Abstract
The quartz-crystal microbalance is a sensitive and universal tool for measuring concentrations of various gases in the air. Biochemical functionalization of the QCM electrode allows a label-free detection of specific molecular interactions with high sensitivity and specificity. In addition, it enables a real-time determination of its kinetic rates and affinity constants. This makes QCM a versatile bioanalytical screening tool for various applications, with surface modifications ranging from the detection of single molecular monolayers to whole cells. Various types of biomaterials, including peptides mapping the binding sites of olfactory receptors, can be deposited as a sensitive element on the surface of the electrodes. One of key ways to ensure the sensitivity and accuracy of the sensor is provided by application of an optimal and repeatable method of immobilization. Therefore, effective sensors operation requires development of an optimal method of deposition. This paper reviews popular techniques (drop-casting, spin-coating, dip-coating) for coating peptides on piezoelectric crystals surface. Peptide (LEKKKKDC-NH2) derived from an aldehyde binding site in the HarmOBP7 protein was synthesized and used as a sensing material for the biosensor. The degree of deposition of the sensitive layer was monitoring by variations in the sensors frequency. The highest mass threshold for QCM measurements for peptides was approximately 16.43 µg·mm−2 for spin coating method. Developed sensor exhibited repeatable response to acetaldehyde. Moreover, responses to toluene was observed to evaluate sensors specificity. Calibration curves of the three sensors showed good determination coefficients (R2 > 0.99) for drop casting and dip coating and 0.97 for the spin-coating method. Sensors sensitivity vs. acetaldehyde were significantly higher for the dip-coating and drop-casting methods and lower for spin-coating one.
Highlights
IntroductionEngineering synthetic materials that mimic the complex behavior of smell sense is currently the biggest challenge [2]
The expanding knowledge of the mechanisms governing odour perception in the biological olfactory systems is accompanied by a significant progress in the field of odour biosensors [1].Engineering synthetic materials that mimic the complex behavior of smell sense is currently the biggest challenge [2]
The results of preliminary studies allowed to select peptide for the synthesis, mapping the aldehyde binding site in the HarmOBP7 protein, which is located in the antenna of Helicoverpa armigera [38]
Summary
Engineering synthetic materials that mimic the complex behavior of smell sense is currently the biggest challenge [2]. Improvement of biosensors’ basic parameters can be achieved by implementing materials which imitate biological materials, e.g., synthetic polypeptides, [3,4,5,6,7,8,9,10]. Sensors 2018, 18, 3942 depends on the sensing material used. Molecules implemented on sensor’s surface need to be designed and synthesized in such way as to achieve recognition site specific to particular analyte [11]. Polypeptides have some benefits owing to the fact that they retain in the solution stable secondary structures in the solution stabilized with hydrogen bonds
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