Development and application of molecularly imprinted polymer - Mn-doped ZnS quantum dot fluorescent optosensing for cocaine screening in oral fluid and serum

摘要

A molecularly imprinted polymer - Mn-doped ZnS quantum dot-based fluorescence probe for cocaine abuse screening has been prepared and applied to complex samples such as serum and oral fluid. The fluorescent sensing material was prepared by anchoring a selective MIP for COC on the surface of polyethylene glycol (PEG) modified Mn-doped ZnS quantum dots (QDs). Simple and low cost methods have thus been optimized for assessing cocaine abuse in serum and oral fluid by monitoring fluorescence quenching when cocaine (COC) is present (optimized operating conditions with 1.5 mL of 200 mg L-1 MIP-coated QDs solution, pH 5.5, and 15 min before fluorescence scanning). The matrix effect was found to be important when analyzing oral fluid and serum, and several strategies based on centrifugation for oral fluid and solid phase extraction (SPE) for serum were explored. Two analytical methods were developed for oral fluid. The first one (direct method) requires a centrifugation step (6 degrees C, 4000 rpm, 20 min) to avoid the matrix effect, and allows for cocaine determination by using an aqueous calibration (1:20 dilution). The second method was developed for oral fluid sampled by Salivette devices, and also requires a further centrifugation (6 degrees C, 4000 rpm, 20 min) of the recovered oral fluid. This method, however, requires the standard addition technique (1:20 dilution) because of the existence of the matrix effect. Regarding serum samples, a direct method (serum dilution) was not possible, and an SPE procedure was needed to avoid the matrix effect (use of aqueous calibration). The limits of detection and quantification when using the Salivette method were 0.035 mg L-1 and 0.117 mg L-1 respectively; whereas, 0.015 mg L-1 (LOD) and 0.050 mg L-1 (LOQ) were obtained for serum.