Development of a Surface Plasmon Resonance Immunosensor for Detecting Melamine in Milk Products and Pet Foods

A sensitive and stable surface plasmon resonance (SPR) immunosensor based on the inhibition format was developed and validated for detecting melamine (MEL) in milk products and pet foods. The sensitivity and the limit of detection (LOD) of the proposed method for MEL were 2.32 × 10–2 and 1.4 × 10–3 μg/mL, respectively. The immunosensor was highly specific to MEL, which displayed only low cross-reactivity (CR) (<0.01%) for cyanuric acid, cyanuric chloride, and atrazine. The assay was validated for the detection of MEL in full-cream milk, skim milk powder, infant formula, dog food, and cat food. Most of the recovery results ranged between 76 and 115%. The sensitivities of the assay in each type of sample were 2.57 × 10–2 μg/mL, 2.32 × 10–2 μg/kg, 2.51 × 10–2 μg/kg, 2.66 × 10–2 μg/kg, and 2.68 × 10–2 μg/kg, respectively, which were much lower than the maximum residue levels (MRLs) of MEL

Adsorption–Desorption Behavior of Black Phosphorus Quantum Dots on Mucin Surface

Black phosphorus quantum dots (BPQDs) as novel nanomaterials have many potential applications in biomedicine. However, the interaction of BPQDs with proteins and their biological effects and potential risks are still unclear. Here, mucin, which serves biologically as a physical barrier against foreign substances entering tissues, was chosen as a model substrate for studying the adsorption–desorption behavior of BPQDs using surface plasmon resonance sensing and a quartz crystal microbalance with dissipation monitoring. We found that the surface modification of BPQDs with poly­(ethylene glycol)-amine (PEG-NH₂) reduces the adsorption rate of the quantum dots but increases their adsorbed amount on the mucin surface. The pH value, ionic strength, and ionic valence also had significant effects on the adsorption behavior of BPQDs. Upon increasing the pH from 2 to 7, the amount of BPQD adsorption decreased from 14.1 to 3.2 ng/cm². A high ionic strength and ionic valence (e.g., Mg²⁺, Al³⁺) also inhibit the surface adsorption of BPQDs. Furthermore, the adsorption–desorption mechanisms of BPQDs on the mucin surface were proposed. The adsorption–desorption behavior under different conditions may be attributed to the steric hindrance of PEG, the electrostatic interaction, and/or charge screening. These findings provide useful insights into the interfacial behavior of BPQDs before they enter the tissues

Fabrication of an Antifouling Surface Plasmon Resonance Sensor with Stratified Zwitterionic Peptides for Highly Efficient Detection of Peanut Allergens in Biscuits

Peanut allergen monitoring is currently an effective strategy to avoid allergic diseases, while food matrix interference is a critical challenge during detection. Here, we developed an antifouling surface plasmon resonance sensor (SPR) with stratified zwitterionic peptides, which provides both excellent antifouling and sensing properties. The antifouling performance was measured by the SPR, which showed that stratified peptide coatings showed much better protein resistance, reaching ultralow adsorption levels (2). Atomic force microscopy was used to further analyze the antifouling mechanism from a mechanical perspective, which demonstrated lower adsorption forces on hybrid peptide coatings, confirming the better antifouling performance of stratified surfaces. Moreover, the recognition of peanut allergens in biscuits was performed using an SPR with high efficiency and appropriate recovery results (98.2–112%), which verified the feasibility of this assay. Therefore, the fabrication of antifouling sensors with stratified zwitterionic peptides provides an efficient strategy for food safety inspection

Lubricin-Inspired Loop Zwitterionic Peptide for Fabrication of Superior Antifouling Surfaces

Biofouling represents great challenges in many applications, and zwitterionic peptides have been a promising candidate due to their biocompatibility and excellent antifouling performance. Inspired by lubricin, we designed a loop-like zwitterionic peptide and investigated the effect of conformation (linear or loop) on the antifouling properties using a combination of surface plasma resonance (SPR), surface force apparatus (SFA), and all atomistic molecular dynamics (MD) simulation techniques. Our results demonstrate that the loop-like zwitterionic peptides perform better in resisting the adsorption of proteins and bacteria. SFA measurements show that the loop-like peptides reduce the adhesion between the modified surface and the modeling foulant lysozyme. All atomistic MD simulations reveal that the loop-like zwitterionic peptides are more rigid than the linear-like zwitterionic peptides and avoid the penetration of the terminus into the foulants, which lower the interaction between the zwitterionic peptides and foulants. Besides, the loop-like zwitterionic peptides avoid the aggregation of the chains and bind more water, improving the hydrophilicity and antifouling performance. Altogether, this study provides a more comprehensive understanding of the conformation effect of zwitterionic peptides on their antifouling properties, which may contribute to designing novel antifouling materials in various biomedical applications

Quantitative Ratiometric Biosensors Based on Fluorescent Ferrocene-Modified Histidine Dipeptide Nanoassemblies

Fluorescent proteins (FPs) provide a ratiometric readout for quantitative assessment of the destination of internalized biomolecules. FP-inspired peptide nanostructures that can compete with FPs in their capacity are the most preferred building blocks for the synthesis of fluorescent soft matter. However, realizing a ratiometric emission from a single peptide fluorophore remains exclusive since multicolor emission is a rare property in peptide nanostructures. Here, we describe a bioinspired peptidyl platform for ratiometric intracellular quantitation by employing a single ferrocene-modified histidine dipeptide. The intensiometric ratio of green to blue fluorescence correlates linearly with the concentration of the peptide by three orders of magnitude. The ratiometric fluorescence of the peptide is an assembly-induced emission originating from hydrogen bonds and aromatic interactions. Additionally, modular design enables ferrocene-modified histidine dipeptides to use as a general platform for the construction of intricate peptides that retain the ratiometric fluorescent properties. The ratiometric peptide technique promises flexibility in the design of a wide spectrum of stoichiometric biosensors for quantitatively understanding the trafficking and subcellular fate of biomolecules

Rethreading Design of Ratiometric roGFP2 Mimetic Peptide for Hydrogen Peroxide Sensing

Reconstruction of the miniaturized peptide to mimic the tailored functions of protein has been attractive but challenging. Herein, initialized from the crystal structure of redox-sensitive green fluorescent protein-2 (roGFP2), we propose a practical approach to construct the roGFP2 mimetic peptide by rethreading the aromatic residues adjacent to the chromophore fragment. By fine-tuning the residues of peptides, a mini tetrapeptide (Cys-Phe-Phe-His) was designed, which can act as a hydrogen peroxide sensor using its ratiometric fluorescence. The roGFP2 mimetic tetrapeptide is biocompatible and photostable and has competitive fluorescent properties with roGFP2 by the virtue of its assembly induced emissions. We expand the ratiometric tetrapeptide for sensing hydrogen peroxide in acidic chambers. The results provide a promising approach for the artificial design of miniaturized peptides with the desired function

Reassembled One-Dimensional VB₂ Submicrorods with Enhanced Photosensitivity and H₂O₂ Supply for Efficient Antibacterial Therapy

Recent advances in photocatalytic micro-nanoarchitecture have enlightened emerging photosensitizer-based photodynamic bactericidal therapies, which have been fruitful in addressing the thorny issue of multidrug-resistant bacterial infections. Nevertheless, the clinical feasibility of current photodynamic sterilization has been constrained by the biosafety of the photosensitizer and the maintenance of a relatively mild physiological microenvironment during treatment. Herein, we assemble a rodlike monocrystal on the sub-microscale from bioactive vitamin B2 (VB2) through a precise control strategy. The internal VB2 single molecules form a one-dimensional submicrostructure driven by π–π stacking interactions and hydrogen bonds. As expected, the dimensional submicronization tuning strategy ameliorates the aqueous solubility and dispersion stability of ordinary VB2 crystals while endowing them with enhanced superoxide radical yield and H2O2 supply under illumination. Photodynamic therapy (PDT) based on VB2 submicrorods demonstrated remarkable in vitro killing effects against Gram-positive and Gram-negative bacteria by mediating ROS bursts. Furthermore, the superior biocompatibility of VB2 submicrorods enables them to accelerate the closure of exposed lesions during PDT of multidrug-resistant bacterial infections without inducing perceptible side effects. This work aims to pursue photosensitizers with high biosafety, efficiency, and practical feasibility and focuses on developing biologically active VB2 as an environmentally friendly and cost-effective multifunctional photodynamic bactericide

Synergy between Zwitterionic Polymers and Hyaluronic Acid Enhances Antifouling Performance

Challenges associated with nonspecific adsorption of proteins on sensor surfaces have steered the development of novel antifouling materials and strategies. Inspired by human synovial fluid composition and structure, we designed synergistic antifouling coatings with mixtures of hyaluronic acid (HA) and a zwitterionic bottlebrush polymer (BB). Using a fast and convenient online surface modification method, the polymers were immobilized on the Au surface, significantly increasing its hydrophilicity. Using surface plasmon resonance (SPR), a 10:1 ratio of HA to BB was found optimal to provide the best antifouling performance. Bovine serum albumin (BSA) adsorption on HA-BB coated surfaces was 0.2 ng/cm2, which was 60 times lower than BB or HA alone and 25 times lower than the commonly accepted ultralow adsorption limit (2), demonstrating the synergistic effect of HA and BB against nonspecific protein adsorption. This was found to be independent of BSA concentration up to physiological concentrations. Furthermore, the antifouling performance of HA-BB coated surfaces was tested against milk and serum, showing almost 92% lower protein adsorption than that on bare surfaces, suggesting the potential efficacy of this antifouling coating in real life settings