Rapid and selective aptamer-based fluorescence detection of salivary lysozyme using plasmonic metal-enhanced fluorescence of ZnSSe alloyed quantum dots-gold nanoparticle nanohybrid

We report on the construction of an aptamer (Apt)-based fluorescent biosensor platform for salivary lysozyme using plasmonic metal-enhanced fluorescence of ZnSSe alloyed quantum dots (QDs)-gold nanoparticle (AuNP) nanohybrid. Salivary lysozyme was used as a model analyte to develop the Apt fluorescence biosensor assay for real-life detection of human saliva. To construct the biosensor, thiolated anti-salivary lysozyme DNA Apt was immobilised on the L-cysteine-ZnSSe QDs surface to form a functionalised Apt-ZnSSe-QDs. Thereafter, citrate-AuNPs was bonded to the Apt-ZnSSe-QDs to form an Apt-ZnSSe-QDs-AuNP fluorescence biosensor probe. Using affinity-based biomolecular binding interaction between the Apt and target lysozyme, the binding effect induced localised surface plasmon resonance (LSPR) signal from AuNPs to amplify the fluorescence signal of the QDs upon lysozyme recognition. Probing the LSPR signal amplifying effects of different plasmonic NPs, our analysis showed that spherical citrate-AuNPs of size 6 nm was most effective in amplifying the fluorescence signal of the biosensor probe. Under optimum experimental reaction conditions, salivary lysozyme was detected quantitatively within 5 min with a detection limit of 22.9 μg/mL and was highly selective against other tested enzymes. Application of the Apt-ZnSSe QDs-AuNP biosensor probe to detect real human saliva samples was successfully achieved.