Microdialysis is a sampling technique first introduced in the late 1950s. Although this technique was originally designed to study endogenous compounds in animal brain, it is later modified to be used in other organs. Additionally, microdialysis is not only able to collect unbound concentration of compounds from tissue sites; this technique can also be used to deliver exogenous compounds to a designated area. Due to its versatility, microdialysis technique is widely employed in a number of areas, including biomedical research. However, for most in vivo studies, the concentration of substance obtained directly from the microdialysis technique does not accurately describe the concentration of the substance on-site. In order to relate the results collected from microdialysis to the actual in vivo condition, a calibration method is required. To date, various microdialysis calibration methods have been reported, with each method being capable to provide valuable insights of the technique itself and its applications. This paper aims to provide a critical review on various calibration methods used in microdialysis applications, inclusive of a detailed description of the microdialysis technique itself to start with. It is expected that this article shall review in detail, the various calibration methods employed, present examples of work related to each calibration method including clinical efforts, plus the advantages and disadvantages of each of the methods.

A tri‐functionality magnetic nanoparticles (MNPs) are crucial for environmental remediation. This research focused on the synthesis of pH‐catalytic‐magnetic polymer beads for dye removal by using phase inversion technique. In 15 wt% of polyethersulfone (PES) polymer possessed the highest porosity (80%) was used in the synthesis of MNPs‐PES beads. The methylene blue (MB) removal efficiency of MNPs‐PES beads and PES beads was 72.94% and 62.67%, respectively. Similarly, the removal efficiency of methyl orange (MO) dye is higher for MNPs‐PES beads (38.56%) compared to PES beads (34.16%). Besides, the removal efficiency for MB dye by MNPs‐PES beads increased from 77.59% to 96.90% when solution pH increased from 3 to 9 while removal of MO dye increased from 61.14% to 74.35% when solution pH decreased from 9 to 3. Moreover, the removal efficiency for MB dye increased from 72.94% to 93.43% when H2O2 is added. Additionally, MNPs‐PES beads were recollected successfully using external magnet. These indirectly proved that the MNPs‐PES beads were responsive towards the tri‐functionalities of pH‐catalytic‐magnetic. Lastly, the adsorption of MB dye onto MNPs‐PES beads were fitted well to Langmuir isotherm model and pseudo‐second‐order model with both correlations R2 of more than 0.98.

Preliminary screening was performed to investigate the effects of different types of alkaline solution (2%, w/v NaOH and Ca(OH)2) on total reducing sugar (TRS) recovery. The results showed that usage of Ca(OH)2 yields higher TRS as compared to NaOH. Therefore, Ca(OH)2 was chosen for further studies in this effort. One-Factor-A-Time (OFAT) approach was employed to determine possible optimum ranges of chosen independent variables (i.e., pre-treatment temperature, concentration of Ca(OH)2 and reaction time). It is found that for both biomasses, rice straw gives the higher yield of TRS. The optimum temperature for rice straw and sugarcane bagasse are 70 °C and 80 °C, respectively. Increasing the concentration of Ca(OH)2 and reaction time gives an overall negative effect on the yield of TRS.

Microdialysis is a popular sampling technique that utilizes a probe, which can be simplified as a membrane attached to a hollow needle. Although well accepted, this technique is hampered by performance issues. Many researchers argued that these issues can be addressed if mass transfer through the membrane is properly evaluated. However, due to the nature of the probe (small in size, fragile, etc.), experimental evaluation is not something typical or straightforward. Mathematical models are seen as a reliable alternative, but the success of building such representative model shall depend on various parameters that need to be identified through characterization. This paper aims to characterize the probe’s membrane using the scanning electron microscope (SEM). It is envisaged that the characterization efforts shall provide necessary information to complement various unknown parameters in the proposed mathematical framework.

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Adsorption is the most common methods used in industry for the removal of dye. In this study, magnetic multi-walled carbon nanotubes (MMWCNTs) was served as adsorbent for the removal of methylene blue (MB). Statistical optimization of the MB removal efficiency via response surface methodology coupled with central composite design was performed and reported. It was observed that all three experimental parameters: adsorption temperature (25-50°C), MB concentration (10-50 ppm) and MMWCNTs dosage (0.01-0.05 g/20mL) were significant in the removal of MB. The optimized conditions of 99.21 % MB removal efficiency can be achieved at adsorption temperature of 38°C, MB concentration of 23 ppm and MMWCNTs dosage of 0.033 g/20mL. The verification of the prediction was performed with 3 repeated experiments and the results were found to be in good agreement with the experimental data with only 0.21 % error.

The severe water pollution from effluent dyes threatens human health. This study created pH-magnetic-photocatalytic polymer microspheres to conveniently separate the photocatalyst nanoparticles from the treated water by applying an external magnetic field. While fabricating magnetic nanoparticles’ (MNPs) microspheres, incorporating 0.5 wt.% iron oxide (Fe3O4) showed the best magnetophoretic separation ability, as all the MNPs microspheres were attracted toward the external magnet. Subsequently, hybrid organic–inorganic polyoxometalates (HPOM), a self-synthesized photocatalyst, were linked with the functionalized magnetic nanoparticles (f-MNPs) to prepare augmented magnetic-photocatalytic microspheres. The photodegradation dye removal efficiency of the augmented magnetic-photocatalytic microspheres (f-MNPs-HPOM) was then compared with that of the commercial titanium dioxide (TiO2) photocatalyst (f-MNPs-TiO2). Results showed that f-MNPs-HPOM microspheres with 74 ± 0.7% photocatalytic removal efficiency better degraded methylene orange (MO) than f-MNPs-TiO2 (70 ± 0.8%) at an unadjusted pH under UV-light irradiation for 90 min. The excellent performance was mainly attributed to the lower band-gap energy of HPOM (2.65 eV), which required lower energy to be photoactivated under UV light. The f-MNPs-HPOM microspheres demonstrated excellent reusability and stability in the photo-decolorization of MO, as the microspheres retained nearly the same removal percentage throughout the three continuous cycles. The degradation rate was also found to follow the pseudo-first-order kinetics. Furthermore, f-MNPs-HPOM microspheres were pH-responsive in the photodegradation of MO and methylene blue (MB) at pH 3 (acidic) and pH 9 (alkaline). Overall, it was demonstrated that using HPOM photocatalysts in the preparation of magnetic-photocatalytic microspheres resulted in better dye degradation than TiO2 photocatalysts.

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