Abstract
Recently, High Fundamental Frequency Quartz Crystal Microbalance (HFF-QCM) immunosensors have successfully been developed [1]. Therefore, sensitivity of QCM biosensors is no longer a drawback. Taking advantage of this previous work, we have developed a renewed highly sensitive HFF piezoelectric immunosensor using carbaryl insecticide as a model analyte for pesticide detection. To this purpose, 100 MHz quartz crystal sensors were used as the transducer elements of the biosensor and a monoclonal antibody-based competitive immunoassay was integrated as the sensing specific bio-recognition event. The biosensing interface was improved by employing mixed self-assembled monolayers (mSAMs) of alkane thiols as intermediate layers for surface functionalization. This approach allowed the covalent attachment of the assay conjugate (20.0 µg mL-1 of BSA-CNH conjugate) onto the gold electrode surface in a more orderly and stable way than with simple SAMs. A very low concentration (1.0 µg mL-1) of LIB-CNH45 monoclonal antibody was used for the competitive immunoassays. All immunosensor assays were performed in the AWS A10 test platform from AWSensors.
Figure 1 shows the carbaryl standard curve obtained with the new HFF-QCM immunosensor. Its analytical performance was compared with that of the previously reported employing the same HFF (100 MHz) sensors [1]. Analytical parameters clearly showed one order of magnitude enhancement of the limit of detection (LOD) and around four-fold improvement of sensitivity (I50 value): 0.1 µg L-1 vs 0.01 µg L-1 LOD and 0.66 µg L-1 vs 0.16 µg L-1 (I50 value) for the previous an the new carbaryl HFF-QCM immunosensors, respectively. Moreover, the HFF immunosensor LOD value reaches that of the most sensitive reported ELISA for carbaryl [2]. The sensitivity enhancement achieved turns this HFF-QCM pesticide immunosensor into one of the most sensitive analytical tools for this kind of low molecular compounds.
