Magnetic/Fluorescent Barcodes Based on Cadmium-Free Near-Infrared-Emitting Quantum Dots for Multiplexed Detection

Magnetic/fluorescent barcodes, which combine quantum dots (QDs) and superparamagnetic nanoparticles in micrometer-sized host microspheres, are promising for automatic high-throughput multiplexed biodetection applications and point of care biodetection. However, the fluorescence intensity of QDs sharply decreases after addition of magnetic nanoparticles (MNPs) due to absorption by MNPs, and thus, the encoding capacity of QDs becomes more limited. Furthermore, the intrinsic toxicity of cadmium-based QDs, the most commonly used QD in barcodes, has significant risks to human health and the environment. In this work, to alleviate fluorescence quenching and intrinsic toxicity, cadmium-free NIR-emitting CuInS2/ZnS QDs and Fe3O4 MNPs are successfully incorporated into poly(styrene-co-maleic anhydride) microspheres by using the Shirasu porous glass membrane emulsification technique. A single-wavelength encoding model is successfully constructed to guide the encoding of NIR QDs with wide emission spectra. Then, a single-wavelength encoding combined with size encoding is used to produce different optical codes by simply changing the wavelength and the intensity of the QDs as well as the size of the barcode microspheres. 48 barcodes are easily created due to the greatly reduced energy transfer between the NIR-emitting QDs and MNPs. The resulting bifunctional barcodes are also combined with a flow cytometer using one laser for multiplexed detection of five tumor markers in one test. Assays based on these barcodes are significantly more sensitive than non-magnetic and traditional ELISA assays. Moreover, validating experiments also show good performance of the bifunctional barcodes-based suspension array when dealing with patient serum samples. Thus, magnetic/fluorescent barcodes based on NIR-emitting CuInS2/ZnS QDs are promising for multiplexed bioassay applications.