A Sandwich-type Lateral Flow Strip Using a Split, Single Aptamer for Point-of-Care Detection of Cocaine

The sandwich-type lateral flow assays relying on dual aptamers with high sensitivity and specificity have been broadly explored. However, it is unlikely to match a pair of specific aptamers that can bind a small molecular target (e.g., cocaine) simultaneously due to the steric hindrance. In response, we herein introduced the strategy of "one divides into two" into the construction of sandwich-type lateral flow strip assay (LFSA). Specifically, we split a single cocaine-recognizing aptamer into two segments, either of which was conjugated with gold nanoparticles (AuNPs) or labeled with biotin, serving as signal probe and capture probe, respectively. Upon the presence of the target molecule, a ternary sandwich complex comprised of the two halves of the aptamer and the target formed. Such sandwich-type LFSA exhibited an excellent nonlinear logarithmic response in the range from 10 mu mol/L to 5 mmol/L with R-2 = 0.9994. The sensitive on-site detection of cocaine in artificial biological samples including urine and sweat was achieved within 15 min, with the visual limit of detection as low as 50 mu mol/L for urine and 200 mu mol/L for sweat, and the recovery rates of 83.6-107.4%.