The detection of thrombin by using CdS nanocrystals (CdS NCs), gold nanoparticles (AuNPs) and luminol is investigated in this work. Thrombin is detected by three methods. One is called the quenching method. It is based on the quenching effect of AuNPs on the yellow fluorescence of CdS NCs (with excitation/emission wavelengths of 355/550 nm) when placed adjacent to CdS NCs. The second method (called amplification method) is based on an amplification mechanism in which the plasmonics on the AuNPs enhance the emission of CdS NCs through distance related Förster resonance energy transfer (FRET). The third method is ratiometric and based on the emission by two luminophores, viz. CdS NCs and luminol. In this method, by increasing the concentration of thrombin, the intensity of CdS NCs decreases, while that of luminol increases. The results showed that ratiometric method was most sensitive (with an LOD of 500 fg.mL-1), followed by the amplification method (6.5 pg.mL-1) and the quenching method (92 pg.mL-1). Hence, the latter is less useful.
In this work, we proposed a new wireless sensor to contribute to research aimed at continuous monitoring of nitrate and ammonium in water, which are important agents causing water pollution, which is a very important problem today. In this research, a well-implemented application of electroanalytical sensor was achieved by combining it with the internet of things (IoT) concept, which is the most modern form of wireless data collection technique. We developed a portable IoT system and ion-selective nitrate and ammonium electrodes and monitored the nitrate and ammonium levels of the water online. The system was produced in a low-cost manner (under $25) and it enabled data acquisition without energy related problems, thanks to the support of solar energy and mobile power bank. The recovery rates of the sensors were tested with the standard addition method and response was obtained between 101.74% and 147.01%.
A coated wire calcium selective microelectrode for biological use was developed, comprising a PVC selective matrix containing calcium ionophore IV coated on copper wire, previously covered with a solid-state contact mixture. The obtained calcium microsensor presented a Nernstian answer in a concentration range of 10-1 to 10-6 mol/L. The selectivity coefficients over the main interfering ions of biological interest proved that the calcium microelectrode is highly selective. Also, the response time (6s) and repeatability have been determined. The pH variation did not significantly modify the calcium microelectrode answer, being stable over the pH range (6.7-7.3) of interest. The obtained calcium microelectrode is simple, inexpensive and able to give reliable electrochemical response, recommending itself as a solution for assessing the level of inorganic ions of the gingival crevicular fluid and saliva.
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