispersive magnetic solid-phase extraction, and solid-phase microextraction, greatly depend on the extraction materials. In recent decades, a vast number of materials have been studied and used in sample preparation for chromatography. Due to the unique structural properties, extraction materials significantly improve the performance of extraction devices. Endowing extraction materials with suitable structural properties can shorten the pretreatment process and improve the extraction efficiency and selectivity. To understand the structure-performance relationships of extraction materials, this review systematically summarizes the structural properties, including the pore size, pore shape, pore volume, accessibility of active sites, specific surface area, functional groups and physicochemical properties. The mechanisms by which the structural properties influence the extraction performance are also elucidated in detail. Finally, three principles for the design and synthesis of extraction materials are summarized. This review can provide systematic guidelines for synthesizing extraction materials and preparing extraction devices.

Recent Advances in Affinity MOF-Based Sorbents with Sample Preparation Purposes

This review summarizes the recent advances concerning metal-organic frameworks (MOFs) modified with several biomolecules (e.g., amino acids, nucleobases, proteins, antibodies, aptamers, etc.) as ligands to prepare affinity-based sorbents for application in the sample preparation field. The preparation and incorporation strategies of these MOF-based affinity materials were described. Additionally, the different types of ligands that can be employed for the synthesis of these biocomposites and their application as sorbents for the selective extraction of molecules and clean-up of complex real samples is reported. The most important features of the developed biocomposites will be discussed throughout the text in different sections, and several examples will be also commented on in detail.

Facile extraction and determination of organophosphorus pesticides in vegetables via magnetic functionalized covalent organic framework nanocomposites

Facile enrichment and determination of trace organophosphorus pesticides (OPPs) in foods has been a constantly pursuing goal in food safety field. Herein, Zr⁴⁺-immobilized covalent organic frameworks (Fe₃O₄@COF@Zr⁴⁺) have been first constructed and utilized as the powerful adsorbents for magnetic solid-phase extraction (MSPE) of OPPs. Owing to the π-π stacking interaction, hydrogen bonding and Zr⁴⁺-phosphate coordination reaction, the composites exhibited excellent selectivity and superior affinity to OPPs. Under optimized conditions, the proposed MSPE method coupled with GC-FPD showed good linearity (R² ≥ 0.9990) and yielded low limits of detection (0.7-3.0 μg kg^-1) for OPPs. Moreover, the developed method was successfully employed for the quantitation of OPPs in spiked vegetable samples and obtained satisfactory recoveries in the range of 87-121% with the relative standard deviations (RSDs) ≤ 8.9%. These results demonstrated that the prepared nanoparticles hold unique advantages for trace OPPs analysis in foodstuffs.

Determination of sulfadimethoxine in milk with aptamer-functionalized Fe3 O4 /graphene oxide as magnetic solid-phase extraction adsorbent prior to HPLC

An aptamer (Apt) functionalized magnetic material was prepared by covalently link Apt to Fe₃ O₄ /graphene oxide (Fe₃ O₄ /GO) composite by 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride and N-hydroxysuccinimide, and then characterized by FTIR spectroscopy, X-ray diffraction, and vibration sample magnetometry. The obtained composite of Fe₃ O₄ /GO/Apt was employed as magnetic solid-phase extraction adsorbent for the selective preconcentration of sulfadimethoxine prior to analysis by high-performance liquid chromatography. Under the optimal conditions (sample pH of 4.0, sorbent dosage of 20 mg, extraction time of 3 h, and methanol-5% acetic acid solution as eluent), a good linear relationship was obtained between the peak area and concentration of sulfadimethoxine in the range of 5.0 to 1500.0 µg/L with correlation coefficient of 0.9997. The limit of detection (S/N = 3) was 3.3 µg/L. The developed method was successfully applied to the analysis of sulfadimethoxine in milk with recoveries in the range of 75.9-92.3% and relative standard deviations less than 8.1%. The adsorption mechanism of Fe₃ O₄ /GO/Apt toward sulfadimethoxine was studied through the adsorption kinetics and adsorption isotherms, and the results show that the adsorption process fits well with the pseudo-second-order kinetic model and the adsorbate on Fe₃ O₄ /GO/Apt is multilayer and heterogeneous.

Covalent Organic Frameworks in Sample Preparation

Covalent organic frameworks (COFs) can be classified as emerging porous crystalline polymers with extremely high porosity and surface area size, and good thermal stability. These properties have awakened the interests of many areas, opening new horizons of research and applications. In the Analytical Chemistry field, COFs have found an important application in sample preparation approaches since their inherent properties clearly match, in a good number of cases, with the ideal characteristics of any extraction or clean-up sorbent. The review article is meant to provide a detailed overview of the different COFs that have been used up to now for sample preparation (i.e., solid-phase extraction in its most relevant operational modes-conventional, dispersive, magnetic/solid-phase microextraction and stir-bar sorptive extraction); the extraction devices/formats in which they have been applied; and their performances and suitability for this task.

A composite consisting of a deep eutectic solvent and dispersed magnetic metal-organic framework (type UiO-66-NH2) for solid-phase extraction of RNA

A cactus-shaped magnetic composite was prepared for solid-phase extraction of RNA. It is composed of the metal organic framework UiO-66-NH₂ that was modified with Fe₃O₄ nanoparticles. The composite was then dispersed in a lactic acid-based deep eutectic solvent (DES, Fe₃O₄-COOH@UiO-66-NH₂@DES). The structures of the sorbents were characterized by transmission electron microscopy, scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectrometry, vibrating sample magnetometry and thermogravimetric analysis. The extraction performance of sorbents was optimized and the maximum extraction capacity reached 246 mg·g^-1. Extraction is shown to mainly rely on chelation interaction, electrostatic interaction, hydrophobic interaction and hydrogen bonding interaction. The sorbent can selectively extract RNA over DNA, bovine hemoglobin and amino acids. Regeneration studies indicated that the sorbent can be re-used (after regenreation with DES) several times without obvious change of the extraction capacity. The successful extraction of RNA from yeast testified the practical application of the sorbent. Graphical abstractSchematic representation of the fabrication Fe₃O₄-COOH@UiO-66-NH₂@DES, and its application in the magnetic solid phase extraction of RNA.

Determination of Chloramphenicol in Honey and Milk by HPLC Coupled with Aptamer-Functionalized Fe3 O4 /Graphene Oxide Magnetic Solid-Phase Extraction

An aptamer-functionalized Fe₃ O₄ /graphene oxide was synthesized by chemical co-precipitation method and then employed in the magnetic solid-phase extraction for selective enrichment of chloramphenicol before HPLC. The aptamer was covalently bonded to the Fe₃ O₄ /graphene oxide complex by 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide. Parameters affecting extraction efficiency including solution pH, extraction time and temperature, types and volume of elution solvent, and elution time were investigated in detail. Under the optimal conditions, good linearity was obtained between the peak area and analyte concentration in the range of 7.0 to 1.0 × 10³  µg/L with the correlation coefficient of 0.9994. The limit of detection and quantitation were 0.24 µg/L and 0.79 µg/L, respectively. The developed method was employed to the analysis of chloramphenicol in honey and milk samples. The recoveries ranged from 80.5% to 105.0% with relative standard deviations less than 8.9%. PRACTICAL APPLICATION: An aptamer-functionalized Fe₃ O₄ /graphene oxide was synthesized and employed in magnetic solid phase extraction for the enrichment of chloramphenicol before HPLC. The presented assay was employed for the determination of chloramphenicol in honey and milk with satisfactory results.

pH-responsive polymer assisted aptamer functionalized magnetic nanoparticles for specific recognition and adsorption of proteins

A new adsorbent based on pH-responsive polymer assisted aptamer functionalized magnetic nanoparticles was developed for specific recognition and efficient adsorption of proteins. Arising from the synergistic effect of specific affinity of apatamer on protein and tunable hydrophobic/hydrophilic property of pH-responsive polymer, the adsorbent exhibited excellent adsorption capacity for target protein. Notably, because of the pH-responsive property of the polymer, the adsorption and desorption process could be regulated through varying environmental pH. The resultant adsorbent that immobilized with lysozyme binding aptamer was successfully applied in specific recognition and efficient adsorption of lysozyme in egg white samples and good recovery results in the range of 95.2-103.2% were obtained. Moreover, the adsorbent immobilized with cytochrome C binding aptamer also exhibited satisfactory adsorption to cytochrome C. The synergistic effect of pH-responsive polymer and aptamer promoted the recognition selectivity and adsorption capacity to target protein, illustrating a facile way for construction of more specific protein adsorbents.

Recent advances in the construction of functionalized covalent organic frameworks and their applications to sensing

Covalent organic frameworks (COFs), as an emerging class of porous crystalline polymers, are built by the combination of the light elements through the strong covalent bonds. In the past decade, COFs have been reported to show plenty of unique properties (such as ordered channels, large specific surface area, highly tunable porosity, optional building blocks, predictable and stable structure, and abundant functional groups), and have been widely applied in multiple fields. Recently, to further improve the potential performances of COFs and extend their applicability, a number of COFs with various functionalities have been successfully developed through the functionalization modification. In this review, we summarized the advanced design and construction of functionalized COFs, including COFs with post-synthetic modification, COFs-based composites (e.g. COFs-metal nanoparticles composites, COFs-metal oxide nanoparticles composites, COFs-MOFs composites, and COFs-enzyme composites), and molecularly imprinted COFs. Impressively, the applications of functionalized COFs to sensing also have been comprehensively summarized, including colorimetric sensing, fluorescent sensing, electrochemical sensing, and other sensing (such as quartz crystal microbalance (QCM) sensing, photoelectrochemical sensing, and humidity sensing). In the end, future opportunities and challenges in this promising field are tentatively proposed.

Ionic liquids skeleton typed magnetic core-shell molecularly imprinted polymers for the specific recognition of lysozyme

The novel ionic liquids skeleton typed magnetic core-shell molecularly imprinted polymers (Fe₃O₄-COOH@IL-MIP) were firstly constructed with 1-vinyl-3-aminoformylmethyl imidazolium chloride ionic liquid ([VAFMIM]Cl-IL) modified magnetic particles as the substrate materials, [VAFMIM]Cl-IL as functional monomer, 1,6-hexanediyl-3,3'-bis-1-vinylimidazolium dichloride ionic liquid as cross-linker and Lysozyme (Lys) as template protein via surface-imprinting technique. The structure of Fe₃O₄-COOH@IL-MIP were confirmed by transmission and scanning electron microscopy, dynamic light scattering, thermo-gravimetric analysis, fourier transform infrared spectrometry and X-ray diffraction. The adsorption mechanism was discussed from the perspective of amino acid residues of Lys. The maximum adsorption capacity of MIPs was 166.36 mg g^-1 and imprinting factor was 2.67. The competitive adsorption experiments demonstrated the favorable recognition ability of MIPs toward Lys. Reusability studies indicated MIPs can be reused ten times without obvious loss of rebinding ability. The Lys conformation maintained intact after elution and the elution rate was as high as 74%. The adsorption experiment of egg white manifested that MIPs can effectively separate Lys in practical samples. Only ILs and Fe₃O₄ were utilized to fabricate MIPs, this strategy realized the goal of energy and cost saving while achieving simple synthesis of imprinted materials, and is expected to provide a new feasible idea to exploit synthetic methods for protein-MIPs.

Boric-Acid-Functionalized Covalent Organic Framework for Specific Enrichment and Direct Detection of cis-Diol-Containing Compounds by Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry

Design and synthesis of a novel matrix that serves as highly selective adsorption material are significant for the matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) analysis of small molecules in complicated biosamples. In this work, we presented a facile one-pot strategy for the synthesis of boric-acid-functionalized covalent organic frameworks (B-COFs) by using 2,4,6-trihydroxy-1,3,5-benzenetrialdehyde, benzidine, and 4-aminophenyl-boronic acid as ligands. Compared with bare COFs, the B-COFs have similar crystallinity, specific surface, and well-developed pore structure. The surface area and average pore size of B-COFs were 238.0 m²/g and 1.2 nm, respectively. The resulting material was used as an adsorbent for selective enrichment of cis-diol-containing compounds based on an affinity reaction between phenylboronic acid and cis-diol. Using luteolin, riboflavin, and pyrocatechol as model analytes, the enrichment ability of B-COFs as a matrix was examined by MALDI-TOF MS assay, and its high selectivity against target analytes was obtained in the presence of 100 times more anti-nonspecific compounds than that even in the complicated biosample. The limits of detection for luteolin, riboflavin, and pyrocatechol were as low as fg/mL with B-COF enrichment. The B-COFs were further employed and validated for specific enrichment and direct detection of target analytes with complex samples such as human serum, milk, and Capsicum samples. Large surface area, numerous boric-acid active sites, and super stability make B-COFs with high enrichment capacity, high selectivity and sensitivity, satisfying reproducibility, and excellent applicability in MALDI-TOF MS assays.

Recent progress in the development of recognition bioelements for polychlorinated biphenyls detection: Antibodies and aptamers

Polychlorinated biphenyls (PCBs) are persistent pollutants, which have expanded in foods and the environment. Detection of PCBs is considered essential due to recognized side-effects of PCBs on health and the public concerns in this regard. On the other hand, due to the trace levels of these organic chlorine compounds, reliable and sensitive assays must be developed. Recognition elements are essential parts of analytical detection assays and sensors of PCBs since these elements are involved in the selective identification of the analytes of interest. Understanding the fundamentals of the recognition elements of PCBs and the benefits of the sensor strategies result in the development of next-generation recognition devices. This review aimed to highlight the recent progress in the recognition elements as key parts of biosensors. We initially, focused on the developed antibody-based biosensors for the detection of PCBs, followed by discussing the aptamers as novel recognition elements. Furthermore, the recent advancement in the development of aptamer-based solid phase extractions has been evaluated. These findings could contribute to improving the design of commercial PCB-kits in the future.

Porous Organic Frameworks: Advanced Materials in Analytical Chemistry

Porous organic frameworks (POFs), a general term for covalent-organic frameworks (COFs), covalent triazine frameworks (CTFs), porous aromatic frameworks (PAFs), etc., are constructed from organic building monomers with strong covalent bonds and have generated great interest among researchers. The remarkable features, such as large surface areas, permanent porosity, high thermal and chemical stability, and convenient functionalization, promote the great potential of POFs in diverse applications. A critical overview of the important development in the design and synthesis of COFs, CTFs, and PAFs is provided and their state-of-the-art applications in analytical chemistry are discussed. POFs and their functional composites have been explored as advanced materials in "turn-off" or "turn-on" fluorescence detection and novel stationary phases for chromatographic separation, as well as a promising adsorbent for sample preparation methods. In addition, the prospects for the synthesis and utilization of POFs in analytical chemistry are also presented. These prospects can offer an outlook and reference for further study of the applications of POFs.