Oxygen reduction reaction (ORR), essential in many energy conversion devices, takes particular relevance in facing the increasing global demand for clean energy sources and vectors. In this context, desirable features for ORR-based electrochemical cells are operability under environmentally friendly conditions, such as pH 7 biocompatible electrolytes, and the usage of relatively low electrocatalyst loadings. On the other hand, the improvement of the cathode performance in neutral solutions is commonly focused on the development of electrocatalyzers for reducing the ORR overpotential. In this work, we took advantage of the possibilities brought by a novel strategy toward construction of complex interfacial architectures, the so-called "nanoarchitectonics" approach. In order to achieve enhanced ORR currents and reduced overpotentials, we combined three different building blocks with defined functionalities: a conducting polymer (CP) nanofilm (the connecting electroactive matrix), well dispersed Pt-nanoparticles (the electrocatalyzer), and a layer of a Zn-based metal−organic framework (MOF) nanocrystals (the in situ oxygen reservoir). The sequential synthetic procedure includes the electrosynthesis of a polyaniline-like electroactive film, the synthesis of Pt nanoparticles within this film, and the deposition of a layer of MOF nanocrystals, which adds micro/mesoporosity to the assembly. The incorporation of the MOF nanocrystals layer incorporates two fundamental aspects: it allows for the ionic transport through its interparticle interstices, and also selectively promotes the O 2 preconcentration, which is then available for the ORR on the embedded catalytically active metallic nanoparticles. The rational integration of these blocks yields a functional interfacial architecture for enhanced ORR currents in eco-friendly neutral pH KCl solutions.

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The biofunctionalization of graphene field‐effect transistors (GFETs) through vinylsulfonated‐polyethyleneimine nanoscaffold is presented for enhanced biosensing of severe acute respiratory‐related coronavirus 2 (SARS‐CoV‐2) spike protein and human ferritin, two targets of great importance for the rapid diagnostic and monitoring of individuals with COVID‐19. The heterobifunctional nanoscaffold enables covalent immobilization of binding proteins and antifouling polymers while the whole architecture is attached to graphene by multivalent π–π interactions. First, to optimize the sensing platform, concanavalin A is employed for glycoprotein detection. Then, monoclonal antibodies specific against SARS‐CoV‐2 spike protein and human ferritin are anchored, yielding biosensors with limit of detections of 0.74 and 0.23 nm, and apparent affinity constants () of 6.7 and 8.8 nm, respectively. Both biosensing platforms show good specificity, fast time response, and wide dynamic range (0.1–100 nm). Moreover, SARS‐CoV‐2 spike protein is also detected in spiked nasopharyngeal swab samples. To rigorously validate this biosensing technology, the GFET response is matched with surface plasmon resonance measurements, exhibiting linear correlations (from 2 to 100 ng cm−2) and good agreement in terms of KD values. Finally, the performance of the biosensors fabricated through the nanoscaffold strategy is compared with those obtained through the widely employed monopyrene approach, showing enhanced sensitivity.

Graphene is a two-dimensional semiconducting material whose application for diagnostics has been a real game-changer in terms of sensitivity and response time, variables of paramount importance to stop the COVID-19 spreading. Nevertheless, strategies for the modification of docking recognition and antifouling elements to obtain covalent-like stability without the disruption of the graphene band structure are still needed. In this work, we conducted surface engineering of graphene through heterofunctional supramolecular-covalent scaffolds based on vinylsulfonated-polyamines (PA-VS). In these scaffolds, one side binds graphene through multivalent π–π interactions with pyrene groups, and the other side presents vinylsulfonated pending groups that can be used for covalent binding. The construction of PA-VS scaffolds was demonstrated by spectroscopic ellipsometry, Raman spectroscopy, and contact angle measurements. The covalent binding of −SH, −NH2, or −OH groups was confirmed, and it evidenced great chemical versatility. After field-effect studies, we found that the PA-VS-based scaffolds do not disrupt the semiconducting properties of graphene. Moreover, the scaffolds were covalently modified with poly­(ethylene glycol) (PEG), which improved the resistance to nonspecific proteins by almost 7-fold compared to the widely used PEG-monopyrene approach. The attachment of recognition elements to PA-VS was optimized for concanavalin A (ConA), a model lectin with a high affinity to glycans. Lastly, the platform was implemented for the rapid, sensitive, and regenerable recognition of SARS-CoV-2 spike protein and human ferritin in lab-made samples. Those two are the target molecules of major importance for the rapid detection and monitoring of COVID-19-positive patients. For that purpose, monoclonal antibodies (mAbs) were bound to the scaffolds, resulting in a surface coverage of 436 ± 30 ng/cm2. K D affinity constants of 48.4 and 2.54 nM were obtained by surface plasmon resonance (SPR) spectroscopy for SARS-CoV-2 spike protein and human ferritin binding on these supramolecular scaffolds, respectively.

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Graphene field-effect transistors (gFETs) are promising tools for the development of precise and affordable techniques for the study of molecular binding kinetics, crucial in applications such as biomolecule therapies, drug discovery, and medical diagnostics. Nevertheless, determining the reliability and modeling the gFET signal for the monitoring of molecular binding and adsorption are still needed. Here, we prove that the gFET technology allows monitoring in real time the adsorption of both positive and negative polyelectrolytes, used as model charged macromolecules, using a low-cost portable gFET setup (Zaphyrus-W10), whose graphene channel was produced by reduction of graphene oxide. The gFET response is compared and validated against the surface plasmon resonance (SPR) technique. Remarkably, the electronic response is directly correlated with the mass adsorption, and very similar kinetic profiles are obtained for both techniques. Moreover, the adsorption kinetics of a polyelectrolyte assembled in a layer-by-layer give evidence that, even at ionic strengths near to the physiological conditions, the electrostatic interactions can be sensed at large distances from the graphene surface (20-fold higher in comparison to the solution Debye length). Biasing the gFET with a Ag/AgCl coplanar gate electrode avoids capacitive current contributions from nonbinding phenomena and displays a transistor signal proportional to the adsorbed mass. Furthermore, a marked amplification of the electronic signal without alteration of the macromolecule adsorption kinetics by using a Ag/AgCl gate in comparison with a nongated device is evidenced. Thus, the suitability of the coplanar-gated gFET technology for the study of molecular binding kinetics is illustrated.

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