Raman-AFM Instrumentation and Characterization of SERS Substrates and Carbon Nanotubes

Atomic force microscopy (AFM) is a powerful tool for structural determination at sub-nanometer resolution and nano-mechanical characterization with pico-Newton molecular force sensitivity. Raman spectroscopy, on the other hand, can provide fingerprint chemical information of samples with sub-micron resolution. Through in-house engineering and integration of commercial components, we have developed a multi-modality biological AFM and Raman-spectroscopic instrument featuring a number of unique advantages including an independent closed-loop X-Y scanning stage and Z-piezo control, high-performance optical gratings, thermoelectrically cooled and electron-multiplying charge-coupled detectors (EMCCD), active vibration inhibition, and biological environmental controls. With this new instrument, we have obtained correlated surface enhanced Raman spectroscopy (SERS) mapping and AFM topographic images of a home-grown gold-on-mica substrate with putative SERS hot spots. We have also investigated carbon nanotubes (CNTs) via AFM tip enhanced Raman spectroscopy (TERS), where the enhancement factor is quantified from the difference Raman spectrum of the CNT’s G-band signature between an engaged and retracted state of a gold-coated AFM tip. The developed instrument can obtain simultaneous nanoscale structural and chemical information under controlled environmental conditions, a capability that is critical for meaningful interpretation of many anticipated biomedical applications.