Long-range energy transfer between dye-loaded nanoparticles observed for the first time

Outcomes:

• Excitation energy can propagate far beyond the Förster radius
• The study used polymeric nanoparticles loaded with donor or acceptor dyes
• The researchers found that FRET efficiency decays as a power four of the distance
• This is the first study of energy transfer between two fluorescent organic nanoparticles
• Researchers applied this NP-NP FRET system for the detection of a DNA fragment encoding cancer marker surviving

The study demonstrated that excitation energy transfer is crucial in the development of optical materials for light harvesting, photovoltaic, and biosensing applications. In particular, long-range energy transfer in nanomaterials is a route to biosensors with high brightness and sensitivity to the target, which is important for molecular diagnostics applications. The present work is the first study of energy transfer between two fluorescent organic nanoparticles, which demonstrates that the excitation energy can propagate far beyond the Förster radius. The researchers designed polymeric NPs loaded with donor or acceptor dyes and studied energy transfer between them at different distances controlled by DNA duplexes. The FRET efficiency in the NP-NP systems decays as a power four of the distance, which was previously reported for a single dye emitter as the donor and a gold NP as the acceptor. Based on the previous works on the lipid bilayers, researchers developed a numerical model for FRET from a single dye emitter to a half-sphere with surface-located acceptors. However, it suggested that the power four distance dependence can be only achieved when the number of acceptors on the surface of NPs is much higher than the researchers actually used in their acceptor NPs. The unique features of the NP-NP FRET system are that its donor contains more than 5000 dyes and its acceptor is an emissive nanoparticle, which requires much fewer dyes distributed all over NP. These features can be explained by ultrafast excitation energy migration (EET) within dyes in both donor and acceptor NPs, which ensures that the energy transfer between NPs takes place from the surface of the donor NP to the surface of the acceptor NP. As a proof-of-concept, researchers applied this NP-NP FRET system for the detection of a DNA fragment encoding cancer marker survivin. The donor and acceptor NPs were functionalized with sequences complementary to the two parts of this fragment.

Long-range energy transfer between dye-loaded nanoparticles: observation and amplified detection of nucleic acids

Biswas; Gaki; Cruz; Silva; Combes; Reisch; Didier; Klymchenko []

Full-text link: https://doi.org/10.1002/adma.202301402

What this paper is about

• Previous works showed that the use of gold nanoparticles as an energy acceptor with a molecular donor dye resulted in the phenomenon of surface energy transfer, which displayed a decay as a power four of distance, allowing energy transfer well beyond 10 nm.
• On the other hand, dye-loaded NPs are expected to be efficient energy acceptors, because their large number of dyes generates a high molar absorption coefficient, while their much larger size compared to molecular acceptors could generate phenomena similar to SET with gold NPs as acceptors.
• Researchers found that the energy transfer between donor and acceptor NPs can reach 0.45 for ~20 nm distance between their surfaces, which is much higher than the Frster radius.

What you can learn

• For this purpose, Researchers designed a derivative of ATTO647, because, according to our previous work, it was an efficient FRET acceptor dye for R18/F5-TPB-loaded NPs, displaying remarkably high photostability.
• Donor NPs of two different sizes were prepared by the nanoprecipitation of PMMA-MA polymer with R18/F5-TPB dye in phosphate buffer at pH 7.4 and in phosphate-buffered saline, which yielded NPs of 68 and 113 nm hydrodynamic diameter, respectively, according to DLS.
• The size increase in PBS can be explained by the higher salt concentration in this buffer, which favors formation of larger NPs, in line with our earlier studies.
• FRET efficiency in our NP-NP systems decays as a power four of the distance, which was previously reported for a single dye emitter as the donor and a gold NP as the acceptor.
• Based on the previous works on the lipid bilayers, Researchers developed a numerical model for FRET from a single dye emitter to a half-sphere with surface-located acceptors.
• Second, its acceptor is an emissive nanoparticle and it requires much less dyes distributed all over NP, unlike the numerical model above. These unique features can be explained by ultrafast excitation energy migration within dyes in both donor and acceptor NPs, which ensures that the energy transfer between NPs takes place from the surface of the donor NP to the surface of the acceptor NP.

Core Q&A related to this research

1. What is the main topic of the paper “Long-range energy transfer between dye-loaded nanoparticles: observation and amplified detection of nucleic acids”?

• The paper is about long-range energy transfer between two fluorescent organic nanoparticles and its potential applications in biosensors, light harvesting, and photovoltaic devices.

2. What is the importance of excitation energy transfer?

• Excitation energy transfer is essential for developing optical materials for various applications, including biosensors, light harvesting, and photovoltaic devices.

3. What is the difference between the energy transfer in gold nanoparticles and dye-loaded nanoparticles?

• The energy transfer in gold nanoparticles as acceptors with a molecular donor dye results in the phenomenon of surface energy transfer, which displays decay as a power four of distance, allowing energy transfer well beyond 10 nm. On the other hand, dye-loaded nanoparticles are expected to be efficient energy acceptors because of their large number of dyes generating a high molar absorption coefficient, while their much larger size compared to molecular acceptors could generate phenomena similar to surface energy transfer (SET) with gold nanoparticles as acceptors.

4. What is the unique feature of the NP-NP FRET system?

• The NP-NP FRET system has two unique features. First, its donor contains more than 5000 dyes, making it much brighter than a single dye emitter, owing to the strong light-harvesting capacity of this dye ensemble and high fluorescence quantum yield. Second, its acceptor is an emissive nanoparticle, requiring much fewer dyes distributed all over the nanoparticle, unlike gold nanoparticles. These unique features can be explained by ultrafast excitation energy migration (EET) within dyes in both donor and acceptor nanoparticles, which ensures that the energy transfer between nanoparticles takes place from the surface of the donor nanoparticle to the surface of the acceptor nanoparticle.

5. How did the researchers apply the NP-NP FRET system in the detection of a DNA fragment encoding cancer marker survivin?

• The donor and acceptor nanoparticles were functionalized with sequences complementary to the two parts of the DNA fragment encoding cancer marker survivin, so that they could get together in a sandwich-like complex at a distance of… The FRET response was measured both in solution and on surfaces using a variety of fluorescence techniques.

Basic Q&A related to this research

Q: What is long-range energy transfer?

A: Long-range energy transfer refers to the transfer of energy over a relatively large distance between two or more entities, such as molecules or nanoparticles, without direct physical contact. This phenomenon is typically mediated by mechanisms such as Förster resonance energy transfer (FRET) or surface energy transfer, and it plays an important role in various applications, including energy harvesting, biosensing, and molecular diagnostics.

Q: What are dye-loaded nanoparticles?

A: Dye-loaded nanoparticles are nanoparticles that have been loaded or encapsulated with dye molecules. These nanoparticles can be designed to have specific properties, such as high stability, controlled release, and targeted delivery, making them useful in a wide range of applications, including imaging, drug delivery, and sensing.

Q: What are nucleic acids?

A: Nucleic acids are biomolecules that are essential for storing, transmitting, and expressing genetic information. They include DNA (deoxyribonucleic acid) and RNA (ribonucleic acid), which are made up of sequences of nucleotides and play critical roles in genetic inheritance, protein synthesis, and cellular processes.

Q: What are gold nanoparticles?

A: Gold nanoparticles are nanoscale particles made of gold atoms. They exhibit unique properties, such as high surface area, tunable optical properties, and excellent biocompatibility, which make them attractive for various applications, including drug delivery, imaging, catalysis, and sensing.

Q: What is an energy acceptor?

A: An energy acceptor is a molecule or entity that receives energy from another molecule or entity, typically through mechanisms such as energy transfer or absorption. In the context of long-range energy transfer or FRET, the energy acceptor is the molecule or nanoparticle that absorbs energy from an energy donor, leading to a change in its optical properties, such as fluorescence.

Q: What is surface energy transfer?

A: Surface energy transfer is a phenomenon where energy is transferred between two entities, such as molecules or nanoparticles, that are in close proximity to each other but without direct physical contact. This type of energy transfer can occur at the surface of a material or between two different materials, and it is commonly utilized in various applications, including sensing, imaging, and energy harvesting.

Q: What is the molar absorption coefficient?

A: The molar absorption coefficient is a measure of the ability of a molecule or nanoparticle to absorb light at a specific wavelength. It is typically expressed in units of cm^2/mol and represents the extent to which a substance can absorb light per unit concentration. The molar absorption coefficient is an important parameter used in quantitative analysis, such as determining the concentration of a sample based on its absorbance at a specific wavelength.

Q: What is Förster radius?

A: The Förster radius, also known as the Förster distance or critical transfer distance, is a characteristic distance that determines the efficiency of energy transfer between a donor and an acceptor molecule or nanoparticle through mechanisms such as FRET. It is calculated based on the overlap of the donor’s emission spectrum and the acceptor’s absorption spectrum, as well as their relative orientation and other factors. The Förster radius is an important parameter that influences the efficiency of long-range energy transfer and is used in the design and optimization of various optical materials and devices.

Q: What is ATTO647?

A: ATTO647 is a specific type of fluorescent dye molecule that is commonly used as an energy acceptor in FRET-based applications. It has unique optical properties, including a high extinction coefficient and high fluorescence quantum yield, which make it suitable for various applications, such as imaging, sensing, and molecular diagnostics.