Colorimetric and bare eye determination of urinary methylamphetamine based on the use of aptamers and the salt-induced aggregation of unmodified gold nanoparticles

Methamphetamine (METH) is second only to marijuana as a widely used illicit drug. We are presenting a simple colorimetric assay for sensitive and visual detection of METH in human urine using a METH-specific aptamer as the recognition element and unmodified gold nanoparticles as indicators. The meth... Full description

Methamphetamine (METH) is second only to marijuana as a widely used illicit drug. We are presenting a simple colorimetric assay for sensitive and visual detection of METH in human urine using a METH-specific aptamer as the recognition element and unmodified gold nanoparticles as indicators. The method is based on the finding that the presence of METH results in AuNPs solution’s color change from red to blue. Normally, aptamers attach to the surface of AuNPs and thereby increasing their resistance to NaCl-induced aggregation. If, however, the aptamer bind to METH via G-quartets, rapid salt induced aggregation occurs associated with the formation of a blue colored solution. Urinary METH can be quantified via this effect either visually or by measurement of the absorbance ratios at 660 and 525 nm, respectively. It works in the 2 μM to 10 μM concentration range with a detection limit at 0.82 μM. The method is fast and also works well in human urine. It is believed to represent a widely applicable aptamer-based detection scheme. Graphical Abstract We present a simple colorimetric assay for ultrasensitive and highly specific detection of Methamphetamine (METH) in human urine using a METH-aptamer as the recognition element and unmodified gold nanoparticles (AuNPs) as indicators. It works in the 2 μM to 10 μM concentration range with a detection limit at 0.82 μM