Confocal Raman Microscopy for Investigating Synthesis and Characterization of Individual Optically Trapped Vinyl-Polymerized Surfactant Particles

Abstract

Small polymeric particles are increasingly employed as adsorbent materials, as molecular carriers, as delivery vehicles, and in preconcentration applications. The rational development of these materials requires in situ methods of analysis to characterize their synthesis, structure, and applications. Optical-trapping confocal Raman microscopy is a spectroscopic method capable of acquiring information at several stages of the development of such dispersed particulate materials. In the present study, an example material is developed and tested using confocal Raman microscopy for characterization at each stage of the process. Specifically, the method is used to investigate the synthesis, structure, and applications of individual polymeric surfactant particles produced by the vinyl polymerization of sodium 11-acrylamidoundecanoate (SAAU). The kinetics of polymerization can be monitored over time by measuring the loss of the acrylamide C=C functional groups using confocal Raman microscopy of particles optically trapped by the excitation laser, where, within the limits of detecting the vinyl functional group, the complete polymerization of the SAAU monomer was achieved. The polymerized SAAU particles are spherical, and they exhibit uniform access to water throughout their structure, as tested by the penetration of heavy water (D2O) and collection of spatially resolved Raman spectra from the interior of the particle. These porous particles contain hydrophobic domains that can be used to accumulate molecules for adsorption or carrier applications. This property was tested by using confocal Raman microscopy to measure the accumulation equilibria and kinetics of a model compound, dioxybenzone. The partitioning of this compound into the polymer surfactant could be determined on a quantitative basis using relative scattering cross sections of the SAAU monomer and the adsorbate. The study points out the utility of optical-trapping confocal Raman microscopy for investigating the synthesis, structure, and potential carrier applications of polymeric particle materials.

Single Particle Automated Raman Trapping Analysis

“…In addition to particle compositional analysis, prior studies have shown the possibility of investigating dynamic events or reactions occurring on the particle surface by monitoring the spectrum of optically-trapped particles over an extended time. Examples include observation of polymerisation reactions 23 , solid phase particle assisted peptide synthesis 24 or measurements of analyte concentrations in liposomes 25 . Further analysis of trapped particles includes the investigation of the influence of optical trapping forces on micrometre-sized liposomes through the addition of a solution marker such as perchlorate ions 12 .…”

Confocal Raman Microscopy for pH-Gradient Preconcentration and Quantitative Analyte Detection in Optically Trapped Phospholipid Vesicles

“…Preconcentration is a well-known method for enhancing the sensitivity of detecting trace-level analytes in a sample. Common materials used for sample preconcentration include functionalized chromatographic silica, − low-viscosity and porous polymers, − or functionalized magnetic particles. − Typically the collector is isolated from the source phase and then washed to release the concentrated analyte for subsequent ex situ analysis by chromatographic or spectroscopic detection. − With the application of microfluidics and lab-on-a-chip sample manipulation, there has arisen a need to reduce the scale of preconcentration methods. In order to reduce the large sample volumes required for extraction, one may consider analysis of the contents of a single microscopic particle used as a concentrator phase.…”

“…In order to reduce the large sample volumes required for extraction, one may consider analysis of the contents of a single microscopic particle used as a concentrator phase. Utilizing the small volumes of single particles would be especially useful when quantifying precious or biological compounds when there is a limited volume supply of sample. , …”

“…Utilizing the small volumes of single particles would be especially useful when quantifying precious or biological compounds when there is a limited volume supply of sample. 7,11 The use of a pH gradient in phospholipid vesicles or liposomes is a potentially powerful means of concentrating ionizable analytes into small volumes for detection and quantification. 12 The loading of lipid vesicles or liposomes by a pH gradient was first developed as a means of transferring therapeutic compounds into liposomes for applications in drug delivery.…”

Improving spatial resolution of confocal Raman microscopy by super-resolution image restoration

“…Confocal Raman microscopy (CRM) is widely used as an important tool in frontier areas such as physical chemistry, materials science, biomedical science [1][2][3][4][5][6][7], because of its micro-spectral optical section detection capability. However, the pinhole size of conventional confocal Raman microscopy has to be a few hundred microns to ensure the sensitivity of micro-spectrum detection, so it restricts the improvement of CRM spatial resolution.…”