Traditional immunoassays based on the format of 96-well microtiter plates are widely used in analytical laboratories and have become increasingly automated with the introduction of robotics technology in recent years, thereby enhancing assay throughput. Most clinical analyzers essentially operate as “stand-alone laboratories,” featuring precise, accurate, and highly reproducible programmatic liquid handling, sample addition, and washing steps. However, aside from cost, the size limitations of these automated analyzers mean they are not suitable for remote applications. Point-of-care (POC) testing traditionally revolves around nitrocellulose-based lateral flow assays, offering rapid, user-friendly solutions for explicit diagnostic needs. Unfortunately, these types of tests (e.g., pregnancy tests) are often qualitative (pregnant/not pregnant) or at most semi-quantitative. While such tests offer usability and flexibility, they typically come with increased variability, thus compromising sensitivity.

Advancements in microfluidics, detection strategies, antibody engineering, and immunoassay readers are driving the development of novel “next-generation” rapid POC diagnostics, with sensitivity approaching that of current “gold standard” clinical analyzers. There is a growing demand for higher-content readings in immunoassay formats, thus the focus of immunoassay development may shift towards highlighting high-throughput, multiplex methods. Immunoassays are steadily moving towards miniaturization and automation, making them easier and more reliable to use outside traditional laboratory settings. Nanomaterial engineering is rapidly becoming a common technique for improving optical detection in various applications. Nanoparticles possess unique chemical and physical properties, offering important possibilities as probes in biological analysis. They have several potential advantages over traditional dyes, such as low background levels since they do not scatter light. Lower detection limits can be achieved due to the lower background. Polystyrene particles exhibit visual tracking, multi-color or fluorescent labeling, stability, tunability, and biocompatibility, making them essential tools and materials in microfluidic research and experimentation.

DiagPoly™ Fluorescent Polystyrene Particles

Unveiling the Microfluidic Advantage

The application of microfluidics can effectively overcome the time constraints and labor demands of traditional immunoassays, offering numerous advantages. These advantages include:

• Increased surface-to-volume ratio: Microfluidic systems enhance antigen-antibody interactions by increasing the surface-to-volume ratio, thereby improving detection sensitivity and accuracy.
• Reduced reagent consumption: Microfluidic systems effectively reduce the usage of reagents, saving costs and lowering experimental expenses.
• Precise liquid control: Microfluidic systems enable precise liquid control, enhancing experimental reproducibility and accuracy.
• Enhanced automation: Microfluidic systems improve automation, increasing experimental throughput while reducing the potential for human errors.

The growing demand for point-of-care (POC) diagnostics has accelerated the rapid development of “lab-on-a-chip” devices. These devices aim to provide comprehensive testing, including sample preparation, analysis execution, and diagnostics, without the need for additional equipment or specialized operators.

The adoption of disposable microfluidic-based devices can meet diagnostic needs with minimal additional instrumentation. This demand primarily arises in situations where the expenditure on expensive equipment is unreasonable, the volume of specific test requirements is small, or sporadic. Potential niche markets include healthcare in developing countries, home testing in developed countries, and diagnostic or bioanalytical tools for use by emergency personnel in urgent situations.

These lab-on-a-chip devices offer an ideal pathway for the development of next-generation POC diagnostics. By leveraging the multiple advantageous characteristics of microfluidics, including laminar flow, low reagent consumption, minimal hazardous material handling, rapid response times, multiplexed sample detection, and portability, these devices hold tremendous potential in producing multifunctional diagnostic tests.

The Allure of Polystyrene Particles

Unlike PDMS, thermoplastic plastics can be manufactured using some mature industrial-scale production methods. Many types of thermoplastic materials are now available for designing POC chips. Typical thermoplastic materials used for microfluidic chips include PC, PMMA, polyethylene terephthalate (PET), and polystyrene (PS). Compared to PDMS, these materials have better solvent compatibility and offer more options for bonding (such as thermal bonding, adhesive bonding, and ultrasonic bonding). Utilizing these materials allows for the fabrication of precise microfluidic chips.

Polystyrene particles offer several advantages in microfluidic applications, including:

• Visual tracking: Colored polystyrene particles can be visually tracked by their color, facilitating easy observation and monitoring of particle movement and behavior within microfluidic systems. This visual tracking is crucial for studying processes like mixing, separation, and blending in microfluidics.
• Multi-color labeling: Polystyrene particles can be distinguished by different colors, enabling simultaneous tracking of multiple types of particles or conducting various experiments. This is significant for complex microfluidic studies and multiplexed analyses.

Colored Polystyrene Particles

• Stability: Polystyrene particles exhibit good stability in microfluidic environments, resisting disruption from fluid shear forces, thus maintaining their shape and color characteristics over time.
• Tunability: The size and color of colored polystyrene particles can be controlled through synthetic methods to meet the diverse needs of microfluidic experiments. This tunability makes them essential tools in the field of microfluidics.
• Biocompatibility: Polystyrene materials typically possess good biocompatibility, making them a safe choice for certain biological experiments or biomedical applications.

For example, Sato et al. immobilized antibodies on polystyrene microbeads and then filled them in a channel with a dam structure to keep the microbeads in the channel and serve as adsorbents for antigens to carry out immune reactions. This method achieved extremely low detection limits. Kuntaegowdanahalli et al. designed a simple inertial microfluidic device that achieves continuous fluorescent polystyrene particles of different diameters separation using the principle of Dean-coupled inertial migration in spiral microchannels, with a capture rate of 90%. At the same time, the chip was used to sort CTCs, with a capture rate of 80% and cell viability of 90%.

Conclusion

The integration of polystyrene particles into microfluidics and lab-on-a-chip platforms offers several key advantages. These include enhanced visualization and tracking of particles, reduced reagent consumption, precise fluid control, and increased automation. This technology has the potential to revolutionize immunoassays by improving sensitivity, reproducibility, and throughput while reducing costs.

By leveraging the benefits of polystyrene particles, microfluidic systems can optimize antigen-antibody interactions and streamline diagnostic processes. This integration holds promise for democratizing access to affordable and efficient diagnostics, particularly in resource-limited settings and emergency healthcare scenarios. Overall, polystyrene particles represent a significant advancement in immunoassay technology, paving the way for transformative improvements in diagnostics and healthcare accessibility.

References

1. Sato, K., Tokeshi, M., Odake, T., Kimura, H., Ooi, T., Nakao, M., Kitamori, T. (2000). Integration of an immunosorbent assay system: analysis of secretory human immunoglobulin A on polystyrene beads in a microchip. Analytical chemistry, 72(6), 1144-1147.
2. Kuntaegowdanahalli, S. S., Bhagat, A. A. S., Kumar, G., Papautsky, I. (2009). Inertial microfluidics for continuous particle separation in spiral microchannels. Lab on a Chip, 9(20), 2973-2980.