Noninvasive Optical Sensor for the Detection of Cocaine and Methamphetamine in Saliva Using Rhodamine B-Labeled Polymersomes

Drug abuse is an alarming subject affecting modern society. Unlike alcohol consumption control, substance abuse monitoring still lacks standardized, non-invasive, and efficient biosensors for on-site diagnostics. Most of the approaches are based on blood sampling and traditional chromatographical techniques. Here, we propose two colorimetric lateral flow immunoassays (LFIA) using Rhodamine B-loaded polymersomes for cocaine (COC) and methamphetamine (METH) detection on saliva samples. Polymersomes were synthesized from methoxy polyethylene glycol and polycaprolactone and then loaded with the dye. Furthermore, the bioconjugation of the specific antibodies on the surface was confirmed via various analytical methods. The LFIA platform was based on a competitive type that is more suitable for detecting small-sized molecules. The sensitivity of the LFIA was quantitatively measured using smartphone-assisted imaging analysis and showed a limit of detection (LOD) of 0.49 ng/mL (COC) and 0.37 ng/mL (METH). Moreover, the specificity was also investigated against various interferents. The analytical performance of the LFIA platform was tested over synthetic and real human saliva, which showed an overall accuracy of 97% and 98.4%, respectively. The LFIA offers excellent stability under various salivary conditions (pH and incubation time) and keeps steady performance when comparing spiked buffer with synthetic and human saliva. The use of non-invasive sampling such as saliva in combination with on-site sensing devices can be of great potential for future applications and implementation of portable biosensors.