Determination of alkaline phosphatase activity and of carcinoembryonic antigen by using a multicolor liquid crystal biosensor based on the controlled growth of silver nanoparticles

摘要

An ultrasensitive liquid crystal biosensor is described for multicolor visualization of the activity of alkaline phosphatase (ALP) based on the controlled growth of silver nanoparticles. The enzymatic product is accumulated on the surface of the LC sensing film by means of silver deposition, and the birefringent signal (observed with a polarizing microscope) is strongly enhanced as a result. The presence of AuNPs also enhances the sensitivity by about 4 orders of magnitude. The bright spots in polarized optical microscopy (POM) images increase with increasing activities of ALP. The signal intensities of the spots are then calculated by using Photoshop software and by multiplying the average brightness of the spots by the pixel value. The detection limit for ALP is 1.2 nUmL(-1), which is 5-7 orders of magnitude lower than other colorimetric or fluorometric methods. The method was applied to a highly sensitive immunoassay for the carcinoembryonic antigen (CEA) by integrating immunomagnetic separation. The immunoassay was applied to the analysis of complex samples without tedious sample pretreatment, and a detection limit as low as 0.35pgmL(-1) of CEA was achieved. The method has attractive features in that it provides an ultrasensitive multicolor visualization approach for enzymes such as ALP, but also paves the way to a new kind of immunoassay coupled to immunomagnetic separation.