Advanced sensing technologies have significantly shortened the detection period of bacteria; however, bringing bacteria to the sensing surfaces is challenging at low concentrations because of their continuous swinging and tumbling movement in new directions. The natural diffusion of bacteria to the sensing surface requires a long sensing duration. In this contribution, the spontaneous detection of bacteria is reported using a magnetic nanoparticle encapsulation methodology. Bacteria are encapsulated by magnetic nanoparticles and brought to the reduced graphene oxide (rGO) sensing surface under an external magnetic force in less than 1 min. Finally, magnetic nanoparticle encapsulated bacteria are detected by aptamer functionalized rGO field‐effect‐transistor sensors. The encapsulation of bacteria by magnetic nanoparticles is confirmed by scanning electron microscopy and super‐resolution confocal laser scanning microscopy. In addition, the substrate‐independent fabrication of rGO sensors is demonstrated using an ultralow‐volume dispenser that allows the centimeter‐scale patterning of graphene oxide. rGO patterns are highly sensitive to surface charge density.
Novelty of our biosensor sensors:
Although researchers have reported the use of rGO in various biomolecule sensing applications, most of the rGO sensors have been patterned in the small scale by transfer steps or selective reduction processes. Whereas transfer methods are complicated and cause contamination, selective reduction processes induce current leakage and noise through connected GO. Consequently, the main challenge lies in the reproducible direct patterning of rGO on a large scale. To overcome the above-mentioned issues, herein, rGO sensors were patterned by a facile method using ultralow volume dispenser patterning.
In a parallel effort, we have developed a novel methodology for the efficient and spontaneous detection of E. coli using rGOFETs. E. coli were successfully encapsulated by magnetic nanoparticles and their movements were manipulated under a magnetic field. At the selected conditions, simulated and experimental results showed that a magnetic attraction method needs less than 1 min to bring all E. coli from a height of 1 cm to the rGO sensing surfaces. For the first time, we have successfully demonstrated the spontaneous detection of magnetic nanoparticle encapsulated E. coli by aptamer functionalized rGOFETs. Capitalizing on the high selectivity of aptamers and fast movement of MFNP-E. coli under a magnetic field, rGOFETs were used for the detection of E. coli as low as 10^2 cfu/ml.