Abstract
BackgroundEarly malaria diagnosis and its profiling require the development of new sensing platforms enabling rapid and early analysis of parasites in blood or saliva, aside the widespread rapid diagnostic tests (RDTs).MethodsThis study shows the performance of a cost-effective optical fiber-based solution to target the presence of Plasmodium falciparum histidine-rich protein 2 (PfHRP2). Unclad multimode optical fiber probes are coated with a thin gold film to excite Surface Plasmon Resonance (SPR) yielding high sensitivity to bio-interactions between targets and bioreceptors grafted on the metal surface.ResultsTheir performances are presented in laboratory conditions using PBS spiked with growing concentrations of purified target proteins and within in vitro cultures. Two probe configurations are studied through label-free detection and amplification using secondary antibodies to show the possibility to lower the intrisic limit of detection.ConclusionsAs malaria hits millions of people worldwide, the improvement and multiplexing of this optical fiber technique can be of great interest, especially for a future purpose of using multiple receptors on the fiber surface or several coated-nanoparticles as amplifiers.
Highlights
Malaria diagnosis and its profiling require the development of new sensing platforms enabling rapid and early analysis of parasites in blood or saliva, aside the widespread rapid diagnostic tests (RDTs)
They target histidine-rich protein 2 (PfHRP2) proteins using monoclonal antibodies, as HRP2 is present in abundance during the asexual cycle and in early gametocyte stages of P. falciparum parasites [5, 6]
These probes have already proven their high potential for biomarkers detection in very different media, especially inside human tissues [24, 25] and body fluids [26, 27] among others [28, 29]. In this evolution to develop and evaluate new molecular detection techniques for malaria, the behaviour of our sensors is studied in different conditions to test their response and sensitivity against pfHRP2 biomarkers. This original experimental study on Plasmodium falciparum cultures could open the door towards the integration of these optical fiber (OF) probes into smaller biochips or bio-sticks connected to smartphone or designed microfluidic packages
Summary
Materials Phosphate Buffer Saline (PBS) came from Thermo Fisher Scientific (Waltham, MA, USA). 6-mercapto-1-hexanol was purchased from Sigma-Aldrich (Merck, Darmstadt, Germany). OFs were immersed during 16 h in closed chambers of mercaptoundecanoic acid 2 mM in absolute ethanol at room temperature (RT) They were washed in absolute ethanol and placed into 125 μL vials of 50 mM WSC and 50 mM NHS in activation buffer during 10 min at RT. They were washed with PBS and immersed during 1h30 in anti-PfHRP2 antibodies. Cultures were left to sediment for 90 min in the incubator. After this period, the supernatant was taken up without disturbing the red blood cell layer. Were diluted 1:1000 using culture medium or control blood and incubated on the microtitre plate in triplicates following the supplier recommendations
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