Rapid diagnostic tests, such as lateral flow immunoassays may enable diagnostics in resource poor areas, thus improving health outcomes by helping to control and eliminate infectious diseases. This thesis focuses on the development of sensitive tools for the rapid diagnosis of three infectious diseases prevalent in resource poor areas: hepatitis C, pertussis and malaria. For malaria and hepatitis C, rapid diagnostic tests with improved sensitivity could help in ongoing efforts to eliminate the diseases. For pertussis (whooping cough), a field-usable rapid serodiagnostic test would help in disease surveillance and control.

New methods to enhance the sensitivity of lateral flow immunoassays include preconcentrating the sample before the immunoassay takes place, controlling the flow of reagents in the lateral flow strip to allow more complex assays and using high-sensitivity luminescent instrument-read labels. All the above methods involve trade-offs between the sensitivity, complexity, and affordability of the test.

In publication I of this thesis, immunoassays for anti-HCV antibodies were developed using a single multiepitope protein antigen and a luminescent europium-chelate label. In II and III, quantitative lateral flow immunoassays utilizing luminescent europium nanoparticle labels were developed and assessed. The results obtained with patient samples using the lateral flow immunoassay for anti-pertussis antibodies (II) correlated well with a traditional enzyme immunoassay. In IV, an higly sensitive lateral flow immunoassay utilizing up-converting nanophosphor labels was developed for Plasmodium falciparum infection i.e. malaria, and the test performance was evaluated with P. falciparum culture samples. The analytical sensitivity of P. falciparum detection was improved up to 250-fold as compared to a standard lateral flow test.

The results of the publications included in this thesis show that the use of intrumentread luminescent labels in rapid lateral flow immunoassays allows the development of highly sensitive and quantitative point-of-care tests, which could be used in-resource poor areas. Particularly, an ultrasensitive test for the detection of P. falciparum could detect asymptomatic carriers of the malaria parasite and thus support malaria elimination efforts.