Paper-Based Biosensor With Smartphone Readout

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Researchers from the Nanobioelectronics and Biosensors research group at the ICN2 have published details of their new biosensor system in Scientific Reports by Nature. Paper embedded with a graphene structure is used together with a 3D-printable mini “darkroom” and smartphone technology to screen for different compounds found in food and environmental samples. The innovative system provides a low-cost portable alternative to lab testing for qualitative and quantitative pollutant detection and monitoring. 

Simple, inexpensive biosensors that can give results in real time are in high demand in a number of fields, such as diagnostics, health and safety, and environmental monitoring. The use of paper is a back-to-basics approach enabled thanks to advances in the manipulation of materials at the nanoscale. Here, researchers at the ICN2 Nanobioelectronics and Biosensors group led by ICREA Research Prof. Dr Arben Merkoçi have infused paper strips with graphene quantum dots (QD), a key structure in the nanoworld, and combined them with smartphone technology. The result is an intuitive, portable and disposable biosensing system that has already given promising results in food and environmental samples. 

This technology was recently published in Scientific Reports, with Dr Ruslan Álvarez-Diduk as first author and Dr Jahir Orozco as co-author. It was also showcased at the Mobile World Congress 2017 in Barcelona as part of the Graphene Experience Zone curated by the Graphene Flagship. A video of the system in action can be viewed here. 

So how does it work? 

This new biosensor system uses luminescent graphene quantum dots as sensor probes to detect not only the presence but also the concentration of the compound being monitored. The probes used in this device were prepared from citric acid using pyrolysis and fixed into place onto paper strip (nitrocellulose) via adsorption and wax tracing. 

Following exposure to the sample, the graphene QDs are activated using ultraviolet light, causing them to luminesce at different intensities depending on the amount of analyte present: the greater the concentration, the lower the intensity, since the effect of the analyte on the QDs is to quench their luminescence. The ultraviolet light is applied inside a 3D-printable portable “darkroom” in order to prevent interference from other light sources during this process. For further portability, this light source can be run off a smartphone, connected via USB port. The smartphone camera is then used to capture the light emitted by each dot individually, upon which software installed on the smartphone quantifies said light to give readings in real time.    

So far the device has been used to correctly identify the age of vintage wines based on their phenolic content, opening the door to potential broader applications in the food industry, and to screen for toxic pollutants in seawater samples. It is also expected to find applications in clinical diagnostics. But beyond these specific applications, the key outcome of the study is the validation of disposable paper-based sensors as a promising means of screening for relevant organic compounds for use in low-income and remote settings where more expensive and sophisticated equipment is not readily available. 

The ICN2 is currently looking for industrial partnerships to further advance this technology. It is also interested in licensing the technology to medical device companies.