The development of end-user orientated tools for the detection of major food contaminants including pesticides, mycotoxins, pathogens, allergens, antibiotics and aquatic toxins is discussed in this thesis. Special attention is given to smartphone-based devices (SBDs), which have the potential to create a paradigm shift in food contaminant sensing, and the developing of such tools for the detection of a regulated marine toxin (domoic acid) in shellfish. This target is chosen since shellfish are produced in remote locations and toxin occurrence is increasing due to climate change. The first two chapters of the thesis critically analyse the state-of-the-art in screening and confirmatory methods, EU food safety legislation and the current research efforts in SBD development. In the third chapter an online biosensor database for food contaminant analyses is described and used to identify critical technology gaps. In chapter 4-7 experimental research is conducted which aims to contribute to further developing the most interesting technology identified in the previous chapters. In chapter four an immunoassay based on plasmonic coupling of nanoparticles for the detection of domoic acid was conducted. In chapter five and six the potential of smartphone based image analyses of colorimetric assays was thoroughly assessed. In chapter seven an electrochemical immunoassay was developed for domoic acid detection in shellfish. Here the focus was on the performance of screen printed electrodes that were modified with various materials. Finally, in chapter eight, a synopsis of the thesis is given. The work reported in this thesis critically analysed the potential of smartphones for point-of-site sensing and contributes to the development of this intriguing field.