Method for Quantitative Determination of Spatial Polymer Distribution in Alginate Beads Using Raman Spectroscopy

Abstract

A new method based on Raman spectroscopy is presented for non-invasive, quantitative determination of the spatial polymer distribution in alginate beads of approximately 4 mm diameter. With the experimental setup, a two-dimensional image is created along a thin measuring line through the bead comprising one spatial and one spectral dimension. For quantitative analysis of the Raman spectra, the method of indirect hard modeling was applied to make use of the information contained in the entire recorded spectra. For quantification of the alginate signals from within the beads, a calibration curve acquired from sodium alginate solutions was used after it was shown that only negligible differences occur between signals from alginate solutions and alginate gels. The distribution of alginate over the bead gel matrix was acquired with high spatial (51 microm) and time (12 s) resolution. The inhomogeneous distribution obtained using the new measuring technique is qualitatively in excellent agreement with data from the literature. In contrast to known measuring techniques, correct quantitative information about the spatial polymer distribution within the matrix was derived. It gave an alginate mass fraction of approximately 0.045 g/g at the edges and 0.02 g/g in the center of the beads. Next to the determination of mere polymer concentrations, the excellent time resolution of the presented method will enable investigation of the dynamic process of gel formation and it will also serve as a basis for investigation of mass transfer of small diffusing molecules in alginate matrices.

Model-based experimental analysis of enzyme kinetics in aqueous–organic biphasic systems

“…For the bead production process used in this work, the alginate density distribution has been measured using Raman spectroscopy (Heinemann et al, 2005). The quadratic equation 4-14 was used to fit the alginate density profile, where w alg is the alginate mass fraction, lg a w the average alginate mass fraction, d a model parameter to be fitted, and R the bead radius.…”

“…Since Ca-alginate beads exhibit an inhomogeneous density distribution (Heinemann et al, 2005), κ-carrageenan is chosen as hydrogel material. In contrast to Ca-alginate, the κ-carrageenan hydrogel beads are produced by cryogelation, which results in a homogeneous density distribution.…”

Sol/Gel Transition of Aqueous Alginate Solutions Induced by Fe2+ Cations

“…For example, IR studies have revealed that Ca 2+ ions preferentially bind to G blocks in agreement with other techniques. Confocal Raman spectroscopy (CRM) is a more powerful technique than IR because it is characterised by a high specificity, revealing usually sharper and clearer bands than IR spectra and low water background 20, 21. Raman spectroscopy can be employed for the determination of M/G ratio in alginic acid 22.…”

Isolation of monoclonal microcarriers colonized by fluorescent E. coli

“…This suspension is then compartmentalized into single small droplets by one of several available techniques (13)(14)(15). Next, the droplets are reinforced by gelation, which in the case of agaroses is induced by cooling (16) and in the case of alginates by chemically induced cross linking (17,18). As a result, cells become immobilized within the microcarrier.…”