Real-time monitoring of cyanobacterial harmful algal blooms by graphene field-effect transistor

Demands for clean water are increasing due to factors such as population growth, global warming, and environmental degradation. One of the main obstacles to achieving this purpose is the cyanobacterial blooms, which are the overgrowth of cyanobacteria well known as blue-green algae. Since many cyanobacteria strains are reported to produce geosmin (GSM) or 2-methylisoborneol (MIB) as metabolites, monitoring the level of those two odor compounds is available to the detection of cyanobacterial bloom. The limit of detection (LOD) of the pre-developed equipment is high to detect the initial proliferation of cyanobacteria. To overcome the limitation, we fabricated graphene field-effect transistors (GFETs) based bioelectronic nose which use human olfactory receptors (hORs) 51S1 and 3A4 as bioprobe. The hOR51S1 and 3A4 were reconstituted to nanodiscs (NDs) due to their stable, sensitive, and selective interaction with GSM and MIB, respectively. The LOD (10 fM) of the fabricated device was the lowest among previously developed detection platforms. In addition, the device demonstrated high selectivity for GSM and MIB with other odor compounds, such as IBMP and IPMP. To evaluate sensing properties of the bioelectronic nose, the real samples from river water containing GSM and MIB were prepared and monitored by bioelectronics nose to measure its sensitivity and selectivity. Furthermore, the developed platform, a bioelectronic nose mimicking the human sense of smell, can be applied to detect other harmful compounds in environmental areas by using various bioprobes.