Ultrasensitive electrochemical sensor based on synergistic effect of Ag@MXene and antifouling cyclic multifunctional peptide for PD-L1 detection in serum.

A sensing interface co-constructed from the two-dimensional conductive material (Ag@MXene) and an antifouling cyclic multifunctional peptide (CP) is described. While the large surface area of Ag@MXene loads more CP probes, CP binds to Ag@MXene to form a fouling barrier and ensure the structural rigidity of the targeting sequence. This strategy synergistically enhances the biosensor's sensitivity and resistance to contamination. The SPR results showed that the binding affinity of the CP to the target was 6.23 times higher than that of the antifouling straight-chain multifunctional peptide (SP) to the target. In the 10 mg/mL BSA electrochemical fouling test, the fouling resistance of Ag@MXene + CP (composite sensing interface of CP combined with Ag@MXene) was 30 times higher than that of the bare electrode. The designed electrochemical sensor exhibited good selectivity and wide dynamic response range at PD-L1 concentrations from 0.1 to 50 ng/mL. The lowest detection limit was 24.54 pg/mL (S/N = 3). Antifouling 2D materials with a substantial specific surface area, coupled with non-straight chain antifouling multifunctional peptides, offer a wide scope for investigating the sensitivity and antifouling properties of electrochemical sensors.

2D MOF-enhanced SPR detector based on tunable supramolecular probes for direct and sensitive detection of DOX in serum.

Therapeutic drug monitoring of doxorubicin (DOX) is important to study pharmacokinetics in patients undergoing chemotherapy for reduction of side effects and improve patient survival by rationally controlling the dose of DOX. A fast and ultra-sensitive surface plasmon resonance (SPR) detector without sample pre-handling was developed for DOX monitoring. First, the two-dimensional metal-organic framework was modified on the Au film to enhance SPR, and then, the supramolecular probes with tunable cavity structure were self-assembled at the sensing interface for direct detection of DOX through specific host-guest interactions with a low detection limit of 60.24 pM. The precise monitoring of DOX in serum proved the possibility of clinical application with recoveries in the range 102.86-109.47%. The mechanisms of host-guest interactions between supramolecular and small-molecule drugs were explored in depth through first-principles calculations combined with SPR experiments. The study paves the way for designing facile and sensitive detectors and provides theoretical support and a new methodology for the specific detection of small molecules through calixarene cavity modulation.

Interface-Engineered 2D Heterojunction with Photoelectric Dual Gain: Mxene@MOF-Enhanced SPR Spectroscopy for Direct Sensing of Exosomes.

MXene is widely used in the construction of optoelectronic interfaces due to its excellent properties. However, the hydrophilicity and metastable surface of MXene lead to its oxidation behavior, resulting in the degradation of its various properties, which seriously limits its practical application. In this work, a 2D metal-organic framework (2D MOF) with matching 2D morphology, excellent stability performance, and outstanding optoelectronic performance is grown in situ on the MXene surface through heterojunction engineering to suppress the direct contact between reactive molecules and the inner layer material without affecting the original advantages of MXene. The photoelectric dual gain MXene@MOF heterojunction is confirmed. As a photoelectric material, its properties are highly suitable for the demand of interface sensitization layer materials of surface plasmon resonance (SPR). Therefore, using SPR as a platform for the application of this interface material, the performance of MXene@MOF and its potential mechanism to enhance SPR are analyzed in depth using experiments combined with simulation calculations (FDTD/DFT). Finally, the MXene@MOF/peptides-SPR sensor is constructed for rapid and sensitive detection of the cancer marker exosomes to explore its potential in practical applications. This work offers a forward-looking strategy for the design of interface materials with excellent photoelectric performance.

Tunable Au@SiO2/Au Film Metasurface as Surface Plasmon Resonance Enhancer for Direct and Ultrasensitive Detection of Exosomes.

Surface plasmon resonance (SPR) spectroscopy with non-labelling, sensitive, and real-time properties is critical for clinical diagnosis applications. However, conventional SPR sensors face the challenge of lower sensitivity and selectivity for trace exosomes assay in complex serum. We proposed a core-shell Au@SiO2-Au film (Au@SiO2-Au film) metasurface to enhance SPR signal based on systematic study on the relationship between gap modes and SPR enhancement. The self-assembled multifunctional peptide was designed as recognition layer with antifouling properties for ultrasensitive and selective detection of PD-L1+ exosomes in serum. The tuning electromagnetic (EM) field model by manipulating the gap was established to guide the preparation of Au@SiO2-Au film metasurface. The in-plane and out-of-plane coupling of Au@SiO2 nanoparticles (NPs) could greatly enlarge and enhance three-dimensional EM field to meet the size of exosomes located in the evanescent field. At the structural level, we achieved high sensitivity (0.16 particles/mL) and a broad response range (10-5 × 103 particles/mL) through optimizing the thickness of SiO2 and surface coverage of Au@SiO2. Furthermore, clinical sample assay achieved the optimal diagnostic accuracy (AUC = 0.97) for differentiating cancer patients from healthy controls. This work provides an opportunity for the construction of a tunable gap mode as SPR enhancer in a total internal reflection architecture. The systematic study on the relationship between gap modes and SPR sensitivity provides a broad scope for promoting direct, efficient, highly selective, and sensitive detection of SPR sensors for clinical application.

2D MOF-enhanced SPR sensing platform: Facile and ultrasensitive detection of Sulfamethazine via supramolecular probe.

Sulfamethazine (SMZ) is widely present in the environment and can cause severe allergic reactions and cancer in humans. Accurate and facile monitoring of SMZ is crucial for maintaining environmental safety, ecological balance, and human health. In this work, a real-time and label-free surface plasmon resonance (SPR) sensor was devised using a two-dimensional metal-organic framework with superior photoelectric performance as an SPR sensitizer. The supramolecular probe was incorporated at the sensing interface, allowing for the specific capture of SMZ from other analogous antibiotics through host-guest recognition. The intrinsic mechanism of the specific interaction of the supramolecular probe-SMZ was elucidated through the SPR selectivity test in combination with analysis by density functional theory, including p-π conjugation, size effect, electrostatic interaction, π-π stacking, and hydrophobic interaction. This method facilitates a facile and ultrasensitive detection of SMZ with a limit of detection of 75.54 pM. The accurate detection of SMZ in six environmental samples demonstrates the potential practical application of the sensor. Leveraging the specific recognition of supramolecular probes, this direct and simple approach offers a novel pathway for the development of novel SPR biosensors with outstanding sensitivity.

Copper metal organic framework as natural oxidase mimic for effective killing of Gram-negative and Gram-positive bacteria.

Nanozymes have been widely studied as substitutes for natural enzymes. However, the delicacy of their structures and their unclear catalytic sites make it difficult to maintain their structural robustness and catalytic durability. By mimicking active catalytic sites of natural enzymes and combining them with distinct channels of metal organic frameworks (MOFs), an active copper mimetic oxidase enzyme (Cu-MOF) was designed and synthesized with good structure and clear catalytic sites for improvement in catalytic activity. The Cu-MOFs showed excellent oxidase-like activity with a low Km of 1.09 mM and exogenous ROS generation capacity. The Cu-MOFs exhibited antibacterial efficacy at a low concentration of 12.5 µg mL-1 by an oxidative stress response. These Cu-MOFs with their simple design and effective oxidase mimicking show attractive application prospects in the field of antibacterial and enzyme catalysis.

Rapid and sensitive detection of PD-L1 exosomes using Cu-TCPP 2D MOF as a SPR sensitizer.

Two-dimensional metal organic framework (2D MOF Cu-TCPP) with significantly enhanced photoelectric properties was synthesized by a simple hydrothermal method. The π-stacked electroactive porphyrin molecules of TCPP-based 2D MOF carry out charge transport in the MOF structure. The d-d band transition of Cu2+ and its 2D ultra-thin characteristics can produce excellent near-infrared light absorption to couple with SPR. Three key parameters including the refractive index sensitivity, detection accuracy and quality factor were improved significantly for 2D MOF modified gold chips. Especially, the refractive index sensitivity was increased from 98 to 137.67°/RIU after modified with 2D MOF. Thus, for the first time, we applied it as a signal enhancer to improve direct SPR assay for the Programmed death ligand-1 (PD-L1) exosomes. Owning to its large specific surface area, excellent photoelectric properties, highly ordered structure, good dispersion and biocompatibility, the LOD of the SPR sensor was 16.7 particles/mL. The reliability and practicability were further validated by analysis of PD-L1 exosomes in human serum samples. The recovery rate was 93.43 %-102.35%, with RSD of 5.79 %-14.6%. Given their excellent signal amplification ability, 2D MOF Cu-TCPP could serve as an ideal SPR sensitizer for rapid and sensitive detection of trace disease markers.

Facile Surface Functionalization of Cyclic Olefin Copolymer Film with Anhydride Groups for Protein Microarray Fabrication.

Immobilization of protein at high efficiency is a challenge for fabricating polymer-based protein chips. Here, a simple but effective approach was developed to fabricate a cyclic olefin copolymer (COC)-based protein microarray with a high immobilization density. In this strategy, poly(maleic anhydride-co-vinyl acetate) (poly(MAH-co-VAc)) brushes were facilely attached on the COC surface via UV-induced graft copolymerization. The introduction of poly(MAH-co-VAc) brushes resulted in an obvious increase in the surface roughness of COC. The functionalized COC showed little reduction in transparency compared with pristine COC, indicating that the photografting treatment did not alter its optical property. The graft density of the anhydride groups on the modified COC could be tuned from 0.46 to 3.2 µmol/cm2. The immobilization efficiency of immunoglobulin G (IgG) on functionalized COC reached 88% due to the high reactivity between anhydride groups and amine groups of IgGs. An immunoassay experiment demonstrated that the microarray showed high sensitivity to the target analyte.

Layered Co-Immobilization of ß-Glucosidase and Cellulase on Polymer Film by Visible-Light-Induced Graft Polymerization.

Exploring a suitable immobilization strategy to improve catalytic efficiency and reusability of cellulase is of great importance to lowering the cost and promoting the industrialization of cellulose-derived bioethanol. In this work, a layered structure with a thin PEG hydrogel as the inner layer and sodium polyacrylate (PAANa) brush as the outer layer was fabricated on low density polyethylene (LDPE) film by visible-light-induced graft polymerization. Two enzymes, ß-glucosidase (BG) and cellulase, were separately coimmobilized onto this hierarchical film. As supplementary to cellulase for improving catalytic efficiency, BG was in situ entrapped into the inner PEG hydrogel layer during the graft polymerization from the LDPE surface. After graft polymerization of sodium acrylate on the PEG hydrogel layer was reinitiated, cellulase was covalently attached on the outer PAANa brush layer. Owing to the mild reaction condition (visible-light irradiation and room temperature), the immobilized BG could retain a high activity after the graft polymerization. The immobilization did not alter the optimal pH and temperature of BG or the optimal temperature of cellulase. However, the optimal pH of cellulase shifts to 5.0 after immobilization. Compared with the original activity of single cellulase system and isolated BG/cellulase immobilization system, the dual-enzyme system exhibited 82% and 20% increase in catalytic activity, respectively. The dual-enzyme system could maintain 93% of carboxymethylcellulose sodium salt (CMC) activity after repeating 10 cycles of hydrolysis and 89% of filter paper activity after 6 cycles relative to original activity, exhibiting excellent reusability. This layer coimmobilization system of BG and cellulase on the polymer film displays tremendous potential for practical application in a biorefinery.

Highly Transparent Cyclic Olefin Copolymer Film with a Nanotextured Surface Prepared by One-Step Photografting for High-Density DNA Immobilization.

Compared with conventional glass slides and two-dimensional (2D) planar microarrays, polymer-based support materials and three-dimensional (3D) surface structures have attracted increasing attention in the field of biochips because of their good processability in microfabrication and low cost in mass production, as well as their improved sensitivity and specificity for the detection of biomolecules. In the present study, UV-induced emulsion graft polymerization was carried out on a cyclic olefin copolymer (COC) surface to generate 3D nanotextures composed of loosely stacked nanoparticles with a diameter of approximately 50 nm. The introduction of a hierarchical nanostructure on a COC surface only resulted in a 5% decrease in its transparency at a wavelength of 550 nm but significantly increased the surface area, which markedly improved immobilization density and efficiency of an oligonucleotide probe compared with the functional group and polymer brush-modified substrates. The highest immobilization efficiency of the probes reached 93%, and a limit of detection of 75 pM could be obtained. The hybridization experiment demonstrated that the 3D gene chip exhibited excellent sensitivity for target DNA detection and single-nucleotide polymorphism discrimination. This one-step approach to the construction of nanotextured surfaces on the COC has promising applications in the fields of biochips and immunoassays.

Decorating an individual living cell with a shell of controllable thickness by cytocompatible surface initiated graft polymerization.

Surface engineering of individual living cells is a promising field for cell-based applications. However, engineering individual cells with controllable thickness by chemical methods has been rarely studied. This article describes the development of a new cytocompatible chemical strategy to decorate individual living cells. The thicknesses of the crosslinked shells could be conveniently controlled by the irradiation time, visible light intensity, or monomer concentration. Moreover, the lag phase of the yeast cell division was extended and their stability against lysis was improved, which could also be tuned by controlling the shell thickness.