Surface-enhanced raman scattering detection of pH with silica-encapsulated 4-mercaptobenzoic acid-functionalized silver nanoparticles

TitleSurface-enhanced raman scattering detection of pH with silica-encapsulated 4-mercaptobenzoic acid-functionalized silver nanoparticles
Publication TypeJournal Article
Year of Publication2012
AuthorsWang, F., Widejko R. G., Yang Z., Nguyen K. T., Chen H., Fernando L. P., Christensen K. A., and Anker J. N.
JournalAnal Chem
Volume84
Pagination8013-9
Date PublishedSep 18
ISBN Number1520-6882 (Electronic)<br/>0003-2700 (Linking)
Accession Number22881392
Keywords*Spectrum Analysis, Raman, Animals, Benzoates/*analysis, Cattle, Cell Line, Gold/chemistry, Hydrogen-Ion Concentration, Metal Nanoparticles/*chemistry, Mice, Serum Albumin, Bovine/chemistry/metabolism, Silicon Dioxide/*chemistry, Silver/*chemistry, Sulfhydryl Compounds/*analysis, Surface Properties
Abstract

Sensors based upon surface-enhanced Raman spectroscopy (SERS) are attractive because they have narrow, vibrationally specific spectral peaks that can be excited using red and near-infrared light which avoids photobleaching, penetrates tissue, and reduces autofluorescence. Several groups have fabricated pH nanosensors by functionalizing silver or gold nanoparticle surfaces with an acidic molecule and measuring the ratio of protonated to deprotonated Raman bands. However, a limitation of these sensors is that macromolecules in biological systems can adsorb onto the nanoparticle surface and interfere with measurements. To overcome this interference, we encapsulated pH SERS sensors in a 30 nm thick silica layer with small pores which prevented bovine serum albumin (BSA) molecules from interacting with the pH-indicating 4-mercaptobenzoic acid (4-MBA) on the silver surfaces but preserved the pH-sensitivity. Encapsulation also improved colloidal stability and sensor reliability. The noise level corresponded to less than 0.1 pH units from pH 3 to 6. The silica-encapsulated functionalized silver nanoparticles (Ag-MBA@SiO(2)) were taken up by J774A.1 macrophage cells and measured a decrease in local pH during endocytosis. This strategy could be extended for detecting other small molecules in situ.

Short TitleSurface-Enhanced Raman Scattering Detection of pH with Silica-Encapsulated 4-Mercaptobenzoic Acid-Functionalized Silver Nanoparticles