Facile synthesis of Ti(4+)-immobilized Fe3O4@polydopamine core-shell microspheres for highly selective enrichment of phosphopeptides

Facile fabrication of Ti4+-immobilized magnetic nanoparticles by phase-transitioned lysozyme nanofilms for enrichment of phosphopeptides

In this study, titanium (IV)-immobilized magnetic nanoparticles (Ti4+-PTL-MNPs) were firstly synthesized via a one-step aqueous self-assembly of lysozyme nanofilms for efficient phosphopeptide enrichment. Under physiological conditions, lysozymes readily self-organized into phase-transitioned lysozyme (PTL) nanofilms on Fe3O4@SiO2 and Fe3O4@C MNP surfaces with abundant functional groups, including -NH2, -COOH, -OH, and -SH, which can be used as multiple linkers to efficiently chelate Ti4+. The obtained Ti4+-PTL-MNPs possessed high sensitivity of 0.01 fmol μL-1 and remarkable selectivity even at a mass ratio of β-casein to BSA as low as 1:400 for phosphopeptide enrichment. Furthermore, the synthesized Ti4+-PTL-MNPs can also selectively identify low-abundance phosphopeptides from extremely complicated human serum samples and their rapid separation, good reproducibility, and excellent recovery were also proven. This one-step self-assembly of PTL nanofilms facilitated the facile and efficient surface functionalization of various nanoparticles for proteomes/peptidomes.

A novel carbon-based material with titanium and zirconium ions etched on hollow mesoporous carbon tubes for specific capture of phosphopeptides and exosomes

The analysis of low abundance phosphopeptides in organisms and specific capture exosomes are crucial for unraveling the pathogenesis of diseases. For this reason, titanium-zirconium ions and highly biocompatible dopamine and polyimide tubes (PITs) were introduced, and a novel carbon-based material with titanium and zirconium ions etched on hollow mesoporous carbon tubes (HMCT), denoted as G@C@Ti-Zr-HMCT, comes into being after high-temperature calcination. Attributing to the tightly bound titanium and zirconium ions to HMCT and the high carbon content of the polydopamine carbonaceous layer, G@C@Ti-Zr-HMCT displays satisfactory capability of enriching phosphopeptides with satisfactory detection limit (0.2 fmol), extraordinary selectivity (1:2000), and good loading capacity (100 μg/mg). In addition, 25 phosphopeptides related to 25 phosphoproteins from the serum of Parkinson's disease (PD) patients and 30 phosphopeptides attributed to 26 phosphoproteins from the serum of healthy individuals were enriched by G@C@Ti-Zr-HMCT, respectively. In addition, bioinformatics analysis of the above results revealed that PD were associated with serine, threonine, and leucine of high frequency, blood coagulation in BP, Golgi apparatus and mitochondrial outer membrane in CC, and heparin binding in MF. Moreover, the phospholipid bilayer of exosomes and metallic titanium and zirconium ions interact to produce the following results: this highly biocompatible carbon-based material was successfully applied to capture exosomes, which offers a promising platform for isolating exosomes. To sum up, these delightful results confirmed without doubt that G@C@Ti-Zr-HMCT has enjoyed a splendiferous future in the specific capture of phosphopeptides and exosomes isolation.

Synthesis of Ni2+-functionalized polydopamine magnetic beads for facilitated purification of histidine-tagged proteins

Facilitated purification of proteins, at a low cost and a short time, is one of the key steps in the industrial production of recombinant proteins. In the current study, polydopamine nanoparticles (PDA-NPs) are considered in the synthesis of magnetic beads for purifying recombinant proteins due to advantages such as biocompatibility/ biodegradability, easy synthesis, as well as the ability to directly chelate metal ions. They were synthesized in Tris buffer (pH: 8:5), then chelated with Fe3+(20 mg) and Ni2+ ions at concentrations of 2, 3, 5, and 7 mg/ml. Prepared nanoparticles were characterized through scanning electron microscopy (SEM), ultraviolet-visible spectroscopy (UV-vis), dynamic light scattering (DLS), Inductively Coupled Plasma (ICP), and vibrating sample magnetometer (VSM). The size distribution of the particles was reported in the narrow range of 120-140 nm and 200 to 220 nm by the SEM image and DLS analysis, respectively. The chelation of ions on the surface of the nanoparticle was confirmed by the ICP technique with a magnetization of 35.42 emu/g. The highest adsorption rate of Ni2+ ions to polydopamine was obtained at a ratio of 1.4. The SDS-PAGE and western blot analysis confirmed the purification of eGFP and Hsp40 by PDA/Fe3+/Ni2+ at 26 and 40 kDa compared to the commercial nickel column. Moreover, the concentration of purified eGFP by PDA/Fe3+/Ni2+ was reported 138.83 µg/ml by the fluorescent signals, which is almost equal to or more than the protein purified by commercial Ni-NTA column (108.28 µg/ ml). The stability of PDA/Fe3+/Ni2+ has also been evaluated by ICP-OES for 10 days, and the result suggested that PDA magnetic beads were stable. Therefore, it can be concluded that PDA/Fe3+/Ni2+ have the ability to purify recombinant proteins in one less step and shorter time.

Advances in proteomics sample preparation and enrichment for phosphorylation and glycosylation analysis

As the common and significant chemical modifications, post-translational modifications (PTMs) play a key role in the functional proteome. Affected by the signal interference, low concentration, and insufficient ionization efficiency of impurities, the direct detection of PTMs by mass spectrometry (MS) still faces many challenges. Therefore, sample preparation and enrichment are an indispensable link before MS analysis of PTMs in proteomics. The rapid development of functionalized materials with diverse morphologies and compositions provides an avenue for sample preparation and enrichment for PTMs analysis. In this review, we summarize recent advances in the application of novel functionalized materials in sample preparation for phosphoproteomes and glycoproteomes analysis. In addition, this review specifically discusses the design and preparation of functionalized materials based on different enrichment mechanisms, and proposes research directions and potential challenges for proteomic PTMs research.

Characterization of Gentisate 1,2-Dioxygenase from Pseudarthrobacter phenanthrenivorans Sphe3 and Its Stabilization by Immobilization on Nickel-Functionalized Magnetic Nanoparticles

The aim of this study was the biochemical and kinetic characterization of the gentisate 1,2-dioxygenase (GDO) from Pseudarthrobacter phenanthrenivorans Sphe3 and the development of a nanobiocatalyst by its immobilization on Ni2+-functionalized Fe3O4-polydopamine magnetic nanoparticles (Ni2+-PDA-MNPs). This is the first GDO to be immobilized. The gene encoding the GDO was cloned with an N-terminal His-tag and overexpressed in E. coli. The nanoparticles showed a high purification efficiency of GDO from crude cell lysates with a maximum activity recovery of 97%. The immobilized enzyme was characterized by Fourier transform infrared spectroscopy (FTIR). The reaction product was identified by 1H NMR. Both free and immobilized GDO exhibited Michaelis–Menten kinetics with Km values of 25.9 ± 4.4 and 82.5 ± 14.2 μM and Vmax values of 1.2 ± 0.1 and 0.03 ± 0.002 mM*s−1, respectively. The thermal stability of the immobilized GDO was enhanced at 30 °C, 40 °C, and 50 °C, compared to the free GDO. Stored at −20 °C, immobilized GDO retained more than 60% of its initial activity after 30 d, while the free enzyme completely lost its activity after 10 d. Furthermore, the immobilized nanoparticle–enzyme conjugate retained more than 50% enzyme activity up to the fifth cycle.

Development of New Lanthanide(III) Ion-Based Magnetic Affinity Material for Phosphopeptide Enrichment

Lanthanide (III) ion-based magnetic IMAC materials consisting of core-shell-like silica-coated magnetic nanoparticles as supporting material, chelidamic acid as chelating agent, and Ln3+ ions were developed in this study. Magnetic nanoparticles...

Facile synthesis of Ti4+-immobilized magnetic covalent organic frameworks for enhanced phosphopeptide enrichment

In this work, core-shell structured Ti⁴⁺-immobilized magnetic covalent organic frameworks (denoted as Fe₃O₄@TAPTDHTA-Ti⁴⁺ composites) were prepared for enhanced phosphopeptide enrichment by one-pot synthesis of COFs shell with inherent bifunctional groups on Fe₃O₄ NPs and further Ti⁴⁺ immobilization. The widely distributed bifunctional groups could provide abundant chelating sites for Ti⁴⁺ immobilizing. Combining with the high specific surface area and mesoporous structure, the Fe₃O₄@TAPTDHTA-Ti⁴⁺ composites exhibited excellent enrichment efficiency for phosphopeptides, such as low detection limit (0.05 fmol μL^-1), high selectivity (1:5000 of molar ratio of β-casein/bovine serum albumin (BSA) tryptic digests), high adsorption capacity (62.9 μg mg^-1) and strong size-exclusive effect (1:250:250 of molar ratio of β-casein tryptic digest/β-casein/BSA). In addition, this method was general for immobilizing other metal ions (Zr⁴⁺ and Fe³⁺). Notably, the Fe₃O₄@TAPTDHTA-Fe³⁺ composites exhibited controllable affinity towards mono-phosphopeptides and multi-phosphopeptides. Furthermore, the Fe₃O₄@TAPTDHTA-Ti⁴⁺ composites were successfully applied to selectively capture phosphopeptides from complex biological samples including the tryptic digest of nonfat milk, human serum and human saliva. More significantly, 3333 phosphopeptides derived from 1409 phosphoproteins with 3492 phosphorylation sites were clearly identified from the tryptic digest of HeLa cell lysate. In addition to providing a potential excellent enrichment probe for comprehensive phosphoproteomic analysis, this study also offers a new perspective for the functionalization of COFs.

Engineering of nanomaterials for mass spectrometry analysis of biomolecules

Mass spectrometry (MS) based analysis has received intense attention in diverse biological fields. However, direct MS interrogation of target biomolecules in complex biological samples is still challenging, due to the extremely low abundance and poor ionization potency of target biological species. Innovations in nanomaterials create new auxiliary tools for deep and comprehensive MS characterization of biomolecules. More recently, growing research interest has been directed to the compositional and structural engineering of nanomaterials for enriching target biomolecules prior to MS analysis, enhancing the ionization efficiency in MS detection and designing biosensing nanoprobes in sensitive MS readout. In this review, we mainly focus on the recent advances in the engineering of nanomaterials towards their applications in sample pre-treatment, desorption/ionization matrices and ion signal amplification for MS profiling of biomolecules. This review will provide a toolbox of nanomaterials for researchers devoted to developing analytical methods and practical applications in the biological MS field.

WIDENING THE BOTTLENECK OF PHOSPHOPROTEOMICS: EVOLVING STRATEGIES FOR PHOSPHOPEPTIDE ENRICHMENT

Phosphorylation is a form of protein posttranslational modification (PTM) that regulates many biological processes. Whereas phosphoproteomics is a scientific discipline that identifies and quantifies the phosphorylated proteome using mass spectrometry (MS). This task is extremely challenging as ~30% of the human proteome is phosphorylated; and each phosphoprotein may exist as multiple phospho-isoforms that are present in low abundance and stoichiometry. Hence, phosphopeptide enrichment techniques are indispensable to (phospho)proteomics laboratories. These enrichment methods encompass widely-adopted techniques such as (i) affinity-based chromatography; (ii) ion exchange and mixed-mode chromatography (iii) enrichment with phospho-specific antibodies and protein domains, and (iv) functionalized polymers and other less common but emerging technologies such as hydroxyapatite chromatography and precipitation with inorganic ions. Here, we review these techniques, their history, continuous development and evaluation. Besides, we outline associating challenges of phosphoproteomics that are linked to experimental design, sample preparation, and proteolytic digestion. In addition, we also discuss about the future outlooks in phosphoproteomics, focusing on elucidating the noncanonical phosphoproteome and deciphering the "dark phosphoproteome". © 2020 John Wiley & Sons Ltd.

Post-synthesis of biomimetic chitosan with honeycomb-like structure for sensitive recognition of phosphorylated peptides

Chemical modification of biological materials is indispensable for enrichment of phosphorylated peptides. In this work, we synthesized a biomimetic honeycombed affinity chromatography (IMAC) adsorbent by preparing Crosslinked Chitosan, chelating aminomethyl phosphate decorated with Ti (IV) cation. The as-prepared CTSM@AMPA-Ti⁴⁺ composites with stable structure, low steric hindrance, and high Ti⁴⁺ loading amount were used as a promising adsorbent for enrichment of phosphopeptides. CTSM@AMPA-Ti⁴⁺ showed extremely high sensitivity (0.4 fmol) and selectivity at a low composition molar ratio of β-casein/BSA (1:1000). What's more, it can keep its performance in the case that used to capture phosphorylated peptides from standard protein ten times or soaking in the acid/base solution for a long time. In addition, CTSM@AMPA-Ti⁴⁺ successfully captured 35 phosphorylated peptides from human saliva. This study offers a way about diversiform functionalization of CTSM in phosphoproteome analysis and disease research.

Efficient separation of phosphopeptides employing a Ti/Nb-functionalized core-shell structure solid-phase extraction nanosphere

A strategy for effectively enriching global phosphopeptides was successfully developed by using ammonia methyl phosphate (APA) as a novel chelating ligand and Ti⁴⁺ and Nb⁵⁺ as double functional ions (referred to as Fe₃O₄@mSiO₂@APA@Ti⁴⁺/Nb⁵⁺). With the advantage of large specific surface area (151.1 m²/g), preeminent immobilized ability for metal ions (about 8% of total atoms), and unbiased enrichment towards phosphopeptides, Fe₃O₄@mSiO₂@APA@Ti⁴⁺/Nb⁵⁺ displays high selectivity (maximum mass ratio β-casein to BSA is 1:1500), low limit of detection (LOD, as low as 0.05 fmol), good relative standard deviation (RSD, lower than 7%), recovery rate of 87% (¹⁸O isotope labeling method), outstanding phosphopeptide loading capacity (330 μg/mg), and at least five times re-use abilities. In the examination of the actual sample, 24 phosphopeptides were successfully detected in saliva and 4 phosphopeptides were also selectively extracted from human serum. All experiments have shown that Fe₃O₄@mSiO₂@APA@Ti⁴⁺/Nb⁵⁺ exhibits exciting potential in view of the challenge of low abundance of phosphopeptides. Graphical abstract.

An Integral Recognition and Signaling for Electrochemical Assay of Protein Kinase Activity and Inhibitor by Reduced Graphene Oxide-Polydopamine-Silver Nanoparticle-Ti4+ Nanocomposite

A novel electrochemical biosensing method for protein kinase (PKA) activity was demonstrated by using a reduced graphene oxide-polydopamine-silver nanoparticle-Ti4+ (rGO-PDA-AgNPs-Ti4+) nanocomposite. The obtained nanocomposite possessed an integral capability for phosphopeptide recognition and signal readout. The polydopamine modified reduced graphene oxide (rGO-PDA) was firstly prepared based on a self-polymerization method of dopamine. The silver ions were adsorbed onto polydopamine (PDA) layer and directly reduced into silver nanoparticles (AgNPs), which was used for electrochemical signal reporting. Then, the Ti4+ cations were attached onto the PDA layer for phosphopeptide recognition according to the strong coordination ability of PDA with Ti4+ and phosphate group. The prepared rGO-PDA-AgNPs-Ti4+ nanocomposites were characterized with different methods. The developed rGO-PDA-AgNPs-Ti4+ nanocomposites were then employed for electrochemical analysis of PKA-catalyzed kemptide phosphorylation. The sensitive detection toward PKA activity was realized with an experimental detection limit of about 0.01 U/mL. It may be also extended for the inhibitor evaluation. Thus, it provided a facile and sensitive means for electrochemical analysis of PKA activity and inhibitor screening.

Facile preparation of polymer-grafted ZIF-8-modified magnetic nanospheres for effective identification and capture of phosphorylated and glycosylated peptides

As a member of MOFs, Zn-MOFs (ZIF-8) are seldom used in phosphopeptide enrichment because ZIF-8 is soluble in acid solutions. Therefore, properly designing a novel strategy to overcome the defect of ZIF-8 is necessary. In this study, a novel multifunctional nanoprobe was designed by uniting magnetic core, titania shell and hydrophilic metal-organic frameworks (named as Fe3O4@PDA@mTiO2@PEI-g-ZIF-8). Integrating the strategies of hydrophilic interaction affinity chromatography (HILIC), immobilized metal ion affinity chromatography (IMAC) and metal oxide affinity chromatography (MOAC), the Fe3O4@PDA@mTiO2@PEI-g-ZIF-8 mesoporous microspheres can enrich phosphorylated peptides and glycosylated peptides simultaneously. Fe3O4@PDA@mTiO2@PEI-g-ZIF-8 has high selectivity (maximum molar ratio β-casein/HRP : BSA = 1 : 1000), low detection limit (2 fmol) towards phosphopeptides and glycopeptides. Besides, the Fe3O4@PDA@mTiO2@PEI-g-ZIF-8 also exhibited a fine performance in the actual sample detection. In the experiment, taking saliva as a sample, 16 phosphorylated peptides were identified, and from a human serum sample, 4 phosphorylated peptides were selectively identified. All in all, the materials show great potential in the future study of phosphoproteomics and glycoproteomics.

Design of Functional Magnetic Nanocomposites for Bioseparation

Magnetic materials have been widely used in bioseparation in recent years due to their good biocompatibility, magnetic properties, and high binding capacity. In this review, we provide a brief introduction on the preparation and bioseparation applications of magnetic materials including the synthesis and surface modification of magnetic nanoparticles as well as the preparation and applications of magnetic nanocomposites in the separation of proteins, peptides, cells, exosomes and blood. The current limitations and remaining challenges in the fabrication process of magnetic materials for bioseparation will be also detailed.

Preparation of Magnetic CuFe2O4@Ag@ZIF-8 Nanocomposites with Highly Catalytic Activity Based on Cellulose Nanocrystals

A facile approach was successfully developed for synthesis of cellulose nanocrystals (CNC)-supported magnetic CuFe2O4@Ag@ZIF-8 nanospheres which consist of a paramagnetic CuFe2O4@Ag core and porous ZIF-8 shell. The CuFe2O4 nanoparticles (NPs) were first prepared in the presence of CNC and dispersant. Ag NPs were then deposited on the CuFe2O4/CNC composites via an in situ reduction directed by dopamine polymerization (PDA). The CuFe2O4/CNC@Ag@ZIF-8 nanocomposite was characterized by TEM, FTIR, XRD, N2 adsorption-desorption isotherms, VSM, and XPS. Catalytic studies showed that the CuFe2O4/CNC@Ag@ZIF-8 catalyst had much higher catalytic activity than CuFe2O4@Ag catalyst with the rate constant of 0.64 min-1. Because of the integration of ZIF-8 with CuFe2O4/CNC@Ag that combines the advantaged of each component, the nanocomposites were demonstrated to have an enhanced catalytic activity in heterogeneous catalysis. Therefore, these results demonstrate a new method for the fabrication of CNC-supported magnetic core-shell catalysts, which display great potential for application in biocatalysis and environmental chemistry.

Self-assembly of poly(ionic liquid) functionalized mesoporous magnetic microspheres for the solid-phase extraction of preservatives from milk samples

In this work, a novel, rapid, and simple analytical method was proposed for the detection of parabens in milk sample by gas chromatography coupled with mass spectrometry. At the same time, milk sample was pretreated by magnetic solid phase extraction, which detected up to five parabens. A series of important parameters of magnetic solid phase extraction were investigated and optimized, such as pH value of loading buffer, amount of material, adsorption time, ionic strength, eluting solvents, and eluting time. Under the optimized conditions, the corresponding values were more than 0.9991, limits of detection and the limit of quantification were 0.1 and 0.5 ng/mL, respectively. In addition, the recoveries were achieved in range of 95-105%, the liner range were within 0.1-600 ng/mL, and the relative standard deviations were even lower than 5%.

Polydopamine-tailored paclitaxel-loaded polymeric microspheres with adhered NIR-controllable gold nanoparticles for chemo-phototherapy of pancreatic cancer

Chemotherapeutic drugs often used as a first-line treatment of pancreatic cancer (PC) exhibit challenges due to resistance development, lack of selectivity, and tumor heterogeneity. Currently, combination chemo-photothermal therapy is known to enhance the therapeutic efficacy of chemotherapeutic drugs in PC. In this study, we develop adherent gold nanoparticles (GNPs) and paclitaxel (PTX)-loaded PLGA microspheres for the treatment of PC. Polydopamine (pD) was used as a linker to adhere GNPs to the surface of PLGA-Ms and characterized using TEM. Short-term cytotoxicity of GNPs-pD-PTX-PLGA-Ms with or without NIR treatment was evaluated using CCK-8 assays. ROS and western blot assay were performed to determine the intensity of ROS following the treatment of GNPs-pD-PTX-PLGA-Ms with or without NIR in Panc-1 cell line. Successful adhesion of GNPs on the microspheres was confirmed by TEM. CCK-8 assay revealed that GNPs-pD-PTX-PLGA-Ms with NIR showed three-fold higher cytotoxicity, compared to the group without NIR. Furthermore, ROS and western blot assay suggest that GNPs-pD-PTX-PLGA-Ms with NIR showed more ROS generation, followed by downregulation of the expression levels of antioxidant enzyme (SOD2 and CATALASE). These results suggest that the GNPs-pD-PTX-PLGA-Ms in combination with NIR irradiation can provide a synergistic chemo-photothermal therapy for the treatment of PC.

Effect of shell structure of Ti-immobilized metal ion affinity chromatography core-shell magnetic particles for phosphopeptide enrichment

Magnetic materials in sample preparation for shotgun phosphoproteomics offer several advantages over conventional systems, as the enrichment can be achieved directly in solution, but they still suffer from some drawbacks, due to limited stability and selectivity, which is supposed to be affected by the hydrophilicity of the polymeric supports used for cation immobilization. The paper describes the development of an improved magnetic material with increased stability, thanks to a two-step covering of the magnetic core, for the enrichment of phosphopeptides in biological samples. Four materials were prepared featuring a polymeric shell with tunable hydrophilicity, obtained by "grafting from" polymerization of glycidyl methacrylate with 0-8.3% of polyethylene glycol methacrylate (PEGMA), the latter used to modulate the hydrophilicity of the material surface. Finally, the materials were functionalized with iminodiacetic acid for Ti4+ ion immobilization. The materials were analyzed for their composition by a combination of CHN elemental analysis and thermogravimetric analysis, also hyphenated to gas chromatography and mass spectrometric detection. Surface characteristics were evaluated by water contact angle measurements, scanning electron microscopy and energy dispersive X-ray spectrometry. These materials were applied to the enrichment of phosphopeptides from yeast protein digests. Peptides were identified by proteomics techniques using nano-high performance liquid chromatography coupled to mass spectrometry and bioinformatics. Qualitatively the peptides identified by the four systems were comparable, with 1606-1693 phosphopeptide identifications and a selectivity of 47-54% for all materials. The physico-chemical features of the identified peptides were also the same for the four materials. In particular, the grand average of hydropathy index values indicated that the enriched phosphopeptides were hydrophilic (ca. 90%), and only some co-enriched non-phosphorylated peptides were hydrophobic (21-28%), regardless of the material used for enrichment. Peptides had a pI ≤ 7, which indicated a well-known bias for acidic peptides binding, attributed to the interaction with the metal center itself. The results indicated that the enrichment of phosphopeptides and the co-enrichment of non-phosphorylated peptides is mainly driven by interactions with Ti4+ and does not depend on the amount of PEGMA chains in the polymer shell.

Novel Ti4+-Chelated Polyoxometalate/Polydopamine Composite Microspheres for Highly Selective Isolation and Enrichment of Phosphoproteins

Selective isolation and enrichment of phosphoproteins play critical roles for identification of biomarkers in biological applications. Herein, a kind of polyoxometalate (P₅W₃₀)/polydopamine (PDA) composite microspheres is readily synthesized via an in situ polymerization way, followed by immobilization of Ti⁴⁺ on the surface of the microspheres to obtain P₅W₃₀/PDA-Ti⁴⁺. Due to metal affinity and π stacking interaction, this novel material exhibits high selectivity to β-casein (β-ca), and the theoretical maximum adsorption capacity is as high as 1250 mg g^-1, fitting well with the Langmuir model. The captured β-ca can be collected by using Britton-Robinson (B-R) buffer at pH 7.0, and a recovery of 81.5% is acquired. The enrichment factor is over 150 at a mass ratio of BSA/β-ca = 100:1, indicating that phosphoproteins can be purified by P₅W₃₀/PDA-Ti⁴⁺. Moreover, the application of P₅W₃₀/PDA-Ti⁴⁺ as sorbent in real biological samples has been investigated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis, and the consequences show that this kind of material is able to selectively isolate phosphoproteins from complex samples such as drinking milk and chicken egg white.

A polydopamine-based platform for anti-cancer drug delivery

Cancer is the second leading cause of death in the world with around 9.6 million deaths in 2018, approximately 70% of which occurred in the middle- and low-income countries; moreover, the economic impact of cancer is significant and escalating day by day. The total annual economic cost of cancer treatment in 2010 was estimated at approximately US$ 1.16 trillion. Researchers have explored cancer mitigation therapies such as chemo-thermal therapy, chemo-photothermal therapy and photodynamic-photothermal therapy. These combinational therapies facilitate better control on the tunability of the carrier for effectively diminishing cancer cells than individual therapies such as chemotherapy, photothermal therapy and targeted therapy. All these therapies come under novel drug delivery systems in which anti-cancer drugs attack the cancerous cells due to various stimuli (e.g. pH, thermal, UV, IR, acoustic and magnetic)-responsive properties of the anti-cancer drug carriers. Compared to conventional drug delivery systems, the novel drug delivery systems have several advantages such as targeted drug release, sustained and consistent blood levels within the therapeutic window, and decreased dosing frequency. Among the numerous polymeric carriers developed for drug delivery, polydopamine has been found to be more suitable as a carrier for these drug delivery functions due to its easy and cost-effective fabrication, excellent biocompatibility, multi-drug carrier capacity and stimuli sensitivity. Therefore, in this review, we have explored polydopamine-based carriers for anti-cancer drug delivery systems to mitigate cancer and simultaneously discussed basic synthesis routes for polydopamine.

Hydrophilic Phytic Acid-Coated Magnetic Graphene for Titanium(IV) Immobilization as a Novel Hydrophilic Interaction Liquid Chromatography-Immobilized Metal Affinity Chromatography Platform for Glyco- and Phosphopeptide Enrichment with Controllable Selectivity

In this work, multifunctional Ti⁴⁺-immobilized phytic acid-modified magnetic graphene (denoted as MagG@PEI@PA-Ti⁴⁺) nanocomposites were fabricated through a facile route for simultaneous/respective enrichment of N-glyco- and phosphopeptides. Phytic acid (PA), with six phosphate groups, possesses excellent hydrophilicity and metal ion coordination ability, which endowed the MagG@PEI@PA-Ti⁴⁺ with combined properties of immobilized metal ion affinity chromatography (IMAC)- and hydrophilic interaction liquid chromatography (HILIC)-based materials. On the basis of the different binding ability of N-glyco- and phosphopeptides on MagG@PEI@PA-Ti⁴⁺, the MagG@PEI@PA-Ti⁴⁺ nanocomposites could enrich N-glyco- and phosphopeptides simultaneously or respectively by using different enrichment conditions, achieving controllable selective enrichment of N-glyco- and phosphopeptides. The proposed nanocomposites demonstrated an outstanding performance for selective enrichment of N-glycopeptides (selectivity, 1:1000 molar ratios of IgG/BSA; sensitivity, 0.5 fmol/μL IgG; loading capacity, 300 mg g^-1; recovery, >90%) and phosphopeptides (selectivity, 1:5000 molar ratios of α-casein/BSA; sensitivity, 0.1 fmol/μL α-casein; loading capacity, 100 mg g^-1; recovery, >90%). Taking advantage of these merits, a total of 393 N-glycopeptides derived from 259 glycoproteins and 574 phosphopeptides derived from 341 phosphoproteins were identified from 200 μg of HeLa cell extracts through a single-step enrichment using MagG@PEI@PA-Ti⁴⁺.

Self-Assembling Hydrophilic Magnetic Covalent Organic Framework Nanospheres as a Novel Matrix for Phthalate Ester Recognition

The development of covalent organic framework (COF)-derived materials with additional functions and applications is highly desired. In this work, a unique COF-functionalized hydrophilic magnetic nanosphere (Fe₃O₄@PDA@TbBd) with Fe₃O₄ as a magnetic core, polydopamine (PDA) as a hydrophilic middle layer, and TbBd as an outer COF shell was facilely prepared as a novel hydrophilic platform for efficient detection of phthalic acid esters (PAEs). The resultant Fe₃O₄@PDA@TbBd nanosphere displayed strong magnetic response, high surface area, and good hydrophilicity. Accordingly, the newly synthesized COF exhibited great potential in phthalate analysis with a wide linearity (50-8000 ng/mL), good recovery (92.3-98.9%), a low limit of detection (0.0025-0.01 ng/mL), and a small relative standard deviation (for intraday less than 4.6% and for interday less than 6.8%). More excitingly, the new COF was applied to analyze nine PAEs in the human plasma sample. This work opens up new avenues for the development and application of functionalized COF-derived materials.

Facile loading of Ag nanoparticles onto magnetic microsphere by the aid of a tannic acid-Metal polymer layer to synthesize magnetic disinfectant with high antibacterial activity

In this article, Ag nanoparticles (NPs) were easily loaded onto magnetic material through a tannic acid-metal polymer (PTA) intermedia layer to synthesize Fe₃O₄@PTA@Ag magnetic composite and the potential application as bactericidal agent for water disinfection was investigated. The as-obtained composite, with a Fe₃O₄ core of 150nm, has plenty of Ag NPs of 15nm adhered onto the PTA layer outside the core. The PTA layer, like the famous polydopamine complex, possesses excellent adhesive capacity to load more Ag NPs tightly and has specific antibacterial activity due to the numerous catechol groups. Therefore, remarkable bactericidal activity was achieved and 31.25mgL^-1 of Fe₃O₄@PTA@Ag disinfectant could inactivate more than 99% of the tested strains within 60min. At the same time, the catechol groups also endow the PTA layer with reduction ability so that additional reductant is unnecessary during the formation of Ag NPs and the PTA complex can be fabricated much more rapidly. As a result, the magnetic composite can be synthesized simply with less cost. Moreover, the composite has a high magnetic saturation value of 55.47emug^-1 owing to the Fe₃O₄ core and the magnetic separation ability can play an important role in the recovery of the disinfectant.

Polydopamine Based Colloidal Materials: Synthesis and Applications

Polydopamine is a synthetic analogue of natural melanin (eumelanin) produced from oxidative polymerization of dopamine. Owing to its strong adhesion ability, versatile chemical reactivity, biocompatibility and biodegradation, polydopamine is commonly applied as a versatile linker to synthesize colloidal materials with diverse structures, unique physicochemical properties and tunable functions, which allow for a broad scope of applications including biomedicine, sensing, catalysis, environment and energy. In this personal account, we discuss first about the different synthetic approaches of polydopamine, as well as its polymerization mechanism, and then with a comprehensive overview of recent progress in the synthesis and applications of polydopamine-based colloidal materials. Finally, we summarize this personal account with future perspectives.

Yolk-shell magnetic mesoporous TiO2 microspheres with flowerlike NiO nanosheets for highly selective enrichment of phosphopeptides

In this work, we fabricated a yolk-shell magnetic composite that contains mesoporous TiO₂ as the inner shell and flowerlike NiO as the outer shell (denoted as Fe₃O₄@H-TiO₂@f-NiO) to reduce the limitations of single-component metal oxides in phosphopeptide enrichment. The NiO nanosheets play a synergistic role in phosphopeptide enrichment. And the unique flowerlike structure of NiO with sufficient space can facilitate the reversible insertion/extraction of peptides, which will have less impact on the enrichment process of the inner TiO₂ shell. The yolk-shell structure and two types of porous nanostructures endowed this composite with a high surface area (156.58 m² g^-1) and a large pore volume (0.37 cm³ g^-1). Owing to the high surface area and combined properties of TiO₂ and NiO, the Fe₃O₄@H-TiO₂@f-NiO microspheres showed a better performance for phosphopeptide enrichment than the same material without NiO nanosheets (Fe₃O₄@H-TiO₂). According to the LC-MS/MS results, 972 unique phosphopeptides were identified from HeLa cell extracts with a high selectivity (91.9%) by Fe₃O₄@H-TiO₂@f-NiO relative to 837 phosphopeptides (selectivity: 60.2%) by Fe₃O₄@H-TiO₂. The results demonstrated that, compared with single-component metal oxides, composite metal oxides could enhance the selectivity and sensitivity for phosphopeptide enrichment.

Development of immobilized Sn4+ affinity chromatography material for highly selective enrichment of phosphopeptides

In this work, we first immobilized tin(IV) ion on polydopamine-coated magnetic graphene (magG@PDA) to synthesize Sn⁴⁺ -immobilized magG@PDA (magG@PDA-Sn⁴⁺ ) and successfully applied the material to highly selective enrichment of phosphopeptides. The material gathered the advantages of large surface area of graphene, superparamagnetism of Fe₃ O₄ , good hydrophilicity and biocompatibility of polydopamine, and strong interaction between Sn⁴⁺ and phosphopeptides. The enrichment performance of magG@PDA-Sn⁴⁺ toward phosphopeptides from digested β-casein at different concentrations, with and without added digested BSA was investigated and compared with magG@PDA-Ti⁴⁺ . The results showed high selectivity and sensitivity of the Sn⁴⁺ -IMAC material toward phosphopeptides, as good as the Ti⁴⁺ -IMAC material. Finally, magG@PDA-Sn⁴⁺ was applied to the analysis of endogenous phosphopeptides from a real sample, human saliva, with both MALDI-TOF MS and nano-LC-ESI-MS/MS. The results indicated that the as-synthesized Sn⁴⁺ -IMAC material not only has good enrichment performance, but also could serve as a supplement to the Ti⁴⁺ -IMAC material and expand the phosphopeptide coverage enriched by the single Ti⁴⁺ -IMAC material, demonstrating the broad application prospects of magG@PDA-Sn⁴⁺ in phosphoproteome research.

Facile synthesis of Fe3O4@PDA core-shell microspheres functionalized with various metal ions: A systematic comparison of commonly-used metal ions for IMAC enrichment

Metal ions differed greatly in affinity towards phosphopeptides, and thus it is essential to systematically compare the phosphopeptides enrichment ability of different metal ions usually used in the IMAC techniques. In this work, for the first time, eight metal ions, including Nb⁵⁺, Ti⁴⁺, Zr⁴⁺, Ga³⁺, Y³⁺, In³⁺, Ce⁴⁺, Fe³⁺, were immobilized on the polydopamine (PDA)-coated Fe₃O₄ (denoted as Fe₃O₄@PDA-Mⁿ⁺), and systematically compared by the real biosamples, in addition to standard phosphopeptides. Fe₃O₄ microspheres were synthesized via the solvothermal reaction, followed by self-polymerization of dopamine on the surface. Then through taking advantage of the hydroxyl and amino group of PDA, the eight metal ions were easily adhered to the surface of Fe₃O₄@PDA. After characterization, the resultant Fe₃O₄@PDA-Mⁿ⁺ microspheres were applied to phosphopeptides enrichment based on the binding affinity between metal ions and phosphopeptides. According to the results, different metal ions presented diverse phosphopeptides enrichment efficiency in terms of selectivity, sensitivity and the enrichment ability from real complex samples, and Fe₃O₄@PDA-Nb⁵⁺ and Fe₃O₄@PDA-Ti⁴⁺ showed obvious advantages of the phosphopeptides enrichment effect after the comparison. This systematic comparison may provide certain reference for the use and development of IMAC materials in the future.