Self‐assembled structures obtained from organic molecules have shown great potential for applications in a wide range of domains. In this context, short peptides prove to be a particularly versatile class of organic building blocks for self‐assembled materials. These species afford the biocompatibility and polymorphic richness typical of proteins while allowing synthetic availability and robustness typical of smaller molecules. At the nano‐to‐mesoscale, the architectures obtained from peptide units exhibit stability and a large variety of morphologies, the most common of which are nanotubes, nanoribbons, and nanowires. This review describes the formation of peptide‐based self‐assembled structures triggered by different stimuli (e.g., ionic strength, pH, and polarity), and the interactions that drive the assembling processes. It is surveyed how judicious molecular design is exploited to impart favourable assembling properties to afford systems with desired characteristics. A large body of literature provides the experimental and in silico data to predict self‐assembly in a given peptide system and obtain different supramolecular organizations for applications in a wide range of fields, from transport to sensing, from catalysis to drug delivery and tissue regeneration.

An alternative label-free electrochemical immunosensor for the rapid detection of Leishmania braziliensis was developed by immobilizing a peptide-based probe of the promastigote surface antigen (PSA-38S) onto electrospun polyamide-6 (PA6)/chitosan nanofibers. An increase in chitosan content in the spinning solution leads to a decrease in the diameter of the formed fibers, whereas the differential scanning calorimetry (DSC) and X-ray diffraction (XRD) data showed a decrease in crystallinity upon increasing the chitosan content in the formulation. In addition, the incorporation of chitosan into the PA6 nanofibers tends to decrease the resistance to the charge-transfer process at the electrode surface. A 40 wt % chitosan content was used for immobilization of the peptide antigen, which was characterized by scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). The detection was performed by measuring the relative change in impedance before and after the anti-Leishmania braziliensis reaction by EIS. Under the optimized conditions, the relative change in impedance was proportional to the logarithmic value of PSA concentrations in the range of 2.5 to 10 pg•mL −1 (r 2 = 0.9946) with a detection limit of 0.2 pg•mL −1 , which was slightly lower than that of the enzyme-linked immunosorbent assay. Additionally, the sensor was tested against two nonspecific antibodies (T. cruzi and β-actin), whereas multivariate analysis using unsupervised pattern recognition through principal component analysis was successfully applied to identification of the pattern relative to each antibody. Finally, the optimized electrochemical immunoassay can be a favorable approach for Leishmania detection tests, as it is able to differentiate negative and positive visceral leishmaniasis human serum samples.

Limitations of the recognition elements in terms of synthesis, cost, availability, and stability have impaired the translation of biosensors into practical use. Inspired by nature to mimic the molecular recognition of the anti-SARS-CoV-2 S protein antibody (Ab S ) by the S protein binding site, we synthesized the peptide sequence of Asn-Asn-Ala-Thr-Asn-COOH (abbreviated as PEP2003) to create COVID-19 screening label-free (LF) biosensors based on a carbon electrode, gold nanoparticles (AuNPs), and electrochemical impedance spectroscopy. The PEP2003 is easily obtained by chemical synthesis, and it can be adsorbed on electrodes while maintaining its ability for Ab S recognition, further leading to a sensitivity 3.4-fold higher than the full-length S protein, which is in agreement with the increase in the target-to-receptor size ratio. Peptide-loaded LF devices based on noncovalent immobilization were developed by affording fast and simple analyses, along with a modular functionalization. From studies by molecular docking, the peptide–Ab S binding was found to be driven by hydrogen bonds and hydrophobic interactions. Moreover, the peptide is not amenable to denaturation, thus addressing the trade-off between scalability, cost, and robustness. The biosensor preserves 95.1% of the initial signal for 20 days when stored dry at 4 °C. With the aid of two simple equations fitted by machine learning (ML), the method was able to make the COVID-19 screening of 39 biological samples into healthy and infected groups with 100.0% accuracy. By taking advantage of peptide-related merits combined with advances in surface chemistry and ML-aided accuracy, this platform is promising to bring COVID-19 biosensors into mainstream use toward straightforward, fast, and accurate analyses at the point of care, with social and economic impacts being achieved.

Front Cover: In article number 1900085 by Wendel A. Alves and co‐workers, the self‐assembly properties of peptide nanomaterials in relation to their design and composition are surveyed. It is emphasized how environmental conditions can influence the morphology of peptide nanostructures, and how this dependence can be suitably exploited for the design of stimuli‐responsive systems.

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