Abstract The COVID-19 pandemic outbreak made the development of reliable, sensitive, and reproducible testing methods crucial throughout the world. Without proper analytical validation, testing results can be misinterpreted, leading to a certain degree of misinformation in the clinical area. To accurately assess the methods, the determination of an analytical linear range of response of the assay is fundamental. Based on this curve, the evaluation of some parameters as sensitivity, limit of detection, and limit of quantification can be done, as well as the establishment of cut-off values. Statistical treatments of the collected data can be performed for reproducibility and reliability evaluations. In this context, there is a wide range of analytical concerns that should be in-depth discussed in medical, biomedical and chemical areas. This letter aims to briefly clarify some analytical chemistry concepts, as sensitivity, cut-off and limit of detection, and their application towards clinical diagnosis.

Abstract: The combination of UV-visible absorption and electrochemical experiments (spectroelectrochemistry) enables to obtain highly specific spectroscopic information (in situ and operando) from modified surfaces. However, such application can be limited by the self-absorbance, for example, when metallic nanoparticles are present on modified surfaces. Indium-tin oxide onto glass (ITO) is a typical electrode commonly used for spectroelectrochemistry; ITO is an oxide-based semiconductor, and in numerous applications it is necessary to promote the modification of the electrode surface without significant loss of transparency. Here, we report a simple strategy to obtain ITO electrodes modified with self-assembled polyelectrolytes and active dendritic gold nanoparticles (AuNPs), a combination of soft and metallic materials that results in electrodes with significant optical transparency. Self-assembled poly(sodium styrene sulfonate) and polyamidoamine dendrimer (PSS/PAMAN bilayer) were applied successfully as efficient platform for monodisperse dendritic AuNPs electrodeposition, and the electrode containing those materials shows substantial optical transmittance from 400nm to 800nm. The combination of transparency and the presence of AuNPs homogeneously dispersed start to be a practical approach to develop metal-based electrodes for spectroelectrochemistry.

ABSTRACT Bioelectrochemistry can be defined as a branch of Chemical Science concerned with electron-proton transfer and transport involving biomolecules, as well as electrode reactions of redox enzymes. The bioelectrochemical reactions and system have direct impact in biotechnological development, in medical devices designing, in the behavior of DNA-protein complexes, in green-energy and bioenergy concepts, and make it possible an understanding of metabolism of all living organisms (e.g. humans) where biomolecules are integral to health and proper functioning. In the last years, many researchers have dedicated itself to study different redox enzymes by using electrochemistry, aiming to understand their mechanisms and to develop promising bioanodes and biocathodes for biofuel cells as well as to develop biosensors and implantable bioelectronics devices. Inside this scope, this review try to introduce and contemplate some relevant topics for enzyme bioelectrochemistry, such as the immobilization of the enzymes at electrode surfaces, the electron transfer, the bioelectrocatalysis, and new techniques conjugated with electrochemistry vising understand the kinetics and thermodynamics of redox proteins. Furthermore, examples of recent approaches in designing biosensors and biofuel developed are presented.

Hierarchical 3-dimensional flexible carbon fiber (FCF) array is a candidate as flexible electrode for enzyme electrochemistry, with interesting properties for application in enzymatic biofuel cell and implantable biosensors. Here, we show the fabrication of oxidized FCF electrode (FCFO) based on chemical surface treatment, a wet oxidation method by using permanganate ions. Compared with pristine FCF, FCFO is rougher; the scratches become wider and deeper, with some defects in the basal planes and some cracked structures. X-ray photoelectron spectroscopy data suggests a correlation between the carbon structures and the appearance of chemical groups containing oxygen atoms. Finally, we show how the bioelectrocatalysis of ethanol by using FCFO arrays modified with NAD-dependent alcohol dehydrogenase (ADH) is positively influenced by the fibers treatment oxidation process.

Neste trabalho, a síntese e a caracterização de nanopartículas de ouro (AuNPs) estabilizadas com quitosana (Chit), assim como a capacidade deste material para formar filmes automontados multicamadas com ftalocianina tetrassulfonada de cobalto(II) (CoTsPc), são reportadas. Este novo material híbrido baseado em Chit-AuNPs e CoTsPc foi caracterizado por diversas técnicas, e as propriedades eletroquímicas de um eletrodo de ITO (óxido de estanho dopado com índio) modificado com Chit-AuNPs e CoTsPc foram investigadas. A quitosana evitou a aglomeração das AuNPs (diâmetro de 6,0 nm), formando uma suspensão coloidal estável por meses. A interação entre as AuNPs e as moléculas de quitosana ocorre principalmente pelos grupamentos CH2 e NH3+ da quitosana. Para os filmes automontados de Chit-AuNPs/CoTsPc, observou-se uma interação supramolecular entre as multicamadas, além do fato de que as AuNPs influenciaram as propriedades redox da CoTsPc. A presença das nanopartículas não só aumentou a área eletroativa do eletrodo, mas também a velocidade de transferência de carga, indicando que este material é um candidato muito promissor para futuras aplicações em dispositivos eletroquímicos.

In this work, we report the synthesis and characterization of gold nanoparticles (AuNPs) stabilized with chitosan (Chit), as well as the capability of this material to form multilayer films with cobalt(II) tetrasulfonated phthalocyanine (CoTsPc). The new hybrid material based on Chit-AuNPs and CoTsPc was characterized by several techniques, and the electrochemical properties of an ITO (indium tin oxide) electrode modified with Chit-AuNPs and CoTsPc were investigated. Chit prevented AuNPs (diameter of 6.0 nm) agglomeration, forming a colloidal suspension that was stable for months. The interaction between the AuNPs and Chit molecules occurs mainly through the CH2 and NH3+ groups from Chit. Supramolecular interaction was observed for multilayer films of Chit-AuNPs/CoTsPc, and the AuNPs influenced the redox properties of CoTsPc. The presence of the nanoparticles not only increased the electroactive area of the electrodes, but also the rate of charge-transfer, suggesting that this material is a very promising candidate for further applications in electrochemical devices.

O direcionamento por campo magnético tem sido aplicado em Bioeletroquímica, principalmente com intuito de transportar enzimas ou mediadores redox imobilizados em partículas de magnetita (Fe3O4) para a superfície de eletrodos, proporcionando o controle comutável das correntes faradaicas provenientes da biocatálise. Neste trabalho, relata-se um avanço no controle magnético de reações bioeletroquímicas por meio da construção de um sistema que contém simultaneamente partículas magnéticas (para transporte controlado), enzima redox (para biocatálise) e um mediador redox (para mediação da transferência eletrônica). Para isso, sintetizou-se um novo material que consiste em partículas de Fe3O4 modificadas com ferroceno insolúvel (Fc) e quitosana (Chi) entrecruzada com glicose oxidase (GOx). Quando esse material foi utilizado em suspensão em estudos eletroquímicos, observou-se um aumento de 70% da corrente catalítica de oxidação de glicose quando um campo de 0,24 T foi aplicado perpendicularmente ao plano do eletrodo. Esta é a primeira vez que um controle de processos bioeletrocatalíticos foi relatado utilizando enzima, mediador e magnetita em um sistema único controlado por campo magnético.

Magnetic fields have been used in Bioelectrochemistry to carry enzymes or redox mediators immobilized on magnetite (Fe3O4) to the electrodes surface, providing a switchable control of faradaic current from biocatalysis. In this work, it is reported an advance in the magnetic control of bioelectrochemical reactions, by construction of a system containing simultaneously a magnetic particle (for controlled driving), an enzyme (for biocatalysis) and a redox mediator (for mediation of electron transfer). The advance was attained by synthesis of a new material (Fe3O4-Chi-Fc/GOx) that consists of Fe3O4 particles modified with insoluble ferrocene (Fc) and chitosan (Chi) cross-linked with glucose oxidase (GOx). When this material was used in electrochemical studies, an increase of 70% was observed in the catalytic current of glucose oxidation when 0.24 T was applied perpendicularly to electrode plane. This is the first time that a control of the bioelectrocatalytic process was achieved using enzyme, mediator and magnetite in a unique system switched by a magnetic field.