Calixarene Derivatives: A Mini-Review on their Synthesis and Demands in Nanosensors and Biomedical Fields.

Nanotechnology has been widely studied in biomedical applications in the last decade. The revolution in nanotechnology triggers the fabrication of nanomaterials with novel properties and functionalities, making the research in nanosensors and biomedical rapidly expanding. Nanosensor application has improved the sensitivity by enhancing their catalytic activity, conductivity, and biocompatibility. Calixarene is excellent as a sensing element used as a sensor due to its unique host-guest properties. Three major types of calixarene which are extensively studied are calix[4]arene, calix[6]arene, and calix[8]arene. These organic nanomaterials resemble vase-like supramolecular structures and exhibit valuable properties. Calixarene's basic molecular design is the cyclic phenol tetramer with four aryl groups, perfect for molecular recognition such as cations, transition metal ions, and heavy metals. Calixarenes may form stable complexes with biomolecules in developing biosensors for protein, enzyme, and antibody sensing. Calixarene's lower rim can be modified for optimum molecular interaction with guest molecules such as anions, cations, and neutral molecules. The lower ring has welldefined conformation properties and cavities, which allow trapping guest drugs such as imatinib, paclitaxel, and temozolomide. Calixarene also possesses good biocompatibility and innocuousness and gained attention for cancer treatment due to the response to multiple stimuli, stability, avoiding non-specific cell uptake, and reaching the target for treatment effect. This review paper focuses on the synthesis and characteristics of calixarene applied in nanosensors as an ideal complex agent in drug transportation and controlled drug released for biomedical research.

Elastic constant determination of hardwoods using ultrasonic insertion technique.

Ultrasonic insertion technique (IT) is an ultrasonic technique which involves sample immersion in a solution to determine its acoustic properties. IT is normally used to determine the acoustic properties of a medical phantom. We proposed the use of IT as an alternative technique to the common contact ultrasonic technique: through-transmission technique (TT) for determining the elastic constant of hardwoods in longitudinal, tangential and radial directions. The elastic constant of twelve rectangular-shaped Malaysian hardwoods from three different categories; heavy, medium and light with the density ranging from 602 to 992kgm-3 were determined using IT and TT. Both techniques were carried out at 24.0°C surrounding temperature and utilized 2.25MHz ultrasonic transducers. Data from both techniques were compared to validate the use of the proposed technique. Findings indicated that IT offers consistent and accurate results for, tangential and radial elastic constants (TEC and REC) within 8.89% and 5.86% differences, respectively compared to TT for all tested hardwoods. IT offers an alternative technique for TEC and REC determinations of precious wood samples.