An electrochemical immunosensor for simultaneous multiplexed detection of two lung cancer biomarkers using Au nanoparticles coated resin microspheres composed of L-tryptophan and caffeic acid

Abstract

In this study, we report a surfactant-free and template-free method for the high-yield synthesis of tryptophan and caffeic acid-based resin (TCCR) microspheres for the first time. The method is based on the polymerization reaction of tryptophan and caffeic acid in the formaldehyde aqueous solution to generate resin colloidal microspheres. The Au nanoparticles (AuNPs)-decorated TCCR microspheres prepared by a convenient reduction approach show good stability. AuNPs/TCCR microspheres with a lot of activity groups (amino and hydroxy groups) can not only act as suitable immobilization carriers for antibody but can also play an important role in facilitating the electron transfer. A simple label-free electrochemical multiplexed immunosensor based on AuNPs/TCCR microspheres is developed for simultaneous detection of carcinoembryonic antigen (CEA) and neuron-specific enolase (NSE). Owing to the active group of the AuNPs/TCCR microspheres, the redox molecules [toluidine blue (TB) and Prussian blue (PB)] are absorbed on the surface of these microspheres, which is helpful for absorbing antibodies and signal generation. The prepared TB/AuNPs/TCCR and PB/AuNPs/TCCR microspheres are used as substrate to easily construct electrochemical immunosensor. Under the optimized conditions, the linear range of the proposed immunosensor is estimated to be from 0.2 to 25 ng/mL for both CEA and NSE. At a signal to noise rate of 3, the lowest detectable concentration is 0.11 and 0.08 ng/mL for CEA and NSE, respectively. The assay results of serum samples with the proposed method were in a good agreement with the standard ELISA method. The proposed immunosensor hold great promise for applications in clinical diagnosis, due to the negligible cross-reactivity between the two methods.