Magnetic Nanoclusters Increase the Sensitivity of Lateral Flow Immunoassays for Protein Detection: Application to Pneumolysin as a Biomarker for Streptococcus pneumoniae

Abstract

Lateral flow immunoassays for detecting biomarkers in body fluids are simple, quick, inexpensive point-of-care tests widely used in disease surveillance, such as during the coronavirus disease 2019 (COVID-19) pandemic. Improvements in sensitivity would increase their utility in healthcare, food safety, and environmental control. Recently, biofunctional magnetic nanoclusters have been used to selectively label target proteins, which allows their detection and quantification with a magneto-inductive sensor. This type of detector is easily integrated with the lateral flow immunoassay format. Pneumolysin is a cholesterol-dependent cytolysin and one of the most important protein virulence factors of pneumonia produced by Streptococcus pneumoniae. It is recognized as an important biomarker for diagnosis in urine samples. Pneumonia is the infectious disease that causes the most deaths globally, especially among children under five years and adults over 65 years, most of them in low- and middle-income countries. There especially, a rapid diagnostic urine test for pneumococcal pneumonia with high sensitivity and specificity would be helpful in primary care. In this work, a lateral flow immunoassay with magnetic nanoclusters conjugated to anti-pneumolysin antibodies was combined with two strategies to increase the technique’s performance. First, magnetic concentration of the protein before the immunoassay was followed by quantification by means of a mobile telephone camera, and the inductive sensor resulted in detection limits as low as 0.57 ng (telephone camera) and 0.24 ng (inductive sensor) of pneumolysin per milliliter. Second, magnetic relocation of the particles within the test strip after the immunoassay was completed increased the detected signal by 20%. Such results obtained with portable devices are promising when compared to non-portable conventional pneumolysin detection techniques such as enzyme-linked immunosorbent assays. The combination and optimization of these approaches would have excellent application in point-of-care biodetection to reduce antibiotic misuse, hospitalizations, and deaths from community-acquired pneumonia.

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“…147,148 Biofunctional magnetic nanoclusters have been used for selective labelling of target proteins, which permits their detection and quantication using a magnetically induced sensor. 147,[149][150][151] Ojodomo J. Achadu et al developed a novel magnetic/plasmonic-assisted uoro-immunoassay system for inuenza virus detection (Fig. 11c), 144 using magnetic-derivatized plasmonic molybdenum trioxide quantum dots (MP-MoO 3 QDs) as the plasmonic/magnetic agent and uorescent graphitic carbon nitride quantum dots (gCNQDs) as the monitoring agent.…”

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“…Their extensive adoption in POC development is a direct result of their low cost, ease of use, quicker results and simple interpretation. Applications of LFDs include heart disease [ 102 ], monitoring food toxins [ 103 ], food poisoning [ 104 , 105 ], bacterial infection [ 106 ], viral infection [ 107 , 108 ] and many more.…”

Fluorescent and electrochemical detection of nuclease activity associated with Streptococcus pneumoniae using specific oligonucleotide probes

“…8 Consequently, there is an urgent need to develop rapid and precise approaches to identify S. pneumoniae. 12–14 In recent decades, several non-culture methods have emerged as alternatives for detecting S. pneumoniae , such as mass spectrometry, 15,16 immunoassay, 17,18 and PCR-based assays. 19,20 These methods offer significant time saving compared to traditional culture-based approaches.…”

“…pneumoniae, such as mass spectrometry, 15,16 immunoassay, 17,18 and PCR-based assays. 19,20 These methods offer significant time saving compared to traditional culturebased approaches.…”