Reagentless Quantum-Rate-Based Electrochemical Signal of Graphene for Detecting SARS-CoV-2 Infection Using Nasal Swab Specimens.

The quantum-rate model predicts a rate k as a frequency for transporting electrons within molecular structures, which is governed by the ratio between the quantum of conductance G and capacitance Cq, such that k = G/Cq. This frequency, as measured in a single-layer graphene appropriately modified with suitable biological receptors, can be applied as a transducer signal that ranges sensitivities within the attomole for biosensing applications. Here, we applied this label-free and reagentless biosensing transducer signal methodology for the qualitative diagnosis of COVID-19 infections, where this assay methodology was shown to be similar to the gold-standard real-time polymerase chain reaction. The quantum-rate strategy for the diagnosis of COVID-19 was performed by combining the response of the interface for detecting the S and N proteins of SARS-CoV-2 virus as accessed from nasopharyngeal/oropharyngeal patient samples with 80% of sensitivity and 77% of specificity. As a label-free and reagentless biosensing platform, the methodology is decidedly useful for point-of-care and internet-of-things biological assaying technologies, not only because of its real-time ability to measure infections but also because of the capability for miniaturization inherent in reagentless electrochemical methods. This approach effectively permits the rapid development of biological assays for surveillance and control of endemics and pandemics.

Sensing the quantized reactivity of graphene.

We demonstrated that the variations measured in the quantum capacitance of single-layer graphene, envisioned here as a conceptual molecular model, depend on the chemical reactivity of the molecule and can be used as an analytical and sensing tool for environmental conditions. The variations are quantized as a function of the environmental changes and can be correlated with chemical reactivity indexes such as chemical hardness and softness. This not only constitutes a proof-of-principle that the chemical reactivity of graphene, as a single molecule, can be determined in situ by measuring the quantum capacitance, but also that these measurements can be used as an analytical tool.

Facile room temperature synthesis of large graphene sheets from simple molecules.

The largest graphene sample obtained through a chemical reaction under ambient conditions (temperature and pressure), using simple molecules such as benzene or n-hexane as precursors, is reported. Starting from a heterogeneous reaction between solid iron chloride and the molecular precursor (benzene and n-hexane) at a water/oil interface, graphene sheets with micrometric lateral size are obtained as a film deposited at the liquid/liquid (L/L) interface. The pathway involving the cyclization and aromatization of n-hexane to benzene at the L/L interface, and the sequence of conversion of benzene to biphenyl and biphenyl to condensed rings (which originates the graphene structures) was followed by different characterization techniques and a mechanistic proposal is presented. Finally, we demonstrate that this route can be extended for the synthesis of N-doped graphene, using pyridine as the molecular precursor.

Effect of low and high methoxyl citrus pectin on the properties of polypyrrole based electroactive hydrogels.

Electroactive hydrogels were prepared using commercial citric pectin, either raw (PC) or purified through dialysis (dPC), and chemically synthesized polypyrrole (PPy). 1H NMR analyses showed that PC is a low methoxyl pectin (degree of methoxylation, DM=46%) and dPC is a high methoxyl pectin (DM=77%). The pyrrole polymerization was monitored through UV-vis spectroscopy and both samples were observed to be good stabilizers for PPy in aqueous medium. The dispersions were used to prepare the hydrogels h-PC-PPy and h-dPC-PPy. The hydrogel h-dPC-PPy has a higher swelling index (SI≈25%) at pH 1.2 than the hydrogel h-PC-PPy (SI≈7%). Contrastingly, at pH 6.8 both hydrogels lost their mechanical integrity. Raman spectroscopy revealed that PPy is more oxidized in h-PC-PPy. Nevertheless, both hydrogels are electroactive and therefore can be considered for applications in which the control of the degree of swelling is desired.

Silver sulfadiazine loaded chitosan/chondroitin sulfate films for a potential wound dressing application.

Silver sulfadiazine (AgSD) loaded chitosan/chondroitin sulfate (CHI/CS) films were formed to be applied as a potential wound dressing material. The liquid uptake capacity of both, CHI/CS and CHI/CS/AgSD, films exhibited a pH-dependent behavior. Tensile tests showed that the amount of CS used to form the films and the further incorporation of AgSD affect the mechanical properties of the films. In vitro AgSD-release assays showed that the CHI/CS mass ratio influences the AgSD release rate. All the investigated CHI/CS/AgSD films sustain the AgSD release up to 96h at physiological pH. Antibacterial activity and cell viability assays showed that all the CHI/CS/AgSD films have activity against Pseudomonas aeruginosa and Staphylococcus aureus but they were not toxic to Vero cells. The results presented in this work indicate that the CHI/CS/AgSD exhibits potential to be applied as a wound dressing material.