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Inquiry: Respected Sir/Madam The Gold conjugation kits are available at various sizes of the gold nanoparticles. What will be the effect of these sizes? What will be the difference in the signals? Kindly help me choose the most suitable size for a lateral flow chromatography colorimetric detection.
Asked on Mar 22 2017
Thank you for getting in touch.
I can confirm that 40nm gold nanoparticles are the most popular choice for lateral flow assays. This is due to an optimal combination of high contrast colour which appears cherry red and surface area for effective and efficient analyte testing,
30nm and 60nm gold nanoparticle also have specific advantages depending on the design and application of the lateral flow test.
30nm gold nanoparticles have a darker red appearance that improves contrast against white lateral flow assay membranes compared to 40 nm spheres. With increased contrast, due to the smaller size 30 nm gold nanoparticle require more conjugated antibodies to achieve an equivalent mass concentration.
60nm gold nanoparticles have a lighter red appearance which trades contrast efficiency for increased optical absorbance per particle. Thus, less particles are needed to produce a measurable reading. This means 60 nm gold are ideal for immunoassays with low target analyte concentration samples, or when the targeting moiety is very expensive.
In addition to this, the following information may be helpful:
In principle, the smaller gold particles produce a higher labelling intensity. This is due to reduced steric hindrance to antigen detection. For example, a 1nm gold particle, attached to the Fc region should not significantly affect antibody binding. A 20nm particle, however, while being more visible, will produce a greater steric hindrance. In addition, the increased charge repulsion between larger particles reduces the number of labelled antibodies gaining access to the target antigen.The surface of gold nanoparticles have free electron which resonate with the oscillating electric field of a light ray propagating near it, creating a concerted oscillation of electron charge called surface plasmons.
These surface plasmons will cause absorption and reflection of lights, and these absorption and reflection are dependent on the size of the gold nanoparticle. For smaller gold nanoparticle, the reflected light is red – whereas the bigger nanoparticle will start to absorb redder wavelength and reflects more blue wavelength, yielding purple or more blue colour. Since larger nanoparticles have a higher magnitude of absorption and available surface area for antibody conjugation, they can provide better assay sensitivity. However, when larger nanoparticles are used, absorption in the longer wavelengths reduces the contrast on the test strip.
Answered on Mar 22 2017