A Label-Free Immunosensor for Ultrasensitive Detection of Ketamine Based on Quartz Crystal Microbalance

In this study, we have developed a label-free immunosensor with the variation of resonance frequency (Δf) of a quartz crystal microbalance (QCM) as readout signal for ultrasensitive detection of Ketamine (KT). An optimized strategy for immobilization of KT antibody on the surface of the QCM chip was implemented via the self-assembly modification of 3-mercaptopropionic acid, and then activated with 1-ethyl-3- (3-dimethylaminoprophl) carbodiimide and n-hydroxysuccinimide. The specific affinity between the antibody and the antigen ensured a selective response toward KT. The Δf linearly related to the concentration of KT in the range of 1 to 40 pg/mL, with a detection limit of 0.86 pg/mL (S/N = 3). The obtained immunosensor was applied to detect the KT in spiked human urine without any pretreatment but dilution with recoveries from 91.8% to 108%. The developed sensor is promising to perform the portable or on-spot KT detection in clinic or forensic cases.