The Effect of Coating the Surface of the Quartz Crystal Microbalance (QCM) Sensor Using Lauric Acid and Myristic Acid Base Materials on the Response of E. coli Bacteria

The Quartz Crystal Microbalance (QCM) sensor is a biosensor based on a quartz crystal (SiO2) that has a high level of sensitivity. The use of the QCM as a biosensor can be enhanced by coating the biosensor surface with a polymer material. Two materials that can be used as a membrane layer on a biosensor are lauric acid and myristic acid. This membrane layer was varied with five lauric acid : myristic acid ratios of 1:0, 2:1, 1:1, 1:2 and 0:1, and E. coli bacteria at five dilutions were used as the test material for the response time and the sensitivity of the sensor toward the fabricated membrane layer. Membrane coating on the QCM sensor was performed with the airbrush method by adjusting the distance, pressure and a specified time. Before use as a layer on the sensor surface, the functional groups of the membrane were first analysed using Fourier Transform Infrared (FTIR). The membrane used as a layer on the QCM sensor must have a carboxylic group (C=O) that will interact with the E. coli bacteria. The results of the functional-group analysis of the membrane show that the carboxylic-group content of lauric acid is better than that of the other membranes. Consequently, the myristic acid membrane, whose carboxylic-group content produces the most gently-sloping graph among the membranes, behaves differently. A good response-time value is shown when the QCM sensor has not yet been coated with any membrane (bare/pure gold electrode). Meanwhile, the good response-time value after the QCM sensor is coated is obtained for the myristic acid membrane. The highest sensitivity of the QCM sensor is found for the lauric acid : myristic acid membrane layer at a ratio of 2:1, with a test-influence result of 100%. This is most likely due to the presence of a good carboxyl group in lauric acid together with an appropriate ratio between the two membranes, so that the sensitivity produced by this membrane ratio is also better than that of the other membranes. **Keywords:** Quartz Crystal Microbalance (QCM); E. coli bacteria; myristic acid membrane; lauric acid membrane. —