SERS probes for the detection and imaging of biochemical species on the nanoscale

Abstract

We have developed novel surface enhanced Raman scattering (SERS)-based nanoimaging probes for dynamic chemical imaging in a non-scanning format. These probes have been developed for obtaining sub-diffraction limited chemical measurements of various biochemical species (e.g., lipids, proteins, etc.) as well as biological organisms (e.g., bacteria, etc.). They combine qualitative and quantitative information obtained from SERS with the imaging capabilities of coherent fiber optic bundles. Nanoimaging probes are fabricated from coherent fiber optic bundles composed of 30,000 individual 4 &#956;m diameter fiber elements. Using a CO₂ laser based micropipette puller, bundles are tapered on one end resulting in the formation of equi-diameter individual elements tens of nanometers to hundreds of nanometers in diameter. Employing these probes, inherent image magnification and submicron spatial resolution is possible. Across these tapered probe tips, uniformly roughened surface features are creating by HF acid etching. These surface features consist of six cladding peaks that surround each individual fiber elements' core, which are uniform in size, shape, structure, and spacing. SERS active surfaces are created on the tapered tips of the probes by selectively depositing silver onto these cladding peaks, creating an array of highly ordered uniform silver islands across these nanoimaging probes' surfaces. This fabrication process results in a high degree of uniformity in SERS enhancement across the image surface of the probes (< 3.0% RSD), which is essential for reproducible quantitative imaging applications. Further SERS enhancement and specific excitation wavelength tuning can be achieved by controlling the spacing between silver islands and the overall size of the silver islands uniformly arrayed across these SERS probe tips. Characterization and imaging of biochemical species and model compounds using these SERS nanoimaging probes is presented in this manuscript.