Choosing and using Grove gold colloids
On this page
Choose by laser wavelength, surface chemistry or fluorescence, then plan handling and dilution. Optical figures are read from Grove's example spectra on the product pages.
Which colloid for which job
Scroll sideways to see all columns.
| If you need | Start with | Why |
|---|---|---|
| Plasmonic sensing at 514–532 nm | Gold-PVP Red | ~100% of peak absorbance at 532 nm |
| SERS or plasmonic sensing at 633 nm | Gold-PVP Blue or Gold-PEG Blue | ~95% (PVP Blue) and ~100% (PEG Blue) of peak absorbance at 633 nm |
| SERS or plasmonic sensing at 785 nm | Gold-PEG Blue | ~80% of peak absorbance at 785 nm, the most in the range |
| Fluorescence with UV excitation | Gold-L-Cysteine Fluorescent Red | Absorption peak ~370 nm, emission peak ~645 nm |
| A surface you can replace with thiols | Gold-PVP Red or Gold-PVP Blue | Thiols displace PVP, though not always completely |
| A PEG surface | Gold-PEG Blue | The only PEG-coated colloid in the range |
| Carboxyl and amine groups for coupling | Gold-L-Cysteine Fluorescent Red | L-cysteine leaves both groups free |
| Catalysis or electrocatalysis | Gold-PVP Red or Gold-PVP Blue | Listed by Grove as a research use for both |
Matching a laser line
Absorbance at common laser lines, as a percentage of each colloid's own peak, read from Grove's example spectra:
Scroll sideways to see all columns.
| Colloid | Absorption peak | 532 nm | 633 nm | 785 nm |
|---|---|---|---|---|
| Gold-PVP Red ~10 nm | ~525 nm | ~100% | ~60% | ~20% |
| Gold-PVP Blue <220 nm | ~580 nm | ~90% | ~95% | ~50% |
| Gold-PEG Blue <220 nm | ~590 nm | ~90% | ~100% | ~80% |
Absorbance at the laser line is a first guide. A SERS signal also depends on how the particles assemble on your substrate and on your analyte, so compare two colloids on your own set-up if you can. Any two packs cost £349 together, and the starter set has one pack of each colloid for £599.
Gold-L-Cysteine Fluorescent Red is not a plasmonic colloid. Its absorption peak is in the near ultraviolet at ~370 nm, and its broad red emission band peaks at ~645 nm, ~275 nm away. Select a long-pass filter that rejects your UV excitation wavelength and transmits the red emission band.
Surface chemistry
- PVP (Gold-PVP Red, Gold-PVP Blue): A neutral polymer that binds gold less strongly than thiols do. Thiol-terminated molecules such as thiol-PEG, thiolated DNA or peptides with an accessible free cysteine thiol can displace it, but the exchange is not always complete: use an excess of the thiol and check the result before you rely on it.
- PEG (Gold-PEG Blue): A neutral polymer widely used to reduce non-specific protein adsorption in biological media. How well it does so depends on how densely the PEG covers the particles and how it's attached, so test protein adsorption in your own medium.
- L-cysteine (Gold-L-Cysteine Fluorescent Red): L-cysteine binds to gold through sulfur, leaving carboxyl and amine groups available. EDC/NHS activates the carboxyl groups for coupling to primary amines. Because the surface also carries amines, activated particles can link to each other: work at a low particle concentration and remove excess EDC before adding your protein. The surface charge depends on pH and is lowest near cysteine's isoelectric point (~pH 5), where aggregation is most likely, so check that the colloid stays dispersed at your working pH before scaling up.
Grove makes all four by depositing metallic gold in the presence of the ligand. No gold salts, reducing agents, CTAB or CTAC are used.
Handling and storage
- Storage: Keep at 2–8 °C and don't freeze: freezing can aggregate the particles irreversibly.
- Before use: Invert the vial gently to mix. The larger platelets can settle over time.
- Diluting: Use ultrapure water. Salts and buffers can destabilise colloids, so test your buffer on a small volume first.
Amounts and concentration
Planning volumes: The amount in OD·mL is volume multiplied by optical density. For the same colloid, measured at the same wavelength and path length, dilution doesn't change it: one pack (10 mL at OD 1) makes 100 mL at OD 0.1, or 2 mL at OD 5 if concentrated without loss.
Gold content: Grove estimates ~0.05 mg/mL of gold at OD 1, with OD measured at the absorption peak, so a 10 mL pack holds ~0.5 mg of gold. It's an estimate, not an ICP-MS measurement.
Ask us
Tell us your excitation wavelength, buffer and what the particles need to do, and we'll suggest a product. For data on a specific batch, or a value that isn't listed, email info@marixia.co.uk and we'll ask Grove.