Spectroscopic PAT for Real-Time Molecular Fingerprinting

In upstream processing, Raman spectroscopy facilitates automated nutrient control. It achieves this by translating in situ spectral fingerprints of key metabolites into actionable concentration data using multivariate models.

While Raman is excellent for bulk monitoring, complex biologics require higher specificity. A-TEEM (Absorbance-Transmission Excitation-Emission Matrix) integrates absorbance, transmittance, and excitation-emission fluorescence into a single rapid measurement. This generates sensitive three-dimensional molecular fingerprints suitable for detailed molecular characterization across the bioprocess lifecycle.

A-TEEM overcomes the inner filter effect (IFE) inherent in concentrated samples by using absorbance data to mathematically correct fluorescence intensities. This correction linearizes the instrument response from ppb to mg/mL, allowing for the label-free quantification of components like aromatic amino acids and vitamins. Additionally, the technique is insensitive to common non-fluorescent process components like water and simple sugars, simplifying the analysis of complex media.

Because bioprocess samples generate overlapping signals, multivariate analysis is required.

• PARAFAC (Parallel Factor Analysis): This tool resolves overlapping fluorophores into individual spectral components. It provides concentration-like scores for quantitative modeling and is sensitive enough to discriminate between fluorophore microenvironments, such as solvent-exposed versus buried tryptophan.
• PCA (Principal Component Analysis): Applied to unfolded datasets, PCA captures major sources of variance to uncover latent structures. It is used for pattern recognition, clustering, outlier detection, and rapid identification of process deviations.

A-TEEM provides a continuous, label-free method to track degradation and aggregation, which are critical quality attributes. For example, during thermal stress studies of monoclonal antibodies (mAbs), A-TEEM detected early chemical degradation via a red shift in tryptophan emission and a decrease in intensity, signaling the unfolding process. Later, it detected new spectral features representing oxidative degradants or aggregation.

Yes, A-TEEM is effective for characterizing Adeno-Associated Virus (AAV) vectors. It can quantify the full/empty capsid ratio rapidly and without labels because the packaged DNA payload in a full capsid acts as an internal quencher. Consequently, full capsids produce a lower protein signal compared to empty capsids, providing a vital metric for viral vector efficacy.

A-TEEM can monitor biological and chemical reaction dynamics, such as T-cell expansion or protein conjugation. In T-cell cultures, spectral shifts in the NAD(P)H region correlate directly with Total Viable Cell Count. Similarly, during conjugation reactions (e.g., CRM197 with polysaccharides), progress is tracked by observing the quenching of intrinsic protein fluorescence and the emergence of a new band characteristic of the covalent bond.