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A new methodology involving the use of Bovine Serum Albumin (BSA) as a probe and liquid crystal (LC) as a signal reporter for the detection of heavy metal ions in water at neutral pH was developed. BSA acted as a multi-dentate ligand for the detection of multiple metal ions. The LC sensor was fabricated by immobilizing 3 &micro, g mL&minus, 1 BSA solution on dimethyloctadecyl-[3-(trimethoxysilyl)propyl]ammonium chloride (DMOAP)-coated glass slides. In the absence of heavy metal ions, a dark optical image was observed, while in their presence, a dark optical image turned to bright. The optical response was characterized by using a polarized optical microscope (POM). The BSA based LC sensor selectively detected toxic metal ions as compared to s block metal ions and ammonium ions in water. Moreover, the limit of detection was found to be very low (i.e., 1 nM) for the developed new biosensor in comparison to reported biosensors.

Phenol is a common pollutant found in wastewater, and its allowable discharge limit is 0.5 parts-per-million (ppm). Therefore, it is critical to monitor phenol in the sub-ppm range with high sensitivity and a low limit of detection. Herein, we report a quantitative method for detecting phenol in industrial wastewater through square wave voltammetry (SWV), in which phenol is oxidized to phenoxyl radicals and then became catechol and hydroquinone for detection. By using this method, phenol in the sub-ppm range can be detected reliably over a wide pH range. The sensitivity can be further improved by using a pre-concentration step for phenol before scanning. The method has a limit of detection of 0.1 ppb for phenol. Finally, three graphite electrodes were applied as working, counter and reference electrodes, respectively, in a millifluidic device for continuous detection of phenol in industrial wastewater flowing at 300 μL/min. Because of its simplicity, the sensor can be mass-produced and deployed on a large scale to monitor phenol in industrial wastewater.

Additional file 1: Figure S1. FTIR spectra. Figure S2. FTIR spectra. Figure S3. The oxidation of GSH by GO sheets and GO-based materials. Figure S4. The ROS assays. Table S1. Instruments with different functions are used to characterize materials. Figure S5. The mean lateral size.