Application Note | TURBIDI.T™
Rapid Analysis of Protein Aggregation in Microvolume Samples using TURBIDI.T™
by Maya Salame and Dimitria Camasao
Application Scientists
Key Takeaways
- Aggregation kinetics are concentration and condition-dependent: At specific temperature and pH, higher lysozyme concentration yields faster turbidity rise and earlier aggregation onset.
- Microvolume capability: TURBIDI.T™ reliably tracks turbidity in as little as 200 µL, conserving samples and reducing waste.
- Real-time turbidity monitoring: Continuous turbidity measurements capture entire aggregation profiles without labels.
- Versatile, modular and cost-effective platform: Interchangeable optical cartridges allow optimization across wavelengths and applications.
Why is Studying Protein Aggregation Important?
Protein aggregation is a critical concern in biopharmaceutical development and biomedical research. In therapeutic protein stability, aggregation threatens product quality and safety: biologics such as recombinant proteins and monoclonal antibodies are sensitive to stressors like temperature, pH changes, and agitation. Aggregates can reduce activity, alter pharmacokinetics, and increase immunogenicity, necessitating comprehensive aggregation monitoring during formulation and stability studies.
Similarly, protein aggregation underlies the pathology of amyloid diseases (e.g., Alzheimer’s, Parkinson’s), where misfolded proteins self-assemble into oligomers and fibrils. Aggregation testing is essential to understand nucleation, growth kinetics, and toxic intermediates, and to screen potential inhibitors.
Currently, a range of analytical techniques is used to characterize aggregation, including size exclusion chromatography (SEC), dynamic light scattering (DLS), circular dichroism (CD), Fourier-transform infrared spectroscopy (FTIR), Thioflavin T fluorescence assays, and electron microscopy for structural confirmation.
TURBIDI.T™ provides a rapid, affordable, label-free approach to monitor turbidity changes due to aggregate formation in microvolumes as small as 200 µL, enabling sensitive, real-time aggregation kinetics measurement while conserving samples. In this application note, we demonstrate its use to study lysozyme aggregation kinetics at two concentrations, illustrating its utility for both stability assessment and mechanistic aggregation studies.
About TURBIDI.T™
TURBIDI.T™ is a modular, customizable turbidimeter that enhances traditional turbidity measurement through the use of interchangeable optical (laser) cartridges at multiple wavelengths, allowing optimized light-scattering detection for specific applications and particle sizes. Users can select appropriate emitter cartridges and choose between sample holders from 200 µL to larger vials and cuvettes, providing flexibility in sample volume and format. Unlike fixed-wavelength turbidimeters, TURBIDI.T™ enables real-time kinetic turbidity monitoring with adjustable time steps and spectral settings, while its Soft Matter Analytics™ software supports advanced data acquisition, processing, and database management.
Experimental Protocol for Assessing Lysozyme Aggregation Kinetics
Materials
Lysozyme from chicken egg white (Mucopeptide N-acetylmuramoylhydrolase, muramidase; ≥39,000 units/mg protein) was purchased from MilliporeSigma Canada Ltd. (Canada) and used without further purification. Phosphate-buffered saline (PBS) solution was used for all sample preparations to dissolve the lysozyme. Sodium hydroxide (0.1 M) was added to increase the solution pH in order to facilitate protein aggregation.
Sample Preparation
Lysozyme powder was dissolved in PBS to prepare two protein solutions at concentrations of 2.0 mg/mL and 5.0 mg/mL. The solutions were gently mixed to ensure complete dissolution while minimizing mechanical stress.
The pH of each solution was adjusted to pH 11 using sodium hydroxide. Alkaline conditions were selected to promote partial destabilization of the native lysozyme structure and enhance aggregation propensity under controlled conditions. Following pH adjustment, samples were equilibrated at room temperature prior to thermal induction.
Induction of Aggregation
Protein aggregation was thermally induced by incubating the samples at 45 °C. This temperature was chosen to accelerate unfolding and aggregation kinetics while maintaining controlled experimental conditions. Temperature control was maintained throughout the measurement period to ensure reproducibility of kinetic data.
TURBIDI.T Measurement
Aggregation kinetics were monitored using TURBIDI.T™, which measures turbidity changes associated with the formation of protein aggregates. For each measurement, 200 µL of sample was loaded into the measurement vial. The microvolume format minimizes sample consumption while enabling real-time kinetic monitoring.
Turbidity was recorded over time to capture the evolution of aggregate formation. The increase in turbidity reflects the growth of scattering species as soluble monomers and oligomers assemble into larger aggregates.
Turbidity-Based Analysis of Protein Aggregation Kinetics
Turbidity (FTU) – 2 mg/mL vs. Time (min)
Turbidity (FTU) – 5 mg/mL vs. Time (min)
2 mg/mL
0 min
10 min
20 min
30 min
40 min
50 min
5 mg/mL
0 min
5 min
10 min
15 min
The turbidity profiles clearly show a concentration-dependent aggregation behavior for lysozyme at 45 °C and pH 11. The solution at 5.0 mg/mL exhibits a more rapid increase in turbidity compared to the 2.0 mg/mL solution. In addition, the onset of turbidity increase—corresponding to the beginning of detectable aggregate formation—occurs earlier at the higher protein concentration. In both cases, turbidity increases progressively over time, accompanied by the formation of visibly large and amorphous aggregates.
Turbidity arises from light scattering by particles whose size increases. As lysozyme molecules undergo partial unfolding under alkaline and thermal stress, exposed hydrophobic regions promote intermolecular interactions, leading first to the formation of small oligomers and subsequently to larger aggregates. As aggregate size and number increase, light scattering intensifies, producing a measurable rise in turbidity.
The faster kinetics observed at higher concentration can be explained by classical aggregation theory. Protein aggregation is typically a nucleation-dependent process, involving:
- Primary nucleation, where a critical oligomeric nucleus forms.
- Growth/elongation, where additional monomers associate with existing nuclei.
- Possible secondary processes, such as aggregate–aggregate interactions.
At higher protein concentration, the probability of productive intermolecular collisions increases significantly. This reduces the time required to form stable nuclei (shorter lag phase) and accelerates the growth phase. In this study, the subsequent phases of aggregate growth and particle coalescence are also accelerated, leading to the formation of amorphous aggregates that sediment rapidly.
These results demonstrate that turbidity monitoring provides a sensitive and direct method to resolve aggregation kinetics and to discriminate concentration effects on nucleation and growth mechanisms.
Rapid, Cost-Effective Turbidity-Based Protein Aggregation Testing in Microvolumes
This application note demonstrates that TURBIDI.T™ enables sensitive, real-time monitoring of lysozyme aggregation kinetics in microvolume samples. By measuring turbidity changes in 200 µL volumes, TURBIDI.T™ reveals clear concentration-dependent aggregation behaviors and accelerates data acquisition while conserving valuable protein samples. Its flexible, modular design and customizable optical configurations make it a practical tool for both formulation stability assessment and fundamental aggregation research, offering an efficient alternative to traditional aggregation assays.
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