Deeply-dyed nanobead system for rapid lateral flow assay testing of drugs at point-of-care

Point-of-care test (POCT) allows for rapid and sensitive screening of drugs of abuse. However, traditional gold nanoparticle-based lateral flow immunoassay strip is not sensitive enough for detection of trace drugs in hair samples. Herein, we aimed to develop a more specific system using a composite polymer nanobead that is deeply dyed with oil soluble dyes, and termed as deeply dyed nanobead (DDNB). The prepared composite nanobeads displayed a clear core-shell structure and the core/shell ratios were readily controlled by polymer/dye feeding ratios. The absorbance stable nanobeads capped with carboxyl groups were covalently conjugated with antibodies, and were employed for preparation of lateral flow immunoassay strips for sensitive detection of drugs in hair with naked eye. The developed drug strips allow the detection of drugs such as morphine and methamphetamine in hair samples within 13 min (including hair sample processing ~5 min). The cut-off value of DDNB strip for methamphetamine detection with naked eye is down to concentration of 8.0 ng/mL, which is about 3.1 times more sensitive than the traditional gold nanoparticles based lateral flow immunoassay. Moreover, the colorful DDNB system has the potential for multiplexing detection of analytes at point-of-care settings and low cost.