Carboxyl Quantum Dots

What it means: Quantum Dots (QDs) are semiconductor nanocrystals (typically 2–10 nm core diameter) whose optical emission wavelength is determined by particle size — smaller dots emit at shorter (bluer) wavelengths, larger dots at longer (redder) wavelengths. This "size-tunable" emission is a unique property not shared by organic fluorophores.

Why it matters:

• Far superior photostability compared to organic dyes — enabling long time-lapse imaging and repetitive scanning.
• Narrow emission peaks (FWHM < 35 nm) reduce spectral crosstalk in multiplexed detection panels.
• Multiple QD colors can be excited simultaneously from a single UV or blue light source.
• High molar extinction coefficient gives bright signal per molecule.

How to interpret here: This product is a Quantum Dot format. The emission wavelength value shown is the peak output wavelength — select it to match your detector filter/laser combination. All wavelengths can be excited together for multiplexed assay panels.

Tip: QDs are larger than organic dye molecules (~10–20 nm total diameter with coating). This may affect steric accessibility in some applications — test at pilot scale before full assay build-out.

What it means: Carboxyl (–COOH) surface groups are reactive functional groups that enable covalent coupling to primary amines (–NH₂) via EDC/NHS activation chemistry. The carboxyl group itself is not reactive without activation — it requires EDC (with optional Sulfo-NHS) to form an active NHS ester intermediate.

Why it matters:

• Enables coupling to lysine residues or N-terminus of antibodies and proteins — the most commonly used bioconjugation approach.
• Gives a stable, covalent amide bond between the particle surface and the target biomolecule.
• Activation step (EDC ± NHS) must be performed in amine-free buffer (pH 5.5–6.0 for EDC, pH 7.2–7.5 for coupling).
• Low non-specific binding after blocking with BSA or similar makes carboxyl beads well-suited for quantitative assays.

How to interpret here: This product has Carboxyl surface chemistry. Coupling requires EDC/NHS activation as described in the protocol (see Documents). Avoid Tris, glycine, or other amine-containing buffers during activation and coupling steps — they inactivate the NHS ester.

Tip: Add Sulfo-NHS along with EDC to stabilize the activated intermediate. This significantly improves coupling efficiency at neutral pH and longer incubation times.

What it means: Emission Wavelength is the peak fluorescence output of the quantum dot. Available wavelengths: 425 nm–645 nm.

Why it matters:

• Each wavelength corresponds to a specific detector filter/laser channel in your instrument.
• Multiple QD wavelengths can be detected simultaneously with a single UV or blue excitation source — enabling multiplexed panels.
• All wavelengths from 425 nm–645 nm are available as individual products and as a combo pack.
• Narrow emission peaks (FWHM < 35 nm) minimize spectral crosstalk between detection channels.

How to interpret here: Select the emission wavelength that matches your available detector filter set. For multiplex assays, select one wavelength per detection channel. The full range 425 nm–645 nm can be combined in the same experiment with a single excitation source.

Tip: Always verify the exact filter transmittance of your instrument to confirm the selected wavelength is centered within the bandpass. A slight mismatch can reduce signal intensity significantly.

What it means: Activated (Ready-to-conjugate) means the particle surface carries a reactive functional group (carboxyl, amine, NHS ester, maleimide, or azide) that is ready for coupling to your chosen biomolecule. A conjugation reaction step is required before the beads can capture targets.

Why it matters:

• Maximum flexibility: choose the biomolecule you conjugate based on your specific target and assay design.
• Coupling density can be optimized by adjusting protein:bead ratio during conjugation.
• Multiple coupling chemistries available depending on the specific surface group (see Surface Chemistry chip).
• Conjugation kits are available to simplify the workflow and reduce protocol development time.

How to interpret here: This product is Activated (Ready-to-conjugate). You will need to perform a coupling reaction to attach your specific antibody, protein, or oligonucleotide before use. Follow the coupling protocol in the Documents section; conjugation kits providing all required buffers are available separately.

Tip: Always test conjugation efficiency (e.g., by BCA assay on the supernatant after magnetic separation) before scaling up to full assay development.

What it means: Aqueous dispersion means this product is supplied as a colloidal suspension in an aqueous buffer (typically PBS, DI water, or a proprietary storage buffer). The particles are dispersed and ready for use in water-based biological applications without any solvent exchange step.

Why it matters:

• Compatible directly with cell culture media, PBS, HEPES, and other standard biological buffers.
• No solvent exchange or phase transfer required before use in aqueous assay protocols.
• Aqueous colloidal stability maintained by surface coating (polymer, PEG, or functional group layer).
• Bath sonication before use ensures complete resuspension after storage sedimentation.

How to interpret here: This product is in Aqueous dispersion. It can be used directly in your assay buffer after resuspension. Confirm compatibility with your specific buffer conditions (ionic strength, pH, protein concentration) by checking the product specification sheet or running a small-scale stability test.

Tip: High ionic strength buffers (>500 mM) or pH extremes outside the specification range may compromise colloidal stability. Always validate in your specific matrix.

What it means: Applications list the primary experimental workflows this product has been used for: Immunoassay, Multiplexing, Tissue Imaging, Flow Cytometry.

Why it matters:

• Immunoassay: this product can directly support this workflow based on its surface chemistry and particle properties.
• Multiplexing: this product can directly support this workflow based on its surface chemistry and particle properties.
• Tissue Imaging: this product can directly support this workflow based on its surface chemistry and particle properties.

How to interpret here: This product is suited for the listed applications. The most relevant for this product are Immunoassay, Multiplexing. Review the application-specific protocol in the Documents section before beginning workflow development.

Tip: Application suitability depends on specific experimental conditions (buffer, sample matrix, target concentration). Always validate at pilot scale before full assay development.