Novel green-chemistry synthesis of silver nanoparticles (AgNPs) is introduced as a low-cost, rapid and easy-to-use analytical method for mercury ion detection. Aqueous fruit extract of water apple (Syzygium aqueum) was used for the first time as bioreductant to synthesize stable AgNPs. The prepared AgNPs have a yellowish-brown color with a surface plasmon resonance peak at 420 nm. The addition of Hg(II) ions then changes the AgNPs color to colorless. The color change was in proportion to the concentration of Hg(II) ions. The presence of other metal ions in the system was also evaluated. The proposed method shows good selectivity and sensitivity towards Hg(II) ions. Using UV-visible spectrophotometry, the detection limit of the developed method was 8.5 × 10 -7 M. The proposed method has been successfully applied for determination of Hg(II) ions in tap and lake water samples with precision better than 5%.
Epithelial sodium channels (ENaC) is a protein that plays a role in maintaining sodium levels and can be used as a biomarker of hypertension. This study aims to develop an electrochemical immunosensor for detecting ENaC using a screen-printed carbon electrode (SPCE), which was modified with reduced graphene oxide (RGO). The RGO improves the performance of immunosensor because it contains -COOH groups that can form a covalent bond with the terminal -NH2 of anti-ENaC. The result shows that the optimum concentration of anti-ENaC was 1.0 µg/mL for 30 min incubation time. The various concentration of ENaC has a linear relationship with the decreasing of ferricyanide peak current signal with the range of 0.01-1.5 ng/mL, and the limit of detection was 0.198 ng/mL. The level of ENaC concentration in urine samples can be used for the realization of a point-of-care device for early detection of hypertension.
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