Foodborne illnesses are a growing concern for the food industry and consumers, with millions of cases reported every year. Consequently, there is a critical need to develop rapid, sensitive, and inexpensive techniques for pathogen detection in order to mitigate this problem. However, current pathogen detection strategies mainly include time-consuming laboratory methods and highly trained personnel. Electrochemical in-field biosensors offer a rapid, low-cost alternative to laboratory techniques, but the electrodes used in these biosensors require expensive nanomaterials to increase their sensitivity, such as noble metals (e.g., platinum, gold) or carbon nanomaterials (e.g., carbon nanotubes, or graphene). Herein, we report the fabrication of a highly sensitive and label-free laser-induced graphene (LIG) electrode that is subsequently functionalized with antibodies to electrochemically quantify the foodborne pathogen Salmonella enterica serovar Typhimurium. The LIG electrodes were produced by laser induction on polyimide film in ambient conditions, and hence circumvent the need for hightemperature, vacuum environment, and metal seed catalysts commonly associated with graphene-based electrodes fabricated via chemical vapor deposition processes. After functionalization with Salmonella-antibodies, the LIG biosensors were able to detect live Salmonella in chicken broth across a wide linear range (25 to 10 5 CFU mL -1 ) and with a low detection limit (13 ± 7 CFU mL -1 ; n = 3, mean ± standard deviation). These results were acquired with an average response time of 22 minutes without the need for sample preconcentration or redox labeling techniques. Moreover, these LIG immunosensors displayed high selectivity as demonstrated by non-significant response to other bacteria strains. These results demonstrate how LIG-based electrodes can be used for electrochemical immunosensing in general and, more specifically, could be used as a viable option for rapid, low-cost pathogen detection in food processing facilities before contaminated foods reach the consumer.

A corrente de pico de redução do derivativo N-nitroso do herbicida glifosato foi otimizada por planejamentos experimentais, para sua determinação. As variáveis envolvidas na otimização da voltametria de onda quadrada (SWV) foram: incremento de voltagem, amplitude, freqüência, concentração do eletrólito de suporte e a área da gota de mercúrio. Um planejamento fatorial completo 2 5 foi usado para avaliar os efeitos das variáveis. Dos resultados obtidos foram escolhidos três dos fatores mais importantes. Estas variáveis foram estudadas com o planejamento composto central. As condições que proporcionaram a melhor resposta voltamétrica foram: 0,025 volt, 0,125 volt, 70 Hz, 1,25 mol L -1 e 0,60 mm 2 para o incremento de voltagem, amplitude, freqüência, concentração do eletrólito e área da gota de mercúrio, respectivamente. Nestas condições a faixa operacional foi de 0,050 a 100,0 µg mL -1 , os limites de detecção e quantificação foram de 0,025 e 0,080 µg mL -1 , respectivamente.The reduction peak current of the derivative N-nitroso of glyphosate herbicide was optimized by experimental design for their determination. The variables involved in the optimization of the square wave voltammetry (SWV) were: voltage step, amplitude, frequency, concentration of the supporting electrolyte and the area of the mercury drop electrode. A complete 2 5 factorial design was used to evaluate the effects of the variables. From the results obtained by the factorial design was set the three more important factors. These variables were evaluated with a central composite design. The conditions that proportionate the best voltammetric response were: 0.025 volt, 0.125 volt, 70 Hz, 1.25 mol L -1 e 0.60 mm 2 for step voltage, amplitude, frequency, electrolyte concentration and area of the mercury drop, respectively. In these conditions the operational range was from 0.050 up to 100.0 µg mL -1 , the detection and quantification limits were 0.025 and 0.080 µg mL -1 , respectively.

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This paper reports the development and application of a low-cost multifunctional webcam spectrophotometer for the conduct of molecular absorption and fluorometric measurements. The equipment, which costs approximately US$20 to be fabricated, consists of a webcam, a diffraction grating, and a slit, all positioned inside an MDF box. Spectral measurements were carried out using the multifunctional equipment with the aid of a free software. The equipment was found to be suitable for conducting qualitative and quantitative analyses of fluorescence, absorption, and emission spectra and for analytical determinations in the spectral range of 380.00 to 1000.00 nm with 0.8 nm resolution. By simply changing the light radiation source, the equipment allowed us to determine the thermodynamic equilibrium constant of Alizarin Red S (1,2-dihydroxyanthraquinone-3-sodium sulfonate) and to obtain the fluorescence spectra of chlorophyll and anthocyanins (two natural pigments). The multifunctional spectrophotometer allows one to perform real-time spectral analysis, offers an easy and fast calibration process as an alternative to the commonly applied calibration approach by the diffraction grid equation, and does not require the use of lenses for beam collimation since the webcam lens itself performs this function. The equipment was successfully applied in experiments conducted by a class of 30 students from high school in a science fair to aid them in learning chemistry.

RESUMOEm ra zã o das po uc as de in fo rm aç õe s existente na literatura, sobre a mobilidade do glyph os at e e do ima zap yr, em so lo s de ba ixa at iv id ad e, co mu m em pa ís es tr op ic ai s, fo i conduzido, em laboratório, um estudo sobre a mob ili dad e ver tic al des ses her bic ida s em doi s sol os com dif ere nte s comp osi çõe s quí mic as e fi si ca s. Para es tu dar es sa mobi li dade, fo ra m utilizadas colunas de solo com diferentes alturas, as quais, após aplicação dos produtos na dose com erc ial de 4 L ha -1 , for am sub metida s a um regime hídri co de 40 mm h -1 , por um perío do de 4 h. As análises dos resíduos nas diferentes pr of un di da de s fo ra m fe it as ut il iz an do -se os métodos voltamétrico (polarografia) e HPLC, para o glyphosate e imazap yr, respe ctivame nte. Com base nos resultados, foi possíve l conclui r que: a) os métodos voltamétrico, para o glyphosate, e HPLC, para o imazapyr, são adequados para os es tu do s de id en ti fi ca çã o e qu an ti fi ca çã o de res ídu os em ág ua e so lo; b) os limi tes de quantificação dos resíduos foram de 0,4 µg mL -1 e 5 µg L -1 para o glyphosate e o imazapyr, respectivamente; c) a taxa de recuperação do glypho sate, nas amostr as de solo (76 e 78% para os solos de Viçosa e Sabará, respectivamente) foi menor que na amostra de água (83%); d) a taxa de recup era ção do ima zap yr, em águ a e sol o, foi próxima de 100%; e) a lixi viaçã o do glyph osate no s so lo s fo i mu it o ba ix a; e f) o im az ap yr apr ese nto u alt a lix ivi açã o, porém dif ere nci ada entre os solos estudados, sendo essa maior no solo de tex tur a fra nco -are nosa de Viç osa que no de argila de Sabará.Palavras chave: Herbicidas, voltametria, polarografia, cromatografia, HPLC. ABSTRACT Glyphosate and imazapyr leaching in soils with different textures and chemical compositio n. II. Analytical methodDue to the scarce information available in the lit eratu re on the glyph osa te and ima zap yr mobility in low activity soils, which is common in the tropical countries, a laboratory study was co nd uc te d on th e ve rt ic al mo bi li ty of th es e herbicides in two soils with different physical and ch em ic al co mp os it io ns . Fo r st ud yi ng th is mobility, the soil columns with different heights were submitt ed to a water flux of 40 mm h -1 over a 4 h period after the product applications in a co mmer ci al d os ag e of 4 L ha -1 . Th e re si du e analyses at different depths were realized by the voltametric (polar ographic) and HPLC method s for glyphosate and imazapyr respect ively. Based on the re su lts it wa s po ss ib le to co nc lud e tha t: a) the vol tam etr ic met hod for gly pho sat e and the HPL C for ima zap yr are bot h ade qua te f o r s t u d y i n g t h e i d e n t i f i c a t i o n a n d qua nti fic ati on of res idu es in wat er and soi l; b) the boundaries of residue quantification were 1 Recebido para publicação em 28/05/1998 e na forma revisada em 13/11/1998.

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Forty two samples of black soils were collected from superficial horizons of the High Altitude Rocky Complex (HARC) that is situated on top of the most prominent mountain ranges of eastern Brazil. Our objective was to characterize the humic acids extracted from these pedoenvironments and evaluate the effect of natural paleo-fires on thermogravimetric properties, elemental composition, visible and infrared absorption of humic acids (HA). The high thermostability, low H:C ratio, and abundance in carboxylic groups, suggest that the HARC black soil HA present larger biostability and reactivity. The molecular characteristics indicated that HARC black soil HAs have a great contribution of transformed charred vegetable residues on its origin. This persistence and reactivity of black soil HA explain the capacity of these soils to maintain their cation exchange capacity, since the soil clay fraction is composed predominantly by low activity minerals. D 2004 Published by Elsevier B.V.

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