A B S T R A C TThis review addresses recent advances in the development of screen-printed electrode based biosensors modified with different nanomaterials such as carbon nanotubes, graphene, metallic nanoparticles as gold, silver and magnetic nanoparticles, and mediator nanoparticles (Prussian Blue, Cobalt Phthalocyanine, etc.), coupled with biological recognition elements such as enzymes, antibodies, DNA and aptamers to obtain probes with improved analytical features. Examples of clinical applications are illustrated, together with examples of paper-based electrochemical devices, of multiple detections using arrays of screen printed electrodes, and of the most recent developments in the field of wearable biosensors. Also the use of smartphones as final detectors is briefly depicted.

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The use of 3,3A,5,5A-tetramethylbenzidine (TMB) as an electrochemical substrate for horseradish peroxidase (HRP) was investigated. HRP activity has been detected using flow injection analysis at a glassy carbon working electrode polarised at +100 mV versus Ag/AgCl in 0.1 mol l 21 citrate-phosphate buffer (pH 5.0). The optimum concentrations were 2 3 10 24 mol l 21 TMB and 10 23 mol l 21 H 2 O 2 . The detection limit obtained after 15 min of incubation was 8.5 3 10 214 mol l 21 HRP with the amperometric method. This limit was lower than that obtained using hydroquinone as HRP substrate and comparable to that with the p-aminophenyl phosphate-alkaline phosphatase system. Better performance was achieved with amperometric than spectrophotometric detection using TMB in a competitive ELISA for rabbit immunoglobulin G as a model analyte.

Platinum electrodes modified with a cellulose acetate membrane or with poly(1,8-diaminonaphthalene) film were assembled and used for rapid amperometric detection of nitrites and nitrates in water by batch and flow injection analysis.Parameters such as the permeability of the electropolymerised films to nitrites and nitrates, interference effects and recovery studies of these kinds of sensors have been optimised to demonstrate the analytical suitability of the proposed method.Contrary to the standard colorimetric method, which is based on carcinogenic reagents, the amperometric detection of nitrites and nitrates is very simple and rapid and does not require any reagent for nitrite detection. Also, this method could be extended easily to the analysis of nitrites and nitrates in various types of samples such as food, soils, vegetables and fertilisers.

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Salmonella has represented the most common and primary cause of food poisoning in many countries for at least over 100 years. Its detection is still primarily based on traditional microbiological culture methods which are labor-intensive, extremely time consuming, and not suitable for testing a large number of samples. Accordingly, great efforts to develop rapid, sensitive and specific methods, easy to use, and suitable for multi-sample analysis, have been made and continue. Biosensor-based technology has all the potentialities to meet these requirements. In this paper, we review the features of the electrochemical immunosensors, genosensors, aptasensors and phagosensors developed in the last five years for Salmonella detection, focusing on the critical aspects of their application in food analysis.

An electrochemical enzyme-linked immunosorbent assay (ELISA) coupled with flow injection analysis (ELISA-FIA) and a PCR-based method using ST11 and ST15 primers for detecting salmonellae in meat were evaluated in comparison with the International Organization for Standardization (ISO) culture method. The methods were applied to experimentally contaminated and naturally contaminated meat samples. The results showed that both ELISA-FIA and PCR allowed detection of salmonella in a product contaminated with a low number of the microorganisms (1 to 10 salmonellae/25 g) after only 5 h of incubation of preenrichment broth, and they were just as effective as the ISO method.The incidence of foodborne infection by Salmonella continues to be an important problem in the United States (16) and in the European Community (4, 16).Raw and undercooked meat, eggs, milk, and especially poultry are the most commonly implicated vehicles of Salmonella spp. infection (10,15,16,20,24). For foods to be considered "salmonella free," European legislation requires that from 1 to 25 g be tested, depending on the type of food. The standard culture method (ISO 6579/2002) for detection of salmonella in food is rather sensitive and quite inexpensive, but it requires 4 to 5 days to generate results.Given that efforts to prevent salmonellosis must be applied at all phases of the food production chain, based on the Hazard Analysis Critical Control Point (HACCP) system (23), the methods for detecting salmonella need to be more rapid than the ISO method. To this end, new technologies have been used to develop rapid methods. Specifically, a number of antibodyantigen-based methods have been developed to detect Salmonella spp. or specific serotypes in a variety of food (3,8,13,18,21,25). Other authors developed immunoelectrochemical assays or piezoelectric flow injection analysis (FIA) biosensors to detect Salmonella enterica serotype Typhimurium (2, 7, 26). However, although these biosensors have the potential to provide direct label-free detection of bacteria, these piezoelectric FIA systems have a low level of sensitivity, and neither has been applied to food samples.Methods based on PCR for the detection of salmonella in food have also been developed (12,17,19).All of the above methods require that a preenrichment step be performed (5,9,14,18,22).The objective of the present study was to evaluate two rapid techniques for detection of salmonella: an electrochemical enzyme-linked immunosorbent assay (ELISA) coupled with FIA (ELISA-FIA) (6) and a PCR method using ST11 and ST15 primers (1).The experiments were first performed with experimentally contaminated samples to reduce and optimize the preenrichment times; the two methods were then applied to naturally contaminated meat samples, and the results were compared to those obtained with the International Organization for Standardization (ISO) method. MATERIALS AND METHODSThe experiments were performed on the following: (i) experimentally contaminated meat samples, to establish the minimum preenrichment...

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