Detection of Saturated Fatty Acids Associated with a Self-Healing Synthetic Biological Membrane Using Fiber-Enhanced Surface Enhanced Raman Scattering

Abstract

The Synthetic Biological Membrane (SBM) project at NASA Ames developed a portable, self-repairing wastewater purification system. The self-repair process relies upon secreted fatty acids from a genetically engineered organism. However, solubilized fatty acids are difficult to detect using conventional methods. Surface-enhanced Raman scattering (SERS) was used to successfully detect solubilized fatty acids with the following limits of detection: 10, 10, 10, and 10 M for decanoic acid, myristic acid, palmitic acid, and stearic acid, respectively. Additionally, hollow core photonic crystal fiber (HCPCF) was applied as the sampling device together with SERS to develop in situ surveillance of the production of fatty acids. Using SERS + HCPCF yielded an 18-fold enhancement in SERS signal for the CH twist peak at 1295 cm as compared to SERS alone. The results will help the SBM project to integrate a self-healing wastewater purification membrane into future water recycling systems.

Direct Counting and Imaging Chain Lengths of Lipids by Stimulated Raman Scattering Microscopy

“…However, due to the limitation in spectral resolution of the employed broad-band coherent anti-Stokes Raman scattering (CARS) microscopy, it was still challenging to resolve the crowded and overlapped Raman bands in the C–H region. Over the past decade, advanced stimulated Raman scattering (SRS) microscopy has pushed the performance limits of Raman imaging in all aspects including sensitivity, speed, and spatial resolution and enabled delicate spatial and spectral characterization of biological tissues in various vital applications. − However, in all of these successes, the spectral resolution of SRS remained about 10 cm –1 or worse. , In particular, the subtle Raman shifts of C–C stretching, reflecting carbon chain lengths, vary only about 5 cm –1 in a 40 cm –1 spectral range between 1075 and 1115 cm –1 and are hardly resolved by the current SRS microscope. − …”

Pinpointing Alkane Chain Length, Saturation, and Double Bond Regio- and Stereoisomers by Liquid Interfacial Plasmonic Enhanced Raman Spectroscopy

“…Lipid has a very low affinity on the charged surface of noble metals, making it difficult to reach the surface of a noble metal or nano-sized gaps . As well-known, the near-field optical effect causes the SERS signal to drop sharply with the increase in the distance between the molecule and the metal surface . To date, SERS analysis on lipid mainly focuses on the lipid membrane arrangement and the characterization of overall lipid, and there are few reports on glyceride isomers.…”