A Simple and Facile Glucose Biosensor Based on Prussian Blue Modified Graphite String

This work describes the string sensor for the simple and sensitive detection of glucose which is based on Prussian blue (PB) modified graphite utilizing dipping. First, PB modified graphite (PB-G) strings are characterized by physical and electrochemical techniques to optimize the PB-G layer thickness. Then, glucose oxidase (GOx) is immobilized on PB-G string electrode with biocompatible chitosan overlayer (Chi/GOx/PB-G). The Chi/GOx/PB-G string electrode exhibits a sensitivity of 641.3 μA·mM−1·cm−2 to glucose with a linear range of 0.03 to 1.0 mM (R2=0.9957) and a rapid response time (<3 s). Moreover, the Chi/GOx/PB-G string electrodes are less sensitive to common interference materials such as ascorbic acid, uric acid, galactose, and acetaminophen than to glucose. The Chi/GOx/PB-G string electrodes also show excellent reproducibility (<5% RSD). Therefore, our Chi/GOx/PB-G string electrodes can be simple, robust, and reliable tools for glucose sensing which can avoid complicated and difficult multistep fabrication processes. In addition, we expect that they have many potential applications in fields ranging from health care to food analysis, in particular where single use is favorable

Development of paper based amperometric biosensor for glucose content measurement in Malaysian Stingless Bee Honey

Amperometric biosensor for glucose content measurement in Malaysian stingless bee honey was developed using screen printed carbon electrode (SPCE) integrated with paper disc immobilized with enzyme Glucose Oxidase (GOx) using simple physical adsorption method. The paper-based biosensor required only 8 µL of sample solution for glucose analysis. The calibration of glucose biosensor is linear between 0.5 mM to 4.5 mM (R2= 0.9925) and has a detection limit of 0.15 mM. Interference study on several compound affecting the biosensor response and storage stability was investigated. In addition, its performance was demonstrated in the analysis of six honey samples. The results obtained using glucose biosensor was validated by high performance liquid chromatographic (HPLC) method. The addition of glucose in pure honey at various concentration were also tested by this paper-based biosensor where the current obtained shows increasing trend with the addition of glucose. From this research, it can be concluded that, the prototype sensor to determine glucose adulteration in stingless bee honey was successfully developed

Paper-based electrochemical biosensor for lactose monitoring

Dairy products are between one of the most consumed products across the world, however, their consumption is today nearly impossible for around 65% of the world's population, since they possess some kind of intolerance to lactose (one of the main sugars present in these products). As a solution, lactose-free products are often consumed, with the hydrolysis of lactose by lactase, inhibiting the effects attached to lactose consumption. Since these commodities must meet a limit of 0.1% (w/w) of lactose, it has become more important than ever to develop accurate measuring systems that can correctly determine lactose percentage in milk samples. Several methods are used to perform this kind of measurements, however they are in general very expensive and complex, so there is a space in this competitive industry to develop simple, low-cost, and sustainable measuring systems. The reaction between lactase and lactose results in the hydrolysis of lactose, but it also results in the production of glucose and galactose. Glucose, specifically, produces an electrochemical response when reacting with glucose oxidase, producing H2O2 in the process. This molecule, when interacting with a substance like Prussian blue (PB) also produces an electrochemical signal that can be measured by a potentiostat. With that in mind, a biosensor composed of two enzymes and PB was developed to measure lactose in milk. A pre-treated paper substrate, together with a laser induced graphene-based pattern was used, therefore meeting the sustainability goals of this work. The sensor, with 5 mM of glucose oxidase, 100 mM of lactase and 5 mM of PB was able to correctly measure current produced by the milk samples for different concentrations of lactose, presenting a significative difference in current density (442.36 μA/cm2) between semi-skimmed milk and lactose-free semi-skimmed milk.Os lacticínios são dos produtos mais consumidos em todo o mundo, contudo, o seu consumo é hoje quase impossível para cerca de 65% da população mundial, uma vez que estes possuem alguma forma de intolerância à lactose (um dos principais açúcares presentes nestes produtos). Como solução, os produtos sem lactose são frequentemente consumidos, com a hidrólise da lactose pela lactase, inibindo os efeitos ligados ao consumo de lactose. Uma vez que estes produtos têm de cumprir um limite de 0,1% (p/p) de lactose, tornou-se mais importante do que nunca desenvolver sistemas de medição precisos que possam determinar corretamente a percentagem de lactose nas amostras de leite. Vários métodos são utilizados para realizar este tipo de medições, no entanto estes são em geral muito caros e complexos, pelo que existe um espaço nesta competitiva indústria para desenvolver sistemas de medição simples, de baixo custo e sustentáveis. A reação entre lactase e lactose resulta na hidrólise da lactose, mas também resulta na produção de glucose e galactose. A glucose, especificamente, produz uma resposta eletroquímica quando reage com a glucose oxidase, produzindo H2O2 no processo. Esta molécula, ao interagir com uma substância como o azul da Prússia (PB), também produz um sinal eletroquímico que pode ser medido por um potencióstato. Tendo isto em conta, foi desenvolvido um biossensor composto por duas enzimas e PB para medir a lactose no leite. Foi utilizado um substrato de papel previamente tratado, juntamente com um padrão à base de grafeno induzido por laser, cumprindo assim os objetivos de sustentabilidade deste trabalho. O sensor, com 5 mM de glucose oxidase, 100 mM de lactase e 5 mM de PB foi capaz de medir corretamente a corrente produzida pelas amostras de leite para diferentes concentrações de lactose, apresentando uma diferença significativa na densidade de corrente entre o leite meio-gordo e o leite meio-gordo sem lactose (442,36 μA/cm2)

Nanocellulose-based sensors in medical/clinical applications: The state-of-the-art review

In recent years, the considerable importance of healthcare and the indispensable appeal of curative issues, particularly the diagnosis of diseases, have propelled the invention of sensing platforms. With the development of nanotechnology, the integration of nanomaterials in such platforms has been much focused on, boosting their functionality in many fields. In this direction, there has been rapid growth in the utilisation of nanocellulose in sensors with medical applications. Indeed, this natural nanomaterial benefits from striking features, such as biocompatibility, cytocompatibility and low toxicity, as well as unprecedented physical and chemical properties. In this review, different classifications of nanocellulose-based sensors (biosensors, chemical and physical sensors), alongside some subcategories manufactured for health monitoring, stand out. Moreover, the types of nanocellulose and their roles in such sensors are discussed.This work was supported by the University of the Basque Country (Training of Researcher Staff, PIF 20/197)

A Novel Non-Enzymatic Glucose Biofuel Cell with Mobile Glucose Sensing

Herein, we report a novel non-enzymatic glucose biofuel cell with mobile glucose sensing. We characterized the power generation and biosensing capabilities in presence of glucose analyte. This system was developed using a non-enzymatic glucose biofuel cell consisting of colloidal platinum coated gold microwire (Au-co-Pt) employed as an anode and the cathode which was constructed using a Gas diffusion electrode (GDE) with a platinum catalyst. The non-enzymatic glucose biofuel cell produced a maximum open circuit voltage of 0.54 V and delivered and a maximum short circuit current density of 1.6 mA/cm2 with a peak power density of 0.226 mW/cm2 at a concentration of 1 M glucose. The non-enzymatic glucose biofuel cell produced an open circuit voltage of 0.38 V and delivered and a short circuit current density of 0.225 mA/cm2 with a peak power density of 0.022 mW/cm 2 at a concentration of 5 mM glucose. These findings showed that glucose biofuel cells can be further investigated in the development of a self-powered glucose biosensor. When used as self-powered glucose sensor, the system showed a good sensitivity of 0.616 μA mM−1 and linear dependence with a correlation coefficient of 0.995 in the glucose concentration range of 2 mM to 50 mM. The system was further characterized by testing the performance of the system at various temperature, pH and amidst various interfering and competing chemical species such as uric acid, ascorbic acid, fructose, maltose and galactose. A charge pump circuit consisting of a blinking LED was connected to the biofuel cell to amplify the input voltage to power small electronic devices. The blinking frequency of the LED corresponds to the glucose concentration. An android mobile phone camera application was used to measure this LED blinking frequency which was in turn converted into the glucose concentration readings using image processing in MATLAB. The user was notified via text message and an email

Biochar quimicamente ativado : obtenção, caracterização e aplicação no desenvolvimento de sensores eletroquímicos

Orientador: Prof. Dr. Márcio Fernando BergaminiCoorientador: Prof. Dr. Luiz Humberto Marcolino JuniorTese (doutorado) - Universidade Federal do Paraná, Setor de Ciências Exatas, Programa de Pós-Graduação em Química. Defesa : Curitiba, 29/03/2019Inclui referências: p. 191-211Área de concentração: Química AnalíticaResumo: O biochar é um material carbonáceo obtido pela pirólise de biomassa, e altamente funcionalizado, o que permite sua utilização na sorção ou imobilização de espécies. Com isso, o uso de eletrodos modificados com biochar se torna atrativo na pré-concentração espontânea e determinação voltamétrica de analitos. A quantidade de grupos funcionais do biochar pode ser aumenta por tratamentos químicos superficiais, o que melhora as suas propriedades sortivas. Neste trabalho, o biochar foi obtido a partir de resíduos de farelo de mamona, e foi submetido a diferentes condições de ativação química empregando HNO3 e/ou H2O2. As diferentes amostras foram caracterizadas e avaliadas na determinação de espécies inorgânicas e orgânicas. A amostra N2, tratada com HNO3 50 % (v/v), a 60 ºC por 3 horas, apresentou a melhor resposta, e foi utilizada na construção de EPCM para diferentes metodologias. Primeiramente, foi avaliada a capacidade do EPCM-N2 em pré-concentrar e determinar íons Ni(II), monitorando o par redox Ni(II)/Ni(III) em meio básico. A utilização do eletrodo proposto permitiu a determinação de íons Ni(II) em amostras fortificadas de bioetanol e água residuária. Em seguida, foi avaliada a capacidade de pré-concentração e determinação de ácido cafeico. O EPCM-N2 se mostrou eficiente na préconcentração espontânea da espécie orgânica. O método foi aplicado para a determinação em amostras reais e fortificadas de diferentes tipos de vinho, e apresentou resultados satisfatórios e concordantes ao método espectroscópico, por Folin-Ciocalteu. Outra estratégia avaliada foi a capacidade do biochar em imobilizar NiOOH (EPCM-N2-Ni) na determinação não-enzimática de glicose, reação catalisada pela presença de NiOOH. O eletrodo foi empregado na determinação de glicose em amostras reais e fortificadas de fluídos biológicos em um sistema microfluídico baseado em fios têxteis (?TED), o que permitiu a diminuição de reagentes e resíduos, tornando este um método analítico verde, conforme comprovado por cálculos de Eco-Escala. O EPCM-N2 também foi avaliado para a incorporação simultânea de um mediador redox (azul da Prússia) e enzima glicose oxidase na determinação enzimática de glicose. O biossensor apresentou boa afinidade enzima-substrato e estabilidade após dias sucessivos de medida, e foi aplicado com eficiência na determinação de glicose em amostras de fluídos biológicos. Por fim, o EPCM-N2, em conjunto com outros eletrodos, foi aplicado em uma língua eletrônica voltamétrica, visando a distinção e determinação de catecol, 4-etilcatecol e 4-etilguaiacol. A estratégia permitiu a discriminação e determinação das espécies, empregando ferramentas quimiométricas, PCA e redes neurais. Desta maneira, em virtude da capacidade de interação do biochar, melhorada pela sua ativação química, foi possível a aplicação em diferentes sensores eletroquímicos, com resultados satisfatórios em relação ao eletrodo sem modificação e modificado com biochar precursor (não tratado). Isso demonstra a versatilidade e a viabilidade do uso deste material como modificador para sensores, o que também é interessante do ponto de vista econômico e ecológico. Palavras-chave: biochar ativado, sensores eletroquímicos, níquel, compostos fenólicos, glicose, dispositivo microfluídico, língua eletrônica.Abstract: Biochar is a carbonaceous material obtained by the biomass pyrolysis, and highly functionalized, which allows its use in the sorption or immobilization of species. The use of biochar modified electrodes becomes attractive in the spontaneous preconcentration and voltammetric determination of analytes. The amount of biochar functional groups can be increased by surface chemical treatments, improving the sorption properties. In this work, biochar was obtained from castor oil cake biomass, and subject to different chemical activation conditions using HNO3 and/or H2O2. The different samples were characterized and evaluated in the determination of inorganic and organic species. The sample N2, treated with 50 % (v/v) HNO3 at 60 ºC for 3 hours, presented the best response and was used in the construction of CPME for different methodologies. First, the ability of CPME-N2 to Ni(II) ions preconcentration and determination was monitored by Ni(II)/Ni(III) redox couple in basic media. The use of the proposed electrode allowed the determination of Ni(II) ions in spiked bioethanol and wastewater samples. After, the capacity of caffeic acid preconcentration and determination was evaluated. CPME-N2 was efficient in the spontaneous preconcentration of this organic specie. The method was applied for the determination in real and spiked wine samples, and presented satisfactory and concordant results compared to spectroscopic method, by Folin-Ciocalteu. Another strategy evaluated was the biochar ability for immobilize NiOOH (CPMEN2- Ni) for glucose non-enzymatic determination, a reaction catalyzed by the NiOOH presence. The electrode was used for glucose determination in real and spiked biological fluids samples, in a microfluidic system based on textile threads (?TED), which allowed the reduction of reagents and residues, making this a green analytical method as evidenced by the Eco-Scale score. CPME-N2 was also evaluated for the simultaneous incorporation of a redox mediator (Prussian blue) and glucose oxidase enzyme for the glucose enzymatic determination. The biosensor had good enzyme-substrate affinity and stability after successive measurement days, and was applied efficiently for the glucose determination in biological fluid samples. Finally, CPME-N2, with other electrodes, was applied in a voltammetric electronic tongue, aiming the distinction and determination of catechol, 4-ethylcatechol and 4-ethylguaiacol. The strategy allowed the discrimination and determination of these species, using chemometric tools, PCA and neural networks. In this way, due to the interaction capacity of the biochar, improved by the chemical activation, it was possible to apply different electrochemical sensors, with satisfactory results in relation to the electrode without modification and modified with precursor biochar (untreated). This demonstrates the versatility and feasibility of the biochar use as a sensor modifier, which is also interesting from the economic and ecological point of view. Keywords: Activated biochar, electrochemical sensors, nickel, phenolic compounds, glucose, microfluidic device, electronic tongue

Application of graphene-based materials for detection of nitrate and nitrite in water—a review

Nitrite and nitrate are widely found in various water environments but the potential toxicity of nitrite and nitrate poses a great threat to human health. Recently, many methods have been developed to detect nitrate and nitrite in water. One of them is to use graphene-based materials. Graphene is a two-dimensional carbon nano-material with sp2 hybrid orbital, which has a large surface area and excellent conductivity and electron transfer ability. It is widely used for modifying electrodes for electrochemical sensors. Graphene based electrochemical sensors have the advantages of being low cost, effective and efficient for nitrite and nitrate detection. This paper reviews the application of graphene-based nanomaterials for electrochemical detection of nitrate and nitrite in water. The properties and advantages of the electrodes were modified by graphene, graphene oxide and reduced graphene oxide nanocomposite in the development of nitrite sensors are discussed in detail. Based on the review, the paper summarizes the working conditions and performance of different sensors, including working potential, pH, detection range, detection limit, sensitivity, reproducibility, repeatability and long-term stability. Furthermore, the challenges and suggestions for future research on the application of graphene-based nanocomposite electrochemical sensors for nitrite detection are also highlighted

Fe-N-C SINGLE-ATOMIC SITE CATALYSTS ENZYME-LIKE ACTIVITIES AND BIOSENSING APPLICATIONS

From diagnosis of life-threatening diseases to detection of biological agents in the human body and environment, biosensors are becoming a critical part of modern life. The fast detection process and accurate detection results have posed high requirements in the sensitivity and specificity of the biosensors. Recently, some nanomaterials have been found to possess unexpected peroxidase-like activities, and great progress has been made to fabricate colorimetric biosensors based on the peroxidase-like activities of these nanomaterials. These nanomaterials exhibit flexibility in structural design and composition, easy separation and storage, high stability, simple preparation, and tunable catalytic activity. Fe-based single-atomic site catalysts (SASCs), with the natural metalloproteases-like active site structure, have attracted widespread attention in biosensing applications. Precisely controlling the isolated single-atomic Fe-N-C active site density and structure is crucial to improving the SASCs’ performance. In this dissertation, different strategies are used to increase the enzyme-like activity of Fe-N-C SASCs. Using ion-imprinting technology to precisely control ions at the atomic level, form numerous well-defined single-atomic Fe-N-C sites, and achieve in situ detection of H2O2 generated from cells. The use of nanoconfinement force can greatly increase the number of Fe-Nx active sites in the material, thereby greatly improving the enzyme-like properties of the material, which can then be used for biosensing and sensitive and selective detection of disease biomarkers. Furthermore, harnessing the advantages of two-dimensional (2D) materials to synthesize SASCs can further enhance their activity, as the 2D structure can help expose more single-atomic sites that can directly participate in the reaction. This strategy has been successfully used to fabricate biosensing systems for herbicide detection. More importantly, different SASCs can be further designed by using appropriate precursors to achieve structural mimicry of the natural enzyme, through control size and morphology to achieve point-of-care detection via lateral-flow immunoassay.Fe-N-C SASCs synthesized in this work have significant potential to replace natural enzymes for high-sensitive biosensing applications. Their unique single-atomic geometrical structure exhibits significant advantages in biocatalytic activity, stability, and selectivity. We believe the continuously developed strategies can enable the Fe-N-C SASCs to explore their wider applications in various biosensing applications with excellent detection performance.

Imobilização de enzimas em matrizes de sol-gel: novos desenvolvimentos em biossensores de nitrito e glucose

Os trabalhos apresentados nesta dissertação têm como ponto comum a imobilização de enzimas numa matriz de sol-gel à base de silicato de sódio. Na primeira parte, foi continuada o desenvolvimento de um biossensor eletroquímico para nitritos baseado na redutase de nitrito multihémica (ccNiR) extraída de Desulfovibrio desulfuricans ATCC27774. Em concreto, foi realizada uma otimização mais fina dos parâmetros analíticos deste biossensor (desenvolvido no nosso grupo de investigação), através da variação da composição do eletrólito suporte e da incubação prévia da ccNiR em compostos anfifílicos (os surfactantes DDM e SDS) ou hidrofílicos (o polímero, PEG 400). Enquanto que com o PEG 400 se obteve um aumento da resposta catalítica (sensibilidade de 0,78 AM-1cm-2 e intervalo de linearidade de 0,5 a 31 μM), os dois detergentes não contribuíram para uma melhoria da resposta analítica. A remoção de O2 dissolvido é um aspeto importante para o funcionamento de biossensores eletroquímicos baseados em redutases (caso da ccNiR), nomeadamente quando se pretende desenvolver testes rápidos para utilização em célula aberta. Neste sentido, procurou imobilizarse o sistema de remoção de O2 composto pelas enzimas glucose-oxidase (GOx) e catalase, usando uma matriz de sol-gel de silicato de sódio. Refira-se que este método é bastante mais rápido que os protocolos convencionais e menos agressivo para as moléculas biológicas. A imobilização das duas enzimas foi efetuada separadamente ou em conjunto, segundo diferentes configurações. O sistema PGE/catalase/sol-gel com GOx e glucose em solução, mostrou ser o mais eficaz para a remoção de O2, tendo sido incorporado à posteriori no biossensor de nitrito. Por fim, as experiências realizadas neste contexto foram aproveitadas para o desenvolvimento de um biossensor de glucose baseado na imobilização da enzima GOx com a mesma matriz de sol-gel. Ao reagir com a glucose, a GOx consome o O2 dissolvido, levando a um decréscimo da corrente de redução de O2 proporcional à sua concentração. A sensibilidade deste biossensor para a glucose varia entre 2,66 – 6,69 mAM-1cm-2 e o intervalo de linearidade entre 1,2 a 8 mM