Label-free quantum dot conjugates for human protein IL-2 based on molecularly imprinted polymers

•Quantum dots modified with molecularly-imprinted polymer for protein detection.•The first molecularly-imprinted polymer for interleukin-2 reported so far.•Different approaches for the imprinted polymer formation around the quantum dot.•Sensitive material for interleukin-2 detection in diluted serum.•Overall, low-cost, sensitive and selective biomimetic system for interleukin-2 detection. Herein, the development of a fluorescent-based sensor by combining quantum dots (QDs) with molecularly-imprinted technology (MIT), intensively optimized to generate exceptional operating features is presented. This sensor is designed to target human interleukin-2 (IL-2) in synthetic human serum. IL-2 is a regulatory protein released as a triggered response from the immune system towards an inflammation. For this purpose, cadmium telluride (CdTe) QDs are prepared with 3-mercaptopropionic acid (MPA) and modified afterwards to produce an IL-2 imprinted polymer with methacrylic acid and N,N´-methylenebis(acrylamide), upon removal of the template under optimized conditions. During IL-2 rebinding, the fluorescence intensity of CdTe@MPA QDs is quenched in a concentration dependent manner. Using surface imprinting technology, the optimal fluorescence signals yielded a linear response versus logarithm of IL-2 concentration from 35 fg/ml to 39 pg/ml, in a 1000-fold diluted synthetic human serum. The limit of detection obtained is 5.91 fg/ml, lying below the concentration levels of IL-2 with clinical interest for cancer diagnosis (9.4–19.2 pg/ml). Overall, the method presented herein is a demonstration that the combination of MIP and QDs for protein detection constitutes a powerful tool in clinical analysis, providing low cost, sensitive and quick responses. The same concept may be further extended to other proteins of interest.