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Gold Colloid

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The gold colloid will remain stable until at least the expiry date stated on the label if the colloid is
kept unopened at the recommended storage temperature (2-8°C). BBI’s EM Grade gold colloids
are assigned a 12-month expiry date from the date of manufacture (excepting 15nm and 20nm
gold colloids which are given an 18-month and a 15-month expiry date).

Using within one month of opening is what is recommended by BBI (and is the practice BBI follows in-house)
and is due to the lack of preservative agents (such as sodium azide) in the gold colloid. When the bottle is
opened the gold colloid is exposed to contaminants, both from the air and from any pipette tips etc.
inserted in the liquid. This contamination can lead to microbial growth within the colloid.

For best results (to help avoid particle aggregation) the end-user should avoid pipetting directly
from the bottle. Instead they should pour out a small aliquot into a suitable container
(borosilicate glass is recommended) and pipette from this. This protects the bulk solution from
cross-contamination and potential introduction of particulate matter (such as dust) which can
cause particle aggregation.
It is recommended that the bulk volume of gold colloid be kept in its original container.

No. BBI’s colloids and conjugates are not suitable for injection or administration by mouth. BBI
do not accept responsibility for misuse of any of their products.

The exact method is proprietary; however, it can be shared that the gold nanoparticles are
formed by the citrate reduction of a gold chloride solution.

The gold nanoparticles are formed by the citrate reduction of a gold chloride solution. This leaves
the gold particles with a citrate shell which confers a net negative charge upon the particles,
allowing them to repel each other and remain in solution. No other stabilising agents or
preservatives are added to the gold colloid following the manufacture process.

The smallest gold nanoparticle that BBI offers is 5nm in diameter and the largest is 250nm.
The particle sizes available are: 5nm, 10nm, 15nm, 20nm, 30nm, 40nm, 50nm, 60nm 80nm,
100nm, 150nm 200nm and 250nm.

The gold nanoparticles are provided suspended in purified water (as made), with only
residual chemicals left from manufacture also present in solution.

No. Frozen colloids precipitate and become clear in colour with visible aggregates present.
This process is irreversible. Ideally colloids should be stored in the door of a fridge or away
from the chillers in a cold room to prevent accidental freezing.

BBI offers more concentrated versions of the 20nm and 40nm gold colloids, referred to as the HD
Grade range. In addition to the standard concentration (OD520 1) products, OD520 5 (20nm only)
and OD520 10 (20nm and 40nm) products are available in 10ml and 50ml pack sizes.
HD Grade gold colloids do not have an expiry date applied to them as BBI has not carried out a
stability study on this product range. The batch size of the product range is limited to 50ml. For
these reasons, the HD Grade colloid range is not suitable for use in the making of gold conjugates
for lateral flow test manufacture or any other kind of regulated manufacture.

As standard, 40nm gold colloid is manufactured at a concentration of OD520 ~4.5. This undiluted
colloid is available to purchase from BBI under the product code EM.GC40 SPL. As this colloid has
not been through a concentration process, it retains its shelf life of 12 months from the date of
manufacture and is available in batch sizes greater than the HD range (the batch size can be as
large as 80 litres).

As the concentration of the EM.GC40 SPL is close to OD520 5, it can be used as an alternative to a
HD Grade 40nm gold colloid at OD520 5, with the benefit that it is a product with an assigned 12-
month expiry date (from the date of manufacture) and a larger maximum batch size. The
EM.GC40 SPL product is also suitable for use in lateral flow manufacture and development
whereas the HD grade product range is not.

Gold nanoparticles ≥40nm in diameter have too much mass for the negative charge on the
particle surface to keep them suspended. These particles will sink out of solution and settle at
the bottom of their container. Colloids that have settled in this way can be resuspended by

BBI’s gold colloid is manufactured at our ISO 13485:2015 certified facility in Crumlin, South
Wales, UK.

•High stability. A one-year shelf life ensures a settled manufacturing regime saving the
customer time and wastage
•Uniform shape and standard size with a low coefficient of variation. This ensures
even antibody loading giving reliable results in your assay.
•Manufacturing scale. Batch sizes of up to 350+ litres to ensure you have a continuous supply.

If the gold colloid is to be diluted for use, it is recommended to use purified water of a comparable
purity (resistivity ≥18MΩ) to that used in the manufacture process

The gold colloid is shipped at ambient temperature.

The risk of the colloids freezing far outweighs the risk of the colloids being exposed to elevated
temperatures. If the colloids freeze (even if only for a short time) they will completely and
irreversibly collapse. In contrast, the colloids tolerate being exposed to elevated temperatures
well for a short period of time.

We do recommend that the colloid is kept at 2-8°C for long term storage, however over a short
period of time (such as a few days, which will be the case during international shipping) the
colloid will be fine at higher temperatures. Adding cold packs to the shipping carton will increase
the risk of freezing, which should be avoided at all costs.

Good gold versus bad gold 

BBI’s unique manufacturing technique allows for the production of large batches of gold to a high level of reproducibility of size, dispersion and shape. This ensures a firm foundation for conjugation and peace of mind that your rapid assay will provide reliable results. 

To help understand the advantages of using high quality gold. Take a look at our movie

Gold Nanoparticle starter packs 

Are you using gold for the first time, or trying a new process and are unsure of which gold nanoparticles size to purchase? 

Our gold starter packs provide a range of particle sizes to allow a comprehensive evaluation, comprising 100ml each of a selection of our gold nanoparticles.  

High OD Gold 

Our High OD colloid can be used to provide dense uniform monolayers of gold particles on substrates and can also simplify the conjugation procedure. 

By removing centrifugation steps in the concentration process, there is an opportunity to make potential savings in time, reduced labour costs and ensure waste is minimised during the R&D phase of a project. 

Our High OD gold nanoparticles are available as 20nm and 40nm and at concentrations of OD5 and OD10, and are available ONLY in 10ml or 50ml pack sizes. 



Technical Documents

Last updated: 08/03/2021

Products and Services Brochure

Last updated: 08/03/2021

Products and Services Brochure