Controlling distance, size and concentration of nanoconjugates for optimized LSPR based biosensors.

In this report, we have examined the distance- and size-dependent localized surface plasmon resonance (LSPR) between fluorescent quantum dots (QDs) and adjacent gold nanoparticles (AuNPs) to provide a comprehensive evaluation, aiming for practical application in biosensing platform. A series of peptides with different chain lengths, connected between QDs and AuNPs is initially applied to prepare various CdSe QDs-peptide-AuNP systems to optimize LSPR signal. Separation distance between two nanoparticles of these systems before and after conjugation is also confirmed by quantum mechanical modeling and corroborated with their LSPR influenced fluorescence variations. After detailed optimizations, it can be noted that larger sized AuNPs make strong quenching of QDs, which gradually shows enhancement of fluorescence with the increment of distance and the smaller sized AuNPs. Depending on the requirement, it is possible to tune the optimized structure of the CdSe QD-peptide-AuNP nanostructures for the application. In this work, two different structural designs with different peptide chain length are chosen to construct two biosensor systems, observing their fluorescence enhancement and quenching effects, respectively. Using different structural orientation of these biosensors, two nanoconjugates has applied for detection of norovirus and influenza virus, respectively to confirm their application in sensing.