Our standard citrate stabilized spherical gold nanoparticles are prepared using a modified proprietary citrate reduction protocol, are optimized for high protein binding efficiency, and are ideal for use in applications such as conjugate development, lateral flow, dark field microscopy, Localized Surface Plasmon Resonance (LSPR)-based assays and Surfaced Enhanced Raman Spectroscopy (SERS).

The high shape uniformity of our colloidal gold nanoparticles minimizes the variability within your assay by e.g. allowing control over the available surface area while adsorbing proteins to the gold nanoparticles. This translates into higher performance and reduced costs for your specific assay.

Figure 1. Transmission electron microscopy (TEM) images (top) and UV-Vis spectrum (bottom) of Cytodiagnostics gold nanoparticles of different sizes.

Cytodiagnostics Standard Gold Nanoparticles are supplied in 0.1mM phosphate buffered saline (PBS) surface stabilized with citrate and are available with diameters from 5nm to 400nm.

These particles are also available pre-functionalized with a variety of functional groups for easy conjugation of bio-recognition molecules.

Applications

• Conjugate Development (see our gold nanoparticle conjugation kits)
• Immunostaining
• Lateral Flow Assays
• Biological Sensor Development (e.g. LSPR-based assays)
• Electron Microscopy
• Dark Field Microscopy
• Surface Enhanced Raman Spectroscopy (SERS)

Cytodiagnostics Reactant Free Gold Nanoparticles are supplied in 0.1mM phosphate buffered saline (PBS) and are extensively purified to be 99% free of residual reactants from manufacturing. These particles have the same high protein binding efficiency as our standard gold nanoparticle preparations for use in applications such as conjugate development, lateral flow and Surface Enhanced Raman Spectroscopy (SERS) with the added benefit of being reactant free for more sensitive applications such as cell work and nanotoxicology studies.

Applications

• Cell Work
• Conjugate Development
• Immunostaining
• Immunochromatography
• Lateral Flow Assays
• Biological Sensor Development (e.g. LSPR-based assays)
• Electron Microscopy
• Surface Enhanced Raman Spectroscopy (SERS)
• Nanotoxicology

Cytodiagnostics Surfactant Stabilized Gold Nanoparticles are supplied in a citrate buffer supplemented with a proprietary stabilizing solution for prolonged stability, higher salt tolerance and temperature stability.

Our surfactant stabilized preparations have been optimized for adsorption of thiolated ligands such as oligonucleotides and polyethylene glycols and are ideal for use applications requiring harsher conditions (i.e. higher salt concentrations) than those tolerated by standard gold nanoparticles.

Our extensively purified endotoxin free gold nanoparticles are ideal for sensitive applications requiring a minimal amount of contaminants, such as cellular toxicity studies, immunological studies, and aseptic assays. This product is well suited for conjugate development by passive adsorption of proteins and other ligands to the gold nanoparticle surface. The resulting conjugate can then be used in downstream applications.

All of our batches go through stringent quality control prior to shipment to our customers using dynamic light scattering to guarantee size and monodispersity and lot specifications are supplied with each product. The endotoxin levels of all batches are validated by the Limulus amebocyte lysate (LAL) test and do not exceed 0.5EU/mL.

Figure 1. Transmission electron microscopy (TEM) images (top) and UV-Vis spectrum (bottom) of Cytodiagnostics gold nanoparticles of different sizes.

Cytodiagnostics alkylthiol (dodecanethiol) stabilized gold nanoparticles are soluble in a wide range of organic solvents (see table below) and are available both dried and as a suspension in hexane.

Flow cytometry is a commonly used technique in many biological and clinical assays to evaluate cells and particles with sizes of 1μm and above. However, more advanced flow cytometers are now capable of analyzing small molecules down within the nanometer range. This allows for the study, and use of engineered nanoparticles, viruses and small bacteria not traditionally possible.

Cytodiagnostics Size Reference Gold Nanoparticles are specifically designed for the optimization of flow cytometer settings, performance and evaluation of particles or organisms in the 50nm – 400nm range.

Custom Conjugation Services – Nanoparticles

Cytodiagnostics provides an array of options for customers to do their own conjugations. Our gold and silver nanoparticles, and gold nanourchins are optimally designed for efficient passive adsorption of a multitude of proteins, antibodies, thiolated oligos, and more. For covalent conjugates, Cytodiagnostics also provides ready-to-use kits: Gold Conjugation Kits, Silver Conjugation Kits, NanoUrchin Conjugation Kits.

Let Us Do It For You!

Cytodiagnostics custom conjugation services help design and produce your very own custom conjugate. This includes most ligands ranging from proteins to enzymes to oligonucleotides, and this service extends to all the nanoparticles in our expansive catalog. You as a customer tell us the parameters and end-goal you need met, and our team of experts will work out the rest for you.

Cytodiagnostics gold nanoparticle protein conjugates are manufactured to the highest specifications resulting in conjugates with a low size coefficient of variation and excellent sensitivity.

Due to the versatility of gold nanoparticle conjugates, they can be used in a broad range of applications including Western blots, dot-blots, electron microscopy, light microscopy, in situ hybridizations and in lateral flow/vertical flow rapid tests.

Many of our secondary antibody conjugates are also available pre-adsorbed to minimize species cross-reactivity.

Can’t find the conjugate you need in the categories? Contact us and we would be happy to provide you with a custom solution.

Cytodiagnostics NHS-activated Gold Nanoparticle Conjugation Kits have been optimized for high efficiency one-step conjugation of proteins and other primary amine-containing ligands to gold nanoparticles.

The kits contains ready-to-use pre-made mixtures. No activation or manipulation of the gold nanoparticles is required prior to conjugation, which often results in poor performing conjugates. Simply mix your protein with the pre-activated NHS ester gold nanoparticles supplied in the kit to generate your conjugate.

The precisely engineered gold surface on our NHS ester-activated gold nanoparticles results in high conjugation efficiency and stable conjugates while minimizing non-specific binding in your assay.

For quality control of antibody and antigen conjugation our Conjugation QC Lateral Flow Dipstick Kit can be used.

Features & Benefits of NHS-Activated Gold Nanoparticles

• Results in covalently bound ligand and more stable conjugate.
• Fast and convenient one-step conjugation reaction with no pre-activation requirements.
• Spacer between the gold nanoparticle surface and conjugated ligand minimizes effects on the tertiary protein structure, which can lead to poor performing conjugates, a common problem seen in conjugates prepared by passive adsorption.
• Precisely engineering surface coating that reduces non-specific protein binding in biological assays.

Cytodiagnostics Maleimide-Activated Gold Nanoparticle Conjugation Kits have been optimized for high efficiency one-step conjugation of thiol-containing ligands such as oligonucleotides to gold nanoparticles.

The kits contains ready-to-use pre-made mixtures. No activation or manipulation of the gold nanoparticles is required prior to conjugation, which often results in poor performing conjugates. Simply mix your protein with the pre-activated maleimide gold nanoparticles supplied in the kit to generate your conjugate.

The precisely engineered gold surface coat on our maleimide-activated gold nanoparticles results in high conjugation efficiency and stable conjugates while minimizing non-specific binding in your assay.

Features & Benefits of Maleimide-Activated Gold Nanoparticles

• Results in covalently bound ligand and more stable conjugate.
• Fast and convenient one-step conjugation reaction with no pre-activation requirements.
• Spacer between the gold nanoparticle surface and conjugated ligand minimizes effects on the tertiary protein structure, which can lead to poor performing conjugates, a common problem seen in conjugates prepared by passive adsorption.
• Precisely engineered surface coating that reduces non-specific protein binding in biological assays.

Gold Conjugation Kits for Thiolated Oligonucleotides

Cytodiagnostics unique OligoREADY™ gold conjugation kits have been optimized for high efficiency one-step conjugation of thiolated oligonucleotides directly to the gold surface of particles with diameters up to 100nm.

The kit contains ready-to-use pre-made mixtures. No activation, manipulation, or time consuming “salt-aging” steps are require for conjugation. Simply mix your reduced thiol-modified oligonucleotide with the pre-activated gold nanoparticles supplied with the kit. Conjugation of the oligonucleotide is achieved by the formation of a strong and stable gold-thiol bond without any additional linkers.

Features & Benefits

• Allows conjugation of oligonucleotides to gold nanoparticles with sizes between 5nm-100nm.
• Fast and convenient one-step conjugation reaction with no pre-activation requirements or manipulation of the gold nanoparticles.
• Does not require time-consuming “salt-aging” procedures.
• Results in a thiol-oligo conjugated directly to the gold surface without any linkers

Cytodiagnostics carboxyl functionalized gold nanoparticles have precisely engineered surface chemistry that enables coupling to various moieties that react with carboxylic acids. One of the most popular applications of this interaction is EDC/NHS coupling. The EDC activates the carboxylic acid so that it can react with NHS and acquire new functionality. The introduction of the NHS group then allows it to react with primary amines, which enables covalent coupling to proteins and antibodies with exposed amine-containing residues such as lysine. This permanent linkage has thus provided a gold nanoparticle label to the molecule in question and allows easier monitoring and localization within cells.

Cytodiagnostics carboxyl gold nanoparticles are available with diameters ranging from 5nm – 100nm and are also available with 2 different spacer lengths (3 kDa and 5 kDa). This provides the customer with the necessary tools fully optimize their experiment.

Cytodiagnostics amine functionalized gold nanoparticles have precisely engineered surface chemistry that allows for simple and efficient binding to moieties that react with primary amines. An example of such a reaction would be a conjugation to a protein or antibody that has been tagged NHS, which would yield a covalent link between the gold nanoparticle surface and the protein. This permanent linkage allows for further downstream applications such as monitoring the distribution of the now-tagged molecule.

Cytodiagnostics amine gold nanoparticles are available with diameters ranging from 5nm – 100nm and are also available with 2 different spacer lengths (3 kDa and 5 kDa). This provides the customer with the necessary tools to fully optimize their experiment.

Cytodiagnostics biotin functionalized gold nanoparticles are available with diameters in the range of 5nm – 100nm.  These particles have a precisely engineered surface for optimal streptavidin binding while minimizing non-specific binding to other proteins present in your sample.

The gold nanoparticle label allows for convenient binding and detection of streptavidin in applications such as TEM, ELISA and Immuno dot-blots among others.

Figure 1. Cytodiagnostics Biotin gold nanoparticles bound to an avidin-coated surface substrate. Courtesy of Trevor Olsen, University of Alberta. Images taken at the NINT Electron Microscopy Facility.

Cytodiagnostics methoxy gold nanoparticles have precisely engineered surface chemistry that renders them inert in most applications. This inert property allows these nanoparticles to be used as excellent control samples when in combination with one of our many other functionalized nanoparticles. In applications where the nanoparticles are not being used as controls, the surface chemistry enables them to be used in solutions with much higher salt concentrations relative to the corresponding standard or stabilized nanoparticles.
Cytodiagnostics methoxy gold nanoparticles are available with diameters ranging from 5nm – 100nm and are also available with 2 different spacer lengths (2 kDa and 5 kDa), allowing for better optimization.

Cytodiagnostics Ni-NTA gold nanoparticles have precisely engineered surface chemistry consisting of a PEG spacer terminated with a nitrilotriacetic acid (NTA) group chelated to a Ni²⁺ ion. This specific functionality binds to His tags, which are a common modification added to the terminal end of proteins or antibodies, consisting of 6 sequential histidine residues. The interaction between Ni-NTA and His tags enables many applications when coupled to our gold nanoparticles: preparation of gold conjugates, protein purification and isolation, cell localization and uptake studies, use in assays, and more.

Cytodiagnostics Ni-NTA gold nanoparticles are available in 12 different sizes ranging from 5nm – 100nm, are more than 95% spherical and have a uniform size distribution (CV <12%). Products are provided as suspensions at 50 OD.

Cytodiagnostics azide functionalized gold nanoparticles are precisely engineered for covalent conjugation to any molecule tagged with an alkyne group. With the use of a copper(I) catalyst, the azide group on the gold and the alkyne-tagged molecule undergo a cycloaddition to form a stable and permanent linkage. The reaction between these 2 functional groups typically occurs rapidly, in high yield, and with no by-products, meaning that the customer will always have a stable conjugate and enough of it to use in subsequent downstream applications such as lateral flow assays and imaging. These reactions are also especially useful in applications involving oligonucleotides due to the higher prevalence of alkyne modifications.

Cytodiagnostics azide functionalized gold nanoparticles are available in 12 different sizes ranging from 5nm – 100nm, are more than 95% spherical and have a uniform size distribution (CV <12%). Products are provided as suspensions at 50 OD.

Cytodiagnostics alkyne functionalized gold nanoparticles are precisely engineered for covalent conjugation to any molecule tagged with an azide group. With the use of a copper(I) catalyst, the alkyne group on the gold and the azide-tagged molecule undergo a cycloaddition to form a stable and permanent linkage. The reaction between these 2 functional groups typically occurs rapidly, in high yield, and with no by-products, meaning that the customer will always have a stable conjugate and enough of it to use in subsequent downstream applications such as lateral flow assays and imaging. These reactions are also especially useful in applications involving oligonucleotides due to the higher prevalence of azide modifications.

Cytodiagnostics alkyne functionalized gold nanoparticles are available in 12 different sizes ranging from 5nm – 100nm, are more than 95% spherical and have a uniform size distribution (CV <12%). Products are provided as suspensions at 50 OD.

Cytodiagnostics dibenzocyclooctyne (DBCO) functionalized gold nanoparticles are suitable for covalent conjugation of any azide-tagged molecule through click chemistry. The rigid structure of the DBCO allows for quick reactions under more moderate conditions, and eliminates the need for a copper catalyst. This chemistry confers higher stability in aqueous conditions and the lack of copper greatly increases its overall biocompatibility, enabling a multitude of biological applications.

Our DBCO functionalized gold nanoparticles are available in 9 different sizes ranging from 20 – 100nm, are more than 95% spherical and have uniform size distribution (CV <12%).

For custom sizes, formulations or bulk quantities please contact our customer service department, info@stratech.co.uk.

Cytodiagnostics Gold NanoUrchins have unique optical properties compared to spherical gold nanoparticles of the same core diameter. The spiky uneven surface causes a red shift in the surface plasmon peak and a larger enhancement of the electromagnetic field at the tips of the Gold NanoUrchin spikes compared to that of a spherical particles. As an example, 100nm spherical gold nanoparticles have an SPR peak at 570nm while 100nm Gold NanoUrchins have a SPR peak at around 680nm.

Reactant Free Gold NanoUrchins are supplied in 0.1mM phosphate buffered saline (PBS) and are extensively purified to be 99% free of residual reactants from manufacturing. These particles have the same high protein binding efficiency as our standard gold nanoparticle preparations for use in applications such as conjugate development, lateral flow and Surface Enhanced Raman Spectroscopy (SERS) with the added benefit of being reactant free for more sensitive applications such as cell work and nanotoxicology studies.

Our extensively purified endotoxin free gold nanourchins are ideal for sensitive applications requiring a minimal amount of contaminants, such as cellular toxicity studies, immunological studies, and aseptic assays. This product is well suited for conjugate development by passive adsorption of proteins and other ligands to the gold nanourchins surface. The resulting conjugate can then be used in downstream applications.

All of our batches go through stringent quality control prior to shipment to our customers using dynamic light scattering to guarantee size and monodispersity and lot specifications are supplied with each product. The endotoxin levels of all batches are validated by the Limulus amebocyte lysate (LAL) test and do not exceed 0.5EU/mL.

Custom Conjugation Services – Nanoparticles

Cytodiagnostics provides an array of options for customers to do their own conjugations. Our gold and silver nanoparticles, and gold nanourchins are optimally designed for efficient passive adsorption of a multitude of proteins, antibodies, thiolated oligos, and more. For covalent conjugates, Cytodiagnostics also provides ready-to-use kits: Gold Conjugation Kits, Silver Conjugation Kits, NanoUrchin Conjugation Kits.

Let Us Do It For You!

Cytodiagnostics custom conjugation services help design and produce your very own custom conjugate. This includes most ligands ranging from proteins to enzymes to oligonucleotides, and this service extends to all the nanoparticles in our expansive catalog. You as a customer tell us the parameters and end-goal you need met, and our team of experts will work out the rest for you.

Gold nanourchin protein conjugates are a great alternative to traditional gold protein conjugates if peak absorbance is desired in the 570nm-680nm range.
Cytodiagnostics unique gold nanourchin protein conjugates can be used for a variety of applications including use as secondary detection agents in immunoblotting, lateral flow/vertical flow devices, ELISA, light microscopy and electron microscopy.

If you are interested in having your own antibody, or other protein conjugated to our gold nanourchins as a custom service please contact us.

Browse Our Available Gold NanoUrchin Conjugates

Cytodiagnostics NHS-activated Gold NanoUrchin Conjugation Kits have been optimized for high efficiency one-step conjugation of proteins and other primary amine-containing ligands to gold nanoparticles.

The kits contains ready-to-use pre-made mixtures. No activation or manipulation of the gold nanourchins is required prior to conjugation, which often results in poor performing conjugates. Simply mix your protein with the pre-activated NHS ester gold nanourchins supplied in the kit to generate your conjugate.

The precisely engineered gold surface coat on our NHS ester-activated gold nanourchins results in high conjugation efficiency and stable conjugates while minimizing non-specific binding in your assay.

For quality control of antibody and antigen conjugation our Conjugation QC Lateral Flow Dipstick Kit can be used.

Features & Benefits of NHS-Activated Gold NanoUrchins

• Results in covalently bound ligand and more stable conjugate.
• Fast and convenient one-step conjugation reaction with no pre-activation requirements.
• Spacer between the gold nanourchin surface and conjugated ligand minimizes effects on the tertiary protein structure, which can lead to poor performing conjugates, a common problem seen in conjugates prepared by passive adsorption.
• Precisely engineering surface coating that reduces non-specific protein binding in biological assays.

Cytodiagnostics Maleimide-activated Gold NanoUrchin Conjugation Kits have been optimized for high efficiency one-step conjugation of proteins and other thiol-containing ligands to gold nanoparticles.

The kits contains ready-to-use pre-made mixtures. No activation or manipulation of the gold nanourchins is required prior to conjugation, which often results in poor performing conjugates. Simply mix your protein with the pre-activated maleimide gold nanourchins supplied in the kit to generate your conjugate.

The precisely engineered gold surface coat on our maleimide-activated gold nanourchins results in high conjugation efficiency and stable conjugates while minimizing non-specific binding in your assay.

Features & Benefits of Maleimide-Activated Gold NanoUrchins

• Results in covalently bound ligand and more stable conjugate.
• Fast and convenient one-step conjugation reaction with no pre-activation requirements.
• Spacer between the gold nanourchin surface and conjugated ligand minimizes effects on the tertiary protein structure, which can lead to poor performing conjugates, a common problem seen in conjugates prepared by passive adsorption.
• Precisely engineering surface coating that reduces non-specific protein binding in biological assays.

Cytodiagnostics biotin functionalized gold nanourchins are available with diameters in the range of 50nm – 100nm and have their surface plasmon resonance absorption and scattering characteristics in the 580-680nm range. These particles have a precisely engineered surface for optimal streptavidin binding while minimizing non-specific binding to other proteins present in your sample.

The gold nanourchin label allows for convenient binding and detection of streptavidin in applications such as Lateral Flow, TEM, ELISA and Immuno dot-blots among others.

Carboxyl functionalized gold nanourchins are ideal for conjugation of proteins and other primary amine containing ligands using standard EDC/NHS coupling chemistry.

Our carboxylated gold nanourchins are available in 6 different sizes ranging from 50-100nm and have uniform size distribution (CV <15%).

Features

• Precisely engineered surface with an optimized carboxyl group density for easy conjugation.
• Available with SPR absorption maximum in the 600nm range.
• Enhanced LSPR properties compared to spherical gold nanoparticles.

Applications

Ideal for development of gold nanourchin conjugates for use in for example:

• Immunoblotting
• Lateral Flow Assays
• LSPR Assays
• Microscopy Applications (e.g. TEM)

Cytodiagnostics methoxy gold nanourchins have precisely engineered surface chemistry that renders them inert in most applications. This inert property allows these nanoparticles to be used as excellent control samples when in combination with one of our many other functionalized nanourchins. In applications where the nanourchins are not being used as controls, the surface chemistry enables them to be used in solutions with much higher salt concentrations relative to the corresponding standard nanourchins.
Cytodiagnostics methoxy gold nanourchins are available with diameters ranging from 50nm – 100nm and are also available with 2 different spacer lengths (2 kDa and 5 kDa), allowing for better optimization.

Cytodiagnostics spherical silver nanoparticles are available with core sizes of 10nm – 100nm.

Our unique silver nanoparticles synthesis and purification protocols consistently produce high quality monodisperse silver nanoparticles with a narrow size distribution (CV <15%) and high purity. Cytodiagnostics nano silver products are ideal for a wide range of applications including photovoltaics, biological sensor development and nanotoxicology studies.

Cytodiagnostics unique Reactant Free Silver Nanoparticles have the same properties as our Standard Silver Nanoparticles with the added benefit of higher purity (99%).

The reactant free formulation is ideal when performing for example toxicity studies by isolating the effects of the nanoparticles while minimizing those from contaminating reactants remaining from the manufacturing process.

Custom Conjugation Services – Nanoparticles

Cytodiagnostics provides an array of options for customers to do their own conjugations. Our gold and silver nanoparticles, and gold nanourchins are optimally designed for efficient passive adsorption of a multitude of proteins, antibodies, thiolated oligos, and more. For covalent conjugates, Cytodiagnostics also provides ready-to-use kits: Gold Conjugation Kits, Silver Conjugation Kits, NanoUrchin Conjugation Kits.

Let Us Do It For You!

Cytodiagnostics custom conjugation services help design and produce your very own custom conjugate. This includes most ligands ranging from proteins to enzymes to oligonucleotides, and this service extends to all the nanoparticles in our expansive catalog. You as a customer tell us the parameters and end-goal you need met, and our team of experts will work out the rest for you.

Silver nanoparticle protein conjugates are a great alternative to traditional gold protein conjugates if peak absorbance is desired in the 400-500nm range.

Cytodiagnostics silver nanoparticle protein conjugates can be used for a variety of applications such as secondary detection agents in immunoblotting, lateral flow/vertical flow devices, ELISA, light microscopy and electron microscopy.

If you are interested in having your own antibody, or other protein conjugated to our silver nanoparticles as a custom service please contact us.

Browse Our Available Silver Nanoparticle Conjugates

Cytodiagnostics NHS-activated Silver Nanoparticle Conjugation Kits have been optimized for high efficiency one-step conjugation of proteins and other primary amine-containing ligands to silver nanoparticles.

The kits contains ready-to-use pre-made mixtures. No activation or manipulation of the silver nanoparticles is required prior to conjugation, which often results in poor performing conjugates. Simply mix your protein with the pre-activated NHS ester silver nanoparticles supplied in the kit to generate your conjugate.

The precisely engineered silver surface coat on our NHS ester-activated silver nanoparticles results in high conjugation efficiency and stable conjugates while minimizing non-specific binding in your assay.

Features & Benefits of NHS-Activated Silver Nanoparticles

• Results in covalently bound ligand and more stable conjugate.
• Fast and convenient one-step conjugation reaction with no pre-activation requirements.
• Spacer between the silver nanoparticle surface and conjugated ligand minimizes effects on the tertiary protein structure, which can lead to poor performing conjugates, a common problem seen in conjugates prepared by passive adsorption.
• Precisely engineering surface coating that reduces non-specific protein binding in biological assays.

Carboxyl functionalized silver nanoparticles are ideal for conjugation of proteins and other primary amine containing ligands using standard EDC/NHS coupling chemistry.

Our carboxylated silver nanoparticles are available in 8 different sizes ranging from 10-100nm, are more than 95% spherical and have uniform size distribution (CV <18%). In addition, the choice of two different length PEG surface spacer allows control of the distance between a conjugated molecule and the silver surface.

Features

• Superior size distribution compared to the leading competitor; available from 10nm to 100nm.
• Precisely engineered surface with an optimized carboxyl group density for easy conjugation.

Applications

• Ideal for development of silver conjugates for use in for example:
• Immunoblotting
• Lateral Flow Assays
• LSPR Assays
• Microscopy Applications (e.g. TEM, Darkfield)

Cytodiagnostics methoxy silver nanoparticles have precisely engineered surface chemistry that renders them inert in most applications. This inert property allows these nanoparticles to be used as excellent control samples when in combination with one of our many other functionalized nanoparticles. In applications where the nanoparticles are not being used as controls, the surface chemistry enables them to be used in solutions with much higher salt concentrations relative to the corresponding standard nanoparticles.
Cytodiagnostics methoxy silver nanoparticles are available with diameters ranging from 10nm – 100nm and are also available with 2 different spacer lengths (2 kDa and 5 kDa), allowing for better optimization.

Cytodiagnostics biotin functionalized silver nanoparticles are available with diameters in the range of 10nm – 100nm and have surface plasmon resonance absorption and scattering characteristics in the 400nm-500nm range. These particles have a precisely engineered surface for optimal streptavidin binding while minimizing non-specific binding to other proteins present in your sample.

The silver nanoparticle label allows for convenient binding and detection of streptavidin in applications such as TEM, ELISA and Immuno dot-blots among others.

Cytodiagnostics carboxyl functionalized gold nanorods have precisely engineered surface chemistry that enables coupling to various moieties that react with carboxylic acids. One of the most popular applications of this interaction is EDC/NHS coupling. The EDC activates the carboxylic acid so that it can react with NHS and acquire new functionality. The introduction of the NHS group then allows it to react with primary amines, which enables covalent coupling to proteins and antibodies with exposed amine-containing residues such as lysine. This permanent linkage has thus provided a gold nanoparticle label to the molecule in question and allows easier monitoring and localization within cells.

Cytodiagnostics carboxyl gold nanorods are available in 3 different aspect ratios, with absorption maxima of 650nm, 700nm or 770nm, and are also available with 2 different spacer lengths (3 kDa and 5 kDa). This provides the customer with the necessary tools fully optimize their experiment.

Cytodiagnostics amine functionalized gold nanorods have precisely engineered surface chemistry that allows for simple and efficient binding to moieties that react with primary amines. An example of such a reaction would be a conjugation to a protein or antibody that has been tagged NHS, which would yield a covalent link between the gold nanoparticle surface and the protein. This permanent linkage allows for further downstream applications such as monitoring the distribution of the now-tagged molecule.

Cytodiagnostics amine gold nanorods are available with 3 different aspect ratios, with maxima of 650nm, 700nm, or 770nm, and are also available with 2 different spacer lengths (3 kDa and 5 kDa). This provides the customer with the necessary tools to fully optimize their experiment.

Cytodiagnostics methoxy gold nanorods have precisely engineered surface chemistry that renders them inert in most applications. This inert property allows these nanorods to be used as excellent control samples when in combination with one of our other functionalized nanorods. In applications where the nanorods are not being used as controls, the surface chemistry enables them to be used in solutions with much higher salt concentrations.
Cytodiagnostics methoxy gold nanorods are available in 3 different aspect ratios, with absorption maxima of 650nm, 700nm or 770nm, and are also available with 2 different spacer lengths (2 kDa and 5 kDa), allowing for better optimization.

Lateral Flow Assay

While rapid assay methods have made a major impact on a variety of diagnostic testing over the last twenty years only a handful of development can make the claim to have taken testing out of the laboratory.

One that can, and is in widespread use as a result, is the lateral flow immunoassay test, also known as the immunochromatography assay, or strip test. Like many of the best ideas, lateral flow immunoassays take clever and sophisticated technology and turn it into something so simple to operate that almost anyone can use it.

The Technology

The basic technology that underlies lateral flow immunoassays was first described in the 1960s, but the first real commercial application was Unipath’s Clearview home pregnancy test launched in 1988. Since then, this technology has been employed to develop a wide and ever-growing range of assays for clinical, veterinary, agricultural, food industry, bio-defence and environmental applications.

Strip assays are extremely versatile and are available for an enormous range of analytes from blood proteins to mycotoxins and from viral pathogens to bacterial toxins. Assays has even been developed for wine producers to assess the amount of botrytis rot in newly harvested grapes as well as for use in the clinical lab identifying cardiac markers. This shows the vast range that this technology can be applied too.

Lateral flow immunoassays are essentially immunoassays adapted to operate along a single axis to suit the test strip format. There are a number of variations of the technology that have been developed into commercial products one being Vertical Flow Technology, but they all operate using the same basic principle.

Figure 1. Advantages of lateral flow assays.

How Does a Lateral Flow Assay Work?

A typical lateral flow rapid test strip consist of the following components:

Sample pad – an adsorbent pad onto which the test sample is applied.

Conjugate or reagent pad – this contains antibodies specific to the target analyte conjugated to coloured particles (usually colloidal gold nanoparticles, or latex microspheres).

Reaction membrane – typically a nitrocellulose or cellulose acetate membrane onto which anti-target analyte antibodies are immobilized in a line that crosses the membrane to act as a capture zone or test line (a control zone will also be present, containing antibodies specific for the conjugate antibodies).

Wick or waste reservoir – a further absorbent pad designed to draw the sample across the reaction membrane by capillary action and collect it.

The components of the strip are usually fixed to an inert backing material and may be presented in a simple dipstick format or within a plastic casing with a sample port and reaction window showing the capture and control zones.

Figure 2. Principle of lateral flow assay.

Cytodiagnostics manufactures a full product line of gold nanoparticles (colloidal gold) for use in a variety of lateral flow assays. Our diverse product line of different type of nanoparticles offers you products with a narrow size distribution (CV of less than 12%), exceptional adsorption and conjugation properties and with greater than 95% spherical particles. In addition, our batch to batch variability is extremely low (+/- 2nm), which assures that you our customer will always end up with a product within the specified size range that you ordered.

The high shape uniformity of our colloidal gold will minimize the variability within your assay by e.g. allowing control over the available surface area while absorbing or covalently conjugating proteins to our gold nanoparticles. It will also ensure a more uniform flow rate across your membrane for improved reproducibility and overall results.

Background

Vertical flow immunoassays rely on the same basic principles as the more common lateral flow immunoassay format with some modifications. The most apparent difference between the two methods being the vertical and lateral flow of fluid. However, vertical flow technology has several advantages over traditional lateral flow assays with the most significant being the reduced assay time (<5 minutes), table I.

Vertical flow immunoassays can be used for rapid detection of an antigen(s) in a sample of interest. Samples can come from a wide range of application areas such as clinical, veterinary, agricultural, food, bio-defence and environmental industries. Detection sensitivity is generally in the lower nanogram per ml range even in complex sample matrices.

Table I. Features and benefit of rapid vertical flow technology compared to lateral flow and other rapid flow type tests.

How does a Vertical Flow Assay Work

As with lateral flow, vertical flow immunoassays rely on the immobilization of a capture antibody on a reagent pad to which the sample of interest (with or without antigen to be detected) is applied. Detection of the bound antigen is subsequently achieved through the binding of an antigen specific antibody gold conjugate. This step completes a sandwich consisting of a capture antibody, an antigen and finally the gold conjugate and results in a direct and permanent visually detectable red coloured dot indicating the presence of the antigen, figure 1.

Of interest is that alternative colour of detection can easily be achieved by using a different type of nanoparticle conjugate probe for detection. One example being antibody conjugated gold nanourchins, which will yield a blue coloured dot upon positive detection in the assay.

Figure 1. Illustration of the appearance of the Miriad™ vertical flow cartridge after applying a gold conjugate (A) or a gold nanourchin conjugate (B) when target is present (A, B) and not present (C) in the sample analyzed.

Multiplexing Capabilities in Vertical Flow Immunoassays
Vertical flow technology also allows for easy multiplexing. In the Miriad™ vertical flow test cartridges distributed by Cytodiagnostics Inc., the presence of 4 targets can be evaluated simultaneously in a single sample in 5 minutes or less.

Multiplexing is easily achieved by spotting capture antibodies against different antigens at pre-determined locations and/or patterns on the membrane. For easier visualization this multiplexing can also be coupled with nanoparticle probes of different colours, e.g. using a gold conjugate and a gold nanourchin conjugate with red and blue detection colours, respectively.

Figure 2. Multiplex detection in a vertical flow immunoassay. Left image shows positive detection of 2 out of 3 antigens (red dots) and the control. The right image shows positive detection of two different antigens using two nanoparticle probes with different colours (red: gold nanoparticles, blue: gold nanourchins.

Cytodiagnostics offers flexible solutions for development and manufacturing of lateral flow assays based on our noble-metal nanoparticles (standard gold nanoparticles and our unique gold nanourchins).

By leveraging years of experience in nanoparticle manufacturing and assay development we can reduce the time from project inception to a finished product. Whether it is a smaller project or full-scale assay development project with the goal of launching a commercial product, Cytodiagnostics is here to help.

Common service and project types:

• Antibody conjugation and screening
• New assay development
• Transfer and optimization of existing proof-of-concept assay into a flow based rapid test setting.
• Deposition of your gold conjugate on conjugate pads

If you are interested in our custom assay development services please contact us and we would be delighted to discuss your project.

Our ELISA Research and Development team has over 20 years of experience with immunoassay development, sample handling, data analysis, and proteomics. We employ high-quality validation and testing procedures to ensure all custom assays we develop perform according to desired specifications.

Is a suitable or affordable assay not commercially available for your target of interest?

Read below for more information on Cytodiagnostics ELISA development services or contact us today to discuss your project.

Custom Immunoassay Development and Services We Offer

• Development of a unique ELISA specific to your target, with defined project milestones and progress reports to suit your needs.
• QC testing
• Bulk manufacturing

Required materials and reagents to begin assay development:

1. Analyte
2. Antibodies
3. Analyte negative samples
4. Analyte positive samples

Typical ELISA Development Project Phases

Step 1: Antibody Pair Identification and Assay Titration

1. Selection of compatible capture and detection antibody pairs.
2. Determination of an optimal capture and detection antibody conjugate pair providing optimal signal-to-noise ratio: titration experiments.
3. Development and optimization of ELISA plate coating procedures for optimal antigen capture: titration experiment.

Step 2: Assay Optimization

1. Selection of proper sample diluent for signal generation and detection.
2. Assessment and elimination of sample matrix effects, i.e., interference or non-specific binding.
3. Construction of a standard curve that reflects the characteristics of the sample matrix: Parallelism.
4. Development of an assay protocol that can detect the analyte of interest within the target sensitivity range.

Step 3: Assay Validation

1. Determining sensitivity and precision of the assay.
2. Determining performance of the assay in various sample matrices: Spike-in and recovery and Linearity of dilution.
3. Optimizing assay components and incubation protocols to meet final detection requirements.

Step 4. Production of Finished Kits

1. Quality control assessment of final components.
2. Assembly, packaging, and delivery of ELISA kit.

If you are interested in learning more about the services we offer or want to discuss your custom ELISA development project please contact us.