Colleen Loynachan1 Michael Thomas1 Eleanor Gray2 Daniel Richards1 Vijay Chudasama2 Rachel McKendry2 Molly Stevens1

1, Imperial College London, London, , United Kingdom
2, University College London, London, , United Kingdom

Paper-based lateral flow immunoassays (LFIAs) are one of the most widely used point-of-care (PoC) devices. However, their application in early disease diagnostics is often limited due to insufficient sensitivity for the requisite sample sizes and the short time frames of PoC testing.1 To address this, we developed a serum-stable, nanoparticle catalyst-labeled LFIA with sensitivity surpassing that of both current commercial and published sensitivities for paper-based detection of p24, one of the earliest and most conserved biomarkers of HIV.2

Due to their high catalytic efficiency and extraordinary stability in harsh environments, such as high temperature and extreme pH, mixed noble-metal catalytic nanoparticles have emerged as promising materials for signal amplification in colorimetric immunoassays.3 We report the synthesis and characterization of peroxidase-mimicking porous platinum core-shell nanocatalysts (PtNCs), which retain high catalytic activity when exposed to complex human blood serum samples. We explored the application of antibody functionalized PtNCs with strategically and orthogonally modified nanobodies with high affinity and specificity toward p24, and establish the key larger nanoparticle size regimes needed for efficient amplification and performance in LFIA. Harnessing the catalytic amplification of PtNCs to generate an intensely colored product at the test line enabled naked-eye detection of p24 spiked into sera in the low femtomolar range (ca. 0.8 pg/mL).

The PtNC-labeled LFIA exhibits a dual dynamic range spanning over four orders of magnitude, which arises from both the inherent coloration of the nanomaterials and their catalytic ability. The 100-fold signal amplification provided by the PtNCs allowed for the detection of acute phase HIV in clinical human plasma samples in under 20 minutes. This provides a versatile absorbance-based and rapid LFIA with sensitivity capable of significantly reducing the HIV acute phase detection window. This diagnostic may be readily adapted for detection of other biomolecules; as an ultrasensitive screening tool for infectious and non-communicable diseases, and can be capitalized upon in PoC settings for early disease detection.

1. Howes, P. D., Chandrawati, R. & Stevens, M. M. Colloidal nanoparticles as advanced biolgical sensors. Science 346, 1247390-1-1247390–10 (2014).
2. Loynachan, C. N., Thomas, M. R. et al. Platinum Nanocatalyst Amplification: Redefining the Gold Standard for Lateral Flow Immunoassays with Ultrabroad Dynamic Range. ACS Nano (2017). doi:10.1021/acsnano.7b06229
3. Xia, X. et al. Pd-Ir Core-Shell Nanocubes: A Type of Highly Efficient and Versatile Peroxidase Mimic. ACS Nano 9, 9994–10004 (2015).