Bridging the Gap in the Development of Gold Nanoparticle-based Enzyme Biosensing

Quantitatively measuring enzyme activity is a great challenge since the product of this activity is often altered by only a single molecular bond. Many current methods rely on the creation of fluorescent analogues that exhibit an increase or decrease in brightness when modified by enzymes. This approach is problematic, though, because the addition of a bulky fluorescent group can change the molecular interaction. Furthermore, it is often a slow and tedious process to redesign these tests for new applications. In contrast, we have developed an array of assays based on the unique optical properties of gold nanoparticles, which do not suffer from these drawbacks.

By selectively functionalising the surface of gold nanoparticles, we are able to make them either aggregate or disperse in response to enzyme activation. This change in physical state then manifests itself as a dramatic colour change of the solution. This property naturally lends itself to both qualitative and quantitative measurements of enzyme activity.

Over the past several years, we have developed and tested a number of assays based on this basic concept. The two most successful to date have been a protease assay and a lipase assay, both of which are of great clinical relevance. We have explored using the protease assay to test for HIV biomarkers and, since proteases are involved in a number of viral and parasitic infections, we expect that there will be many more applications to come. Lipases are also medically important, as their level in the body can become too high due to arthritis, acute sepsis and certain types of cancer. Because of this wide-ranging involvement, efforts are currently underway in the pharmaceutical industry to develop drugs that will target lipases.

One of the great advantages of our technology is the fact that, in addition to diagnosing disease, it can also potentially help in the search for new drugs to treat those diseases. In contrast to methods that simply measure enzyme concentration, our method actually measures enzyme activity. We are just now starting to take advantage of this capability by using our assays to help screen chemical libraries for new drug candidates.

In the course of this Follow-on fund project, we will address some of the practical questions involved in the transition from benchtop to bedside. In particular, we will look at scalability, manufacturing and storage and determine the commercial landscape and route forwards. These are concerns that are typically not addressed at the level of fundamental research but are important for the creation of a practical product. At the conclusion of this work, we will be in a strong position to immediately commercialise this technology, bringing its benefits to the broader healthcare market.

The twenty first century has been predicted to be the age of personalised medicine. Already, there are drugs being developed that target specific subsets of patients, and this trend will only gain momentum in the future. However, there is a hidden challenge in this progression. Pharmaceutical treatments can only be as specific as the tests that determine their necessity and efficacy. Without a new generation of bioassays, there can be no new generation of treatment. Due to its fundamental flexibility, our enzyme assay platform is uniquely amenable to enabling this advance. Overall, this work will have four broad societal and economic benefits.

1) The first of these is a new method for rapidly diagnosing disease states. Starting with a few highly relevant specific diseases such as HIV, we will show that our nanoparticle-based assays can reduce healthcare costs and increase accuracy in the diagnostic field. The clear beneficiaries of this approach will be patients with those diseases who have access to faster and more accurate testing. Eventually, by applying our platform to a broader range of disease states, we hope to change the standard management practice of acute inflammation by offering doctors a rapid classification of infection. Such changes could significantly alter public health policy and management plans by decreasing incorrectly prescribed treatments and allowing routine screening for atypical presentations.

2) The second societal benefit will be the deployment of a test to more accurately screen drug candidates that act on enzymes. Many drugs are now abandoned late in clinical trials, wasting vast quantities of time and money. The public will directly benefit from the more effective drug pipeline that our methods could enable. By cooperating closely with pharmaceutical companies, we will ensure that the product we are offering has the features and capabilities that they, as the eventual customers, will need.

3) Third, the UK economy will directly benefit from the revenue and job creation associated with commercialisation of these assays. To remain competitive in a global market, we will need to drive innovation. Nanotechnology is clearly one of the most important frontiers in modern research and it is of great importance that we work now to found and support the next generation of high tech companies. The spinout diagnostics company that we plan to form will serve as an excellent example of how this transition from fundamental to applied research can be accomplished.

4) And finally, the economy will benefit over the longer term by the unique combination of fundamental and practical training that this project will offer the researchers involved. Only if groups such as ours continue to address the needs of science and industry simultaneously will the next generation of researchers be able to get the skills they need to make a practical difference in the years ahead.