Synthesis of a red fluorescent dye-conjugated Ag@SiO2 nanocomposite for cell immunofluorescence.

In this work we describe a one-step approach for incorporating a red fluorophore (2SBPO) into core-shell nanoparticles for metal-enhanced fluorescence immunolabels. The 2SBPO-MEF nanoparticles are particularly attractive as cell labels because their ∼ 670 nm emission has minimal overlap with cell autofluorescence and from overlap with many conventional probes. 2SBPO was incorporated through physical entrapment during the Stöber process. Antibody-based cell labels were then synthesized using covalent linkage. The nanoparticle fluorescence was 7.5-fold higher than control nanoparticles lacking a metal core. We demonstrated labeling of CD4 + HuT 78 T lymphocytes using anti-CD4-conjugated nanoparticle labels. Cells labeled with anti-CD4 nanoparticles showed a 35-fold fluorescence signal compared to anti-CD4 coreless controls. This simple synthesis protocol can be applied to a variety of hydrophilic fluorophore types and has broad potential in bioanalytical and biosensing applications.