Monitoring of Lactococcus Lactis Growth Based on Reduced-Graphene Oxide TFT for Dairy Industry Applications

Thin-film transistors (TFTs) are a cutting-edge technology for biosensing applications due to their fast response time, low signal-to-noise ratio, and straightforward miniaturization into electronic circuitry. Liquid-gated reduced graphene oxide TFTs (rGO-TFTs) are particularly promising as biosensors since they allow direct coupling between the active material and any (bio-) chemical species dissolved in aqueous solution. In this work, we explore the use of ambipolar rGO-TFTs as transducers for biosensing, focusing on the detection of bacteria proliferation in laboratory-made samples. We choose Lactococcus lactis (L. lactis) as a reference bacterial species due to the potential final applications for the dairy industry. We performed electrical characterization of two different rGO-TFTs based on Si substrate (Si-TFT) and PET substrate (PET-TFT), assessing the devices’ stability, and extrapolating the parameters through a suitable model. The characterization is carried out using M17 broth as the liquid gate. The L. lactis detection is based on the evident parametric shifts of threshold potential caused by the bacterial presence at the liquid gate. The experimental results are compared with optical absorbance measurements at 600 nm to validate the proposed method. Experimental tests with laboratory-made L. lactis samples confirm that PET-TFTs have a higher detection capability compared to Si-TFTs, being also suitable to monitor the bacteria proliferation during observation of 370 min. rGO-TFTs show evident shifts of threshold potential of more than −100 mV in L. lactis spiked M17 broth compared to the pristine one.