

Gold Conjugates
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FAQs
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The antibodies are passively conjugated to the gold nanoparticle surface (no covalent or linker chemistry is used). Protein binds to gold colloid through amino acid residues: charge attraction (lysine), hydrophobic attraction (tryptophan), and sulphur bonding (cysteine).
IgG is the most popular isotype for conjugation and can be conjugated with a high success rate. The antibody binds to the gold nanoparticles through the Fc region, leaving the Fab region exposed and able to bind the antigen of interest. IgG3 antibodies are more difficult to work with so these should
be avoided if possible.
IgM conjugations have a lower success rate. Cross-linking can occur when they are conjugated, and the Fc regions cannot always be exposed without damaging the integrity of the antibody.
IgE antibodies are raised in an allergic response, these antibodies can be conjugated to gold nanoparticles.
IgY antibodies are functionally similar to IgG antibodies and these can be conjugated to gold nanoparticles with a high success rate. Antigen conjugations are possible, although the success rate is lower. BBI can also conjugate antibody fragments- Fab, Fc, ScFv and limited experience with nanobodies.
The majority of gold conjugates (BA Grade and Custom Conjugates) are presented in a low molarity Borax buffer. EM grade conjugates are presented in a Tris-buffer saline solution containing 30% glycerol.
EM Grade gold conjugates can be frozen for long term storage and thawed for usage as these conjugates contain glycerol in their final buffer.
BA Grade and Custom conjugates cannot be frozen. Freezing of these products will cause the gold nanoparticles to completely and irreversibly aggregate and should be avoided.
It is recommended to store the gold conjugates (BA Grade and Custom Conjugates) at 2-8°C. EM Grade conjugates can be kept frozen at -20°C for long term storage.
BA refers to BioAssay. These conjugates are stock products which are routinely manufactured at BBI Solutions. These are most commonly used in lateral flow diagnostic tests. The particle size is 40nm.
CC refers to custom conjugates. These conjugates are similar to BA Grade conjugates but are usually manufactured on a custom basis by request of a customer. The particle size most
commonly used is 40nm.
EM refers to Electron Microscopy. These conjugates are different to BA and CC conjugates, are usually made with smaller nanoparticles and are most often used in electron microscopy. The particle size most commonly used is 10nm.
In BBIs experience, 40nm is the preferred particle size. 40nm provides good signal visibility whilst encountering relatively little steric hindrance.
Our gold nanoparticles have a high level of single particle dispersion.
Conjugates are tested under the Transmission Electron Microscope (TEM) and have set specifications for % singlets and cluster size.
40nm conjugates are tested using the MonoDispersity Index (MDI). MDI uses UV-Vis readings to assess the ratio achieved between the A520nm (absorbance at which 40nm OD readings are taken) and A600nm (associated with stability) of the conjugate. A pass/ fail criterion is assigned to the ratio which is deemed acceptable to produce a stable product.
Other gold colloid sizes are assessed using TEM and are tested to a set specification.
EM Grade conjugates are available in 0.25ml and 1ml pack sizes.
BA Grade conjugates are available in 5ml, 100ml and 500ml pack sizes. 5ml will be for samples only.
Custom conjugates are available in any pack size. Minimum order volume is usually 5ml. For orders >500ml, individual pack sizes do not exceed 500ml.
The expiry date is stated on the label of each batch. In general BA Grade conjugates have a shelf life of 2 years from the point of manufacture when stored at 2-8°C. BA.GAM40 stability studies are ongoing- this is currently not supplied with an expiry date.
No expiry date is applied to EM Grade conjugates. Anecdotally, these have been used 5+ years after the date of manufacture with no loss of functionality.
No expiry date is applied to Custom Conjugates, unless at request of the customer. A cost would apply for the panel of work required to assign an expiry date.
The gold conjugates are manufactured at our ISO 13485:2015 certified facility in Crumlin, South Wales, UK.
Your inputs, following discussion of your application with our team,
â–ª Selected detector protein (antibody/protein). Supplied by customer or BBI can source and recharge the customer.
â–ª Identify target sensitivity
â–ª Identify particle size
â–ª Concentration of final conjugate required
â–ª Provide 3-5mg of protein for conjugation and QC materials (capture, target antigen). Antigen no
more than Cat II Biohazard level
BBI outputs
▪ Initial 5-10ml of final conjugate – (enough for 1000 prototype lateral flow strips*)*using a 1:5
dilution of OD10 conjugate per strip
â–ª Excess reagents banked for future production
â–ª Full laboratory report on performance customised to your requirements
â–ª Access to technical team post conjugation
For a custom conjugation to a 40nm particle, BBI request 3mg antibody/protein. Minimum concentration 1.0mg/mL. This allows for a full assessment of conjugation parameters prior to committing material to a batch.
Antibody quantity will be slightly more for smaller particle sizes and for alternative detectors (e.g. antigens).
Initial antibody requirement may be higher than expected but the benefit is gained as conjugate production volume increases. Antibody mg per ml of conjugate is lower with BBI’s manufacture method which is designed with long-term scale-up in mind up to 24L OD10 equivalent.
Antibody pI- this helps with assessment of conjugation parameters
Antibody source- Monoclonal/Polyclonal/Human/Recombinant. This will determine how we assess the antibody pre-conjugation.
Antibody subtype- this helps with assessment of conjugation parameters
Antibody buffer- no thimerosal in antibody buffer- this can affect binding
Antibody Supplier- considerations around robust long-term supply, availability of multiple lots
Assay format- Sandwich/Competitive/Inhibition/Serological/Non Lateral Flow- different assay formats require different considerations around conjugation parameters.
All testing is performed in liquid format.
OD at 520nm- measure of concentration
Dipstick Testing- either anti-species or specific functional system if provided. Determines performance compared to approved past batches.
Free Antibody Check- identify if free antibody is in solution that could interfere with assay.
Mono Dispersity Index (MDI)- for 40nm conjugates. A spectral reading as an indicator of potential conjugate stability.
Cluster Check – for conjugate sizes other than 40nm- indicator of potential conjugate stability. A visual count of particles under TEM to check for clustering of particles that may impact stability, performance, and reproducibility.
It is always best to perform in-process assessment and final QC testing with specific functional materials. This is not always possible if material stocks are low or costs high.
BBI requests 0.5mg capture at minimum concentration of 1.0mg/mL.
BBI request approx. 0.1-0.2mg antigen/analyte at 0.1mg/ml (minimum concentration), along with SDS or details of hazards and disposal.
No materials above Biohazard Level II are permitted.
BBI can perform stability studies at customer request. A charge will apply.
Following assessment of conjugate batches in the intended final format by the customer, further optimisation of parameters and conjugate formulation is often required.
BBI request feedback from conjugation events to determine improvements to conjugate formulation to achieve desired performance. This can take the format of emails, presentations or technical calls.
Gold Conjugation- why quality gold matters
One of the most important factors in the development of a reliable assay is the quality of the gold conjugate. At BBI Solutions, we use the highest quality grades of gold nanoparticles and apply our unique conjugation protocol to deliver an optimised product that meets the demands of your assay.
Whether you are looking to bind gold to a specific antibody and need a custom conjugation, or off the shelf products, BBI can help and deliver.
Custom conjugation service from BBI Solutions
Our custom conjugation service allows us to develop high-quality conjugates using reagents provided by you or sourced by us.
Our service includes:
Advice on the optimum nanoparticle and size to use for your application |
Conjugation of your antibody or protein to a nanoparticle and size of your choice |
Particle Analysis |
Batch sizes up to 24L at OD10 |
Sourcing your required antibody or protein |
Long term stability analysis (on request) |
Selection of appropriate final buffer for the conjugate |
Custom OD preparation (not limited to OD10) |
Antibody Screening |
QC test development |
Optimisation of sensitivity and potential stability |
Comprehensive lab report on conjugate performance |
 
Designed to meet your individual needs
Specificity, sensitivity and reproducibility should define the specification and fulfil your absolute minimum expectations of the conjugate.
Our scientists work in partnership with customers to bring all the vital ingredients together and provide sensitive, stable, reproducible conjugates time after time.
At the start of the project we will ask you for the following customer inputs and deliver the listed outputs:
Customer inputs |
BBI outputs |
Choose your target protein (antibody/protein) |
Initial 10ml of final optimised product – (enough for 1000 prototype lateral flow strips*) |
Identify target sensitivity |
Excess reagents banked for future production |
Identify particle size |
Full laboratory report on performance customised to your requirements |
Concentration of final conjugate required |
Access to technical team post conjugation |
Provide 3-5mg of protein for conjugation and QC materials |
*using a 1:5 dilution of OD10 conjugate per strip |
 
A quality solution
Every custom conjugation is QC tested with customer supplied materials. Your unique sign-off procedure is brought into BBI to ensure every batch of gold we deliver meets your requirements and works with your in-house system.
Bulk production
Following collaboration on the optimisation of the conjugate to test specifications, we are able to provide conjugate in bulk. We can put a commercial supply plan in place and supply single batch volumes of up to 24l at OD10, delivered on a two-week turnaround.
To find out more about our conjugation service, contact us »
Off the shelf conjugates
For optimal performance, cost effectiveness and guaranteed quality, we offer off the shelf catalogue gold conjugates, designed to help you develop and manufacture your assay at a rapid and economical rate.
Our catalogue range includes:
- Anti-biotin
- Anti-human
- Control line
- Anti-species
- Disease state conjugates
- Fertility conjugates
All conjugates are manufactured using our unique gold nanoparticles, providing outstanding performance and long term stability.
If you are looking for a conjugate which is not in our standard product range, please contact us with your requirements.
Anti-Biotin |
Anti-Human |
Control line |
Anti-species |
Fertility |
Monoclonal anti Biotin 40nm |
Goat anti Human IgG (H+L) 40nm |
Chicken IgY 40nm |
Goat anti Rabbit 40nm |
Human Chorionic Gonadtrophin (HCG) 40nm |
Goat anti Biotin 40nm |
Goat anti Human IgG 40nm |
Mouse IgG 40nm |
Goat anti Mouse IgG (H+L) 40nm |
Human Lutienizing Hormone (LH) 40nm |
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Goat anti Human IgM 40nm |
Bovine Serum Albumin 40nm * |
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Goat anti Human IgA 40nm |
Goat anti Mouse IgG (H+L) 40nm |
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Protein A 40nm |
Goat anti Rabbit 40nm |
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*Negative control conjugate
Gold Conjugates for Microscopy
Gold labels offer an effective method of labelling antigens for visualisation in the electron microscope. BBI has a range of EM grade conjugates that combine different antibodies on a range of particles, predominantly 2, 5, 10, 15, 20, 30 & 40nm. For researchers beginning to work with immunogold labelling, we recommend 10nm gold conjugates for observation, at a range of magnifications.
The main advantages of gold labelling lie in the high contrast and unequivocal nature of the label, the range of particle sizes suitable for different magnifications, the extreme sensitivity and the stability of the signal.
Our technical team are available to discuss which conjugate is right for your application or to answer your nanoparticle based questions here.
Applications
BBI Solutions’ gold nanoparticles are renowned for their use in lateral flow tests; however, the use of nanoparticles ranges from health and material technology to the environment and energy sectors.
The technology sectors and applications listed below provide a summary of where our gold nanoparticles are being used by our customers and partners:
Size range of nanoparticles |
Area of use |
Function |
Small (2nm -15nm) |
Immunohistochemistry |
Antibody/antigen detection in cells |
Medium (20nm – 80nm) |
Lateral flow assays |
Detection of food borne pathogens |
Large (80nm – 250nm) |
Flow cytometry |
Detection of CD4 cells using flow cytometry |