Aura GT System

Significance of the Topic

The reliable detection, counting and characterization of viral capsid aggregates and subvisible particles is critical for quality control in gene therapy products. Aggregation can affect potency, safety and immunogenicity of viral vectors; rapid, low-volume, clog-free measurement solutions that can distinguish capsid-derived particles from protein, cellular or extrinsic contaminants and identify potential DNA leakage are therefore highly valuable for development, manufacturing, and lot release testing.

Objectives and Overview

This document summarizes the technical capabilities and intended use of the Aura GT System, a dedicated imaging platform for high-throughput quantitation and identification of capsid and other subvisible aggregates in gene therapy applications. The system aims to provide: full-well, 100% sampling efficiency; low minimum sample volume workflows; differentiation of capsid versus non-capsid aggregates; rapid throughput with minimal maintenance or clogging risk; and compatibility with automated workflows.

Methodology

The Aura GT combines three complementary membrane-imaging modalities to deliver particle counts, sizing, and compositional identification:

• Backgrounded Membrane Imaging (BMI) — brightfield-based full-well imaging enabling count, size, and morphological assessment with 100% sampling efficiency.
• Fluorescence Membrane Microscopy (FMM) — two fluorescence channels to label and discriminate capsid, protein, cellular, or extrinsic material and to probe DNA leakage as an aggregation source.
• Side Illumination Membrane Imaging (SIMI) — side-scatter illumination to enhance detection of scattering particles and morphological contrast.

The platform employs filter membranes as the capture substrate (white polycarbonate for brightfield and black polycarbonate for fluorescence) and acquires images using a 4x objective over a 24.6 mm2 imaging area. Dual fluorescence channels with defined excitation/emission ranges allow targeted labeling strategies to distinguish particle types.

Instrumentation Used

Key instrument characteristics and operating parameters:

• System: Aura GT (Waters)
• Imaging modalities: BMI, FMM, SIMI
• Imaging area: 24.6 mm2
• Objective: 4x
• Sampling efficiency: 100% (full-well imaging)
• Brightfield LED: 455 nm
• Side scatter LED: 465 nm
• Fluorescence LEDs and channels: Channel 1 Ex 440 nm / Em 500 nm; Channel 2 Ex 488 nm / Em 550 nm
• Resolution: ~1.0 pixel/µm
• Detectable particle size: approximately >1 µm (equivalent circular diameter) up to <5 mm
• Minimum sample volume: 5 µL (assay-dependent)
• Read times: Brightfield ~1 min/sample; Fluorescence ~30 s/sample
• Sample format: 24-well or 96-well filter membrane plates
• Membranes: white polycarbonate (BF), black polycarbonate (FL)
• Software: Particle Vue 5.x (image capture and analysis)
• Robotic compatibility and Windows-based operation
• Physical: ~13.5 x 18 x 13 in; weight ~57 lb; universal power 90–265 VAC

Main Capabilities and Discussion of Performance

The Aura GT is designed for high-throughput, low-volume workflows typical of preclinical and early-stage process development in gene therapy. Notable performance features include full-well imaging for true 100% sampling efficiency (reducing sampling bias typical of flow-based methods), minimal sample consumption enabling scarce-sample analysis, and a fluidics-free design that eliminates clogging and reduces carryover and maintenance. Rapid read times (approximately 90 seconds total if both BF and FL are used) facilitate screening of multiple conditions or lots. Dual fluorescence channels permit targeted assays for capsid identification and nucleic acid staining to detect DNA leakage as a contributor to aggregation.

Limitations and practical considerations:

• Sensitivity floor of ~1 µm ECD limits detection of smaller submicron particles; complementary nanoparticle methods may be needed for <100–1000 nm range.
• Performance for distinguishing aggregate composition depends on appropriate fluorescent probes and assay optimization.
• Dependence on filter membranes means sample preparation (filtration and capture) is required and may introduce artifacts if not carefully controlled.
• Fixed fluorescence channel wavelengths constrain fluorophore choices; multicolor expansion would increase multiplexing capability.

Benefits and Practical Applications

The Aura GT offers several practical advantages for analytical laboratories and industry:

• Product quality control and lot release testing of viral vectors (e.g., AAV) by providing counts, sizing, and morphological QC metrics.
• Formulation and stability studies to monitor aggregation kinetics and identify conditions that minimize capsid aggregation.
• Process development and upstream/downstream troubleshooting by distinguishing capsid-derived aggregates from host-cell or protein contaminants and by detecting DNA leakage.
• High-throughput screening in 24- and 96-well formats with automation compatibility, conserving valuable sample and accelerating data generation.
• Low maintenance, fluidics-free design reduces downtime and simplifies routine operation in regulated environments.

Future Trends and Applications

Potential developments and broader uses for membrane-imaging platforms in gene therapy analytics include:

• Integration of advanced machine learning and AI-driven image analysis to improve particle classification, reduce operator variability, and enable predictive fingerprinting of aggregate types.
• Expanded fluorescence capabilities (additional channels, spectral unmixing) to support multiplexed labeling for simultaneous detection of capsids, proteins, nucleic acids, and host-cell markers.
• Improved optical and sensor technologies to lower the detection limit below 1 µm and bridge the gap to nanoparticle analysis techniques.
• Tighter integration with laboratory automation and LIMS for streamlined data workflows and regulatory traceability.
• Standardization and validation protocols to support regulatory acceptance of membrane-imaging as part of release testing for gene therapy products.

Conclusion

The Aura GT System targets a specific and growing need in the gene therapy field for fast, low-volume, clog-free characterization of capsid aggregates and subvisible particles. Its combination of full-well brightfield imaging and dual-channel fluorescence provides practical capabilities to quantify particles, distinguish aggregate origins, and screen for DNA leakage with minimal sample consumption. While not a replacement for submicron particle techniques, it fills an important niche for >1 µm particulate analysis, especially where sample sparing and high throughput are priorities.

Reference

Waters Corporation. Aura GT System product specifications and brochure. November 2025.