Smartphone-based lateral flow immunoassay for sensitive determination of lactate dehydrogenase at the point of care.

Lactate dehydrogenase (LDH), a prevalent enzyme involved in anaerobic glycolysis, is released into body fluids following cell damage and has long been a general marker of tissue injury. However, due to its lack of selectivity and the advent of more accurate biomarkers, the clinical utility of LDH has been largely limited to confirming hemolysis. LDH has been recognized as a valuable prognostic biomarker for various cancers, making its monitoring crucial during cancer management. Traditional LDH methods include spectrophotometric analysis of NADH at 340 nm, native electrophoresis, or enzyme-linked immunosorbent assay. This study presents the first lateral flow immunoassay (LFIA) for the smartphone-based quantification of serum LDH levels at the point of care. Highly-affinity and specific antibodies have been produced, with 5 nM equilibrium dissociation constant and no cross-reactivity with human serum albumin and human immunoglobulin G. Utilizing carbon nanoparticles as signal transducers significantly enhanced the quantification limit 55-fold, compared to the conventional gold nanoparticles-based LFIA, achieving a quantification limit of 1.5 ng mL -1 . The developed assay demonstrated a mean recovery rate of 115 ± 21 % when evaluating LDH-spiked serum samples. This method can be an interesting home-testing tool for monitoring cancer progression or therapy effectiveness.