In every field of science, new techniques for target molecule detection are increasingly required. This work presents itself as a method for developing new sensors that can detect target molecules even in samples with low concentrations. The aim of the current research project is to create an optical sensor substrate that is precise and specific for fluorescent or fluorescently marked targets. We produced nanostructured surfaces on bulk silver substrates using a femtosecond pulsed laser (Laser Libra Ti:Saphira from Coherent). These surfaces have a larger superficial area, which increases the fluorescence of molecules nearby by due to the surface plasmon resonance, in the effect of metal-enhanced fluorescence (MEF). The COVID virus spike antibody (SARS-CoV-2(2019-nCoV)) and a secondary fluorescently marked antibody (Alexa Fluor™ 633 goat anti-human IgG (H+L)) was used to functionalize the nanostructures. Initial results indicated that the functionalization process was successful in achieving our initial goals, presenting the proposal's methods as an effective route for the development of biosensors. The primary antibody was initially detected in a very low concentration (0.0525 ng/uL), and the fluorescent signal was enhanced on the nanostructured portion of the surface by 6.3 times more than it was on the surface without modification.
Curcumin is a natural compound used for medical and food-industrial applications due to its antioxidant, antiinflammatory, antifungal, antiviral, and antiseptic properties. In addition to these applications, curcumin can be used for fluorescence labeling in disease diagnostics/theranostics and monitoring photodynamic antimicrobial inactivation. In terms of fluorescence-based applications, the sensitivity to detect curcumin depends on the curcumin bioavailability or the formulation concentration. In this study, we used 375 nm and 445 nm laser excitation to characterize the wavelength dependent fluorescence spectra for curcumin in ethanol solutions of 10, 20, 50 and 75 μg/ml (i.e., 27.15, 54.30, 135.75 and 203.625 μM, respectively). Our results suggested the fluorescence intensity as a function of concentration saturates around 135.75 μM. Fluorescence intensity increase as a function of concentration was observed between 650 nm and 800 nm for the 445 nm excitation. Increase in the same wavelength range was obtained for the difference between the fluorescence spectra generated between the 375 nm and 445 nm excitation wavelengths. The spectral features reported in our study can be used on the design of curcumin formulations using Sigma Aldrich curcumin C7727 for fluorescencebased applications, determination of bioavailability of curcumin formulations and photodynamic dosimetry.
Curcumin is a natural and biocompatible compound that has been used for a variety of medical applications. These applications include treatment of several tumor cells, skin diseases, wound healing, and inflammation. Moreover, curcumin has potential to be used for theranostic of neurodegenerative diseases involving formation of Aβ plaques, as it can stain amyloid-β (Aβ) plaques and slightly improve the cognitive function in elderly. However, the diagnosis contrast and the treatment efficiency curcumin can provide are dependent on its molecular microenvironment, as it can change curcumin physical and chemical properties. In this paper, we characterize these properties for two types of curcumin formulations and suggest a quantum yield approach to enhance the detection of Aβ plaques with one of these formulations. The first formulation is synthetic curcumin (100% curcumin) and the second is Sigma Aldrich curcumin has 94% of curcuminoid content and 80% curcumin. Our measurements show that solutions containing only curcumin provided highest fluorescence signal with relatively lower optical densities, i.e., an increase of 73.2% (375 nm excitation) and 55% (445 nm excitation) in the quantum yield for the concentration of 20 μg/ml (54.30 μM). This suggests the synthetic curcumin formulation may be more efficient when used as a biomarker for diagnostics purposes or monitoring the efficiency of curcumin treatments using fluorescence spectroscopy.
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