In this study, cortisol, which is a key stress hormone, could be detected sensitively via the colorimetric assay of a polycarbonate (PC) and glass substrate by the sandwich assay of cortisol monoclonal antibody (c-Mab) and cortisol specific binding aptamer (c-SBA). A highly sensitive change in colorimetry with a limit of detection (LOD) of cortisol of 100 fM could be attained on the optically transparent substrate using the antibody aptamer sandwich (AAS) assay by corresponding stacks of 5 nm gold nanoparticles (Au NPs). The Au NPs were conjugated by the c-SBA and the c-Mab was tethered on the PC and glass substrates. For the AAS method, a simple UV-Vis spectrophotometer was adopted to quantify the cortisol concentrations at an absorbance wavelength of 520 nm. Therefore, this study demonstrates the versatility of the AAS method to measure very low concentrations of cortisol in diagnostic applications.

Recently, various waste microplastics sensors have been introduced in response to environmental and biological hazards posed by waste microplastics. In particular, the detrimental effects of nano-sized plastics or nanoplastics have been reported to be severe. Moreover, there have been many difficulties for sensing microplastics due to the limited methodologies for selectively recognizing nanoplastics. In this study, a customized gold nanoparticles (Au NPs) based localized surface plasmon resonance (LSPR) system having bio-mimicked peptide probes toward the nanoplastics was demonstrated. The specific determination through the oligo-peptide recognition was accomplished by chemical conjugation both on the LSPR chip’s 40~50 nm Au NPs and sandwiched 5 nm Au NPs, respectively. The peptide probe could selectively bind to polystyrene (PS) nanoplastics in the forms of fragmented debris by cryo-grinding. A simple UV-Vis spectrophotometer was used to identify the LSPR sensing by primarily measuring the absorbance change and shift of absorption peak. The sandwich-binding could increase the LSPR detection sensitivity up to 60% due to consecutive plasmonic effects. In addition, microwave-boiled DI water inside of a styrofoam container was tested for putative PS nanoplastics resource as a real accessible sample. The LSPR system could be a novel protocol overcoming the limitations from conventional nanoplastic detection.