A fast and sensitive method was established for an in-solution selection of cancer cell-targeting peptides at “single-residue resolution” by using the switchable fluorescence of tetraphenylethylene. The selected peptides have potential for biomarker tracing and can be used for targeted delivery of different cargos into living cancer cells.

•Peptides were screened with SPRi and fluoroimmuno assays for the binding with HSA.•A hetero bivalent peptide with nM-level affinity to HSA was identified.•The hetero dimer can sense the small structural difference between HSA and BSA.•The hetero dimer inhibited the binding between HSA and its antibody (IC50 83 nM).Peptide-protein interactions mediate numerous biologic processes and provide great opportunity for developing peptide probes and analytical approaches for detecting and interfering with recognition events. Molecular interactions usually take place on the heterogeneous surface of proteins, and the spatial distribution and arrangement of probes are therefore crucial for achieving high specificity and sensitivity in the bioassays. In this study, small linear peptides, homogenous peptide dimers and hetero bivalent peptides were designed for site-specific recognition of human serum albumin (HSA). Three hydrophilic regions located at different subdomains of HSA were chosen as targets for the molecular design. The binding affinity, selectivity and kinetics of the candidates were screened with surface plasmon resonance imaging (SPRi) and fluoroimmuno assays. Benefiting from the synergistic effect from the surface-targeted peptide binders and the flexible spacer, a heterogenetic dimer peptide (heter-7) with fast binding and slow dissociation behavior was identified as the optimized probe. Heter-7 specifically recognizes the target protein HSA, and effectively blocks the binding of antibody to HSA. Its inhibitory activity was estimated as 83 nM. It is noteworthy that heter-7 can distinguish serum albumins from different species despite high similarities in sequence and structure of these proteins. This hetero bivalent peptide shows promise for use in serum proteomics, disease detection and drug transport, and provides an effective approach for promoting the affinity and selectivity of ligands to achieve desirable chemical and biological outcomes.

Smart and versatile nanostructures have demonstrated their effectiveness for biomolecule analysis and show great potential in digging insights into the structural/functional relationships. Herein, a nanoscale molecular self-assembly was constructed for probing the site-specific recognition and conformational changes of human serum albumin (HSA) with tunable size and emission. A tetraphenylethylene derivative TPE-red-COOH was used as the building block for tailoring fluorescence-silent nanoparticles. The highly specific and sensitive response to HSA was witnessed by the fast turn-on of the red fluorescence and simultaneous disassembly of the nanostructures, whereas various endogenous biomolecules cannot induce such response. The mechanism investigation indicates that the combination of multiple noncovalent interactions is the driving force for disassembling and trapping TPE-red-COOH into HSA. The resultant restriction of intramolecular rotation of TPE-red-COOH in the hydrophobic cavity of HSA induces the significant red emission. By using the fluorescence activatable nanosensor as the structural indicator, the stepwise conformational transitions of HSA during denaturing and the partial refolding of subdomain IIA of HSA were facilely visualized. Benefiting from its activatable signaling, sensitivity, and simplicity, such molecular assembly provides a kind of soft nanomaterial for site-specific biomolecule probing and conformational transition detection concerning their structure, function, and biomedical characteristics.

A peptide-guided prodrug incorporating a tumor-specific peptide, doxorubicin, and a pH-sensitive hydrazone bridge was developed for targeted ablation of cancer cells with minimal side cytotoxicity.

The construction of molecularly imprinted polymers on magnetic nanoparticles gives access to smart materials with dual functions of target recognition and magnetic separation. In this study, the superparamagnetic surface-molecularly imprinted nanoparticles were prepared via surface-initiated reversible addition–fragmentation chain transfer (RAFT) polymerization using ofloxacin (OFX) as template for the separation of fluoroquinolones (FQs). Benefiting from the living/controlled nature of RAFT reaction, distinct core–shell structure was successfully constructed. The highly uniform nanoscale MIP layer was homogeneously grafted on the surface of RAFT agent TTCA modified Fe3O4@SiO2 nanoparticles, which favors the fast mass transfer and rapid binding kinetics. The target binding assays demonstrate the desirable adsorption capacity and imprinting efficiency of Fe3O4@MIP. High selectivity of Fe3O4@MIP toward FQs (ofloxacin, pefloxacin, enrofloxacin, norfloxacin, and gatifloxacin) was exhibited by competitive binding assay. The Fe3O4@MIP nanoparticles were successfully applied for the direct enrichment of five FQs from human urine. The spiked human urine samples were determined and the recoveries ranging from 83.1 to 103.1% were obtained with RSD of 0.8–8.2% (n = 3). This work provides a versatile approach for the fabrication of well-defined MIP on nanomaterials for the analysis of complicated biosystems.Keywords: core−shell; fluoroquinolones; human urine; molecularly imprinted polymer; reversible addition−fragmentation chain transfer polymerization; superparamagnetic;

A novel quartz crystal microbalance (QCM) sensor for rapid, highly selective and sensitive detection of copper ions was developed. As a signal amplifier, gold nanoparticles (Au NPs) were self-assembled onto the surface of the sensor. A simple dip-and-dry method enabled the whole detection procedure to be accomplished within 20 min. High selectivity of the sensor towards copper ions is demonstrated by both individual and coexisting assays with interference ions. This gold nanoparticle mediated amplification allowed a detection limit down to 3.1 μM. Together with good repeatability and regeneration, the QCM sensor was also applied to the analysis of copper contamination in drinking water. This work provides a flexible method for fabricating QCM sensors for the analysis of important small molecules in environmental and biological samples.

The cyclic oxidation and reduction of methionine (Met) containing peptides and proteins play important roles in biological system. This work was contributed to analysis the cyclic oxidation and reduction processes of a methionine containing peptide which is very likely to relate in the cell signal transduction pathways. To mimic the biological oxidation condition, hydrogen peroxide was used as the reactive oxygen species to oxidize the peptide. Reversed-phase high-performance liquid chromatography and mass spectrometry were employed to monitor the reactions and characterize the structural changes of the products. A rapid reduction procedure was developed by simply using KI as the reductant, which is green and highly efficient. By investigation of the cyclic oxidation and reduction process, our work provides a new perspective to study the function and mechanism of Met containing peptides and proteins during cell signaling processes as well as diseases.Highlights► The cyclic oxidation and reduction of methionine (Met) containing peptides and proteins. ► Structural changes monitored by RP-HPLC, MALDI-TOF MS and ESI MS/MS. ► A rapid, highly efficient and universal reduction method. ► The interconversion of the Met containing peptide implies its importance during cancer signaling.

A peptide-guided prodrug incorporating a tumor-specific peptide, doxorubicin, and a pH-sensitive hydrazone bridge was developed for targeted ablation of cancer cells with minimal side cytotoxicity.