Carboxyl Quantum Dots: Selection, Synthesis, and Applications

Carboxyl quantum dots (CQDs) are ultra-small fluorescent nanoparticles typically with a diameter less than 10 nanometers. They are characterized by their carbon-based composition, containing carbon, hydrogen, and oxygen atoms, often with carboxyl (COOH) functional groups on their surface. This surface functionalization plays a crucial role in improving water solubility and bioconjugation abilities, rendering them highly attractive for biological and biomedical applications.

Selection for Carboxyl Quantum Dots

• Size: Opt for CQDs with a size distribution tailored to suit the specific intended application, as small variations in size can significantly influence their optical, electronic, and surface properties.
• Functional Groups: Assess the nature and density of functional groups on the CQDs' surface to ensure compatibility with the desired bioconjugation or surface functionalization strategies.
• Optical Properties: Evaluate the fluorescence emission wavelength, quantum yield, and photostability to match the requirements of the application, such as bioimaging, sensing, or optoelectronic devices.
• Biocompatibility: Prioritize CQDs with proven biocompatibility profiles for biological and biomedical applications, ensuring minimal cytotoxicity and immunogenicity.

Carboxyl Quantum Dots from Alfa Chemistry

Catalog	Product Name
ACMA00013533	Carboxyl Quantum Dots, Dispersion, λex = 425nm
ACMA00014276	Carboxyl Quantum Dots, Dispersion, λex = 525nm
ACMA00014277	Carboxyl Quantum Dots, Dispersion, λex = 540nm
ACMA00014282	Carboxyl Quantum Dots, Dispersion, λex = 560nm
ACMA00014287	Carboxyl Quantum Dots, Dispersion, λex = 580nm
ACMA00014300	Carboxyl Quantum Dots, Dispersion, λex = 600nm
ACMA00014316	Carboxyl Quantum Dots, Dispersion, λex = 620nm
ACMA00014342	Carboxyl Quantum Dots, Dispersion, λex = 645nm
ACMA00014347	Carboxyl Quantum Dots, Dispersion, λex = 665nm

Synthesis Methods of Carboxyl Quantum Dots

Several synthesis methods have been employed to prepare carboxyl quantum dots, often focusing on green, low-cost, and environmentally friendly approaches.

• Aqueous Synthesis

The aqueous synthesis method is a versatile and environmentally friendly approach to prepare nanoparticles, including quantum dots like carboxyl quantum dots. According to different induction or reaction conditions, aqueous phase synthesis can be further subdivided into hydrothermal, microwave-assisted, ultrasonic-driven, etc. Herman S. Mansur et al. used colloidal chemistry to obtain CdSe quantum dots in aqueous solutions of carboxyl PVA.

Synthesis for the CdSe-PVA-COOH colloidal system. [1]

• Hydrothermal Method

Involves the hydrothermal treatment of carbonaceous precursors in the presence of appropriate reactants, resulting in well-defined carboxyl quantum dots with controlled properties.

• Microwave-Assisted Synthesis

Utilizes microwave irradiation to accelerate the formation of carboxyl quantum dots, offering efficiency and control over particle size and surface functionalization.

• Ultrasonic-Driven Synthesis

Involves the cavitation-induced generation of carboxyl quantum dots from carbonaceous precursors under ultrasonic irradiation, providing a rapid and scalable synthesis route.

• Photochemical Synthesis

Involves the use of light-induced reactions to convert suitable precursors into carboxyl quantum dots, capitalizing on the energy of photons to achieve precise control over their properties.

Applications of Carboxyl Quantum Dots

• Biomedical Imaging

CQDs are used as fluorescent probes for bioimaging due to their excellent photostability, high quantum yield, and tunable emission wavelengths, enabling precise visualization and tracking of biological structures and processes. Zhenyu He et al. prepared CdTe/CdS core-shell quantum dots through microwave-assisted aqueous synthesis method, and further modified their surface with carboxymethyl chitosan (CMC). These modified quantum dots were successfully used as fluorescent probes for imaging of in vivo Madin-Darby canine kidney (MDCK) cells.

CdTe/CdS core-shell quantum dots for live cell imaging. [2]

• Drug Delivery

The exceptional surface functionalization abilities of CQDs enable their use as carriers for drug delivery, facilitating targeted delivery and controlled release of therapeutic agents.

• Sensors and Biosensors

CQDs function as efficient sensing elements for detecting various analytes, including heavy metals, biomolecules, and environmental pollutants, owing to their high surface-to-volume ratio and surface modification versatility. The carboxyl-functionalized CdS quantum dots prepared by Anil H. Gore et al. can be used as colorimetric probes for highly selective and sensitive identification of cobalt (II) ions in aqueous solutions.

Carboxyl-functionalized CdS QDs for inspection of Co²⁺ ions. [3]

• Optoelectronics

Utilized in optoelectronic devices such as light-emitting diodes (LEDs) and solar cells, where their excellent photoelectric conversion efficiency and light emission properties are harnessed for enhanced device performance.

References

1. Herman S. Mansur, et al. Materials Chemistry and Physics, 2011, 125(3), 709-717.
2. Zhenyu He, et al. Journal of fluorescence, 2012, 22, 193-199.
3. Gore, Anil H., et al. ACS Applied Materials & Interfaces, 2012, 4(10), 5217-5226.

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