*Article* **Electrical Characterization of Cellulose-Based Membranes towards Pathogen Detection in Water †**

**Grégoire Le Brun 1,\*, Margo Hauwaert 1, Audrey Leprince 2, Karine Glinel 3, Jacques Mahillon 2 and Jean-Pierre Raskin 1**


 † This paper is an extended version of our paper published in: Le Brun, G.; Hauwaert, M.; Leprince, A.; Glinel, K.; Mahillon, J.; Raskin, J.-P. Electrochemical Characterization of Nitrocellulose Membranes towards Bacterial Detection in Water. In Proceedings of the 1st International Electronic Conference on Biosensors, 2–17 November 2020.

**Abstract:** Paper substrates are promising for development of cost-effective and efficient point-of-care biosensors, essential for public healthcare and environmental diagnostics in emergency situations. Most paper-based biosensors rely on the natural capillarity of paper to perform qualitative or semiquantitative colorimetric detections. To achieve quantification and better sensitivity, technologies combining paper-based substrates and electrical detection are being developed. In this work, we demonstrate the potential of electrical measurements by means of a simple, parallel-plate electrode setup towards the detection of whole-cell bacteria captured in nitrocellulose (NC) membranes. Unlike current electrical sensors, which are mostly integrated, this plug and play system has reusable electrodes and enables simple and fast bacterial detection through impedance measurements. The characterized NC membrane was subjected to (i) a biofunctionalization, (ii) different saline solutions modelling real water samples, and (iii) bacterial suspensions of different concentrations. Bacterial detection was achieved in low conductivity buffers through both resistive and capacitive changes in the sensed medium. To capture *Bacillus thuringiensis*, the model microorganism used in this work, the endolysin cell-wall binding domain (CBD) of Deep-Blue, a bacteriophage targeting this bacterium, was integrated into the membranes as a recognition bio-interface. This experimental proof-of-concept illustrates the electrical detection of 10<sup>7</sup> colony-forming units (CFU) mL−<sup>1</sup> bacteria in low-salinity buffers within 5 min, using a very simple setup. This offers perspectives for affordable pathogen sensors that can easily be reconfigured for different bacteria. Water quality testing is a particularly interesting application since it requires frequent testing, especially in emergency situations.

**Keywords:** paper-based sensors; nitrocellulose; impedance measurements; dielectric properties; parallel-plate electrodes; interdigital electrodes; endolysins; *Bacillus thuringiensis*
