Controlled chemical functionalization of water-soluble nanoprobes for site-specific biomedical diagnosis

We propose mono-, di-, or tri-probe functionalized water-soluble gold nanoparticles (AuNPs) (~2 nm) based on our aqueous-phase serial solid-phase monofunctionalization (monof-) approach. They exhibit both electrical and optical sensing capabilities when specifically coupled with distinctive one- or diametric-functionality. Using ferrocene redox derivative for electrical detection scheme, the monof-, bif-, and trif-NPs show distinctively proportionated current peaks, which could allow quantitative biosensing as well as precise bioconjugation. TEM images verified the covalent bond-directed assembly of 1D and 2D structures. While typical individual AuNPs are not NIR responsive, the assembled nanosensing units exhibit longitudinal surface plasmon resonance, indicating their high promises for the high functional NIR-based medical applications. These exemplify a significant stride towards `multiplex' nanosensors with enhanced functionality, selectivity, and complexity.