Combined release of LL37 peptide and zinc ion from a mussel-inspired coating on porous titanium for infected bone defect repairing

Implant-associated infections impose great burden on patient health and public healthcare. Antimicrobial peptides and metal ions are generally incorporated onto implant surface to deter bacteria colonization. However, it is still challenging to efficiently prevent postoperative infections at non-cytotoxic dosages. Herein, a scaffold based on porous titanium coated with a mussel-inspired dual-diameter TiO2 nanotubes is developed for loading dual drugs of LL37 peptide and Zn2+ with different sizes and characteristics. Benefiting from in-situ formed polydopamine layer and dual-diameter nanotubular structure, the scaffold provides an efficient platform for controllable drugs elution: accelerated release under acidic condition and sustained release for up to 28 days under neutral/alkalescent circumstances. Such combination of dual drugs simultaneously enhanced antibacterial efficacy and osteogenesis. In antibacterial test, LL37 peptide serving as bacteria membrane puncture agent, and Zn2+ acting as ROS generator, cooperatively destroyed bacterial membrane integrity and subsequently damaged bacterial DNA, endowing dual-drug loaded scaffold with remarkable bactericidal efficiency of > 92 % in vitro and > 99 % in vivo. Noteworthily, dual-drug loaded scaffold promoted bone-implant osteointegration under infectious microenvironment, overmatching single-drug load ones. It provides a promising strategy on surface modification of implant for infected bone defect repairing.

Magnetic-gold nanoparticle-mediated paper-based biosensor for highly sensitive colorimetric detection of food adulteration

Food adulteration presents a significant challenge due to the evasion of legal oversight and the difficulty of identification. Addressing this issue, there is an urgent need for on-site, rapid, visually based small-scale equipment, along with large-scale screening technology, to enable prompt results without providing opportunities for dishonest traders to react. Colorimetric reactions offer advantages in terms of speed, visualization, and miniaturization. However, there is a scarcity of suitable colorimetric reactions for food adulteration detection, and interference from colored food impurities and easily comparable color results affects accuracy. To overcome limitations, this study introduces a novel approach utilizing polydopamine magnetic nanoparticles to enrich DNA in food samples, effectively eliminating interfering components. By employing gold nanoparticles to generate magnetic-gold nanoparticles, a single magnetic bead achieves simultaneous enrichment, impurity removal, and detection. The use of paper-based biosensors and visualization equipment allows for the visualization and digital analysis of results, achieving a low detection limit of 4.59 nmol mL-1. The method also exhibits high accuracy and repeatability, with a RSD ranging from 1.6 % to 4.0 %. This innovative colorimetric method addresses the need for rapid, miniaturized, and large-scale detection, thus providing a solution for food adulteration challenges.

Ion and Molecular Sieving With Ultrathin Polydopamine Nanomembranes

In contrast to biological cell membranes, it is still a major challenge for synthetic membranes to efficiently separate ions and small molecules due to their similar sizes in the sub-nanometer range. Inspired by biological ion channels with their unique channel wall chemistry that facilitates ion sieving by ion-channel interactions, the first free-standing, ultrathin (10-17 nm) nanomembranes composed entirely of polydopamine (PDA) are reported here as ion and molecular sieves. These nanomembranes are obtained via an easily scalable electropolymerization strategy and provide nanochannels with various amine and phenolic hydroxyl groups that offer a favorable chemical environment for ion-channel electrostatic and hydrogen bond interactions. They exhibit remarkable selectivity for monovalent ions over multivalent ions and larger species with K+/Mg2+ of ≈4.2, K+/[Fe(CN)6]3- of ≈10.3, and K+/Rhodamine B of ≈273.0 in a pressure-driven process, as well as cyclic reversible pH-responsive gating properties. Infrared spectra reveal hydrogen bond formation between hydrated multivalent ions and PDA, which prevents the transport of multivalent ions and facilitates high selectivity. Chemically rich, free-standing, and pH-responsive PDA nanomembranes with specific interaction sites are proposed as customizable high-performance sieves for a wide range of challenging separation requirements.

Molecular Imprinting-Based SERS Detection Strategy for the Large-Size Protein Quantitation and Curbing Non-Specific Recognition

Molecular imprinting-based surface-enhanced Raman scattering (MI-SERS) sensors have shown remarkable potential from an academic standpoint. However, their practical applications, especially in the detection of large-size protein (≥10 nm), face challenges due to the lack of versatile sensing strategies and nonspecific fouling of matrix species. Herein, we propose a Raman reporter inspector mechanism (RRIM) implemented on a protein-imprinted polydopamine (PDA) layer coated on the SERS active substrate. In the RRIM, after large-size protein recognition, the permeability of the PDA imprinted cavities undergoes changes that are scrutinized by Raman reporter molecules. Target proteins can specifically bind and fully occupy the imprinted cavities, whereas matrix species cannot. Then, Raman reporter molecules with suitable size are introduced to serve as both inspectors of the recognition status and inducers of the SERS signal, which can only penetrate through the vacant and nonspecifically filled cavities. Consequently, changes in the SERS signal exclusively originate from the specific binding of target proteins, while the nonspecific recognition of matrix species is curbed. The RRIM enables reproducible quantitation of the large-size cyanobacteria-specific protein model (≥10 nm), phycocyanin, at the level down to 2.6 × 10-3 μg L-1. Finally, the practical applicability of the RRIM is confirmed by accurately analyzing crude urban waterway samples over 21 min without any pretreatment.

Polydopamine Nanosystems in Drug Delivery: Effect of Size, Morphology, and Surface Charge

Recently, drug delivery strategies based on nanomaterials have attracted a lot of interest in different kinds of therapies because of their superior properties. Polydopamine (PDA), one of the most interesting materials in nanomedicine because of its versatility and biocompatibility, has been widely investigated in the drug delivery field. It can be easily functionalized to favor processes like cellular uptake and blood circulation, and it can also induce drug release through two kinds of stimuli: NIR light irradiation and pH. In this review, we describe PDA nanomaterials' performance on drug delivery, based on their size, morphology, and surface charge. Indeed, these characteristics strongly influence the main mechanisms involved in a drug delivery system: blood circulation, cellular uptake, drug loading, and drug release. The understanding of the connections between PDA nanosystems' properties and these phenomena is pivotal to obtain a controlled design of new nanocarriers based on the specific drug delivery applications.

Polydopamine-functionalized electrospun poly(vinyl alcohol)/chitosan nanofibers for the removal and determination of Cu(II)

Environmentally friendly and recycled polydopamine-functionalized electrospun poly(vinyl alcohol)/chitosan nanofibers (PVA/CS/PDA) were prepared through a low-energy-consumption procedure. The PDA coating endows PVA/CS/PDA nanofibers with good water stability. The PVA/CS/PDA nanofibers have a fibrillar and porous structure that is favorable for Cu(II) to access the active sites of the nanofibers. The adsorption isotherm and kinetics data preferably conform to the Liu isotherm and pseudo-second-order kinetic models, respectively. The maximum adsorption capacity of Cu(II) ions by PVA/CS/PDA nanofibers from the Liu isotherm model is 326.5 mg g-1. The PVA/CS/PDA nanofibers exhibit higher adsorption capacity than some other reported adsorbents. The adsorption mechanism study demonstrates that the Cu(II) adsorption is mainly ascribed to the complexation of Cu(II) with the imino, amino, and hydroxy moieties in PVA/CS/PDA nanofibers. The nanofibers can be employed for 5 cycles without significantly deteriorating performance. More interestingly, a fluorometry method based on the oxidation mimic enzyme activity of Cu(II) was developed to detect low concentrations of Cu(II) using the nanofibers as an adsorbent to preconcentrate Cu(II). The limit of detection is 0.42 mg L-1. The successful removal and detection of Cu(II) in Pearl River and mineral water samples demonstrates the great potential of PVA/CS/PDA nanofibers to remediate Cu(II)-polluted water.

S-Block Potassium Single-atom Electrocatalyst with K-N4 Configuration Derived from K+ /Polydopamine for Efficient Oxygen Reduction

Currently, single-atom catalysts (SACs) research mainly focuses on transition metal atoms as active centers. Due to their delocalized s/p-bands, the s-block main group metal elements are typically regarded as catalytically inert. Herein, an s-block potassium SAC (K-N-C) with K-N4 configuration is reported for the first time, which exhibits excellent oxygen reduction reaction (ORR) activity and stability under alkaline conditions. Specifically, the half-wave potential (E1/2 ) is up to 0.908 V, and negligible changes in E1/2 are observed after 10,000 cycles. In addition, the K-N-C offers an exceptional power density of 158.1 mW cm-2 and remarkable durability up to 420 h in a Zn-air battery. Density functional theory (DFT) simulations show that K-N-C has bifunctional active K and C sites, can optimize the free energy of ORR reaction intermediates, and adjust the rate-determining steps. The crystal orbital Hamilton population (COHP) results showed that the s orbitals of K played a major role in the adsorption of intermediates, which was different from the d orbitals in transition metals. This work significantly guides the rational design and catalytic mechanism research of s-block SACs with high ORR activity.

Electropolymerization of Polydopamine at Electrode-Supported Insulating Mesoporous Films

Bioinspired, stimuli-responsive, polymer-functionalized mesoporous films are promising platforms for precisely regulating nanopore transport toward applications in water management, iontronics, catalysis, sensing, drug delivery, or energy conversion. Nanopore technologies still require new, facile, and effective nanopore functionalization with multi- and stimuli-responsive polymers to reach these complicated application targets. In recent years, zwitterionic and multifunctional polydopamine (PDA) films deposited on planar surfaces by electropolymerization have helped surfaces respond to various external stimuli such as light, temperature, moisture, and pH. However, PDA has not been used to functionalize nanoporous films, where the PDA-coating could locally regulate the ionic nanopore transport. This study investigates the electropolymerization of homogeneous thin PDA films to functionalize nanopores of mesoporous silica films. We investigate the effect of different mesoporous film structures and the number of electropolymerization cycles on the presence of PDA at mesopores and mesoporous film surfaces. Our spectroscopic, microscopic, and electrochemical analysis reveals that the amount and location (pores and surface) of deposited PDA at mesoporous films is related to the combination of the number of electropolymerization cycles and the mesoporous film thickness and pore size. In view of the application of the proposed PDA-functionalized mesoporous films in areas requiring ion transport control, we studied the ion nanopore transport of the films by cyclic voltammetry. We realized that the amount of PDA in the nanopores helps to limit the overall ionic transport, while the pH-dependent transport mechanism of pristine silica films remains unchanged. It was found that (i) the pH-dependent deprotonation of PDA and silica walls and (ii) the insulation of the indium-tin oxide (ITO) surface by increasing the amount of PDA within the mesoporous silica film affect the ionic nanopore transport.

pH-Mediated Mucus Penetration of Zwitterionic Polydopamine-Modified Silica Nanoparticles

Zwitterionic polymers have emerged as promising trans-mucus nanocarriers due to their superior antifouling properties. However, for pH-sensitive zwitterionic polymers, the effect of the pH microenvironment on their trans-mucus fate remains unclear. In this work, we prepared a library of zwitterionic polydopamine-modified silica nanoparticles (SiNPs-PDA) with an isoelectric point of 5.6. Multiple-particle tracking showed that diffusion of SiNPs-PDA in mucus with a pH value of 5.6 was 3 times faster than that in mucus with pH value 3.0 or 7.0. Biophysical analysis found that the trans-mucus behavior of SiNPs-PDA was mediated by hydrophobic and electrostatic interactions and hydrogen bonding between mucin and the particles. Furthermore, the particle distribution in the stomach, intestine, and lung demonstrated the pH-mediated mucus penetration behavior of the SiNPs-PDA. This study reveals the pH-mediated mucus penetration behavior of zwitterionic nanomaterials, which provides rational design strategies for zwitterionic polymers as nanocarriers in various mucus microenvironments.

Experimental Methods to Get Polydopamine Films: A Comparative Review on the Synthesis Methods, the Films' Composition and Properties

In 2007, polydopamine (PDA) films were shown to be formed spontaneously on the surface of all known classes of materials by simply dipping those substrates in an aerated dopamine solution at pH = 8.5 in the presence of Tris(hydroxymethyl) amino methane buffer. This universal deposition method has raised a burst of interest in surface science, owing not only to the universality of this water based one pot deposition method but also to the ease of secondary modifications. Since then, PDA films and particles are shown to have applications in energy conversion, water remediation systems, and last but not least in bioscience. The deposition of PDA films from aerated dopamine solutions is however a slow and inefficient process at ambient temperature with most of the formed material being lost as a precipitate. This incited to explore the possibility to get PDA and related films based on other catecholamines, using other oxidants than dissolved oxygen and other deposition methods. Those alternatives to get PDA and related films are reviewed and compared in this paper. It will appear that many more investigations are required to get better insights in the relationships between the preparation method of PDA and the properties of the obtained coatings.

Immobilization of blood coagulant factor VII on polycaprolactone membrane through polydopamine grafting

Postoperative bleeding following cardiac surgeries is still an issue that deranges the medical resources and cost. The oral and injection administrations of blood coagulation protein, Factor VII (FVII), is effective to stop the bleeding. However, its short half-life has limited the effectiveness of this treatment and frequent FVII intake may distress the patients. Instead, incorporating FVII into synthetic biodegradable polymers such as polycaprolactone (PCL) that is commonly used in drug delivery applications should provide a solution. Therefore, this study aimed to immobilize FVII on PCL membranes through a cross-linkage polydopamine (PDA) grafting as an intermediate layer. These membranes are intended to provide a solution for cardiac bleeding in coagulating blood and sealing the sutured region. The membranes were evaluated in terms of its physio-chemical properties, thermal behavior, FVII release profile and biocompatibility properties. The ATR-FTIR was used to analyze the chemical functionalities of the membranes. Further validation was done with XPS where the appearances of 0.45 ± 0.06% sulfur composition and C-S peak have confirmed the immobilization of FVII on the PCL membranes. The cross-linked FVIIs were viewed in spherical immobilization on the PCL membranes with a size range between 30 and 210 nm. The surface roughness and hydrophilicity of the membranes were enhanced with a slight shift of melting temperature. The PCL-PDA-FVII0.03 and PCL-PDA-FVII0.05 membranes, with wide area of FVII immobilization released approximately only 22% of FVII into the solution within 60 days period and, it is found that the PCL-PDA-FVIIx membranes projected the Higuchi release model with non-Fickian anomalous transport. While the cytotoxic and hemocompatibility analyses showed advance cell viability, identical coagulation time and low hemolysis ratio on the PCL-PDA-FVIIx membranes. The erythrocytes were viewed in polyhedrocyte coagulated structure under SEM visualization. These results validate the biocompatibility of the membranes and its ability to prolong blood coagulation, thus highlighting its potential application as cardiac bleeding sealant.

Emulsion-oriented assembly for Janus double-spherical mesoporous nanoparticles as biological logic gates

The ability of Janus nanoparticles to establish biological logic systems has been widely exploited, yet conventional non/uni-porous Janus nanoparticles are unable to fully mimic biological communications. Here we demonstrate an emulsion-oriented assembly approach for the fabrication of highly uniform Janus double-spherical MSN&mPDA (MSN, mesoporous silica nanoparticle; mPDA, mesoporous polydopamine) nanoparticles. The delicate Janus nanoparticle possesses a spherical MSN with a diameter of ~150 nm and an mPDA hemisphere with a diameter of ~120 nm. In addition, the mesopore size in the MSN compartment is tunable from ~3 to ~25 nm, while those in the mPDA compartments range from ~5 to ~50 nm. Due to the different chemical properties and mesopore sizes in the two compartments, we achieve selective loading of guests in different compartments, and successfully establish single-particle-level biological logic gates. The dual-mesoporous structure enables consecutive valve-opening and matter-releasing reactions within one single nanoparticle, facilitating the design of single-particle-level logic systems.

The Convenience of Polydopamine in Designing SERS Biosensors with a Sustainable Prospect for Medical Application

Polydopamine (PDA) is a multifunctional biomimetic material that is friendly to biological organisms and the environment, and surface-enhanced Raman scattering (SERS) sensors have the potential to be reused. Inspired by these two factors, this review summarizes examples of PDA-modified materials at the micron or nanoscale to provide suggestions for designing intelligent and sustainable SERS biosensors that can quickly and accurately monitor disease progression. Undoubtedly, PDA is a kind of double-sided adhesive, introducing various desired metals, Raman signal molecules, recognition components, and diverse sensing platforms to enhance the sensitivity, specificity, repeatability, and practicality of SERS sensors. Particularly, core-shell and chain-like structures could be constructed by PDA facilely, and then combined with microfluidic chips, microarrays, and lateral flow assays to provide excellent references. In addition, PDA membranes with special patterns, and hydrophobic and strong mechanical properties can be used as independent platforms to carry SERS substances. As an organic semiconductor material capable of facilitating charge transfer, PDA may possess the potential for chemical enhancement in SERS. In-depth research on the properties of PDA will be helpful for the development of multi-mode sensing and the integration of diagnosis and treatment.

Exploring the pH Sensitivity of Ion-Pair Interactions on a Self-Assembled Monolayer by Scanning Electrochemical Microscopy

Insights into the chemical essence of weak interactions on the surface of biomacromolecules may help to regulate biological processes. In this work, the pH sensitivity of ion-pair interactions occurring on a cysteine self-assembled monolayer (Cys SAM) that simulates the local surface of a protein was probed by scanning electrochemical microscopy (SECM). Cys SAM and the ion-pair interactions subsequently formed with the introduced aspartic acid (Asp) were both pH-sensitive, as confirmed by the tip current changes in the feedback mode. After continuous pH measurements, the most significant negative feedback was observed at pH 5.50, indicating the most robust ion-pair interactions, which were simultaneously identified by voltammetry. In this case, the extra addition of the inorganic cation (i.e., Ca²⁺) did not disrupt the existing ion-pair interactions, and the binding constant (K) and Gibbs free energy (ΔG^o) of the ion pair were finally determined to be 6.44 × 10⁵ M^-1 and -33.14 kJ mol^-1, respectively. Overall, the pH sensitivity of ion-pair interactions was found to be mainly attributable to pH-induced changes in the deprotonated/protonated states of the α-amino acid moieties, which may provide insights into the artificial manipulation of complex binding events at the molecular level on the biological surface.

Engineering Active-Site-Induced Homogeneous Growth of Polydopamine Nanocontainers on Loading-Enhanced Ultrathin Graphene for Smart Self-Healing Anticorrosion Coatings

Engineering nanocontainers with encapsulated inhibitors onto graphene has been an emerging technology for developing self-healing anticorrosion coatings. However, the loading contents of inhibitors are commonly limited by inhomogeneous nanostructures of graphene platforms. Here, we propose an activation-induced ultrathin graphene platform (UG-BP) with the homogeneous growth of polydopamine (PDA) nanocontainers encapsulated with benzotriazole (BTA). Ultrathin graphene prepared by catalytic exfoliation and etching activation provides an ideal platform with an ultrahigh specific surface area (1646.8 m²/g) and homogeneous active sites for the growth of PDA nanocontainers, which achieves a high loading content of inhibitors (40 wt %). The obtained UG-BP platform exhibits pH-sensitive corrosion inhibition effects due to its charged groups. The epoxy/UG-BP coating possesses integrated properties of enhanced mechanical properties (>94%), efficient pH-sensitive self-healing behaviors (98.5% healing efficiency over 7 days), and excellent anticorrosion performance (4.21 × 10⁹ Ω·cm² over 60 days), which stands out from previous related works. Moreover, the interfacial anticorrosion mechanism of UG-BP is revealed in detail, which can inhibit the oxidation of Fe²⁺ and promote the passivation of corrosion products by a dehydration process. This work provides a universal activation-induced strategy for developing loading-enhanced and tailor-made graphene platforms in extended smart systems and demonstrates a promising smart self-healing coating for advanced anticorrosion applications.

Polydopamine surface-modified hyperbranched polymeric nanoparticles for synergistic chemo/photothermal therapy of oral cancer

A novel drug delivery system for the treatment of oral cancer was developed using a facile polydopamine (PDA)-based surface modification and a binding mechanism linking folic acid-targeting ligands. The system was able to achieve the following objectives: loading of chemotherapeutic agents, active targeting, pH responsiveness, and prolonged in vivo blood circulation. DOX-loaded polymeric nanoparticles (DOX/H20-PLA@PDA NPs) were functionalized with amino-poly (ethylene glycol)-folic acid (H₂N-PEG-FA) after coating them with PDA to form the targeting combination, DOX/H20-PLA@PDA-PEG-FA NPs. The novel NPs exhibited drug delivery characteristics similar to DOX/H20-PLA@ PDA NPs. Meanwhile, the incorporated H₂N-PEG-FA contributed to active targeting, as illustrated in cellular uptake assays and animal studies. In vitro cytotoxicity and in vivo anti-tumor studies have shown that the novel nanoplatforms exhibit extremely effective therapeutic effects. In conclusion, the multifunctional PDA-modified H20-PLA@PDA-PEG-FA NPs offer a promising chemotherapeutic strategy to improve the treatment of oral cancer.

Genetically engineered bacterium-modified magnetic particles assisted chiral recognition and colorimetric determination of D/L-tryptophan in millets

Chiral recognition of enantiomers has always been a thorny issue since they exhibit the same properties under an achiral environment. Herein, polydopamine-functionalized magnetic particles (MP@PDA) were synthesized to immobilize the genetically engineered bacterium Escherichia coli DH5α (MP@PDA-E. coli). L-tryptophan (Trp) instead of D-Trp can be stereo-specifically degraded by tryptophanase in E. coli. The degradation product indole reacts with 4-dimethylaminobenzaldehyde to generate a rose-red adduct. Thus, MP@PDA-E. coli was employed to fabricate a chiral colorimetric method for chiral recognition and determination of L-Trp. The method averts the purification of tryptophanase. More importantly, tryptophanase demonstrates excellent enantioselective ability for L-Trp. The method can not only quantitatively detect L-Trp but also realize the measurement of the enantiomer percentage in the enantiomeric mixture. The feasibility was verified by detecting L-Trp in millet samples from different origins. Furthermore, a portable device was fabricated to make the method more convenient.

Modulating the Charge Transfer Plasmon in Bridged Au Core-Satellite Homometallic Nanostructures

The localized surface plasmon resonance (LSPR) is one of the important properties for noble metal nanoparticles. Tuning the LSPR on demand thus has attracted tremendous interest. Beyond the size and shape control, manipulating intraparticle coupling is an effective way to tailor their LSPR. The charge transfer plasmon (CTP) is the most important mode of conductive coupling between subunits linked by conductive bridges that are well studied for structures prepared on substrates by lithography method. However, the colloidal synthesis of CTP structure remains a great challenge. This work reports the colloidal synthesis of extraordinary bridged Au core-satellite structures by exploiting the buffer effect of polydopamine shell on Au core for Au atom diffusion, in which the Au bridge is well controlled in terms of width and length. Benefiting from the tunable Au bridges, the resonance energy of the CTP can be readily controlled. As a result, the LSPR absorptions of the core-satellite structures are continuously tuned within the NIR spectral range (from 900 to >1300 nm), demonstrating their great potentials for ultrafast nano-optics and biomedical applications.

Label-free MIP-SERS biosensor for sensitive detection of colorectal cancer biomarker

Early diagnosis of colorectal cancer can significantly improve the overall survival rate of patients, thus selective and sensitive detection of biomarkers in serum samples is vital for early detection and dynamic monitoring of cancer. Nucleoside diphosphate kinase NM23-H2 (NDKB) is an important biomarker and therapeutic target for the diagnosis of colorectal cancer (CRC). Here, a label-free and ultrasensitive biosensor for NDKB protein markers is presented for the first time, combining the characteristic capture selectivity of molecularly imprinted polymers (MIPs) and the ultrasensitivity of surface-enhanced Raman Spectroscopy (SERS) technique. The imprinted cavity serves as the only channel for Raman reporter to approach the SERS substrate, providing highly complementary non-covalent binding sites that selectively capture the target protein based on ionic, hydrogen bonding or hydrophobic interactions. Specific recognition of the NDKB protein will perfectly fill the imprinted cavity, which makes it difficult for the Raman reporter to get close to the SERS substrate, and the Raman signal decreases significantly, while the proteins of other structural sizes can not match the imprinted cavity. Through the change of the Raman signal, the proposed biosensor can realize the ultra-sensitive detection of NDKB, and the limit of detection (LOD) is 0.82 pg/mL. Compared with the traditional immunoassay technology, this combined approach with the advantages of low cost, fast response, high sensitivity and selectivity, provides clinical application potential for the early diagnosis of CRC.

Chiral molecular imprinting-based SERS detection strategy for absolute enantiomeric discrimination

Chiral discrimination is critical in environmental and life sciences. However, an ideal chiral discrimination strategy has not yet been developed because of the inevitable nonspecific binding entity of wrong enantiomers or insufficient intrinsic optical activities of chiral molecules. Here, we propose an "inspector" recognition mechanism (IRM), which is implemented on a chiral imprinted polydopamine (PDA) layer coated on surface-enhanced Raman scattering (SERS) tag layer. The IRM works based on the permeability change of the imprinted PDA after the chiral recognition and scrutiny of the permeability by an inspector molecule. Good enantiomer can specifically recognize and fully fill the chiral imprinted cavities, whereas the wrong cannot. Then a linear shape aminothiol molecule, as an inspector of the recognition status is introduced, which can only percolate through the vacant and nonspecifically occupied cavities, inducing the SERS signal to decrease. Accordingly, chirality information exclusively stems from good enantiomer specific binding, while nonspecific recognition of wrong enantiomer is curbed. The IRM benefits from sensitivity and versatility, enabling absolute discrimination of a wide variety of chiral molecules regardless of size, functional groups, polarities, optical activities, Raman scattering, and the number of chiral centers.

PDA-Based Drug Delivery Nanosystems: A Potential Approach for Glioma Treatment

Glioma is characterized by high mortality and low postoperative survival. Despite the availability of various therapeutic approaches and molecular typing, the treatment failure rate and the recurrence rate of glioma remain high. Given the limitations of existing therapeutic tools, nanotechnology has emerged as an alternative treatment option. Nanoparticles, such as polydopamine (PDA)-based nanoparticles, are embodied with reliable biodegradability, efficient drug loading rate, relatively low toxicity, considerable biocompatibility, excellent adhesion properties, precisely targeted delivery, and strong photothermal conversion properties. Therefore, they can further enhance the therapeutic effects in patients with glioma. Moreover, polydopamine contains pyrocatechol, amino and carboxyl groups, active double bonds, catechol, and other reactive groups that can react with biofunctional molecules containing amino, aldehyde, or sulfhydryl groups (main including, self-polymerization, non-covalent self-assembly, π-π stacking, electrostatic attraction interaction, chelation, coating and covalent co-assembly), which form a reversible dynamic covalent Schiff base bond that is extremely sensitive to pH values. Meanwhile, PDA has excellent adhesion capability that can be further functionally modified. Consequently, the aim of this review is to summarize the application of PDA-based NPs in glioma and to acquire insight into the therapeutic effect of the drug-loaded PDA-based nanocarriers (PDA NPs). A wealthy understanding and argument of these sides is anticipated to afford a better approach to develop more reasonable and valid PDA-based cancer nano-drug delivery systems. Finally, we discuss the expectation for the prospective application of PDA in this sphere and some individual viewpoints.

Surface Characteristics and Formation of Polyserotonin Thin Films for Bioelectrical and Biocompatible Interfaces

In this study, we examined the fundamental surface characteristics of a polyserotonin (pST) film, which is attractive as a bioelectrical and biocompatible interface of biosensors. The pST film can easily be modified on electrode materials such as Au by self-polymerization and electropolymerization. By a simple cytotoxicity test using nonadhesive living cells, we found that the pST film is biocompatible for culturing cells on it. This finding is also supported by the fact that the surface tension of the pST film is moderate for protein adsorptions. The pST film is thinner and smoother than a poly-dopamine film, the chemical structure of which is similar to that of the pST film, depending on the polymerization time, cycle, and temperature; thus, ST as the main monomer can facilitate the precise control of the thickness and roughness of functional polymer membranes on the nanometer order. In addition, the pST film is useful as a relatively insulative interface for preventing interfering species from approaching electrode surfaces without their nonspecific adsorption, depending on the surface charges of the pST film in solutions of different pHs. The formation of the pST film self-polymerized on electrode materials is derived from the adsorption of pST nanoparticles formed by oxidative polymerization under basic conditions; therefore, the process of pST film formation should be considered in the functionalization of the pST film as a bioelectrical interface that allows biomolecular recognition (e.g., molecularly imprinted polymer membrane) for its application to wearable and biocompatible biosensors.

Green synthesis of polydopamine functionalized magnetic mesoporous biochar for lipase immobilization and its application in interesterification for novel structured lipids production

In this study, the polydopamine functionalized magnetic mesoporous biochar (MPCB-DA) was prepared for immobilization of Bacillus licheniformis lipase via covalent immobilization. Under optimized immobilization conditions, the maximum immobilization yield, efficiency and immobilized lipase amount were found to be 45%, 54% and 36.9 mg/g, respectively. The immobilized lipase, MPCB-DA-Lipase showed good thermal stability and alkali resistance. The MPCB-DA-Lipase retained 56% initial activity after 10 reuse cycles, with more than 85% relative activity after 70 days' storage at 4 or 25 °C. The MPCB-DA-Lipase was efficiently applied in the interesterification of Cinnamomum camphora seed kernel oil and perilla seed oil, with maximum interesterification efficiency of 46%. The produced structured lipids belong to the S₂U and U₂S triacylglycerols, a novel medium-and long-chain triacylglycerol. These results demonstrated that the MPCB-DA-Lipase may be used as an efficient biocatalyst in lipid processing applications of food industries.

Designing electrospun fiber platforms for efficient delivery of genetic material and genome editing tools

Electrospun fibers are versatile biomaterial platforms with great potential to support regeneration. Electrospun fiber characteristics such as fiber diameter, degree of alignment, rate of degradation, and surface chemistry enable the creation of unique, tunable scaffolds for various drug or gene delivery applications. The delivery of genetic material and genome editing tools via viral and non-viral vectors are approaches to control cellular protein production. However, immunogenicity, off-target effects, and low delivery efficiencies slow the progression of gene delivery strategies to clinical settings. The delivery of genetic material from electrospun fibers overcomes such limitations by allowing for localized, tunable delivery of genetic material. However, the process of electrospinning is harsh, and care must be taken to retain genetic material bioactivity. This review presents an up-to-date summary of strategies to incorporate genetic material onto or within electrospun fiber platforms to improve delivery efficiency and enhance the regenerative potential of electrospun fibers for various tissue engineering applications.

Effect of the bio-inspired modification of low-cost membranes with TiO2:ZnO as microbial fuel cell membranes

Microbial fuel cells (MFCs) are a novel technique for converting biodegradable materials into electricity. In this study, the efficiency of mixed crystal (TiO₂:ZnO) as a membrane modifier of a low-cost, antifouling and self-cleaning cation exchange membrane for MFCs was studied. The modification was prepared using polydopamine (PDA) as the bio-inspired glue, followed by gravity deposition of a mixture of catalyst nanoparticles (TiO₂:ZnO 0.03%, 1:1 ratio) as anti-biofouling agents. The effects of the membrane modification were evaluated in terms of power density, open circuit potential, coulombic efficiency, anti-biofouling properties and also color and COD removal efficiency. The results showed that the use of the PDA-modified membrane and a mixture of catalysts facilitated the transfer of cations released during the oxidation process in the anodic compartment of the MFC, which increased the power generation in the MFC by 2.5 times and 5.7 times the current compared to pristine and PDA pristine membranes, decreased the MFC operating cycle time from 5 to 3 days, doubled the lifetime of the membranes and demonstrated higher COD removal efficiency and color removal. Finally, SEM and AFM analysis showed that the modification significantly minimized surface fouling. The modified membranes in this study proved to be a potential alternative to the expensive membranes currently used in MFCs, furthermore, this modification could be an interesting alternative modification for other potential membranes for use in MFCs, due to the fact that the catalyst activation was only performed with visible light (artificial and solar), which could decrease operating costs.

Unlocking the potential of Escherichia coli modified magnetic particles for chiral discrimination of racemic tryptophan

Enzymes possess a highly specific affinity toward their substrates. In this study, an enzyme-based biological method was established for chiral discrimination of D/L-tryptophan (Trp). The polydopamine modified magnetic particles (PDA@Fe₃O₄) were prepared for immobilization of the genetically engineered bacterium Escherichia coli (E. coli) DH5α. The bacteria-magnetic particles conjugates (bacteria@PDA@Fe₃O₄) demonstrate excellent chiral discrimination performance toward D/L-Trp at pH 7.0 and 45 °C. The investigation for the principle exhibits that the immobilized E. coli DH5α can produce tryptophanase, and the enzyme can selectively recognize and degrade L-Trp. The Michaelis constant of tryptophanase produced by bacteria@PDA@Fe₃O₄ was measured to be 25.7 µg mL^-1. This method avoids the purification of tryptophanase and unlocks the potential of bacteria modified magnetic particles for chiral discrimination of racemic tryptophan.

Switchable Ionic Transportation in the Nanochannels of the MOFs Triggered by Light and pH

The construction of a biomimetic ionic channel is of great significance for the fabrication of smart biodevices or logic circuit. Inspired by the selective permeability of the cell membrane toward bioions, a light-induced and pH-modulated artificial nanochannel is herein prepared by integrating the multistimuli-response molecule of carboxylated spiropyran (SP-COOH) into the frameworks of NU-1000 (Zr-based MOFs defined by Northwestern University). The loading density of the SP-COOH could reach as high as 7 wt % while keeping unchanged crystallinity and high porosity. Thanks to the precise matching of pore size of NU-1000 and molecular dimensions of SP-COOH, the loaded molecules could proceed free and reversible for isomerization between the hydrophilic and hydrophobic states. The ion-switchable characteristics of the channel are implemented by the amphiphilic change of the light-controlled gate molecule. Additionally, in the hydrophilic state, the channel presents reversible affinity toward cations or anions due to the reverse charge state induced by pH, thus constructing a pH-controlled subgate. Taking [Ru(NH₃)₆]³⁺ and [Fe(NH₃)]^3- as the model cation and anion, their redox peak currents occur as reversible change under different signal combinations of light and pH. Moreover, in accordance with the ionic selective permeability, several logic circuits/devices are designed to display the relationships between exogenous stimuli and ionic transportations in a computer language, prefiguring their wide application prospects in electronic devices and life sciences.

A universal polymer shell-isolated nanoparticle (SHIN) design for single particle spectro-electrochemical SERS sensing using different core shapes

Shell-isolated nanoparticles (SHINs) have attracted increasing interest for non-interfering plasmonic enhanced sensing in fields such as materials science, biosensing, and in various electrochemical systems. The metallic core of these nanoparticles is isolated from the surrounding environment preventing direct contact or chemical interaction with the metal surface, while still being close enough to enable localized surface plasmon enhancement of the Raman scattering signal from the analyte. This concept forms the basis of the shell isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) technique. To date, the vast majority of SHIN designs have focused on SiO₂ shells around spherical nanoparticle cores and there has been very limited published research considering alternatives. In this article, we introduce a new polymer-based approach which provides excellent control over the layer thickness and can be applied to plasmonic metal nanoparticles of various shapes and sizes without compromising the overall nanoparticle morphology. The SHIN layers are shown to exhibit excellent passivation properties and robustness in the case of gold nanosphere (AuNP) and anisotropic gold nanostar (AuNS) core shapes. In addition, in situ SHINERS spectro-electrochemistry measurements performed on both SHIN and bare Au nanoparticles demonstrate the utility of the SHIN coatings. Correlated confocal Raman and SEM mapping was achieved to clearly establish single nanoparticle SERS sensitivity. Finally, confocal in situ SERS mapping enabled visualisation of the redox related molecular structure changes occurring on an electrode surface in the vicinity of individual SHIN-coated nanoparticles.

A pH-response chemotherapy synergistic photothermal therapy for tumor suppression and bone regeneration by mussel-inspired Mg implant

Primary malignant bone tumors can be life-threatening. Surgical resection of tumor plus chemotherapy is the standard clinical treatment. However, postoperative recovery is hindered due to tumor recurrence caused by residual tumor cells and bone defect caused by resection of tumor tissue. Herein, a multifunctional mussel-inspired film was fabricated on Mg alloy, that is, an inner hydrothermal-treated layer, a middle layer of polydopamine, and an outer layer of doxorubicin. The modified Mg alloy showed excellent photothermal effect and thermal/pH-controlled release of doxorubicin. The synergistic effect of chemotherapy and photothermal therapy enabled the modified Mg alloy to kill bone tumor in vitro and inhibit tumor growth in nude mice. Moreover, because of the controlled release of Mg ions and biocompatibility of polydopamine, the modified Mg alloy supported extracellular matrix mineralization, alkaline phosphatase activity, and bone-related gene expression in C3H10T1/2. Bone implantation model in rats verified that the modified Mg showed excellent osteointegration. These findings prove that the use of mussel-inspired multifunction film on Mg alloy offers a promising strategy for the therapy of primary malignant bone tumor.

Polymer-functionalization of carbon nanotube by in situ conventional and controlled radical polymerizations

Functionalization of carbon nanotube (CNT) with polymers has drawn much attention due to its wide range of applications. Polymer-functionalized CNT could exhibit variety of properties, such as responsivity to environmental stimuli, ability of complexation with metal ions, increased dispersibility in different solvents, higher compatibility with polymer matrix, etc. Chemical and physical methods have been developed for the preparation of polymer-functionalized CNT. Polymer chains are chemically bonded to the CNT edge or surface in the chemical methods, which results in highly stable CNT/polymer composites. "Grafting to", "grafting from", and "grafting through" methods are the most common chemical methods for polymer-functionalization of CNT. In "grafting to" method, pre-fabricated polymer chains are coupled with the either functionalized or non-functionalized CNT. In "grafting from" and "grafting through" methods, CNT is functionalized by polymers simultaneously synthesized by in situ polymerization methods. Conventional free radical polymerization (FRP) and also controlled radical polymerization (CRP) are the most promising methods for in situ tethering of polymer brushes onto the surface of CNT due to their control over the grafting density, thickness, and functionality of the polymer brushes. The main focus of this review is on the synthesis of polymer-functionalized CNT via both the "grafting from" and "grafting through" methods on the basis of FRP and CRP routs, which is commonly known as in situ polymerizations. Finally, the most important challenges and applications of the in situ polymer grafting methods are discussed, which could be interesting for the future works.

Physicochemical and Electrochemical Characterization of Electropolymerized Polydopamine Films: Influence of the Deposition Process

Polydopamine (PDA) is a synthetic eumelanin polymer which is, to date, mostly obtained by dip coating processes. In this contribution, we evaluate the physical and electrochemical properties of electrochemically deposited PDA films obtained by cyclic voltammetry or pulsed deposition. The obtained PDA thin films are investigated with respect to their electrochemical properties, i.e., electron transfer (ET) kinetics and charge transfer resistance using scanning electrochemical microscopy and electrochemical impedance spectroscopy, and their nanomechanical properties, i.e., Young’s modulus and adhesion forces at varying experimental conditions, such as applied potential or pH value of the medium using atomic force microscopy. In particular, the ET behavior at different pH values has not to date been investigated in detail for electrodeposited PDA thin films, which is of particular interest for a multitude of applications. Adhesion forces strongly depend on applied potential and surrounding pH value. Moreover, force spectroscopic measurements reveal a significantly higher percentage of polymeric character compared to films obtained by dip coating. Additionally, distinct differences between the two depositions methods are observed, which indicate that the pulse deposition process leads to denser, more cross-linked films.

Chitosan-sodium alginate-based coatings for self-strengthening anticorrosion and antibacterial protection of titanium substrate in artificial saliva

A self-strengthening coating with silver nanoparticles (Ag NPs) doped chitosan (CHI) and sodium alginate (SA) polyelectrolytes was constructed on the surface of polydopamine (PDA) coated Ti substrate by a layer-by-layer assembly method. The PDA coating exhibited an excellent bond with Ti substrate, and also can uniformly deposit Ag NPs via a mild method without introducing any exogenous reductant. The CHI coating was assembled through a spin-coating method for controlling Ag⁺ release. The SA was introduced to enhance the anticorrosion performance by forming calcium alginate (CA) in a corrosive medium. The corrosion protection was investigated with electrochemical impedance spectroscopy and polarization curves tests in fluorine-containing artificial saliva. During immersion, the charge-transfer resistance and the protection efficiency (ŋ) presented a continuous increase with the immersion time, demonstrating that this coating possessed a remarkable self-strengthening capability, and the compositions of the outermost film changed from SA to CA with the Ca²⁺ cations of the corrosive medium as a crosslinker by SEM and EDS analysis. Furthermore, the ŋ remained up to 96.8% after immersion of 30 days, and then the coating also displayed a distinct inhibition zone on S. mutans. These results prove this coating possesses an excellent anticorrosion performance and antibacterial property.

Strategy to Chemically Decorate Nanopores of a Carbon Membrane for Filtrating Polyphenolics from Ethanol

This study invents a post-pyrolysis modification approach to render the resulting carbon membrane (CM) competent for organic solvent nanofiltration (OSN). A bitumen coating on a porous stainless-steel disk (PSD) serves as the precursor for the intended carbon membrane (CM), which is attained through pyrolysis in Ar. The bitumen coating casts dual-pore networks in the CM because of the dominant asphaltene constituent in bitumen. The subsequent chemical decoration of CM was pursued through the following protocol: dopamine (DA) was deployed in the nanopores of CM via pressurized infiltration and followed by Tris buffer passes through to trigger in situ conversion of DA to polydopamine (PDA), which was affixed over the pore walls to furnish chemical affinity (termed as CM_PDA). Additionally, the catechol moiety of PDA was arranged to chelate with the Zn²⁺ ion, aiming to trim the -OH anchor (termed as CM_PDA-Zn) to probe the effect of chelate on separation. The three membranes (CM, CM_PDA, and CM_PDA-Zn) were thereafter assessed by the separation of ethanol or isopropanol from phenolics [tannic acid (TA)/tetracycline (TC)]. A significantly improved OSN performance [rejection (%) ↔ permeance (L/(m²·h·bar))] of CM vs CM_PDA was observed: (i) for TA feed, 13% ↔ 85 L/(m²·h·bar) vs 83% ↔ 12 L/(m²·h·bar); and (ii) for TC feed, 20% ↔ 78 L/(m²·h·bar) vs 78% ↔ 12 L/(m²·h·bar). Compared to CM_PDA, CM_PDA-Zn further advances the rejection performance (∼89% for TA and ∼80% for TC) over 50 h separation. They are benchmarked by the latest literature results. The performance enhancements can be attributed to the spreading of PDA or PDA-Zn sites in the dual-pore networks, so that they are able to offer H-bonding and steric blocking roles, a chemicomechanical effect, to seize solute molecules over pore walls. It is this interfacial drag effect that sustains the solute rejection.

Mixed solvent synthesis of polydopamine nanospheres for sustainable multilayer flame retardant nanocoating

Mixed solvent synthesized polydopamine is used in a multilayer nanocoating for protecting foam from fire. The use of LbL technology significantly reduces the processing time often observed with traditional methods polymerized from buffer.

Label-free SERS detection of Raman-Inactive protein biomarkers by Raman reporter indicator: Toward ultrasensitivity and universality

It is still challenging to sensitively detect protein biomarkers via surface-enhanced Raman scattering (SERS) technique owing to their low Raman activity. SERS tag-based immunoassay is usually applied; however, it is laborious and needs specific antibodies. Herein, an ultrasensitive and universal "Raman indicator" sensing strategy is proposed for protein biomarkers, with the aid of a glass capillary-based molecularly imprinted SERS sensor. The sensor consists of an inner SERS substrate layer for signal enhancement and an outer mussel-inspired polydopamine imprinted layer as a recognition element. Imprinted cavities have two missions: first, selectively capturing the target protein, and second, the only passageway of Raman indicator to access SERS substrate. Specific protein recognition means filling imprinted cavities and blocking Raman indicator flow. Thus, the quantity of captured protein can be reflected by the signal decrease of ultra-Raman active indicator molecule. The capillary sensor exhibited specific and reproducible detection at the level down to 4.1 × 10^-3 μg L^-1, for trypsin enzyme in as-received biological samples without sample preparation. The generality of the mechanism is confirmed by using three different protein models. This platform provides a facile, fast and general route for sensitive SERS detection of Raman inactive biomacromolecules, which offers great promising utility for in situ and fast point-of-care practical bioassay.

Polydopamine and Its Derivative Surface Chemistry in Material Science: A Focused Review for Studies at KAIST

Polydopamine coating, the first material-independent surface chemistry, and its related methods significantly influence virtually all areas of material science and engineering. Functionalized surfaces of metal oxides, synthetic polymers, noble metals, and carbon materials by polydopamine and its related derivatives exhibit a variety of properties for cell culture, microfluidics, energy storage devices, superwettability, artificial photosynthesis, encapsulation, drug delivery, and numerous others. Unlike other articles, this review particularly focuses on the development of material science utilizing polydopamine and its derivatives coatings at the Korea Advanced Institute of Science and Technology for a decade. Herein, it is demonstrated how material-independent coating methods provide solutions for challenging problems existed in many interdisciplinary areas in bio-, energy-, and nanomaterial science by collaborations and independent research.

Polydopamine-modified interface improves the immobilization of natural bioactive-dye onto textile and enhances antifungal activity

Dermatomycosis, such as candidiasis and mycosis among others, has emerged recently as the most frequent fungal infection worldwide. This disease is due to the skin's exposure to microorganisms that are able to pass through skin barrier defects. Therefore, textiles in direct contact with skin can serve as a source of contamination and fungus spread. In the current study, a sustainable and eco-friendly method for antifungal cotton finishing using Curcuma longa L extracted from rhizomes was investigated. To enhance the natural bioactive dye uptake and attachment, cellulosic cotton fibers were chemically modified using dopamine, a biocompatible molecule, leading to the deposition of a hydrophilic layer of polydopamine. The efficiency of the polydopamine coating on the cotton surface has been assessed by x-ray photoemission spectroscopy analyses, with the detection of nitrogen, and by water contact angle for the wettability enhancement. Furthermore, characterization of the modified samples confirms that the modification did not affect either the cellulosic fiber morphology or the mechanical properties. The dyeability and bioactive dye immobilization were then assessed by colorimetry. Finally, the effectiveness of the finished fabrics against Trichophyton (rubrum/mentagrophytes) and Candida albicans strains was evaluated and was shown to induce growth inhibition mainly on Candida albicans strains.

Surface Modification of Iron Oxide-Based Magnetic Nanoparticles for Cerebral Theranostics: Application and Prospection

Combining diagnosis with therapy, magnetic iron oxide nanoparticles (INOPs) act as an important vehicle for drug delivery. However, poor biocompatibility of INOPs limits their application. To improve the shortcomings, various surface modifications have been developed, including small molecules coatings, polymers coatings, lipid coatings and lipopolymer coatings. These surface modifications facilitate iron nanoparticles to cross the blood-brain-barrier, which is essential for diagnosis and treatments of brain diseases. Here we focus on the characteristics of different coated INOPs and their application in brain disease, particularly gliomas, Alzheimer's disease (AD) and Parkinson's disease (PD). Moreover, we summarize the current progress and expect to provide help for future researches.

Surface modification of polypropylene membrane for the removal of iodine using polydopamine chemistry

The development of stable and effective iodine removal systems would be highly desirable in addressing environmental issues relevant to water contamination. In the present research, a novel iodine adsorbent was synthesized by self-polymerization of dopamine (PDA) onto inert polypropylene (PP) membrane. This PP/PDA membrane was thoroughly characterized and its susrface propeties was analyzed by various analytical techniques indcluding field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), Brunauer-Emmett-Teller (BET) and Barrett-Joyner-Halenda (BJH), contact angle, and surface free energy measurement. The PP/PDA membranes were subsequently used for batchwise removal of iodine at different temperatures (25-70 °C), pH (2-7), and surface areas (1-10 cm²) to understand the underlying adsorption phenomena and to estimate the membrane capacity for iodine uptake. The increase in temperature and pH both led to higher adsorption of iodine. The present approach showed a removal efficiency of over 75% for iodine using 10 cm² PP/PDA membrane (18.87 m² g^-1) within 2 h at moderate temperatures (∼50 °C) and pH > 4, about 15 fold compared to the PP control membrane. The adsorption kinetics and isotherms were well fitted to the pseudo-second-order kinetic and Langmuir isotherm models (R² > 0.99). This adsorbent can be recycled and reused at least six times with stable iodine adsorption. These findings were attributed to the homogenous monolayer adsorption of the iodide on the surface due to the presence of catechol and amine groups in the PP/PDA membrane. This study proposes an efficient adsorbent for iodine removal.