Molecular fingerprinting of biological nanoparticles with a label-free optofluidic platform

In the field of biosensing, one of the ultimate goals has been the ability to detect multiple substances (analytes) quickly, accurately, and without the need for labels or markers. This is crucial for applications ranging from medical diagnostics to environmental monitoring. However, achieving this high-throughput, label-free detection while handling small sample volumes and ensuring the specificity of the detected analytes has proven to be a significant challenge.

Introducing the Optofluidic Platform

Researchers at ETH Zurich have now developed an innovative solution called an “optofluidic platform,” which combines advanced optical techniques with microfluidics to tackle these challenges. This platform integrates digital holography with PDMS (polydimethylsiloxane) microfluidics and uses supported lipid bilayers as a key component for surface chemistry.

Digital Holography and Microfluidics

Digital Holography: This state-of-the-art optical technique captures detailed images of tiny particles, allowing for precise analysis without the need for labels.

PDMS Microfluidics: These tools are designed to handle very small volumes of liquids, making them ideal for processing tiny biological samples with high efficiency.

Supported Lipid Bilayers: These bilayers act as a foundation for surface chemistry, providing a means to attach specific molecules that can interact with the analytes of interest. This combination allows the platform to accurately detect and profile various biological nanoparticles.

How It Works

The optofluidic platform performs a multiplexed, label-free immunoaffinity assay. This means it can test for multiple substances simultaneously, using antibodies to capture specific analytes. The platform is so sensitive that it can detect single particles, providing a highly detailed analysis.

Concept and workflow of the label-free optofluidic platform

Fig. 1

A Conceptual illustration of the aim of the platform. The platform is based on three main toolboxes. B Microscopy toolbox: schematic of the optical system for large FOV imaging with single particle sensitivity based on spatially incoherent inline holography in a reflection geometry together with four representative zoomed-in images with diffraction-limited spots identified with blue circles. Inset: the working principle relies on detecting the interference between the weakly scattered light from the sample, Es, and the reflection from the substrate/water interface, Er. Scale bars: 5 μm. C Microfluidic toolbox: representative two-layer microfluidic chip design composed of a network of valves (orange) and flow channels (blue). The black arrows highlight the section of independently addressable channels used for sensing. D Surface chemistry toolbox: schematic representation of the in-chip functionalisation scheme based on SLB formation by liposome fusion, which acts as the building block for the immunoaffinity pull-down assays. E Workflow of the platform: representative experimental image scan of a sensing channel obtained by stitching multiple fields-of-view together with the resulting contrast distribution of all localised single particles. The scattering contrast signals are retrieved upon localising all the diffraction-limited spots above a signal-to-noise ratio (SNR) threshold, an example shown in (B).

Application to Ovarian Cell-Derived Extracellular Vesicles

To demonstrate its capabilities, the researchers used the platform to profile extracellular vesicles (small particles released by cells) derived from ovarian cells. By examining these vesicles for different surface protein biomarkers, they were able to create a unique “biomarker fingerprint” for four distinct ovarian cell lines. This kind of detailed profiling is invaluable for understanding cell behavior and could lead to better diagnostic tools and treatments for diseases like cancer.

Future Applications

The potential applications of this optofluidic platform are vast. It could be used wherever detailed and high-throughput analysis of biological nanoparticles is needed. This includes medical diagnostics, where it could help identify disease markers more quickly and accurately, and environmental monitoring, where it could detect pollutants at very low concentrations.

Conclusion

The development of this optofluidic platform marks a significant advancement in the field of biosensing. By combining digital holography with microfluidics and innovative surface chemistry, these researchers have created a tool that can perform high-throughput, label-free detection with exceptional specificity and sensitivity. This breakthrough opens up new possibilities for the routine and detailed analysis of biological nanoparticles, potentially transforming how we diagnose and monitor various conditions.

Stollmann A, Garcia-Guirado J, Hong JS, Rüedi P, Im H, Lee H, Ortega Arroyo J, Quidant R. (2024) Molecular fingerprinting of biological nanoparticles with a label-free optofluidic platform. Nat Commun 15(1):4109. [article]

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