Radio Frequency Characterization of Gold Nanoparticles With 3-D Printed U-Cavity Sensor
Gold nanoparticles (AuNPs) have a wide range of applications, especially in medicine, electronics, cosmetics, biosensing, and sensor technology. Their effectiveness depends on their concentration and physical properties like shape and size. Therefore, characterizing these nanoparticles accurately is essential for optimizing their performance and enabling new applications. Traditional techniques, such as electron microscopy and X-ray diffraction, used for characterization purposes are often time-consuming, complex, and require expensive, specialized equipment.
This paper presents a simpler, faster, and more cost-effective alternative using a micro-cavity sensor. A 3D-printed sensor modeled based on a microstrip patch antenna was fabricated to characterize gold nanoparticles based on their geometric shapes. The sensor utilizes the radio frequency (RF) method to detect and analyze the shape of gold nanoparticles.
The sensor features a U-shaped micro-cavity where liquid samples containing the gold nanoparticles are dispensed. Since it was fabricated using 3D printing technology, the U-cavity could be embedded directly within the substrate in a single-step manufacturing process. The U-cavity design ensured the test liquid sample stays within the cavity during measurement, enhancing accuracy. Moreover, the cavity enabled the use of standard laboratory equipment, such as a pipette, to dispense the test liquid.
Three different gold nanoparticle morphologies (rod-shaped, quasi-spherical, and spherical) were synthesized in various base solutions for the experiment. Each distinct nanoparticles were introduced into the sensor’s cavity, and the resulting return loss of the sensor was measured using a vector network analyzer. As the electrical properties of the test liquid filled into the cavity varied, it brought a change in the resonance characteristics of the sensor.
The resonance frequencies of the sensor for various measurement iterations were analyzed. To subtract the effect of the base solution on which the nanoparticles were synthesized, the three base solutions (without the gold nanoparticles) were also added to the sensor one at a time, and the resulting return loss was measured.
The resonance frequencies of the nanoparticle-infused solutions were subtracted from those of the base solutions. This difference gave the actual shift in resonance frequencies solely due to the gold nanoparticles. This differential shift was termed as “effective shift”. The results showed that the effective shift varied distinctly with the shape of the nanoparticles, with spherical nanoparticles exhibiting the most significant effective shift.
It was noted that the effective shift was more pronounced as the geometric symmetry of the gold nanoparticles increased from cylindrical to quasi-spherical to spherical. This experiment demonstrated that the presence and shape of nanoparticles can be discerned by the effective shift induced by various nanoparticles.
This novel radio frequency-based technique offers a quick, cost-effective, and reliable method for identifying and characterizing nanoparticles. The technique can be efficient in verifying whether a desired nanoparticle has been synthesized or in detecting an unknown nanoparticle in a sample. The sensor has potential for broader applications, including measuring nanoparticle concentration and biosensing applications.