Photoluminescent hydrophilic cyclodextrin-stabilized cysteine-protected copper nanoclusters for detecting lysozyme

Lysozyme (LYZ) sensors have attracted increased attention because rapid and sensitive detection of LYZ is highly desirable for various diseases associated with humans. In this research, we designed L-cysteine-protected ultra small photoluminescent (PL) copper nanoclusters (CuNCs) conjugated with β-cyclodextrin (β-CD) for rapid detection of LYZ in human serum samples at room temperature. The proposed β-CD-CuNCs exhibited excellent water solubility, ultrafine size, good dispersion, bright photoluminescence, and good photostability. The β-CD-CuNCs exhibit an excitation and emission maximum at 370 nm and 492 nm, respectively, with an absolute quantum yield (QY) of 54.6%. β-CD-CuNCs showed a fluorescence lifetime of 12.7 ns. The addition of LYZ would result in PL quenching from β-CD-CuNCs. The lowest detectable LYZ concentration was 50 nM for the naked eye and the limit of detection (LOD) and limit of quantification (LOQ) were 0.36 nM and 1.21 nM, respectively, by emission measurement observed in the LYZ concentration range from 30 to 100 nM. It is important to note that the PL β-CD-CuNC strategy possessed great selectivity toward LYZ relative to other biomolecules. The proposed nanosensor was efficiently applied to determine the LYZ level in human serum sample average recoveries from 96.15 to 104.05% and relative standard deviation (RSD) values lower than 3.0%. Moreover, the proposed sensing system showed many advantages, including high speed, high sensitivity, high selectivity, low cost, and simple preparation.