“Most previous such biosensors contained a number of different electrode materials that could only detect one kind of metabolite,” team leaders Guihua Yu and Lijia Pan tell nanotechweb.org. “Almost no single electrode material was able to detect more than one type of metabolite, until now.

In contrast, our conducting polymer hydrogel-based biosensors can detect a wide range of metabolites. Our work is thus a first step towards fabricating simple and inexpensive integrated sensor arrays on a chip made from just one electrode material.”

Hydrogels are 3D polymer networks that can hold a large amount of water without dissolving and have a structure similar to that of biological tissue. They are also easy to handle and process.

Incorporated enzymes amplify the collected current

The new device made by Yu, Pan and colleagues is based on a platinum nanoparticle (PtNP)-modified conducting polymer hydrogel electrode. The researchers made their sensor by first sequentially depositing the hydrogel precursor, the PtNPs and specific enzymes onto a glassy carbon electrode to form a hybrid bioelectrode. “We then made a synergized biosensor in which the PtNPs catalyse the hydrogen peroxide generated in the enzymatic reaction. We incorporated enzymes into our design to amplify the collected current in the device – that is, to produce a stronger signal from it,” explains Yu.

The hydrogel/PtNP/enzyme electrode system works very well and can detect different metabolites with high sensitivity in the concentrations found in human blood, Pan adds. For example, it can detect uric acid in the 0.07–1 mM range; cholesterol in the 0.3–9 mM range, and triglycerides in the 0.2–5 mM range. And this in around just three seconds.

Applications in patient health monitoring and clinical diagnostics

Being able to detect these metabolites rapidly and easily will be important for monitoring patient health and in clinical diagnostics.

“At the moment we can detect glucose, uric acid cholesterol and triglycerides,” says Pan. “These are implicated in diabetes, gout and cardiovascular disease respectively. The next stage in our work is to expand the range of metabolites that our device can detect. Some examples include glycosylated haemoglobin and haemochrome.”

Zhenan Bao of Stanford University, who was not involved in this work, comments that the new work is a clever way to take advantage of the good compatibility of conducting hydrogels with enzymes to directly incorporate the enzymes during device synthesis. "The performance Yu's team has achieved is really impressive and I expect this method could have great potential for practical applications."

The Texas/Nanjing researchers say that they are “very excited” about using polymer hydrogels to produce multiplexing biosensors on a chip at low cost and on a large scale. “We reckon that such biosensors could make for ‘vital readers’ on the market that could inform patients very accurately of the values of three to four common metabolites in just a single drop of blood,” adds Yu.

The team also says that it is looking to wirelessly connect the biosensors to portable terminals, like mobile phones.

The work is detailed in Nano Lett. DOI: 10.1021/nl504217p.