Real-Time Monitoring Of Nanoparticle Synthesis

INTRODUCTION

Engineered nanoparticles (NPs) are being used for a broad array of high-technology applications, including sensing, imaging, targeted drug delivery, biodiagnostics, catalysis, optoelectronics, and film growth seeding. The enhanced optical, electrical, and catalytic properties of metal NPs are strongly correlated with their size, shape, and structure. As such, the physicochemical characterization of NPs is critically important to ensure their effective use and applicability.

Nanoparticle synthesis is a rapidly evolving field with applications in various industries, including medicine, electronics, and environmental science. The ability to create nanoparticles with specific properties and functions has strongly contributed to the development of the field of technology and research. However, the synthesis of nanoparticles is a complex process that requires precise control over various parameters to ensure the desired outcome. Real-time monitoring of nanoparticle synthesis is crucial for maintaining quality, optimizing efficiency, and achieving the precise characteristics needed for specific applications.

Figure 1: Source of engineered nanoparticles (ENPs) in various industry.

METHODS

Ultraviolet-visible spectroscopy (UV-VIS) is one of the most widely used methods to monitor the synthesis process of NPs. UV-VIS absorption bands are related to important properties such as the diameter, shape, and polydispersion of metallic and semiconductor NPs. Thus, this analytical technique is used during NP synthesis to monitor NP formation, assess suspension stability under different conditions and media, and establish the optical properties of the newly formed nanomaterials.

Using UV-VIS spectroscopy to monitor the synthesis of the silver nanoparticles (AgNPs) as the metallic nanoparticles possess a property known as surface plasmon resonance (SPR) which is primarily because their strong interaction with light occurs because the conduction electrons on the metal surface undergo a collective oscillation when they are excited by light at specific wavelengths and it causes the absorption and scattering intensities of silver nanoparticles to be much higher than identically sized non-plasmonic nanoparticles.

Figure 2: AgNO₃ , M. macrostachyum leaf extract, AgNPs solution and sixty minutes of reaction between 10 ml of M.macrostarchyumleaves extract and 50 ml AgNO₃ 10^-3 M.

For the synthesis of the AgNPs, a volume of Megaphrynium macrostachyum leaf extract (10ml) was added to 50 ml of 10^-3M aqueous AgNO₃ solution and incubated at room temperature in the dark to minimize the photoactivation of silver nitrate. The reactions were made under static conditions. The first hour of reaction was monitored measuring the absorbance at 5, 10, 20, 30, 40, 50, and 60 min. The absorption spectra of the synthesized silver nanoparticles were recorded against water in order to monitor the formation and stability of AgNPs. The color change of the mixture of solution plant extract and silver ion is first recorded through visual observation. The colors of silver nitrate, M. macrostachyum leaf extract, and silver nanoparticles solution are shown in Fig. 2.

Fig. 2 shows the UV–visible spectra of AgNPs as a function of time after the addition of different quantities of M. macrostachyum leaf extract. The reaction time resulted in a gradual increase of absorbance bands. The color intensity of the solution changed from light yellow to deep brown at the end of the reaction because of the increasing amount of AgNPs as well as aggregation. The plant leaf extract from M. macrostachyum acts as a reductant as well as a capping agent, therefore mediating the synthesis as well as stabilization of the silver nanoparticles. The conduction electrons undergo oscillation due to the strong interaction of light with the AgNPs. The UV–vis spectra also revealed that the formation of AgNPs occurred rapidly within a few minutes indicating that M. macrostachyum speeds up the biosynthesis of AgNPs.

Figure 3: a) UV-Vis spectra of synthesized AgNPs with controlled size b) Comparing the experimentally obtained values (black squares) and theoretically estimated values (blue circles).

UV-Vis spectroscopy can reflect the growth of silver nanoparticles (AgNPs) by exhibiting the typical surface plasmon absorption maxima from 391 to 453 nm (see Fig. 3a). The size of AgNPs was measured using dynamic light scattering (DLS) analysis and compared with the theoretically predicted values (using Mie’s theory based on the position of the wavelength with the largest peak of the LSPR position). As it can be seen (Fig. 3b), the experimental results are adequately consistent with the results predicted by the correlation.

The presence of a dipole SPR peak in the extinction spectrum confirms the spherical morphology of the synthesized nanoparticles and the increase in the size of AgNPs leads to a red shift in the local surface plasmon resonance position (LSPR). Because AgNPs are formed through a two-step nucleation and growth mechanism. These silver ions in solution are reduced on the surface of these particles and AgNPs continuously grow thereby increasing the size and number of particles many times. To control this problem of increasing particle size, through the absorption spectrum in the uv-vis region, the maximum wavelength position of each obtained spectral region can be considered.

BUILD SYSTEM

INTINS can provide a complete system for this application. The Ocean SR4 UV-VIS spectrometer is a high-performance spectrometer with high-speed spectral acquisition and excellent signal-to-noise ratio performance for diverse applications. This small-footprint instrument unlocks UV-VIS signature data from 190-1100 nm and entrance slit options in widths of 5 µm to 200 µm. The SR4 spectrometer is compact, versatile, and compatible with Ocean Insight light sources and accessories.

The most important thing about choosing a light source for reflection is to find one with strong output over the wavelength range of interest. In this application, the light source needs to be observed in the Visible spectrum from 400 nm - 900 nm. Our product - Tungsten halogen light source - is suitable to meet these standards. Ocean Insight's HL-2000 series offers models ranging from 380nm – 2400 nm and varies from high power models (HL-2000-HP Light Source) to long life models (HL-2000-FHSA-LL Light Source and HL -2000-LL Light Source), both meet your application requirements.

CONCLUSION

UV spectroscopy plays an important role in monitoring the synthesis process of metal nanoparticles. Its spectrum plays an important role in detecting important properties such as concentration changes, particle size changes, etc. By using our integrated setup for measuring samples through absorbance we can clearly measure the spectrum with high speed and accuracy.