Síntese e caracterização de nanocompósitos de nanotubos de polipirrol e nanopartículas de prata : aplicação na detecção eletroquímica não enzimática do pesticida metil paration

Pesticidas são amplamente empregados em práticas agrícolas para a prevenção, controle ou remoção de pragas como fungos (fungicidas) ou insetos (inseticidas), fazendo com que haja um aumento no rendimento dos cultivos agrícolas. Atualmente, o Brasil é um dos maiores consumidores de agrotóxicos do mundo, com isso tem-se impactos expressivos sobre a saúde da população e o meio ambiente. Portanto, o desenvolvimento de métodos e técnicas para a detecção e monitoramento desses pesticidas é de extrema importância. Biossensores eletroquímicos enzimáticos têm se mostrado como uma ferramenta confiável para detecção destes compostos nocivos, entretanto podem ter alto custo e baixa reprodutibilidade devido ao material biológico requerido. Neste trabalho, estudamos o potencial de nanotubos de polipirrol com nanopartículas de prata para detecção direta do pesticida metil paration. A polimerização do pirrol ocorreu na presença de cloreto férrico (III), alaranjado de metila e do precursor das nanopartículas, nitrato de prata. As amostras foram caracterizadas por microscopia eletrônica de varredura e de transmissão, evidenciando a presença de nanotubos de polipirrol com nanopartículas de prata. De fato, a presença de nanopartículas de prata diminui a resistividade elétrica do material de 252 para 28 Ω cm. As amostras foram também caracterizadas através da técnica de espectroscopia UV-Vis e de infravermelho com transformada de Fourier, que indicaram a inserção do dopante alaranjado de metila na matriz polimérica. A técnica de voltametria cíclica foi realizada frente ao par redox ferri/ferrocianeto [Fe(CN)6]3-/4-. Eletrodos compostos apenas do nanocompósito (sem pasta de carbono) apresentaram processos faradaicos mais evidentes, decorrente da menor resistência à transferência de carga. O nanocompósito responde linearmente ao pesticida metil paration na faixa de 5,3 a 34,1 μmol L-1, com um limite de detecção (LD) de 1,28 μmol L-1. Sendo assim, o nanocompósito obtido respondeu como sensor eletroquímico não enzimático ao pesticida metil paration. A ausência de enzimas na sua montagem, reduz o seu custo de produção.Pesticides are widely used in agricultural to prevent, control or remove pests such as fungi (fungicides) or insects (insecticides), allowing improvements in crop yield. Currently, Brazil is one of the largest consumers of pesticides in the world, this situation has a significant impact on both, the population healthy and the environment. Therefore, the development of methods and techniques for the detection and monitoring of these pesticides is extremely important. Enzymatic electrochemical biosensors have been shown to be a reliable tool for detection of these harmful compounds, however they may have high costs and low reproducibility. In this work, we have studied the potential of polypyrrole nanotubes with silver nanoparticles for non-enzymatic detection of methyl parathion pesticide. The pyrrole polymerization was carried out in the presence of ferric chloride (III), methyl orange and silver nitrate as the nanoparticle precursor. The samples were characterized by scanning and transmission electron microscopies, unveiling the presence of polypyrrole nanotubes with silver nanoparticles. Indeed, the presence of silver nanoparticles reduces the electrical resistivity of the material from 252 to 28 Ω cm. The samples were also characterized using UV-Vis and infrared with Fourier transform spectroscopies, which indicated the insertion of the methyl orange dopant in the polymeric matrix. The cyclic voltammetry technique was performed with the ferri / ferrocyanide [Fe(CN)6]3-/4 redox pair. The electrodes composed only with the nanocomposite (without carbon paste) showed more evident faradaic processes, due to the lower charge transfer resistance. The nanocomposite responded linearly to methyl parathion pesticide in range from 5.3 to 34.1 μmol L-1, with a detection limit (LD) of 1.28 μmol L-1. Therefore, the nanocomposite was sensitive as a non-enzymatic electrochemical sensor for the pesticide methyl parathion. The absence of enzyme in the assembling reduces the production cost

Development of a Novel Optical Biosensor for Detection of Organophoshorus Pesticides Based on Methyl Parathion Hydrolase Immobilized by Metal-Chelate Affinity

We have developed a novel optical biosensor device using recombinant methyl parathion hydrolase (MPH) enzyme immobilized on agarose by metal-chelate affinity to detect organophosphorus (OP) compounds with a nitrophenyl group. The biosensor principle is based on the optical measurement of the product of OP catalysis by MPH (<em>p</em>-nitrophenol). Briefly, MPH containing six sequential histidines (6× His tag) at its <em>N</em>-terminal was bound to nitrilotriacetic acid (NTA) agarose with Ni ions, resulting in the flexible immobilization of the bio-reaction platform. The optical biosensing system consisted of two light-emitting diodes (LEDs) and one photodiode. The LED that emitted light at the wavelength of the maximum absorption for <em>p</em>-nitrophenol served as the signal light, while the other LED that showed no absorbance served as the reference light. The optical sensing system detected absorbance that was linearly correlated to methyl parathion (MP) concentration and the detection limit was estimated to be 4 μM. Sensor hysteresis was investigated and the results showed that at lower concentration range of MP the difference got from the opposite process curves was very small. With its easy immobilization of enzymes and simple design in structure, the system has the potential for development into a practical portable detector for field applications