I. Introduction
The development of highly sensitive point of care technology (POCT) device has become an imperative demand for early diagnosis and treatments of many medical diseases. In recent years, numerous studies have been focused on engineering a fast and non-invasive tool with ultra-sensitivity for trace disease biomarkers [1]–[3]. Among POCT methods, lateral flow assay (LFA) is one of the fastest-growing technologies due to its robustness, simplicity, short assay time and low-cost operation which enables physicians to make an immediate treatment decision for optimal patient care. The concept behind LFA is simply based on antibody-antigen specific interaction. A liquid sample containing the analyte of interest is applied to the sample pad and propelled through the strip by capillary action. The target analytes first migrate to the conjugate release pad to bind with reporter-labeled antibodies. They then flow through the porous membrane and arrive at a previously prepared test line of immobilized antibodies, forming a “sandwich” structure. Excess labeled antibodies then bind to the control line indicating proper liquid flow through the strip. Results are interpreted by the signal generated on the test line that is correlated to the presence of the analyte in the sample and can be read either by eye (qualitative or semi-quantitative) or using a reader (quantitative) [2]–[4]. The best known LFA is the pregnancy test in which human chorionic gonadotropin (hCG) is the target biomarker.