In this work we focus on the electro-chemical detection of bacteria in a nitrocellulose (NC) membrane with interdigital electrodes (IDE) through impedance spectroscopy.
Paper-based sensors are inexpensive, simple and portable tools for environmental monitoring, in particular, in resource-limited settings. They mostly rely on specific bioreceptors and nanoparticles for colorimetric pathogen detection, and perform limited semi-quantitative measurements. Electrical biosensors offer opportunities for quantitative pathogen detection, usually with planar electrodes that sense bacteria attachment to their surface through changes in interfacial impedimetric properties. In particular, impedance spectroscopy allows for impedimetric sensing over a wide frequency range. However, they show limited sensitivity due to low bacteria number attached onto the planar biosensor.
To overcome these limitations, we innovate classic biosensing techniques by depositing planar electrodes directly on the NC, a paper derivative, with the aim of sensing electrical properties on the whole volume of the NC membrane. We take advantage of the natural capillarity of NC to bring bacteria solutions at the testing zone.
The complete sensing device is fabricated and characterized. An analytical model is established and validated by analyzing the conductivity changes of the NC volume, seen by the IDE and caused by the bacteria presence inside the porous NC.
To ensure high specificity and binding capacity to bacteria, the NC membrane is functionalized with phage endolysin cell-wall binding domain (CBD) as bioreceptor, deriving from the endolysin encoded by Deep-Blue, a bacteriophage targeting B. thuringiensis.
A proof of concept of the proposed biosensor is substantiated: 108 CFU/ml of B. thuringiensis are detected in DI water.
Through easy and appropriate modification of the biointerface, this affordable and sensitive biosensor creates opportunities in applications that need frequent and rapid pathogen detection, such as the detection of E. coli in drinking water; or various viruses, which may prove particularly useful regarding COVID-19 pandemic.
