In this paper, we propose an AlGaN/GaN high electron mobility transistor (HEMT)-based biosensor for the detection of C-reactive protein (CRP) using a null-balancing circuit. A null-balancing circuit was used to measure the output voltage of the sensor directly. The output voltage of the proposed biosensor was varied by antigen-antibody interactions on the gate surface due to CRP charges. The AlGaN/GaN HFET-based biosensor with null-balancing circuit applied shows that CRP can be detected in a wide range of concentrations, varying from 10 ng/mL to 1000 ng/mL. X-ray photoelectron spectroscopy was carried out to verify the immobilization of self-assembled monolayer with Au on the gated region.
In this paper, we present a differential-mode biosensor using dual extended-gate metal–oxide–semiconductor field-effect transistors (MOSFETs), which possesses the advantages of both the extended-gate structure and the differential-mode operation. The extended-gate MOSFET was fabricated using a 0.6 µm standard complementary metal oxide semiconductor (CMOS) process. The Au extended gate is the sensing gate on which biomolecules are immobilized, while the Pt extended gate is the dummy gate for use in the differential-mode detection circuit. The differential-mode operation offers many advantages such as insensitivity to the variation of temperature and light, as well as low noise. The outputs were measured using a semiconductor parameter analyzer in a phosphate buffered saline (PBS; pH 7.4) solution. A standard Ag/AgCl reference electrode was used to apply the gate bias. We measured the variation of output voltage with time, temperature, and light intensity. The bindings of self-assembled monolayer (SAM), streptavidin, and biotin caused a variation in the output voltage of the differential-mode detection circuit and this was confirmed by surface plasmon resonance (SPR) experiment. Biotin molecules could be detected up to a concentration of as low as 0.001 µg/ml.
This study explored plant-derived natural antioxidants by evaluating the antioxidant activity of Lamiaceae plant seed extracts. Plants with the percentage of filled seeds at or above 90% and seed germination at or above 50% were selected. Of the ten species studied, the total phenolic content of the seeds was high in the species Phlomis umbrosa Turcz. (6.2 mg GAEs/g of seeds) and Elsholtzia ciliata (Thunb.) Hyl. (4.5 mg GAEs/g of seeds). The total flavonoid content of the seeds was high in E. ciliata (1.0 mg QEs/g of seeds) and P. umbrosa (0.6 mg QEs/g of seeds). Based on the EC 50 value of the seed extracts, 2,2-diphenyl-1-picrylhydrazyl radical scavenging activity was high in the seeds of the plants E. ciliata (27.5 µg/mL), Mosla dianthera (Buch.-Ham. ex Roxb.) Maxim. (29.2 µg/mL), and Prunella vulgaris var. lilacina Nakai (33.3 µg/mL). In addition, 2,2'-Azino-bis(3ethylbenzothiazoline-6-sulfonic acid) radical scavenging activity was high in P. vulgaris var. lilacina (25.6 µg/mL), E. ciliata (25.9 µg/mL), and M. dianthera (27.6 µg/mL) seeds. The ferric reducing antioxidant power of the seed extracts was high in P. vulgaris var. lilacina (2910.4 µM Fe(II)/g of extract), E. ciliata (2836.2 µM Fe(II)/g of extract), and M. dianthera (2754.4 µM Fe(II)/g of extract). According to the cluster analysis based on antioxidant activity, the seeds of the ten species were classified into three groups, from group 1 with low antioxidant activity to group 3 with high antioxidant activity; E. ciliata, M. dianthera, and P. vulgaris var. lilacina were classified as group 3.
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