Modular Label-Free Electrochemical Biosensor Loading Nature-Inspired Peptide toward the Widespread Use of COVID-19 Antibody Tests.

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 (AbS) 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 AbS 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-AbS 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.

An automated flow system for in-line extraction of proteins and separation of jacalin using a low-cost stationary phase.

Lectins are carbohydrate binding proteins with many physiological and biotechnological applications. Isolation of proteins is normally time-consuming and encompasses multiple and, sometimes, complicated steps that hinder reproducibility and yield. Affinity chromatography is an efficient way to simplify and improve protein purification, however often requiring an expensive and fragile stationary phase. In this regard, automated flow-based systems minimize the time for extraction of species from solid samples without hindering the features of batch procedures. In this work, a new inexpensive affinity-based stationary phase was developed for in-line separation of jacalin, a galactose-binding lectin from jackfruit seeds. In the flow manifold, in-line extraction of proteins was also carried out with continuous monitoring using the spectrophotometric Biuret assay. For protein determination, linear response was observed from 3.0 to 15 g L-1. The results of the analysis of protein extracts from jackfruit seeds obtained with the herein described procedure and batch procedure agreed with 95% confidence level. Quantitative extraction of proteins from jackfruit seed powder required recirculation of extraction buffer for 15 min through a lab-made polymethylmethacrylate (PMMA) column containing 200 mg of the crude seed powder. In the chromatographic step, jacalin was isolated after 300 s. Therefore, three essential steps for jacalin isolation were performed in one manifold in a fast way, minimizing sample consumption and solution handling. Additionally, the versatile and multi-task developed flow manifold can be useful for routine analysis and preparative procedures, being adaptable for the extraction and separation of other species from solid matrixes with continuous monitoring of the processes.