Lateral Flow Assays – Maximizing Sensitivity with Gold Nanoshells

 

 

Introduction

Lateral flow assays are widely used in diagnostics and analytical testing due to their simplicity, speed, and portability. These assays rely on the specific binding of a target molecule to a capture molecule immobilized on a nitrocellulose membrane. The resulting complex is then detected by a reporter molecule, which generates a visible signal that can be read by the naked eye or a portable reader. However, the sensitivity of lateral flow assays is often limited, especially when detecting low-abundance targets or complex samples. In this article, we will explore how gold nanoshells can be used to maximize the sensitivity of lateral flow assays and improve their performance.

1: What are gold nanoshells?

Gold nanoshells are nanoparticles composed of a silica core and a gold shell. They have unique optical properties that arise from the interaction between the incoming light and the electrons in the gold shell. Specifically, gold nanoshells exhibit a strong and tunable absorption peak in the near-infrared (NIR) region, which can be used for imaging and sensing applications. The NIR light can penetrate deep into biological tissues and fluids, allowing for non-invasive and real-time detection of targets of interest.

2: How can gold nanoshells improve lateral flow assays?

Gold nanoshells can enhance the sensitivity and specificity of lateral flow assays by several mechanisms. First, they can act as a signal amplifier, increasing the intensity of the signal generated by the reporter molecule. This is achieved by conjugating the reporter molecule to the gold nanoshells, which can scatter and absorb the incoming light and emit a stronger signal. Second, gold nanoshells can improve the stability and shelf-life of lateral flow assays by preventing the aggregation and degradation of the capture and reporter molecules. This is due to the protective effect of the gold shell, which can shield the molecules from external factors such as pH, temperature, and proteases. Third, gold nanoshells can enable multiplexed detection of multiple targets in a single lateral flow assay. This is achieved by functionalizing the gold nanoshells with different capture and reporter molecules that can recognize and generate signals for different targets. The resulting assay can provide a rapid and cost-effective screening tool for complex samples such as blood, urine, and saliva.

3: How to prepare gold nanoshells for lateral flow assays?

The preparation of gold nanoshells for lateral flow assays involves several steps, including synthesis, functionalization, and conjugation. The synthesis of gold nanoshells can be achieved by various methods such as seed-mediated growth, electrochemical deposition, and template-assisted synthesis. However, the seed-mediated growth method is the most widely used due to its simplicity, reproducibility, and scalability. This method involves the reduction of gold ions in the presence of a reducing agent and a stabilizing agent, which can control the size and shape of the gold nanoseeds. The resulting gold nanoseeds are then coated with a silica layer, followed by the deposition of a gold shell by the reduction of gold ions. The thickness of the gold shell can be tuned by adjusting the concentration and ratio of the gold and reducing agents.

Once the gold nanoshells are synthesized, they need to be functionalized with capture and reporter molecules that can recognize and generate signals for the target of interest. The functionalization can be achieved by various methods such as covalent bonding, electrostatic adsorption, and biotin-streptavidin interaction. The choice of the method depends on the nature and properties of the molecules and the desired level of stability and specificity. For example, covalent bonding can provide a strong and permanent linkage between the molecules and the gold nanoshells, but it requires specific functional groups that can react with the linker. On the other hand, electrostatic adsorption can provide a reversible and non-destructive interaction between the molecules and the gold nanoshells, but it requires optimal pH and salt conditions.

Finally, the functionalized gold nanoshells need to be conjugated to the nitrocellulose membrane of the lateral flow assay. This can be achieved by various methods such as physical adsorption, covalent bonding, and inkjet printing. The choice of the method depends on the nature and properties of the nitrocellulose membrane and the desired level of stability and sensitivity. For example, physical adsorption can provide a simple and low-cost method for immobilizing the gold nanoshells on the nitrocellulose membrane, but it requires optimal pH and drying conditions. On the other hand, inkjet printing can provide a precise and reproducible method for patterning the gold nanoshells on the nitrocellulose membrane, but it requires specialized equipment and expertise.

Conclusion

Gold nanoshells have emerged as a promising platform for enhancing the sensitivity, specificity, and multiplexing capability of lateral flow assays. They can act as a signal amplifier, stabilizer, and multiplexer for various targets and sample matrices. The preparation of gold nanoshells for lateral flow assays involves several steps, including synthesis, functionalization, and conjugation. The choice ofthe method depends on the nature and properties of the molecules, gold nanoshells, and nitrocellulose membrane. With further optimization and validation, gold nanoshells-based lateral flow assays could become a valuable tool for point-of-care diagnostics, environmental monitoring, and food safety testing.