title: On-particle detection of Plasmodium falciparum histidine-rich protein II by a "switch-on" iridium(III) probe.
abstract: The need for robust reagents for biomarker detection has become an increasing necessity in designing point-of-care diagnostics. We report a non-emissive, cyclometalated iridium(III) complex, Ir(ppy)2(H2O)2(+) (Ir1), which, on coordination to a histidine-containing protein bound to the surface of a magnetic particle, elicits a rapid, long-lived phosphorescent signal. The interactions between Ir1 and numerous other amino acids were examined for activity, but only the addition of histidine resulted in a four orders of magnitude enhancement in signal intensity. Buffer conditions (pH and temperature) and composition (coordinating vs. non-coordinating and ionic strength) were optimized to achieve maximum signal and stability of Ir1. The activity of the probe under optimized conditions was validated with BNT-II, a histidine-containing branched peptide mimic of the malarial biomarker Plasmodium falciparum histidine-rich protein II (PfHRPII). By comparing Ir1 binding to BNT-II versus L-histidine, steric and quenching effects were noted in the peptide. Despite these deviations from ideal conditions, signal response reached saturation with both BNT-II and recombinant HRPII (rcHRPII). When immobilized on the surface of a 50 μM magnetic agarose particles, the limit of detection of rcHRPII was 14.5 nM. The robust signal response of this inorganic probe lends itself to future applications in on-particle enzyme-linked immunosorbent assay (ELISA)-based assays.
authors.affiliation: Department of Chemistry, Vanderbilt University, Nashville, TN 37235, USA.
authors.forename: Keersten M
authors.initials: KM
authors.lastname: Davis
authors.forename: Anna L
authors.initials: AL
authors.lastname: Bitting
authors.forename: David W
authors.initials: DW
authors.lastname: Wright
mesh_terms: D015415:Biomarkers / Q000032:analysis; D056831:Coordination Complexes / Q000138:chemical synthesis / Q000737:chemistry; D004797:Enzyme-Linked Immunosorbent Assay; D006863:Hydrogen-Ion Concentration; D007495:Iridium / Q000737:chemistry*; D008280:Magnetics; D009994:Osmolar Concentration; D010963:Plasmodium falciparum / Q000378:metabolism*; D011506:Proteins / Q000032:analysis* / Q000235:genetics / Q000378:metabolism; D015800:Protozoan Proteins / Q000032:analysis* / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000032:analysis / Q000235:genetics / Q000378:metabolism; D013696:Temperature; D000099053:Histidine-Rich Glycoprotein
chemical_list: D015415:Biomarkers; D056831:Coordination Complexes; D011506:Proteins; D015800:Protozoan Proteins; D011994:Recombinant Proteins; D000099053:Histidine-Rich Glycoprotein; D007495:Iridium
keywords: Detection; ELISA; Histidine-rich protein; Luminescent probe; Magnetic separation