Malaria is a disease caused by Plasmodium parasite and transmitted by adult female Anopheles mosquitoes. Malaria affects approximately 50% of the world’s population causing millions of deaths every year. Mostly affected are pregnant women and children under 5 years of age. Despite control efforts the disease continues to affect productivity. This can be minimised by early detection of the disease. Methods for malaria detection include blood film microscopy, immunochromatographic, serological and molecular tests. Blood film microscopy shows the highest sensitivity and specificity when used by trained personnel with reliable instruments. It is however time-consuming and cannot be applied as a point -of-care diagnostic method. Therefore, a simple, fast and reliable method of detection such as biosensors is needed.
Two electrochemical biosensors (immunosensors) for malaria biomarkers Plasmodium falciparum histidine rich protein 2 (PfHRP 2) and parasite L-Lactate dehydrogenase (LDH) were developed for the detection and quantification of Plasmodium species. The methods were based on screen-printed gold electrodes (SPGEs) and sandwich assay comprising a ‘capture antibody’ immobilised on the SPGEs and a detector monoclonal antibody conjugated to the enzyme HRP for signal generation. Enhancement of the sandwich assays by the use of gold nanoparticles (AuNP) was also investigated.
The biosensors developed for PfHRP 2 can detect sub-microscopic Plasmodium infection with a limit of detection (LOD) as low as 2.14 ng mL-1 and 2.95 ng mL-1 in buffer and serum assays respectively. When AuNPs were used to enhance the assays, the LODs were lowered to 36 pg mL-1 and 40 pg mL-1. Lactate dehydrogenase (LDH) showed LODs of 1.80 ng mL-1 and 0.70 ng mL-1 in buffer and serum assays. By using AuNP, the LODs were lowered to 19 pg mL-1 and 23 pg mL-1. Further investigation will look at possible use of graphene SPEs (Rashid Solutions, UK) to replace gold based SPEs for sensor performance.
