Desenvolvimento e otimização de métodos analíticos com nanopartículas para a avaliação de adulteração ou contaminação de alimentos
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2017-10-03
Autores
Bittar, Dayana Borges [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
Neste trabalho, desenvolvimento e otimização de métodos foram propostos utilizando nanopartículas metálicas a fim de aumentar a sensibilidade desses métodos e detectar contaminantes/adulterantes em matrizes alimentares complexas como leite e mel. Em um primeiro momento, um método de detecção colorimétrico baseado em nanopartículas de prata foi desenvolvido para a determinação da melamina no leite. As nanopartículas de prata foram sintetizadas sem uso de qualquer agente estabilizante, utilizando borohidreto de sódio como agente redutor. A otimização das variáveis experimentais para a formação das nanopartículas foi realizada utilizando o planejamento fatorial, resultando em nanopartículas de prata coloidal estável com um diâmetro médio de 14,0 ± 2,7 nm. As medidas espectrofotométricas realizadas a 475 nm mostraram uma faixa linear de 0,033-1,50 mg L-1 de melamina (r = 0,999), com limites de detecção e quantificação de 0,009 e 0,031 mg L-1, respectivamente. O método proposto forneceu detecção altamente sensível de melamina no leite. Em um segundo momento, um método sensível, rápido e robusto baseado no uso de nanopartículas de prata isentas de estabilizantes foi desenvolvido para a detecção de chumbo em mel. As nanopartículas de prata foram sintetizadas sem o uso de qualquer estabilizante, utilizando-se como precursores nitrato de prata e borohidreto de sódio; este último como agente redutor. A otimização das variáveis experimentais (AgNO3 e NaBH4) para a formação das nanopartículas foi realizada utilizando-se diferentes volumes dessas soluções. Medições espectrofotométricas a 393 nm foram realizadas mostrando uma faixa linear de trabalho entre 0,0500-0,167 mg L-1 de chumbo (r = 0,994), com limite de detecção (LOD) e quantificação (LOQ) de 0,0135 e 0,0451 mg L-1, respectivamente. O método proposto forneceu detecção significativamente sensível para chumbo em amostras de mel. Na terceira parte, a combinação na mesma análise de múltiplos quantum dots de CdTe-MPA, cada um com uma capacidade particular de interagir com o analito, assegurou uma detecção de multi-ponto que não foi apenas explorada para uma discriminação mais precisa do analito, mas também para a discriminação simultânea de múltiplas espécies mutuamente interferentes, na mesma amostra. A análise de componentes principais (PCA) e a regressão de mínimos quadrados parciais (PLS) foram utilizados para análise de dados de fluorescência. Foram testadas misturas de dois quantum dots de CdTe-MPA, emitindo nos diferentes comprimentos de onda: 549/566, 549/634 e 566/634 nm e os resultados obtidos mostraram que a abordagem desenvolvida é capaz de resolver mistura binária e ternária de Pb (II), Hg (II) e Cu (II), fornecendo informações precisas sobre a concentração de chumbo (II) e mercúrio (II) e sinalizando a ocorrência de Cu (II). Outro método de detecção colorimétrico baseado na análise de imagens digitais, utilizando o sistema de cores RGB (Red – Green – Blue), obtidas após a reação entre as nanopartículas de ouro e a melamina, foi desenvolvido para a determinação do contaminante melamina em leite. As nanopartículas de ouro não modificadas foram sintetizadas utilizando citrato de sódio dihidratado como agente redutor. A otimização dos canais RGB para a obtenção dos melhores resultados de intensidade efetiva foi realizada utilizando o software GIMP 2.8. As nanopartículas de ouro apresentaram um diâmetro médio de 23,0 ± 2,2 nm. As medidas de intensidade efetiva foram obtidas com canal azul e apresentaram linearidade na faixa de 0,100 a 0,275 mg L-1 de melamina (r = 0,998), com limites de detecção (LOD) e quantificação (LOQ) de 0,013 e 0,043 mg L-1, respectivamente. O método proposto apresentou suficiente sensibilidade para a determinação de melamina em leite quando comparado a outros trabalhos encontrados na literatura.
In this work, development and optimization of methods were proposed using metallic nanoparticles in order to increase the sensitivity of these methods and detect contaminants / adulterants in complex food matrices such as milk and honey. In a first step, a colorimetric detection method based on silver nanoparticles was developed for the determination of melamine in milk. Silver nanoparticles were synthesized without the use of any stabilizing agent, using sodium borohydride as a reducing agent. The optimization of experimental variables for nanoparticle formation was performed using factorial design, resulting in stable colloidal silver nanoparticles with a mean diameter of 14.0 ± 2.7 nm. The spectrophotometric measurements performed at 475 nm showed a linear range of 0.033-1.50 mg L-1 melamine (r = 0.999), with detection limits (LOD) and quantification (LOQ) of 0.009 and 0.031 mg L-1 , respectively. The proposed method provided sensitive detection and quantification of melamine in milk. In a second step, a sensitive, rapid and robust method based on the use of stabilizerfree silver nanoparticles was developed for the detection and quantification of lead in honey samples. Silver nanoparticles were synthesized without the use of any stabilizer, using silver nitrate and sodium borohydride as precursors; the latter as a reducing agent. The optimization of the experimental variables (AgNO3 and NaBH4) for the formation of the nanoparticles was carried out using different volumes of these solutions. Spectrophotometric measurements at 393 nm were performed showing a linear working range between 0.0500-0.167 mg L-1 lead (r = 0.994), with LOD and LOQ of 0.0135 and 0.0451 mg L-1 , respectively. The proposed method provided sensitive detection for lead in honey samples. In the third step, the combination in the same analysis of multiple quantum dots of CdTe-MPA, each with a particular ability to interact with the analyte, ensured a multi-point detection that was not only explored for more accurate discrimination of the analyte, but also for the simultaneous discrimination of multiple mutually interfering species in the same sample. Principal component analysis (PCA) and partial least squares regression (PLS) were used for analysis of fluorescence data. Two different quantum dots of CdTe-MPA were tested, emitting different wavelengths: 549/566, 549/634 and 566/634 nm and the results showed that the developed approach is capable of solving binary and ternary Pb mixtures (II) and Cu (II), providing accurate information on the concentration of Pb (II) and Hg (II) and signaling the occurrence of Cu (II). Another method of colorimetric detection based on the analysis of digital images using the RGB color system (Red - Green - Blue), obtained after the reaction between gold nanoparticles and melamine, was developed for the determination of the contaminant melamine in milk. The unmodified gold nanoparticles were synthesized using sodium citrate dihydrate as a reducing agent. The optimization of the RGB channels to obtain the best results of effective intensity was performed using GIMP software 2.8. The gold nanoparticles had a mean diameter of 23.0 ± 2.2 nm. The effective intensity measurements were obtained with blue channel and presented linearity in the range of 0.100 to 0.275 mg L-1 of melamine (r = 0.998), with LOD and LOQ of 0.013 and 0.043 mg L-1 , respectively. The proposed method presented sensitivity for the determination of melamine in milk when compared to other works found in the literature.
In this work, development and optimization of methods were proposed using metallic nanoparticles in order to increase the sensitivity of these methods and detect contaminants / adulterants in complex food matrices such as milk and honey. In a first step, a colorimetric detection method based on silver nanoparticles was developed for the determination of melamine in milk. Silver nanoparticles were synthesized without the use of any stabilizing agent, using sodium borohydride as a reducing agent. The optimization of experimental variables for nanoparticle formation was performed using factorial design, resulting in stable colloidal silver nanoparticles with a mean diameter of 14.0 ± 2.7 nm. The spectrophotometric measurements performed at 475 nm showed a linear range of 0.033-1.50 mg L-1 melamine (r = 0.999), with detection limits (LOD) and quantification (LOQ) of 0.009 and 0.031 mg L-1 , respectively. The proposed method provided sensitive detection and quantification of melamine in milk. In a second step, a sensitive, rapid and robust method based on the use of stabilizerfree silver nanoparticles was developed for the detection and quantification of lead in honey samples. Silver nanoparticles were synthesized without the use of any stabilizer, using silver nitrate and sodium borohydride as precursors; the latter as a reducing agent. The optimization of the experimental variables (AgNO3 and NaBH4) for the formation of the nanoparticles was carried out using different volumes of these solutions. Spectrophotometric measurements at 393 nm were performed showing a linear working range between 0.0500-0.167 mg L-1 lead (r = 0.994), with LOD and LOQ of 0.0135 and 0.0451 mg L-1 , respectively. The proposed method provided sensitive detection for lead in honey samples. In the third step, the combination in the same analysis of multiple quantum dots of CdTe-MPA, each with a particular ability to interact with the analyte, ensured a multi-point detection that was not only explored for more accurate discrimination of the analyte, but also for the simultaneous discrimination of multiple mutually interfering species in the same sample. Principal component analysis (PCA) and partial least squares regression (PLS) were used for analysis of fluorescence data. Two different quantum dots of CdTe-MPA were tested, emitting different wavelengths: 549/566, 549/634 and 566/634 nm and the results showed that the developed approach is capable of solving binary and ternary Pb mixtures (II) and Cu (II), providing accurate information on the concentration of Pb (II) and Hg (II) and signaling the occurrence of Cu (II). Another method of colorimetric detection based on the analysis of digital images using the RGB color system (Red - Green - Blue), obtained after the reaction between gold nanoparticles and melamine, was developed for the determination of the contaminant melamine in milk. The unmodified gold nanoparticles were synthesized using sodium citrate dihydrate as a reducing agent. The optimization of the RGB channels to obtain the best results of effective intensity was performed using GIMP software 2.8. The gold nanoparticles had a mean diameter of 23.0 ± 2.2 nm. The effective intensity measurements were obtained with blue channel and presented linearity in the range of 0.100 to 0.275 mg L-1 of melamine (r = 0.998), with LOD and LOQ of 0.013 and 0.043 mg L-1 , respectively. The proposed method presented sensitivity for the determination of melamine in milk when compared to other works found in the literature.
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Palavras-chave
Melamina, Mel, Metais pesados, Colorimetria, Imagem digital, Fluorescência, Quimiometria de multiplexagem, Silver nanoparticles, Gold nanoparticles, CdTe - quantum dots, Melamine, Honey, Heavy metals, Colorimetry, Digital imaging, Fluorescence, Chemometrics multiplexing