Fluorescent Lateral Flow Assay with Carbon Nanodot Conjugates for Carcinoembryonic Antigen

A lateral flow assay (LFA) sensor on a half-strip platform labeled with blue carbon nanodot-polystyrene (PS-CND) nanoconjugates was developed for the detection of carcinoembryonic antigen (CEA) levels in buffer and serum solutions from healthy and cancer patients. CNDs, biocompatible nanoparticles containing amino groups synthesized by hydrothermal synthesis, were conjugated to spherical polystyrene (PS) beads with an average diameter of 60 nm, followed by the attachment of a detection probe, anti-CEA (M0911042), using a heterobifunctional cross-linker. PS beads were used as a template in CND conjugates to provide uniform size and shape of fluorescent labels without losing CND fluorescence intensity after the antibody conjugation step and to improve fluorescence stability. Upon the interaction of CEA from samples with the anti-CEA (M0911042) probe-modified PS-CND, which was further adsorbed onto a test line composed of the capture anti-CEA (M0911041) physisorbed onto a nitrocellulose membrane, the fluorescent signals on the test line increased as a function of the CEA concentrations under irradiation with a portable 365 nm ultraviolet lamp. A linear concentration range of 0.04–70 nM in buffer was observed, with a limit of detection of 0.3 nM. The applicability of the developed LFA half-strip sensor for disease diagnosis was demonstrated by identifying fluorescent levels on the test line due to the presence of CEA in serum samples from cancer patients. Importantly, signals from healthy human serum solutions because of lower CEA concentrations beyond the sensor detection capability were clearly distinguished from the patient ones.