Abstract
The detection of unknown analytes is a staple of analytical chemistry. Whether it be contaminants, biomarkers, or potential medicine, quantifying the presence of analytes can lead to great benefits. Toxic contaminants in food and water cause many health complications and can often be fatal. Due to industrialization, water contamination has become a more common problem of modern society. Poor environmental awareness in mining practices can yield toxic metal contamination into water supplies. Water containing heavy metals can lead to a regional health crisis, as the local water can no longer be used for drinking or farming practices. One way in which water contamination can be combatted is to develop new ways to detect and remove these toxic materials. Host-guest interactions have been implemented to bind metal cations in solution. There are many different types of molecules capable of host-guest interactions, however, cavitands are among the most well-established. Cavitands are macromolecules named for the cavity in the center of the molecule in which guest molecules can become included. The most common cavitands are based upon the calix[4]arene and possess a negatively charged cavity, which is ideal for host-guest interactions with positively charged metal cations. Most cavitands are poorly soluble, especially in polar solvents such as water. Although solubility limits the use of cavitands in solution, they can be modified to become more amphiphilic by altering the “head” and “tail” groups. By producing amphiphilic cavitands, it is possible to generate one-molecule thick layers of cavitands and observe the host-guest interaction with metal cations through surface chemistry at the air-water interface. By monitoring the host-guest interaction at the air-water interface with spectroscopy, it can be possible to distinguish the type of metal that is interacting with the cavitand. Alternatively, some analytes can be detected to diagnose certain diseases. These analytes are referred to as biomarker, and are any type of molecule whose presence can be indicative of a disease. One example of such an analyte is alpha-L-fucosidase. Alpha-L-fucosidase is an oncofetal enzyme that catalyzes the cleavage of fucose-bound molecules. Standard adult diets do not regularly include fucose, and as such, the production of alpha-L-fucosidase is limited after gestation. Although alpha-L-fucosidase is almost undetectable in healthy blood serum, it has been found to be elevated in the blood serum of individuals suffering from hepatocellular carcinoma. The neoplasm forms upon mutatation of healthy liver tissue that causes the cells to rapidly grow, similar to growth prior to gestation. This reversion back to the growth stage promotes the synthesis alpha-L-fucosidase and can thus be used confirm the presence of a tumor. The detection of alpha-L-fucosidase can be achieved through a variety of methods. Many approaches have been investigated based on the enzyme kinetics of alpha-L-fucosidase, but the detection is limited to relatively high concentrations. It is possible that elevated levels of alpha-L-fucosidase are missed by enzyme-based assays. Immunoassays can enhance the detection of alpha-L-fucosidase by using an immunoglobulin antibody that binds exclusively to an epitope on the enzyme. The development of immunoassays typically involves a solid support to fix the antibody into the proper orientation and lower the amount of antibody needed through packing. Two different supports were used for the detection of alpha-L-fucosidase through an immunoassay. The first approach uses a quartz slide and commonly implemented conjugation techniques. The second approach explores a more recent field of biosensing using nanoparticles. Antibodies immobilized to a gold-nanoparticle were used to develop an optical assay that exploits the energy transfer from a carbon dot probe emission to the surface plamson of the gold nanoparticle. Finally, some unknown analytes are believed to possess medicinal properties. The medicinal properties of molecules are often discovered prior to discovering the source or mechanism of the observed therapeutic benefits. One such analyte is singlet oxygen produced from photoactivation of a sensitizer. The cytotoxic effect exhibited by some porphyrin or dye molecules on cells was recognized long before the source of apoptosis was discovered. The cytotoxicity of certain dye molecules was developed as a new form of disease treatment which is called photodynamic therapy. Photodynamic therapy is most often used in the treatment of cancer due to the site-specific manner treatment can be administered. Photosensitizer molecules are biologically inert until activated by irradiation, allowing the location of the cytotoxicity to be controlled by an external light source. One limitation of this approach is that light must be able to reach to photosensitizer. This limits the use of photodynamic therapy, as not every wavelength of light is capable of penetrating tissue deep enough to reach the disease location. Bacterial keratitis does not suffer from this limitation, as the cornea is exposed and can be irradiated by most wavelengths of light. Photodynamic therapy has been used to treat bacterial keratitis and promising results have been obtained. However, the concentration of sensitizer, the irradiation time, the number of treatments necessary, and the ideal sensitizer drug all remain under investigation. Furthermore, the exact mechanism of cytotoxicity is still under debate. Singlet oxygen and superoxide radicals formed from reactions of the excited photosensitizer with ground state triplet oxygen, are believed to be the source of apoptosis. To confirm the cytotoxic source, the quantum yield of singlet oxygen generation, radical superoxide anions, and the effect they have on bacterial keratitis must be determined.