Quantum Dot Labeling

As a leading CRO, BOC Sciences is committed to providing leading-edge quantum dot labeling services. Our technology enables researchers and medical professionals to see and dissect complex biological mechanisms with unrivalled precision and precision. With our deep expertise in bioconjugation and nanotechnology, we are able to tailor the unique needs of each study and design highly personalized solutions.

What is a quantum dot?

Quantum dots are nanocrystals or semiconductor nanocrystals composed of cadmium selenide (CdSe), cadmium telluride (CdTe), cadmium sulfide (CdS), zinc selenide (ZnSe), indium phosphide (InP) or indium arsenide (InAs), or CdSe nuclei coated with a layer of ZnS or CdS. When a semiconductor material absorbs a photon with an energy greater than its band gap, an electron is excited from the valence electron band to the conduction band, leaving a positively charged hole to form an electron-hole pair, an electron-hole pair is called an exciter. Excitons are like artificial atoms, with a radius of 1 to 10nm, and their size depends on the properties of the semiconductor. Because the semiconductor crystal size and the exciter size are similar, a strong quantum confinement effect changes the exciter properties, and as the crystal size decreases, the exciter behaves more like a particle in a box. Its energy level is primarily determined by the size of the particle (box), rather than by the properties of the entire semiconductor. Such semiconductor nanocrystals, which exhibit a strong quantum-limiting effect in three dimensions, are called quantum dots. Electrons and holes combine to produce light, the length of the light wave is mainly determined by measuring the size of the quantum dot, the existing technology can prepare a particularly uniform size of the quantum dot, and the generated light band width of 10 ~ 50nm.

In medical field, quantum dot labeling technology has received special attention due to its high sensitivity and multicolor labeling capabilities, especially for high-precision biomolecular labeling and live cell imaging.

Methods of quantum dot labelling

Quantum dots can be combined with specific antibodies or small molecules, without changing their chemical properties, and can emit specific wavelengths of fluorescence after being excited by the light source to realize the identification and detection of the target. The binding between quantum dots and biological macromolecules such as nucleic acids, proteins, nutrient carriers, etc., usually has the following methods: electrostatic attraction method, conventional crosslinking agent labeling method and biotin-avidin method.

Electrostatic attraction method

When a positively charged hydrogen nucleus meets another electronegative atom, it generates electrostatic attraction. The surface of the thioglycolated quantum dots is negatively charged, and the surface region of the positively charged protein can be connected by electrostatic attraction without the need for other reagents. For neutrally charged proteins, positively charged structures can be constructed by modifying the proteins at their ends, so that they can be electrostatic adsorbed on the surface of quantum dots. In addition, after modifying the surface of the quantum dot to make it negatively charged, in addition to the above direct electrostatic attraction of the target substance, it can also be electrostatic adsorbed to attach avidin, and then rely on the highly specific binding of biotin-avidin to indirectly connect the quantum dot to the protein molecule. This connection reduces the surface defects of quantum dots and increases the fluorescence intensity of quantum dots. However, when the proportion of proteins is too large, cross-binding between proteins causes some quantum dots to accumulate, thus reducing the fluorescence intensity of quantum dots. Therefore, controlling the ratio of quantum dots to target proteins is crucial for detection sensitivity.

Conventional crosslinker labeling

Crosslinkers are a class of small molecule compounds, the relative molecular mass is generally 200 ~ 600u, with two or more reactive ends for special groups (such as amino, sulfhydryl, etc.), and can be coupled with two or more molecules to bind these molecules together. Commonly used crosslinkers are 1-ethyl-3 - (3-dimethylaminopropyl) carbodiimide (EDC), N, N '-dicyclohexyl carbodiimide (DCC), n-hydroxysuccinimide (NHS), glutaraldehyde, diisocyanate compounds, and dinitrobenzene dihalide. By using these crosslinkers, the modified carboxyl group and the amino group of small molecules on the quantum dots can be coupled and labeled by condensation. By using EDC and NHS crosslinking methods, 1, 3-diamino-2-propyl alcohol has been coupled to carboxylated quantum dots to hydroxylate them, reduce the size of the quantum dots (13 ~ 14nm diameter), increase their fluorescence intensity and stability in acidic or alkaline environments. The nonspecific binding of quantum dots to cell membranes or proteins is greatly reduced (only 1/140 of the carboxylated quantum dots). QDs modified by ligand exchange can be attached to fibroblasts using EDC and NHS methods, and such quantum dots can penetrate the cell membrane and reach the nucleus.

Biotin-avidin method

Biotin-avidin system (BAS) is a new type of biological reaction amplification system developed rapidly in the late 1970s, which has been widely used in the field of life science research. Because of its high affinity between biotin and avidin and its multistage amplification effect, and its organic combination with fluorescein, enzyme, isotope and other immunolabeling technologies, the specificity and sensitivity of various tracer immunoassays are further improved. At present, the most common way to bind quantum dots to biomolecules is through the biotin-chain (mycoavidin) system, which is used for antigen and antibody mutual recognition, in vivo labeling and specific labeling. This quantum dot probe has high sensitivity and strong fluorescence signal.

Other labeling method

Feng et al. used the heterofunctional cross-linking agent succinimide 4- (N-maleimide methyl) -cyclohexane-1-carboxylate to conjugate the quantum dots with the sulfhydryl group of antibodies or ligands through a condensate reaction, which was used for the determination of human IgM by capillary electrophoresis with good results.

Advantage of quantum dot labelling

Quantum dots have several advantages over ordinary fluorescent dyes.

• High fluorescence intensity. The quantum dot efficiency series is 0.5, good stability, photobleaching resistance, ZnS coated CdSe than Rhodamine 6G molecule is 20 times brighter, more than 100 to 200 times more stable, and can withstand multiple excitation.
• A variety of luminous colors. Quantum dots with different particle sizes emit light in different colors, and the color tuning function can also be achieved by changing the composition of nanocrystals (such as: CdS emit blue light, InP emit red light).
• Suitable for multiple transmission of space and spectrum.
• The cold light lifetime of quantum dots is generally 30 ~ 100ns. This time is much longer than the background fluorescence and Raman scattered light of most sample matrices, so the effect of background fluorescence can be weakened or even eliminated.
• Quantum dots have a wide spectrum range. Quantum dots have a wide absorption spectrum, which just extends to the ultraviolet region. The wavelength of emitted light of quantum dots is basically independent of the wavelength of excitation light. Therefore, a single wavelength of excited light, a spectrum of one band, or the entire excitation source can excite quantum dots, causing them to produce a relatively narrow spectrum of fluorescence in the entire visible region.

Quantum dot labelling in the medical field

Quantum dot labeling services are widely used in the field of biomedicine. For example, in cell imaging, quantum dot labeling technology can achieve multicolor imaging and long-term tracking, providing a powerful tool for cell biology research, and quantum dots have been used to label tumor cells for in vivo imaging. In terms of tissue imaging, quantum dot labeling technology can be used for tissue sections and in vivo imaging, providing a new way for pathological diagnosis and disease treatment. In terms of flow cytometry and immunohistochemistry, quantum dot labeling technology can realize the specific labeling and detection of cell surface or intracellular molecules, which provides important support for clinical diagnosis and scientific research. Quantum dots can also be used to track the movement of drugs in the body, or to study the structure of cells and tissues in a patient's body. Quantum dots can produce a variety of colors of light, depending on the size of the dot.

Our quantum dot labeling services

At BOC Sciences, we offer a comprehensive suite of quantum dot labeling services designed to meet the diverse needs of the biomedical research community.

Custom quantum dot synthesis and modification: Quantum dots can be synthesized according to specific emission wavelengths and surface functions. This customization ensures optimal compatibility with your chosen biological target and imaging mode. In order to improve the stability and biocompatibility of quantum dots in biological systems, the surface of quantum dots will be functionalized, such as PEG (polyethylene glycol modification) to reduce non-specific adsorption and extend the cycle time in vivo.

Quantum dot labeling antibody: Antibody can achieve accurate labeling for specific target antigens after binding with quantum dots. This process is mostly accomplished by covalent bonding or efficient bioconjugating strategies such as biotin-avidin, and the complexes formed are outstanding in immunofluorescence imaging. By relying on the bright fluorescence characteristics of quantum dots, the distribution of antigens in cells and tissues can be accurately located.

Quantum dot labeling peptide: By means of chemical modification, quantum dots can effectively bind to peptides and help track the dynamic distribution, transport routes and functional mechanisms of peptides in biological systems, such as applications in monitoring neurotransmitter release activities or revealing the interaction mechanism between peptides and cell receptors.

Quantum dot labeling nucleic acid: DNA and RNA's marriage with quantum dots opens up a new era of gene expression analysis, accurate nucleic acid localization and high sensitivity detection. The use of fluorescence resonance energy transfer (FRET) technology or direct covalent binding strategy to anchor quantum dots to nucleic acid probes or nucleic acid molecules themselves not only broadens the practical boundaries of bioimaging, gene diagnosis and therapeutic intervention, but also provides a powerful tool for basic scientific research.

Quantum dot labeling small molecule: The small molecule world covers the key players in many life activities such as drugs, metabolites, neurotransmitters, etc. Through the subtle combination of quantum dots and these small molecules, scientists can deeply explore their metabolic pathways, mechanisms of action and complex intermolecular interactions in organisms, which is of immeasurable value for clarifying the biological function basis of small molecules, guiding the development of new drugs and optimizing treatment strategies.

Multichannel imaging solutions: Taking advantage of the unique optical properties of quantum dots, we developed a multipath imaging solution that allows multiple targets to be visualized simultaneously in a single sample. This ability is particularly valuable for complex biological systems where multiple interactions and pathways need to be studied simultaneously.

Using advanced quantum dot synthesis and labeling technology, BOC Sciences can efficiently and stably prepare high quality quantum dot-biomolecular conjugates. These conjugates have excellent fluorescence properties and specific recognition capabilities, enabling efficient labeling and imaging of target molecules. And we can provide a variety of different types of quantum dot marking services, including quantum dots of different colors, different sizes, and different surface modifications to meet different experimental needs.

FAQ

1. Why should I choose quantum dot labeling over traditional dyes?

Quantum dots offer several advantages over traditional dyes, including:

• Higher quantum yield for stronger signal intensity.
• Reduced photobleaching for sustained signal over time.
• Allows multiplexing with multiple QDs without significant overlap.

2. What types of biomolecules can be labeled with quantum dots?

Quantum dots can label a variety of biomolecules such as proteins, nucleic acids, antibodies, and peptides. Custom conjugation can be performed to meet specific research needs.

3. What is the process for labeling biomolecules with quantum dots?

• Consultation: Discuss your specific application and requirements.
• Preparation: Conjugation of quantum dots with your biomolecules using optimized protocols.
• Validation: Characterization and validation to ensure successful labeling.
• Delivery: Shipment of the labeled biomolecules with detailed documentation and usage guidelines.

4. How do you ensure the quality and consistency of quantum dot conjugates?

We adhere to stringent quality control measures, including:

• Spectroscopic analysis: Verification of absorption and emission properties.
• Bioconjugation efficiency: Assessment of labeling efficiency and biomolecule activity.
• Purity assessments: Removal of free quantum dots and unbound biomolecules.

5. Are your quantum dot conjugates compatible with live-cell imaging?

Yes, our quantum dots are rigorously tested for biocompatibility and can be used for live-cell imaging under appropriate conditions.

6. How do I store and handle the labeled conjugates?

Labeled conjugates should be stored at recommended conditions (e.g., 4 ℃, protected from light) as specified in the provided guidelines. Handle with care to avoid photobleaching and degradation.