Ni(II)NTA AuNPs as a low-resource malarial diagnostic platform for the rapid colorimetric detection of Plasmodium falciparum Histidine-Rich Protein-2

Abstract

Diagnosing infectious diseases remains a challenge in the developing world where there is a lack of dependable electricity, running water, and skilled technicians. Although rapid immunochromatographic tests (RDTs) have been deployed to diagnose diseases such as malaria, the extreme climate conditions encountered in these regions compounded with the discrepancies in test manufacturing have yielded varying results, so that more innovative and robust technologies are sought. Devoid of antibodies and thermally sensitive materials, we present a robust, colorimetric diagnostic platform for the detection of a malarial biomarker, Plasmodium falciparum Histidine-Rich Protein 2 (PfHRP-II). The assay exploits the optical properties of gold nanoparticles, covalently coupling them to a Ni(II)NTA recognition element specific for PfHRP-II. In the presence of the recombinant malarial biomarker (rcHRP-II), the Ni(II)NTA AuNPs begin to crosslink and aggregate in as little as one minute, triggering a red-to-purple color change in solution. To increase assay sensitivity and platform stability suitable for low-resource regions, the Ni(II)NTA AuNPs were assembled with varying spacer ligands in a mixed monolayer presentation. When assembled with a negatively charged Peg4-thiol ligand, the Ni(II)NTA AuNPs demonstrate low nanomolar limits of rcHRP-II detection in physiological concentrations of human serum albumin and maintain excellent stability at 37°C when stored for four weeks. Detection of the malaria biomarker is also measured by capturing and processing images of aggregated gold nanoparticles with a smartphone camera. By utilizing a smartphone camera and image processing application, there is no significant difference in assay sensitivity and rcHRP-II limit of detection in comparison to a spectrophotometer, further making this diagnostic platform applicable for use in low-resource regions.

Mobile phone imaging and cloud-based analysis for standardized malaria detection and reporting

“…They provide the test interface required for analysis and also have demonstrated reporting capabilities, for example: monitoring travel patterns for epidemiological studies 20 21 and for improved case detection and management 22 . Laboratory-based tests that utilize a mobile phone camera have been developed to image colorimetric assays in a 96-well plate 23 , and to connect mobile phones to conventional microscopes and transmit images of blood films 24 . In an effort to move away from the requirement of an equipped laboratory, optical systems that transform a mobile phone camera into a stand-alone microscope for the diagnosis of global health diseases have been developed 25 26 .…”

Development of Electrochemical Impedance Spectroscopy Based Malaria Aptasensor Using HRP‐II as Target Biomarker

“…Our underlying motivation for substituting antibody with other recognition elements in the sensor platforms for malaria detection has already been explained elsewhere. An optical sensor developed by us for detecting HRP‐II following a chemical principle was an impressive feat from the point of sensitivity . However, when the diagnosis warrants high specificity and sensitivity of the sensors for the cases like, asymptotic malaria, the biological recognition elements are widely recognized as superior candidates.…”

“…The developed aptasensor was found to be suitable for an impedimetric measurement of signal generated from its binding with the target HRP‐II protein as no additional label is essential for this electrochemical technique. Notably, EIS is known as highly sensitive signal transduction technique that has already been validated for aptamer based detection of other protein–based antigens . The Faradic impedance technique we used here could detect HRP‐II down to a picomolar level which can detect asymptomatic malaria patients.…”

Gold Nanoparticles for Diagnostics: Advances towards Points of Care

“…[117], which is of extreme relevance for epidemiological data gathered in isolate populations of remote areas in developing countries [118,119]. Tests for the detection of heavy metals, malaria, tuberculosis and for the quantification of vitamins (such as B 12 and D) and glucose have been reported by taking advantage of approaches relying on smartphones [61,117,119,120,121,122,123]. …”