Salicylic Acid (SA) is a phyto-hormone involved in the regulation of induced plant defense mechanisms, primarily against biotic stresses. Various methods have been reported for detecting SA. The electrochemical methods offer economical, portable, and accurate concentration measurement of bio-chemicals like SA. Electrochemical biosensors often require modification of the working electrode (WE) with specific materials to functionalize it with bio-molecules, needed for target analyte recognition. The proposed biosensor provides a unique methodology of selectively coating the inter-digital electrodes (IDE) and further applying the method to develop a biosensor to detect SA. The electrodes are fabricated using a novel deposition process termed as, Capillary action assisted deposition (CAAD) which consists of IDEs fabricated in the form of small finger-like channels connected to a wider main channel. The drop-casted sample automatically flows from the main channel into the fine fingers under the effect of capillary action. The sensor includes a 3-electrode system arranged in a 3-D geometry, forming an integrated microfluidic channel for analyte solution flow. The WE is selectively coated with, first, Graphene oxide (GO) and next, the bi-enzyme Salicylate Hydroxylase (SH) and Tyrosinase (TYR) recipe using the proposed CAAD process. The bi-enzyme exhibits selectivity towards SA and the proposed sensor shows the detection range of 0.5 μš¯‘€ to 64 μš¯‘€. The electrochemical reactions are characterized by Chrono-amperometry (CA) and shows the sensitivity of 34.4 μA cm-2 per decade change in SA concentration (in μš¯‘€). To the best of our knowledge, the proposed bi-enzyme system in a microfluidic device for SA sensing is the first of its kind.
An impedance measurement based level sensor is proposed using a co-axial probe for sensing liquid level in a container. The co-axial sensing probe is made with a hollow stainless steel outer conductor enclosing an insulated inner conductor. The impedance of the co-axial probe varies with the water level in a nonlinear fashion. The supporting electronics was developed using MSP 432 microcontroller unit (MCU) platform from Texas Instruments (TI) and a newly designed Impedance Analyzer-Analog Front End (IA-AFE) developed at TI. An inverter amplifier based circuit was implemented within the IA-AFE for impedance measurement. Discrete Fourier Transform (DFT) is calculated on the MCU platform from the sampled input and output square wave voltages of the IA-AFE. The proposed sensor shows a maximum error within ±1.5 mm, for the probe of length 40 cm. The proposed system offers an accurate and economical liquid level measurement platform outperforming the state-of-art level sensors to the best of our knowledge.
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