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Wyss Institute Researchers Tackling Biofouling With Electrochemical Platform for Diagnostic Use

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NEW YORK – Researchers at the Wyss Institute at Harvard University are developing a low-cost diagnostic platform, eRapid, that employs electrochemical sensor technology to simultaneously detect a broad range of biomarkers with high sensitivity and selectivity using a drop of blood.

The platform consists of bovine serum albumin (BSA) crosslinked with glutaraldehyde and supported by a network of conducting nanomaterials, including gold nanowires, gold nanoparticles, and carbon nanotubes, Pawan Jolly, one of the test's developers and a senior research scientist at the Wyss Institute, said in an interview.

Jolly and his colleagues described the development of their approach in a study published on Monday in Nature Nanotechnology, in which the system overcame biofouling — a process that has hindered adoption of most electrochemical sensors in development for diagnostics applications.

The developers are looking to commercialize prototype assays running on the electrochemical platform that they have validated in preliminary studies. Further, they are developing new assays, including a panel that includes a biomarker for myocardial infarction and an assay for anaphylaxis, Jolly said.

In the study, he and his colleagues demonstrated the commercial potential of their approach by creating a multiplexed sensor with three separate electrodes, each coated with the BSA/gold nanowire matrix and a layer of antibodies associated with clinically relevant target molecules, including interleukin 6, a biomarker of inflammation.

The ultimate objective is to develop a platform that will enable handheld diagnostic devices that can be used at home or desktop-size systems used by health practitioners in pharmacies, ambulances, doctor's offices, and emergency departments, he said.

The work presented in the study "might be the missing piece of the puzzle that now enables the widespread use of electrochemical biosensors," wrote John Justin Gooding, a researcher in the school of chemistry at the University of New South Wales in Sydney, Australia, in an article published in Nature Nanotechnology.

The approach is "exceptionally simple to produce" and enables developing electrochemical affinity sensors for a variety of biomarkers, Gooding said in the paper, adding that the long-duration resistance to fouling of up to one month "could also be relevant for the in vivo monitoring of biomarkers and for continuous monitoring in biological fluids."

Biofouling from non-specific accumulation of biological materials in blood and other samples tends to interfere with the functionality of sensor detection elements, throwing off test results. The phenomenon is prominent in electrochemical sensing where the signal is a result of specific molecular interaction at the sensor metal surface, Jolly said.

Biofouling is especially problematic for sensing devices that are implanted, Sameer Sonkusale, a principal investigator in the nanotechnology lab at Tufts University, said in an interview.

Sonkusale, who is not involved in the Wyss Institute study, is leading the development of a microfluidic platform to test for several diseases at the point of care in low-resource settings.

"We have seen this with smart bandages and smart sutures that we have developed," he said. "The antifouling mechanism shown [in the Nature Nanotechnology study] is quite simple and scalable. I can see it being applied to the sensors we are developing, and others in the field, for a variety of medical conditions."

Multiple markers

If the Wyss Institute researchers are successful in translating their platform development work to commercial medical diagnostic applications, eRapid could also be implemented for the detection of a range of medical conditions, Jolly said.

The development of low-cost, handheld electrochemical devices using the platform could enable the simultaneous detection of a broad range of biomarkers with high sensitivity and selectivity and using a single drop of blood, he said.

When the researchers incubated the sensor with the respective target molecules in undiluted human plasma, they observed "excellent electrical signals with picogram-per-mL sensitivity," Jolly noted, adding that when they exposed the sensors to the plasma for more than one month, it retained 88 percent of the sensitivity of the original signal.

Other electrochemical sensors in development lose signal so quickly that they can't be used in clinical applications, he said.

Jolly added that losing only 12 percent sensitivity over one month "opens up a plethora of applications. To detect a particular target you now you have a surface onto which you can attach different types of probes — they can be antibodies, DNA aptamers, or peptide aptamers — and that makes it a platform technology."

The greatest challenge in developing the antifouling coating was to prevent accumulation of off-target substances on the sensor's metal electrodes, while maintaining their conductivity to allow sensing of the target, he said.

They experimented with a variety of materials combinations before settling on a coating that used the porous 3D matrix consisting of BSA crosslinked with glutaraldehyde and supported by a network of conducting nanomaterials, including gold nanowires, gold nanoparticles, and carbon nanotubes. The coating prevents biofouling because the small pore size of the BSA matrix excludes larger proteins found in blood and plasma, and the BSA's weak negative charge prevents the strong adhesion of positively charged, unwanted biomolecules onto the sensor.

To functionalize the coated sensors, the researchers attached antibodies to the surface of the nanomaterial coating on top of an electrode and used a sandwich assay to convert the antibody binding event into a chemical signal that precipitates onto the electrode surface. The magnitude of the resulting electrical signal directly correlates with the amount of the precipitate produced, and to the number of target molecules bound to the antibodies, allowing the concentration of the target to be measured.

The group is exploring commercialization options for eRapid, including using it as a point-of-care handheld platform, as a desktop instrument within hospitals, and as an implantable medical device.

The platform enables "multiplex detection of multiple targets in close proximity on the same chip without having any cross reactivity," Jolly said. "However, we are not interested in developing a large multiplex panel that caters to multiple diseases. We are more strategic, looking first into early detection of anaphylaxis and myocardial infarction." The group is also considering developing a panel of several markers that would test a patient's heart health, and includes the myocardial infarction assay with biomarkers for other cardiac conditions, he added.

Jolly noted that for future development and clinical validation of the platform and its assays, the Wyss Institute "is well connected with nearby hospitals," and the group has already engaged with clinical partners that have participated in early validation testing.

It is currently analyzing the best option for commercializing the technology, deciding whether to further develop and commercialize it as part of a spinoff company, through a licensing deal, or via a strategic partnership.

Jolly noted that among the challenges associated with commercializing the platform, the group will need to carefully select the optimal go-to-market application. The time to market will depend on the diagnostic application, and marketing a point-of-care platform will require a CLIA waiver and a demonstration that the test carries a low risk for an incorrect result, he said.

He added that a cardiac assay with predicate tests already in the market could take up to three years to commercialize through the FDA's 510(k) regulatory pathway. However, an early detection anaphylaxis test without a predicate would need to be cleared through a de novo pathway. "That will take longer than a 510(k) submission, because the agency needs to come up with a protocol for us to follow in order to submit an application," he said.

He doesn't see the cost of the platform as being a challenge to its adoption. The team hasn't yet completed an in-depth cost analysis, but the surface chemistry and platform manufacturing process, which employs lithography, is very low cost and scalable, Jolly said.