Zeta potential (ZP) is a parameter that expresses the electrochemical equilibrium between particles and liquids like in nanoparticle (NP) colloidal solutions with applications in medicine, pharmaceuticals, chemical production, mineral processing, and water and soil purification. Smoluchowski's theory applies to the ZP particles that are larger the interfacial layer but neglects surface conductivity. The Debye-Hückel theory correctly approximates the concentration of ions in a double layer but fails to account for the dependence of ZP on the concentration of counterions. Determining ZP of NPs is essential to proper NP characterization. For instance, developing well-defined therapeutic-relevant nanoformulations needs information on NPs size, surface charge, stability and agglomeration behaviour. This approach has many practical challenges, from inadequate knowledge of operating standards to sampling, data interpretation and good laboratory practice for the experiments replicability. However, in drug delivery research, very little literature can provide a clear, succinct explanation of these techniques. Looking for specific guidelines to overcome frequently encountered problems during ZP measurements. This article explores factors influencing colloidal particle stability. Measurement criteria such as applied voltage, number of measurements, electrophoretic mobility (EPM), size distribution, surface shape, temperature, viscosity, particle concentration, zeta potential, nanoparticles, colloidal suspension, electrophoretic mobility, and pH.
UV-vis spectroscopy is an inexpensive, simple, flexible, non-destructive, analytical method appropriate for a wide class of organic compounds and some inorganic species. UV-vis spectrophotometers measure the absorbance or transmittance of light passing through a medium as a function of the wavelength. Chemical engineers apply it for quantitative analysis, to derive liquid phase reaction kinetics, and to identify the mechanism at the molecular scale. High performance liquid chromatography and ultra-high performance liquid chromatography integrate UV-vis detectors to identify and quantify the concentration of compounds in liquid streams. Combining these techniques with mass spectrometry facilitates identifying all species. UV-vis diffuse reflectance spectroscopy is a variant with enhanced scattering properties that measures the properties of solids and powders. A bibliometric analysis of the 10 000 most cited papers referring to UV-vis (2016 and 2017) groups research in four major clusters: nanoparticles and nanostucutres; photocatalysis and water treatment; crystals, complexes, and derivatives; and Ag and Au nanoparticles biological interaction.
Fluorescence is a luminescence phenomenon in which a compound emits light after absorption of electromagnetic irradiation. Specialized terms such as photoluminescence, cathodoluminescence, anodoluminescence, radioluminescence, and x-ray fluorescence sometimes are used to indicate the type of exciting radiation. Fluorescence spectroscopy provides reliable quantitative and qualitative data. It precisely tracks chemical reactions from fluorescent materials compounds with aromatic groups, or conjugated planar, or cyclic molecules. It is up to 1000 times more sensitive than UV-vis or infrared spectroscopy. Fluorescence intensity depends on the fluorophore (compound that fluoresces), its concentration, excitation and emission wavelengths, temperature and contamination. We adjust the slit dimensions, photomultiplier tube voltage and bandpass filter cutoff to maximize the signal while avoiding saturating the detector. Together with x-ray diffraction, it is the most common spectroscopic technique with applications in geology, chemistry, medicine, and astronomy. A bibliometric analysis of the top 10 000 cited papers identified 5 clusters based on keywords centered around: (1) cancer, cells, and proteins;(2) aggregation induced emission, LED, and complexes; (3) live cells, sensors, and probes; (4) quantum dots, DNA, and biosensors; and (5) nanoparticles, in vivo, and drug delivery. Chemical engineers have yet to fully embrace fluorescence spectroscopy as the category is ranked 16th among all scientific categories that exploit it.
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