Multiplex label-free detection of biomolecules with an imprinted suspension array.

Multiplex detection of biomolecules has facilitated clinical diagnosis, drug discovery, and environmental testing. Immunoassays using labeled antibodies are the most popular methods for the detection of biomolecules because of their sensitivity and selectivity. However, labeling protocols are time-consuming and expensive, and may alter the form or physicochemical behavior of the antibodies, which could lead to false negative results. In addition, the reagent stability, high cost, and difficulties associated with antibody production, together with the adverse action of toxic compounds or immunosuppressants on the metabolism and the immune system during the production of antibodies, are often cited as problems. Therefore, it is highly desirable to carry out multiplex label-free detection of biomolecules without using immunoassay methods. Suspension arrays, which use self-encoded microcarriers as elements, have shown obvious advantages in the multiplex detection of biomolecules. However, few of them can be used for the label-free detection of biomolecules. Moreover, these methods are still based on the use of probe antibodies. In contrast, molecularly imprinted polymers (MIPs) have unique properties as mimics of natural molecular receptors that may make them suitable for revolutionary applications in biotechnology. Recently, many kinds of MIP sensors have been developed for the detection of biomolecules based on physicochemical responses of the MIPs, such as changes in refractive index and volume. However, these sensors could respond only to single analytes, and the detection signals from the physicochemical response of the MIPs were not distinct and were difficult to measure with accuracy. Herein, we report a new type of suspension array for the multiplex label-free detection of biomolecules without using immunoassay methods. The microcarriers of our suspension array are molecularly imprinted polymer beads (MIPBs) with photonic crystal structure, which not only provide diffraction peaks for encoding but also convert the slight physicochemical response signals to the obvious changes of optical signals. This technique combines the advantages of suspension arrays, molecular imprinting, and photonic crystal sensors. As a proof of concept for the multiplex label-free detection of biomolecules not based on immunoassay methods, we constructed an imprinted suspension array with affinity for proteins. For large biomacromolecules, surface imprinting was used for the fabrication of the MIPBs with photonic crystal structure due to the easy removal and rapid rebinding characteristics during assays. Scheme 1 outlines the