How to Make PLGA Fluorescent?

by | May 6, 2023

Have you ever wondered how scientists make polymer materials fluorescent? One popular polymer used in biomedical research is PLGA, which is known for its biocompatibility and controlled release properties. But how can PLGA be made fluorescent for imaging and tracking purposes?

Poly(lactic-co-glycolic acid) or PLGA is a copolymer made from lactic acid and glycolic acid. It has been widely used for drug delivery and tissue engineering due to its biodegradability and safety. However, PLGA itself is not naturally fluorescent, which makes it challenging to visualize and monitor in biological systems. Hence, researchers have developed various methods to make PLGA fluorescent, including adding fluorescent dyes or modifying the polymer structure.

In this article, we will explore different approaches to make PLGA polymer fluorescent and their applications in biomedical research. Understanding how to make PLGA fluorescent can broaden the usage of this versatile polymer and enhance our understanding of biological processes.

Why Make PLGA Fluorescent?

Green fluorescent protein

The main benefits of making PLGA fluorescent is the ability to employ imaging techniques such as confocal microscopy and transmission electron microscopy to track the particles within cell cultures and tissues. Researchers can easily observe the uptake and distribution of fluorescent particles in real-time, providing valuable information on the cellular and tissue-level interactions of drug delivery systems.

The use of fluorescently labeled PLGA nanoparticles also allows for precise tracking of particles in vivo. The particles’ in vivo distribution can be monitored through techniques such as fluorescence spectra or confocal laser scanning microscopy, enabling insights into their biodistribution and pharmacokinetics. These imaging techniques offer precise information about the particles, including their location, size, and density, which are crucial for the development of effective drug delivery systems.

Factors Affecting Fluorescence of PLGA

When it comes to making PLGA fluorescent, there are various factors that need to be taken into consideration. Among these factors are the concentration of fluorescent molecules, the polymer properties, and the choice of solvent.

Concentration of Fluorescent Molecules

When making PLGA fluorescent, it is crucial to consider the concentration of fluorescent molecules that will be added to the polymer matrix. The concentration of fluorescent molecules can significantly impact the fluorescent properties of PLGA, including the intensity and spectrum of fluorescence. Thus, without proper consideration of the concentration, it might not be possible to achieve the desired fluorescent properties.

To obtain the desired concentration of fluorescent molecules, the calculated quantity of the stock solution needs to be added to the solvent or S phase. The calculation must take into account the desired concentration as well as the volume of the stock solution required to achieve it. The addition of the stock solution should be done with great care, and it must be ensured that the added quantity is precise to avoid any deviations in the final results.

Polymer Properties

The fluorescence properties of PLGA are influenced by several key polymer characteristics. One of the most important parameters to consider is the molecular weight of the polymer. A higher molecular weight can lead to decreased fluorescence intensity due to reduced particle diffusion in a given area. Conversely, a lower molecular weight can result in increased fluorescence, which could make it easier to detect the particles.

Another important parameter to account for is the size distribution of the PLGA nanoparticles. It is important to ensure a narrow size distribution to maintain consistent fluorescence properties. A broad size distribution could result in a variation in fluorescence due to incomplete nanoparticle formation due to physical differences in the particles.

The biodegradability of the PLGA polymer can also impact the fluorescence of the nanoparticles. The break down of the PLGA polymer can result in the release of fluorescent compounds, which could result in increased fluorescence intensity over time. This property is particularly important in the development of drug delivery systems.

Surface modifications of PLGA nanoparticles, including PEGylation, can also affect the fluorescence properties of the particles. PEGylation can significantly reduce the surface charge of PLGA nanoparticles, which can decrease the overall fluorescence intensity. However, in some cases, surface modifications can enhance bioavailability, cellular uptake, and in vivo distribution of the PLGA particles, ultimately improving their utility as fluorescent markers in studies.

Solvent Choice

chemical solvent

When it comes to making PLGA fluorescent, the choice of solvent plays a crucial role in determining the physicochemical properties of the resulting nanoparticles. During nanoprecipitation, a good solvent is used to dissolve the PLGA polymer, followed by the addition of a non-solvent to trigger nanoparticle formation. In this process, the solvent used for dissolution of PLGA is critical in determining the size and fluorescence properties of the resultant nanoparticles.

The efficiency of fluorescence labeling, as well as the stability and hydrophobicity of the nanoparticles, are largely dependent on the choice of solvent. Organic solvents such as dichloromethane, tetrahydrofuran, and acetonitrile have been commonly used to dissolve PLGA due to their ability to dissolve the hydrophobic PLGA polymer effectively.

However, aqueous solutions pose a challenge due to the hydrophobic nature of PLGA, which makes it difficult to achieve effective nanoparticle formation. Nonetheless, adjusting the pH of the solution can improve the miscibility of PLGA with water, allowing for the successful formation of fluorescent nanoparticles.

It is important to choose a solvent that will ensure the highest quality nanoparticle formation for the intended application. The physicochemical properties of the nanoparticle, such as size, stability, and fluorescence properties, can be controlled by selecting the appropriate solvent. Therefore, careful consideration of solvent choice is critical when making PLGA fluorescent nanoparticles.

Methods to Incorporate Fluorescent Molecules into PLGA

There are various methods to incorporate fluorescent molecules into PLGA, a commonly used biodegradable polymer in drug delivery systems. This can be achieved through covalent attachment, physical mixing, and entrapment. Here are the details one by one.

Covalent Attachment

Covalent attachment

Covalent attachment of fluorescent molecules to PLGA (polylactic-co-glycolic acid) nanoparticles is a highly effective way of creating long-lasting and stable fluorescence imaging agents. This involves the creation of a chemical bond between the fluorescent molecule and the PLGA polymer backbone through the use of reactive groups.

A reactive group, such as an amine, carboxylic acid, or thiol, must be present on both the fluorescent molecule and PLGA polymer to achieve covalent attachment. Coupling agents such as carbodiimide and imidazolium-based reagents can facilitate the formation of a covalent bond.

The use of covalent attachment ensures that the fluorescent markers will not detach from the nanoparticle surface, providing a more stable and long-lasting fluorescence. This method is particularly useful in applications that require the nanoparticles to be exposed to a biological environment for extended periods.

Physical Mixing

Physical mixing is a simple yet effective method to incorporate fluorescent molecules into PLGA for various applications such as drug delivery and cellular imaging. The method involves dispersing the fluorescent molecules into a polymer solution and stirring or sonicating the solution to ensure a homogenous distribution of the fluorescent molecules within the PLGA matrix.


Fluorescent markers are commonly used to visualize biological processes through fluorescence imaging. PLGA nanoparticles have gained attention as promising drug delivery systems due to their biodegradable and biocompatible properties. Entrapping fluorescent molecules into PLGA nanoparticles has therefore become an important area of research.

The process of entrapping fluorescent molecules into PLGA nanoparticles involves dissolving the PLGA polymer and the fluorescent molecule in a solvent of choice. The resulting solution is then added dropwise to a surfactant solution or an aqueous solution to form nanoparticles. The entrapped fluorescent molecules will be encapsulated within the polymer matrix, providing an additional feature that allows for their detection and tracking in vivo.

Characterization of Fluorescent PLGA

Characterizing fluorescent PLGA nanoparticles is an important step in understanding their physical and chemical properties and assessing their potential in biomedical applications. There are various techniques available to characterize these particles, including UV-Vis spectroscopy, fluorescence spectroscopy, and scanning electron microscopy (SEM).

UV-Vis Spectroscopy

UV-Vis spectroscopy is a highly effective technique for analyzing the electronic transitions of fluorescent molecules. When applied to the characterization of fluorescent PLGA, UV-Vis spectroscopy can provide critical information about the absorption and emission behavior of the incorporated fluorescent molecules.

When assessing fluorescent PLGA, it is essential to establish a baseline measurement for the polymer itself before measuring the fluorescent signal. This can be achieved by measuring the absorbance spectrum of PLGA in a solvent that does not absorb in the relevant spectral region. The fluorescence signal from the PLGA can then be easily measured with respect to this baseline.

The resulting spectra obtained through UV-Vis spectroscopy can provide important insights into the identity, concentration, and distribution of the fluorescent molecules within the PLGA matrix. The absorption spectrum gives information about the wavelengths of light that are absorbed by the fluorescent molecule while the emission spectrum provides data on what wavelengths of light are emitted by the molecule when excited by light.

Fluorescence Spectroscopy

Fluorescence spectroscopy is a widely used analytical technique for characterizing fluorescent materials, including PLGA nanoparticles. The basic principle of fluorescence spectroscopy is based on the absorption of light by a molecule, which subsequently leads to its excitation or promotion to a higher energy state. The molecule then releases the excess energy as fluorescence emission, characterized by a specific wavelength and intensity.

In the case of fluorescent PLGA nanoparticles, fluorescence spectroscopy is used to measure the fluorescence intensity, emission spectra, and quantum yield of the nanoparticles. The fluorescence intensity refers to the amount of light emitted by the nanoparticles when excited by a light source, while the emission spectra represent the range of wavelengths emitted by the nanoparticles. The quantum yield represents the efficiency of the fluorescence emission process and is defined as the ratio of the number of photons emitted to the number of photons absorbed.

Scanning Electron Microscopy

Scanning Electron Microscopy (SEM) is a powerful imaging technique used in the characterization of fluorescent PLGA particles. SEM imaging allows for the observation of particle morphology, allowing researchers to determine the size distribution of the nanoparticles.

To prepare a sample for SEM imaging, the PLGA particles should be diluted in purified water and deposited onto a carbon-coated copper grid. The grid should then be washed with purified water and stained with a 2% uranyl acetate water solution. Excess liquid should be blotted off with filter paper, and the sample should be allowed to dry in a desiccator for at least 10 hours.

Once the sample is properly prepared, SEM imaging can be performed using a tool such as the JEOL 1010. Researchers can then acquire images of the fluorescent PLGA particles at various magnifications. Using image analysis software such as ImageJ, particle size can be accurately measured to determine the size distribution of the particles.


The incorporation of fluorescent molecules into PLGA is a promising approach for developing fluorescent nanoparticles for various biomedical applications, including drug delivery and fluorescence imaging. With the use of different methods, the fluorescent PLGA can be synthesized with narrow size distribution, high loading efficiencies, and controlled fluorophore location. Moreover, the characterization and analysis of fluorescent PLGA nanoparticles are essential for evaluating their in vivo distribution and cellular uptake, which can provide important insights into their biological environment and efficacy.